Reinforced concrete structures designed in pre-1970s are vulnerable under earthquakes due to lack of seismic detailing to provide adequate ductility. Typical deficiencies of pre-1970s reinforced concrete structures are (a) use of plain bars as longitudinal reinforcement, (b) inadequate anchorage of beam longitudinal reinforcement in the column (particularly exterior column), (c) lack of joint transverse reinforcement if any, (d) lapped splices located just above joint, and (e) low concrete strength. Furthermore, the use of infill walls is a controversial issue because it can help to provide additional stiffness to the structure on the positive side and on the negative side it can increase the possibility of soft-storey mechanisms if it is distributed irregularly. Experimental research to investigate the possible seismic behaviour of pre-1970s reinforced concrete structures have been carried out in the past. However, there is still an absence of experimental tests on the 3-D response of existing beam-column joints under bi-directional cyclic loading, such as corner joints. As part of the research work herein presented, a series of experimental tests on beam-column subassemblies with typical detailing of pre-1970s buildings has been carried out to investigate the behaviour of existing reinforced concrete structures. Six two-third scale plane frame exterior beam-column joint subassemblies were constructed and tested under quasi-static cyclic loading in the Structural Laboratory of the University of Canterbury. The reinforcement detailing and beam dimension were varied to investigate their effect on the seismic behaviour. Four specimens were conventional deep beam-column joint, with two of them using deformed longitudinal bars and beam bars bent in to the joint and the two others using plain round longitudinal bars and beam bars with end hooks. The other two specimens were shallow beam-column joint, one with deformed longitudinal bars and beam bars bent in to the joint, the other with plain round longitudinal bars and beam bars with end hooks. All units had one transverse reinforcement in the joint. The results of the experimental tests indicated that conventional exterior beam-column joint with typical detailing of pre-1970s building would experience serious diagonal tension cracking in the joint panel under earthquake. The use of plain round bars with end hooks for beam longitudinal reinforcement results in more severe damage in the joint core when compared to the use of deformed bars for beam longitudinal reinforcement bent in to the joint, due to the combination of bar slips and concrete crushing. One interesting outcome is that the use of shallow beam in the exterior beam-column joint could avoid the joint cracking due to the beam size although the strength provided lower when compared with the use of deep beam with equal moment capacity. Therefore, taking into account the low strength and stiffness, shallow beam can be reintroduced as an alternative solution in design process. In addition, the presence of single transverse reinforcement in the joint core can provide additional confinement after the first crack occurred, thus delaying the strength degradation of the structure. Three two-third scale space frame corner beam-column joint subassemblies were also constructed to investigate the biaxial loading effect. Two specimens were deep-deep beam-corner column joint specimens and the other one was deep-shallow beam-corner column joint specimen. One deep-deep beam-corner column joint specimen was not using any transverse reinforcement in the joint core while the two other specimens were using one transverse reinforcement in the joint core. Plain round longitudinal bars were used for all units with hook anchorage for the beam bars. Results from the tests confirmed the evidences from earthquake damage observations with the exterior 3-D (corner) beam-column joint subjected to biaxial loading would have less strength and suffer higher damage in the joint area under earthquake. Furthermore, the joint shear relation in the two directions is calibrated from the results to provide better analysis. An analytical model was used to simulate the seismic behaviour of the joints with the help of Ruaumoko software. Alternative strength degradation curves corresponding to different reinforcement detailing of beam-column joint unit were proposed based on the test results.
The 22 February 2011, Mw6.2-6.3 Christchurch earthquake is the most costly earthquake to affect New Zealand, causing 181 fatalities and severely damaging thousands of residential and commercial buildings, and most of the city lifelines and infrastructure. This manuscript presents an overview of observed geotechnical aspects of this earthquake as well as some of the completed and on-going research investigations. A unique aspect, which is particularly emphasized, is the severity and spatial extent of liquefaction occurring in native soils. Overall, both the spatial extent and severity of liquefaction in the city was greater than in the preceding 4th September 2010 Darfield earthquake, including numerous areas that liquefied in both events. Liquefaction and lateral spreading, variable over both large and short spatial scales, affected commercial structures in the Central Business District (CBD) in a variety of ways including: total and differential settlements and tilting; punching settlements of structures with shallow foundations; differential movements of components of complex structures; and interaction of adjacent structures via common foundation soils. Liquefaction was most severe in residential areas located to the east of the CBD as a result of stronger ground shaking due to the proximity to the causative fault, a high water table approximately 1m from the surface, and soils with composition and states of high susceptibility and potential for liquefaction. Total and differential settlements, and lateral movements, due to liquefaction and lateral spreading is estimated to have severely compromised 15,000 residential structures, the majority of which otherwise sustained only minor to moderate damage directly due to inertial loading from ground shaking. Liquefaction also had a profound effect on lifelines and other infrastructure, particularly bridge structures, and underground services. Minor damage was also observed at flood stop banks to the north of the city, which were more severely impacted in the 4th September 2010 Darfield earthquake. Due to the large high-frequency ground motion in the Port hills numerous rock falls and landslides also occurred, resulting in several fatalities and rendering some residential areas uninhabitable.
The assessment of damage and remaining capacity after an earthquake is an immediate measure to determine whether a reinforced concrete (RC) building is usable and safe for occupants. The recent Christchurch earthquake (22 February 2011) caused a uniquely severe level of structural damage to modern buildings, resulting in extensive damage to the building stock. About 60% of damaged multistorey concrete buildings (3 storeys and up) were demolished after the earthquake, and the cost of reconstruction amounted to 40 billion NZD. The aftermath disclosed issues of great complexities regarding the future of the RC buildings damaged by the earthquakes. This highlighted the importance of post-event decision-making, as the outcome will allow the appropriate course of action—demolition, repair or acceptance of the existing building—to be considered. To adopt the proper strategy, accurate assessment of the residual capacity and the level of damage is required. This doctoral dissertation aims to assess the damage and remaining capacity at constituent material and member level (i.e., concrete material and beams) through a systematic approach in an attempt to address part of an existing gap in the available literature. Since the residual capacity of RC members is not unique and depends on previously applied loading history, post-event residual capacity in this study was assessed in terms of fraction of fatigue life (i.e., the number of cycles required to failure). This research comprises three main parts: (1) residual capacity and damage assessment at material level (i.e., concrete), (2) post-yield bond deterioration and damage assessment at the interface of steel and concrete, and, finally, (3) residual capacity and damage assessment at member level (i.e., RC beam). The first part of this research focused on damage assessment and the remaining capacity of concrete from a material point of view. It aimed to employ appropriate and reliable durability-based testing and image-detection techniques to quantify deterioration in the mechanical properties of concrete on the basis that stress-induced damage occurred in the microstructural system of the concrete material. To this end, in the first phase, a feasibility study was conducted in which a combination of oxygen permeability, electrical resistivity and porosity tests were assessed to determine if they were robust and reliable enough to reveal damage which occurred in the microstructural system of concrete. The results, in terms of change in permeability, electrical resistivity and porosity features of disk samples taken from the middle third of damaged concrete cylinders (200 mm × 100 mm) monotonically pre-loaded to 50%, 70%, 90% and 95% of the ultimate strength (f′c), showed the permeability test is a reliable tool to identify the degree of damage, due to its high sensitivity to the load-induced microcracking. In parallel, to determine the residual capacity, the companion damaged concrete cylinders already loaded to the same level of compressive strength were reloaded up to failure. Comparing the stress–strain relationship of damaged concrete with intact material, it was also found that the strain capacity of the reloaded pre-damaged concrete cylinders decreases while strength remained virtually unchanged. In the second phase of the first part, a fluorescent microscopy technique was used to assess the damage and develop a correlation between material degradation, by virtue of the geometrical features, and damage to the concrete. To account for the effect of confinement and cyclic loading, in the third phase, the residual capacity and damage assessment of unconfined and GFRP confined concrete cylinders subjected to low-cycle fatigue loading, was investigated. Similar to the first phase, permeability testing technique was used to provide an indirect evaluation of fatigue damage. Finally, in the fourth phase of the first part, the suitability of permeability testing technique to assess damage was evaluated for cored concrete taken from three types of RC members: columns, beams and a beam-column joint. In view of the fact that the composite action of an RC member is highly dependent on the bond between reinforcement and surrounding concrete, understanding the deterioration of the bond in the post-yield range of strain in steel was crucial to assess damage at member level. Therefore, in the second phase of this research, a state-of-the- art distributed fibre optic strain sensor system (DFOSSS) system was used to evaluate bond deterioration in a cantilever RC beam subjected to monotonic lateral loading. The technology allowed the continuous capture of strain, every 2.6 mm along the length, in both reinforcing bars and cover concrete. The strain profile provided a basis by which the slip, axial stress and bond stress distributions were then established. In the third part, the study focused on the damage assessment and residual capacity of seven half-scale RC beams subjected to a constant-amplitude cyclic loading protocol. In the first stage, the structural performances of three specimens under constant-amplitude fatigue at 1%, 2% and 4% chord rotation (drift) were examined. In parallel, the number of cycles to failure, degradation in strength, stiffness and energy dissipation were characterized. In the second stage, four RC beams were subjected to loading up to 70% and 90% of their fatigue life, at 2% and 4% drift, and then monotonically pulled up to failure. To determine the residual flexural capacity, the lateral force–displacement results of pre-damaged specimens were compared with an undamaged specimen subjected to only monotonic loading. The study showed significant losses in strength, deformability, stiffness and energy dissipation capacity. A nonlinear finite element analysis (FEA) using concrete damage plasticity (CDP) model was also conducted in ABAQUS to numerically investigate the behaviour of the tested specimen. The results of the FE simulations indicated a reasonable response compared with the behaviour of the test specimen in terms of force–displacement and cracking pattern. During the Christchurch earthquake it was observed that the loading history has a significant influence on structural responses. While in conventional pseudo-static loading protocol, internal forces can be redistributed along the plastic length: there is little chance for structures undergoing high initial loading amplitude to redistribute pertinent stresses. As a result, in the third phase of this part, the effect of high rate of loading on the behaviour of seismically designed RC beams was investigated. Two half-scale cantilever RC beams were subjected to similar constant-amplitude cyclic loading at 2% and 4% drifts, but at a rate of 500 mm/s. Due to the incapability of conventional measuring techniques, a motion-tracking system was employed for data acquisition with the high-speed tests. The effect of rate of loading on the fatigue life of specimens (i.e., the number of cycles required to failure), secant stiffness, failure mode, cracking pattern, beam elongations and bar fracture surface were analysed. Integrating the results of all parts of this research has resulted in a better understanding of residual capacity and the development of damage at both the material and member level by using a low-cycle fatigue approach.
Though rare and unpredictable, earthquakes can and do cause catastrophic destruction when they impact unprepared and vulnerable communities. Extensive damage and failure of vulnerable buildings is a key factor which contributes to seismic-related disasters, making the proactive management of these buildings a necessity to reduce the risk of future disasters arising. The devastating Canterbury earthquakes of 2010 and 2011 brought the urgency of this issue to national importance in New Zealand. The national earthquake-prone building framework came into effect in 2017, obligating authorities to identify existing buildings with the greatest risk of collapse in strong earthquakes and for building owners to strengthen or demolish these buildings within a designated period of time. Though this framework is unique to New Zealand, the challenge of managing the seismic risk of such buildings is common amongst all seismically-active countries. Therefore, looking outward to examine how other jurisdictions legally manage this challenge is useful for reflecting on the approaches taken in New Zealand and understand potential lessons which could be adopted. This research compares the legal framework used to reduce the seismic risk of existing buildings in New Zealand with that of the similarly earthquake-prone countries of Japan and Italy. These legal frameworks are examined with a particular focus on the proactive goal of reducing risk and improving resilience, as is the goal of the international Sendai Framework for Disaster Risk Reduction 2015-2030. The Sendai Framework, which each of the case study countries have committed to and thus have obligations under, forms the legal basis of the need for states to reduce disaster risk in their jurisdictions. In particular, the states’ legal frameworks for existing building risk reduction are examined in the context of the Sendai priorities of understanding disaster risk, strengthening disaster risk governance, and investing in resilience. While this research illustrates that the case study countries have each adopted more proactive risk reduction frameworks in recent years in anticipation of future earthquakes, the frameworks currently focus on a very narrow range of existing buildings and thus are not currently sufficient for promoting the long-term resilience of building stocks. In order to improve resilience, it is argued, legal frameworks need to include a broader range of buildings subject to seismic risk reduction obligations and also to broaden the focus on long-term monitoring of potential risk to buildings.
In 2010 and 2011 Christchurch, New Zealand experienced a series of earthquakes that caused extensive damage across the city, but primarily to the Central Business District (CBD) and eastern suburbs. A major feature of the observed damage was extensive and severe soil liquefaction and associated ground damage, affecting buildings and infrastructure. The behaviour of soil during earthquake loading is a complex phenomena that can be most comprehensively analysed through advanced numerical simulations to aid engineers in the design of important buildings and critical facilities. These numerical simulations are highly dependent on the capabilities of the constitutive soil model to replicate the salient features of sand behaviour during cyclic loading, including liquefaction and cyclic mobility, such as the Stress-Density model. For robust analyses advanced soil models require extensive testing to derive engineering parameters under varying loading conditions for calibration. Prior to this research project little testing on Christchurch sands had been completed, and none from natural samples containing important features such as fabric and structure of the sand that may be influenced by the unique stress-history of the deposit. This research programme is focussed on the characterisation of Christchurch sands, as typically found in the CBD, to facilitate advanced soil modelling in both res earch and engineering practice - to simulate earthquake loading on proposed foundation design solutions including expensive ground improvement treatments. This has involved the use of a new Gel Push (GP) sampler to obtain undisturbed samples from below the ground-water table. Due to the variable nature of fluvial deposition, samples with a wide range of soil gradations, and accordingly soil index properties, were obtained from the sampling sites. The quality of the samples is comprehensively examined using available data from the ground investigation and laboratory testing. A meta-quality assessment was considered whereby a each method of evaluation contributed to the final quality index assigned to the specimen. The sampling sites were characterised with available geotechnical field-based test data, primarily the Cone Penetrometer Test (CPT), supported by borehole sampling and shear-wave velocity testing. This characterisation provides a geo- logical context to the sampling sites and samples obtained for element testing. It also facilitated the evaluation of sample quality. The sampling sites were evaluated for liquefaction hazard using the industry standard empirical procedures, and showed good correlation to observations made following the 22 February 2011 earthquake. However, the empirical method over-predicted liquefaction occurrence during the preceding 4 September 2010 event, and under-predicted for the subsequent 13 June 2011 event. The reasons for these discrepancies are discussed. The response of the GP samples to monotonic and cyclic loading was measured in the laboratory through triaxial testing at the University of Canterbury geomechanics laboratory. The undisturbed samples were compared to reconstituted specimens formed in the lab in an attempt to quantify the effect of fabric and structure in the Christchurch sands. Further testing of moist tamped re- constituted specimens (MT) was conducted to define important state parameters and state-dependent properties including the Critical State Line (CSL), and the stress-strain curve for varying state index. To account for the wide-ranging soil gradations, selected representative specimens were used to define four distinct CSL. The input parameters for the Stress-Density Model (S-D) were derived from a suite of tests performed on each representative soil, and with reference to available GP sample data. The results of testing were scrutinised by comparing the data against expected trends. The influence of fabric and structure of the GP samples was observed to result in similar cyclic strength curves at 5 % Double Amplitude (DA) strain criteria, however on close inspection of the test data, clear differences emerged. The natural samples exhibited higher compressibility during initial loading cycles, but thereafter typically exhibited steady growth of plastic strain and excess pore water pressure towards and beyond the strain criteria and initial liquefaction, and no flow was observed. By contrast the reconstituted specimens exhibited a stiffer response during initial loading cycles, but exponential growth in strains and associated excess pore water pressure beyond phase-transformation, and particularly after initial liquefaction where large strains were mobilised in subsequent cycles. These behavioural differences were not well characterised by the cyclic strength curve at 5 % DA strain level, which showed a similar strength for both GP samples and MT specimens. A preliminary calibration of the S-D model for a range of soil gradations is derived from the suite of laboratory test data. Issues encountered include the influence of natural structure on the peak-strength–state index relationship, resulting in much higher peak strengths than typically observed for sands in the literature. For the S-D model this resulted in excessive stiffness to be modelled during cyclic mobility, when the state index becomes large momentarily, causing strain development to halt. This behaviour prevented modelling the observed re- sponse of silty sands to large strains, synonymous with “liquefaction”. Efforts to reduce this effect within the current formulation are proposed as well as future research to address this issue.
Recent experiences from the Darfield and Canterbury, New Zealand earthquakes have shown that the soft soil condition of saturated liquefiable sand has a profound effect on seismic response of buildings, bridges and other lifeline infrastructure. For detailed evaluation of seismic response three dimensional integrated analysis comprising structure, foundation and soil is required; such an integrated analysis is referred to as Soil Foundation Structure Interaction (SFSI) in literatures. SFSI is a three-dimensional problem because of three primary reasons: first, foundation systems are three-dimensional in form and geometry; second, ground motions are three-dimensional, producing complex multiaxial stresses in soils, foundations and structure; and third, soils in particular are sensitive to complex stress because of heterogeneity of soils leading to a highly anisotropic constitutive behaviour. In literatures the majority of seismic response analyses are limited to plane strain configuration because of lack of adequate constitutive models both for soils and structures, and computational limitation. Such two-dimensional analyses do not represent a complete view of the problem for the three reasons noted above. In this context, the present research aims to develop a three-dimensional mathematical formulation of an existing plane-strain elasto-plastic constitutive model of sand developed by Cubrinovski and Ishihara (1998b). This model has been specially formulated to simulate liquefaction behaviour of sand under ground motion induced earthquake loading, and has been well-validated and widely implemented in verifcation of shake table and centrifuge tests, as well as conventional ground response analysis and evaluation of case histories. The approach adopted herein is based entirely on the mathematical theory of plasticity and utilises some unique features of the bounding surface plasticity formalised by Dafalias (1986). The principal constitutive parameters, equations, assumptions and empiricism of the existing plane-strain model are adopted in their exact form in the three-dimensional version. Therefore, the original two-dimensional model can be considered as a true subset of the three-dimensional form; the original model can be retrieved when the tensorial quantities of the three dimensional version are reduced to that of the plane-strain configuration. Anisotropic Drucker-Prager type failure surface has been adopted for the three-dimensional version to accommodate triaxial stress path. Accordingly, a new mixed hardening rule based on Mroz’s approach of homogeneous surfaces (Mroz, 1967) has been introduced for the virgin loading surface. The three-dimensional version is validated against experimental data for cyclic torsional and triaxial stress paths.
The Canterbury earthquakes of 2010 and 2011 have shone the spotlight on a number of tax issues. These issues, and in particular lessons learned from them, will be relevant for revenue authorities, policymakers and taxpayers alike in the broader context of natural disasters. Issues considered by this paper include the tax treatment of insurance monies. For example, building owners will receive pay-outs for destroyed assets and buildings which have been depreciated. Where the insurance payment is more than the adjusted tax value, there will be a taxable "gain on sale" (or depreciation recovery income). If the building owner uses those insurance proceeds to purchase a replacement asset, legislative amendments specifically enacted following the earthquakes provide that rollover relief of the depreciation recovery income is available. The tax treatment of expenditure to seismically strengthen a building is another significant issue faced by building owners. Case law has determined that this expenditure will usually be capital expenditure. In the past such costs could be capitalised to the building and depreciated accordingly. However, since the 2011-2012 income year owners have been prohibited from claiming depreciation on buildings and therefore currently no deduction is available for such strengthening expenditure (whether immediate or deferred). This has significant potential implications for landlords throughout New Zealand facing significant seismic retrofit costs. Incentives, or some form of financial support, whether delivered through the tax system or some other mechanism may be required. International Financial Reporting Standards (IFRS) require insurance proceeds, including reimbursement for expenditure of a capital nature, be reported as income while expenditure itself is not recorded as a current period expense. This has the effect of overstating current income and creating a larger variation between reported income for accounting and taxation purposes. Businesses have obligations to maintain certain business records for tax purposes. Reconstructing records destroyed by a natural disaster depends on how the information was originally stored. The earthquakes have demonstrated the benefits of ‘off-site’ (outside Canterbury) storage, in particular electronic storage. This paper considers these issues and the Inland Revenue Department (Inland Revenue) Standard Practice Statement which deals with inter alia retention of business records in electronic format and offshore record storage. Employer provided accommodation is treated as income to the benefitting employee. A recent amendment to the Income Tax Act 2007 retrospectively provides that certain employer provided accommodation is exempt from tax. The time aspect of these rules is extended where the employee is involved in the Canterbury rebuild and comes from outside the region.
There is a relationship between inelastic deformation and energy dissipation in structures that are subjected to earthquake ground motions. Thus, if seismic energy dissipation can be achieved by means of a separate non-load bearing supplementary damping system, the load bearing structure can remain elastic with continuing serviceability following the design level earthquake. This research was carried out to investigate the advantages of using added damping in structures. The control system consists of passive friction dampers called ring spring dampers installed in the ground floor of the structure using a tendon to transmit the forces to the other parts of the structure. The ring springs dampers are friction devices consisting of inner and outer ring elements assembled to form a spring stack. External load applied to the spring produces sliding action across mating ring interfaces. The damping forces generated by the dampers and transferred in the supplemental system to the structure by the tendon and horizontal links oppose the internal loads. A four storey-two bay steel frame structure was used in the study. Experimental and analytical studies to investigate the effectiveness of a supplemental control system are presented. The model was subjected to a series of earthquake simulations on the shaking table in the Structural Laboratory of the Civil Engineering Department, at the University of Canterbury. The earthquake simulation tests have been performed on the structure both with and without the supplemental control system. The earthquake simulations were a series of gradually increasing intensity replications of two commonly used earthquake records. This thesis includes detailed description of the structural model, the supplemental control system, the ring springs dampers and the data obtained during the testing. Analyses were then carried out on a twelve storey framed structure to investigate the possible tendon arrangements and the size and type of dampers required to control the response of a real building. Guidelines for determining the appropriateness of including a supplemental damping system have been investigated. The main features of the supplemental control system adopted in this research are: • It is a passive control system with extreme reliability and having no dependence on external power sources to effect the control action. These power sources may not be available during a major earthquake. • Ring springs are steel friction devices capable of absorbing large amounts of input energy. No liquid leakage can occur and minimal maintenance is required for the ring spring dampers. • With a damper-tendon system, the distribution of the dampers throughout the structure is not so critical. Only one or two dampers are used to produce the damping forces needed, and forces are then transferred to the rest of the building by the tendon system. • It is a relatively inexpensive control system with a long useful life.
In major seismic events, a number of plan-asymmetric buildings which experienced element failure or structural collapse had twisted significantly about their vertical axis during the earthquake shaking. This twist, known as “building torsion”, results in greater demands on one side of a structure than on the other side. The Canterbury Earthquakes Royal Commission’s reports describe the response of a number of buildings in the February 2011 Christchurch earthquakes. As a result of the catastrophic collapse of one multi-storey building with significant torsional irregularity, and significant torsional effects also in other buildings, the Royal Commission recommended that further studies be undertaken to develop improved simple and effective guides to consider torsional effects in buildings which respond inelastically during earthquake shaking. Separately from this, as building owners, the government, and other stakeholders, are planning for possible earthquake scenarios, they need good estimates of the likely performance of both new and existing buildings. These estimates, often made using performance based earthquake engineering considerations and loss estimation techniques, inform decision making. Since all buildings may experience torsion to some extent, and torsional effects can influence demands on building structural and non-structural elements, it is crucial that demand estimates consider torsion. Building seismic response considering torsion can be evaluated with nonlinear time history analysis. However, such analysis involves significant computational effort, expertise and cost. Therefore, from an engineers’ point of view, simpler analysis methods, with reasonable accuracy, are beneficial. The consideration of torsion in simple analysis methods has been investigated by many researchers. However, many studies are theoretical without direct relevance to structural design/assessment. Some existing methods also have limited applicability, or they are difficult to use in routine design office practice. In addition, there has been no consensus about which method is best. As a result, there is a notable lack of recommendations in current building design codes for torsion of buildings that respond inelastically. There is a need for building torsion to be considered in yielding structures, and for simple guidance to be developed and adopted into building design standards. This study aims to undertaken to address this need for plan-asymmetric structures which are regular over their height. Time history analyses are first conducted to quantify the effects of building plan irregularity, that lead to torsional response, on the seismic response of building structures. Effects of some key structural and ground motion characteristics (e.g. hysteretic model, ground motion duration, etc.) are considered. Mass eccentricity is found to result in rather smaller torsional response compared to stiffness/strength eccentricity. Mass rotational inertia generally decreases the torsional response; however, the trend is not clearly defined for torsionally restrained systems (i.e. large λty). Systems with EPP and bilinear models have close displacements and systems with Takeda, SINA, and flag-shaped models yield almost the same displacements. Damping has no specific effect on the torsional response for the single-storey systems with the unidirectional eccentricity and excitation. Displacements of the single-storey systems subject to long duration ground motion records are smaller than those for short duration records. A method to consider torsional response of ductile building structures under earthquake shaking is then developed based on structural dynamics for a wide range of structural systems and configurations, including those with low and high torsional restraint. The method is then simplified for use in engineering practice. A novel method is also proposed to simply account for the effects of strength eccentricity on response of highly inelastic systems. A comparison of the accuracy of some existing methods (including code-base equivalent static method and model response spectrum analysis method), and the proposed method, is conducted for single-storey structures. It is shown that the proposed method generally provides better accuracy over a wide range of parameters. In general, the equivalent static method is not adequate in capturing the torsional effects and the elastic modal response spectrum analysis method is generally adequate for some common parameters. Record-to-record variation in maximum displacement demand on the structures with different degrees of torsional response is considered in a simple way. Bidirectional torsional response is then considered. Bidirectional eccentricity and excitation has varying effects on the torsional response; however, it generally increases the weak and strong edges displacements. The proposed method is then generalized to consider the bidirectional torsion due to bidirectional stiffness/strength eccentricity and bidirectional seismic excitation. The method is shown to predict displacements conservatively; however, the conservatism decreases slightly for cases with bidirectional excitation compared to those subject to unidirectional excitation. In is shown that the roof displacement of multi-storey structures with torsional response can be predicted by considering the first mode of vibration. The method is then further generalized to estimate torsional effects on multi-storey structure displacement demands. The proposed procedure is tested multi-storey structures and shown to predict the displacements with a good accuracy and conservatively. For buildings which twist in plan during earthquake shaking, the effect of P-Δλ action is evaluated and recommendations for design are made. P-Δλ has more significant effects on systems with small post- yield stiffness. Therefore, system stability coefficient is shown not to be the best indicator of the importance of P-Δλ and it is recommended to use post-yield stiffness of system computed with allowance for P-Δλ effects. For systems with torsional response, the global system stability coefficient and post- yield stiffness ration do not reflect the significance of P-Δλ effects properly. Therefore, for torsional systems individual seismic force resisting systems should be considered. Accuracy of MRSA is investigated and it is found that the MRSA is not always conservative for estimating the centre of mass and strong edge displacements as well as displacements of ductile systems with strength eccentricity larger than stiffness eccentricity. Some modifications are proposed to get the MRSA yields a conservative estimation of displacement demands for all cases.
Natural hazard disasters often have large area-wide impacts, which can cause adverse stress-related mental health outcomes in exposed populations. As a result, increased treatment-seeking may be observed, which puts a strain on the limited public health care resources particularly in the aftermath of a disaster. It is therefore important for public health care planners to know whom to target, but also where and when to initiate intervention programs that promote emotional wellbeing and prevent the development of mental disorders after catastrophic events. A large body of literature assesses factors that predict and mitigate disaster-related mental disorders at various time periods, but the spatial component has rarely been investigated in disaster mental health research. This thesis uses spatial and spatio-temporal analysis techniques to examine when and where higher and lower than expected mood and anxiety symptom treatments occurred in the severely affected Christchurch urban area (New Zealand) after the 2010/11 Canterbury earthquakes. High-risk groups are identified and a possible relationship between exposure to the earthquakes and their physical impacts and mood and anxiety symptom treatments is assessed. The main research aim is to test the hypothesis that more severely affected Christchurch residents were more likely to show mood and anxiety symptoms when seeking treatment than less affected ones, in essence, testing for a dose-response relationship. The data consisted of mood and anxiety symptom treatment information from the New Zealand Ministry of Health’s administrative databases and demographic information from the National Health Index (NHI) register, when combined built a unique and rich source for identifying publically funded stress-related treatments for mood and anxiety symptoms in almost the whole population of the study area. The Christchurch urban area within the Christchurch City Council (CCC) boundary was the area of interest in which spatial variations in these treatments were assessed. Spatial and spatio-temporal analyses were done by applying retrospective space-time and spatial variation in temporal trends analysis using SaTScan™ software, and Bayesian hierarchical modelling techniques for disease mapping using WinBUGS software. The thesis identified an overall earthquake-exposure effect on mood and anxiety symptom treatments among Christchurch residents in the context of the earthquakes as they experienced stronger increases in the risk of being treated especially shortly after the catastrophic 2011 Christchurch earthquake compared to the rest of New Zealand. High-risk groups included females, elderly, children and those with a pre-existing mental illness with elderly and children especially at-risk in the context of the earthquakes. Looking at the spatio-temporal distribution of mood and anxiety symptom treatments in the Christchurch urban area, a high rates cluster ranging from the severely affected central city to the southeast was found post-disaster. Analysing residential exposure to various earthquake impacts found that living in closer proximity to more affected areas was identified as a risk factor for mood and anxiety symptom treatments, which largely confirms a dose-response relationship between level of affectedness and mood and anxiety symptom treatments. However, little changes in the spatial distribution of mood and anxiety symptom treatments occurred in the Christchurch urban area over time indicating that these results may have been biased by pre-existing spatial disparities. Additionally, the post-disaster mobility activity from severely affected eastern to the generally less affected western and northern parts of the city seemed to have played an important role as the strongest increases in treatment rates occurred in less affected northern areas of the city, whereas the severely affected eastern areas tended to show the lowest increases. An investigation into the different effects of mobility confirmed that within-city movers and temporary relocatees were generally more likely to receive care or treatment for mood or anxiety symptoms, but moving within the city was identified as a protective factor over time. In contrast, moving out of the city from minor, moderately or severely damaged plain areas of the city, which are generally less affluent than Port Hills areas, was identified as a risk factor in the second year post-disaster. Moreover, residents from less damaged plain areas of the city showed a decrease in the likelihood of receiving care or treatment for mood or anxiety symptoms compared to those from undamaged plain areas over time, which also contradicts a possible dose-response relationship. Finally, the effects of the social and physical environment, as well as community resilience on mood and anxiety symptom treatments among long-term stayers from Christchurch communities indicate an exacerbation of pre-existing mood and anxiety symptom treatment disparities in the city, whereas exposure to ‘felt’ earthquake intensities did not show a statistically significant effect. The findings of this thesis highlight the complex relationship between different levels of exposure to a severe natural disaster and adverse mental health outcomes in a severely affected region. It is one of the few studies that have access to area-wide health and impact information, are able to do a pre-disaster / post-disaster comparison and track their sample population to apply spatial and spatio-temporal analysis techniques for exposure assessment. Thus, this thesis enhances knowledge about the spatio-temporal distribution of adverse mental health outcomes in the context of a severe natural disaster and informs public health care planners, not only about high-risk groups, but also where and when to target health interventions. The results indicate that such programs should broadly target residents living in more affected areas as they are likely to face daily hardship by living in a disrupted environment and may have already been the most vulnerable ones before the disaster. Special attention should be focussed on women, elderly, children and people with pre-existing mental illnesses as they are most likely to receive care or treatment for stress-related mental health symptoms. Moreover, permanent relocatees from affected areas and temporarily relocatees shortly after the disaster may need special attention as they face additional stressors due to the relocation that may lead to the development of adverse mental health outcomes needing treatment.
The full scale, in-situ investigations of instrumented buildings present an excellent opportunity to observe their dynamic response in as-built environment, which includes all the real physical properties of a structure under study and its surroundings. The recorded responses can be used for better understanding of behavior of structures by extracting their dynamic characteristics. It is significantly valuable to examine the behavior of buildings under different excitation scenarios. The trends in dynamic characteristics, such as modal frequencies and damping ratios, thus developed can provide quantitative data for the variations in the behavior of buildings. Moreover, such studies provide invaluable information for the development and calibration of realistic models for the prediction of seismic response of structures in model updating and structural health monitoring studies. This thesis comprises two parts. The first part presents an evaluation of seismic responses of two instrumented three storey RC buildings under a selection of 50 earthquakes and behavioral changes after Ms=7.1 Darfield (2010) and Ms=6.3 Christchurch (2011) earthquakes for an instrumented eight story RC building. The dynamic characteristics of the instrumented buildings were identified using state-of-the-art N4SID system identification technique. Seismic response trends were developed for the three storey instrumented buildings in light of the identified frequencies and the peak response accelerations (PRA). Frequencies were observed to decrease with excitation level while no trends are discernible for the damping ratios. Soil-structure interaction (SSI) effects were also determined to ascertain their contribution in the seismic response. For the eight storey building, it was found through system identification that strong nonlinearities in the structural response occurred and manifested themselves in all identified natural frequencies of the building that exhibited a marked decrease during the strong motion duration compared to the pre-Darfield earthquakes. Evidence of foundation rocking was also found that led to a slight decrease in the identified modal frequencies. Permanent stiffness loss was also observed after the strong motion events. The second part constitutes developing and calibrating finite element model (FEM) of the instrumented three storey RC building with a shear core. A three dimensional FEM of the building is developed in stages to analyze the effect of structural, non-structural components (NSCs) and SSI on the building dynamics. Further to accurately replicate the response of the building following the response trends developed in the first part of the thesis, sensitivity based model updating technique was applied. The FEMs were calibrated by tuning the updating parameters which are stiffnesses of concrete, NSCs and soil. The updating parameters were found to generally follow decreasing trends with the excitation level. Finally, the updated FEM was used in time history analyses to assess the building seismic performance at the serviceability limit state shaking. Overall, this research will contribute towards better understanding and prediction of the behavior of structures subjected to ground motion.
In recent years, rocking isolation has become an effective approach to improve seismic performance of steel and reinforced concrete structures. These systems can mitigate structural damage through rigid body displacement and thus relatively low requirements for structural ductility, which can significantly improve seismic resilience of structures and reduce repairing costs after strong earthquakes. A number of base rocking structural systems with only a single rocking interface have been proposed. However, these systems can have significant high mode effect for high rise structures due to the single rocking interface. This RObust BUilding SysTem (ROBUST) project is a collaborative China-New Zealand project sponsored by the International Joint Research Laboratory of Earthquake Engineering (ILEE), Tongji University, and a number of agencies and universities within New Zealand including the BRANZ, Comflor, Earthquake Commission, HERA, QuakeCoRE, QuakeCentre, University of Auckland, and the University of Canterbury. A number of structural configurations will be tested [1, 2], and non-structural elements including ceilings, infilling walls, glazed curtain walls, precast concrete panels, piping system will also be tested in this project [3]. Within this study, a multiple rocking column steel structural system was proposed and investigated mainly by Tongji team with assistance of NZ members. The concept of rocking column system initiates from the structure of Chinese ancient wooden pagoda. In some of Chinese wooden pagodas, there are continuous core columns hanged only at the top of each pagoda, which is not connected to each stories. This core column can effectively avoid collapse of the whole structure under large storey drifts. Likewise, there are also central continuous columns in the newly proposed steel rocking column system, which can avoid weak story failure mechanism and make story drifts more uniform. In the proposed rocking column system, the structure can switch between an elastic rigidly connected moment resisting frame and a controlled rocking column system when subjected to strong ground motion excitations. The main seismic energy can be dissipated by asymmetric friction beam–column connections, thereby effectively reducing residual displacement of the structure under seismic loading without causing excessive damage to structural members. Re–centering of the structure is provided not only by gravity load carried by rocking columns, but also by mould coil springs. To investigate dynamic properties of the proposed system under different levels of ground excitations, a full-scale threestory steel rocking column structural system with central continuous columns is to be tested using the International joint research Laboratory of Earthquake Engineering (ILEE) facilities, Shanghai, China and an analytical model is established. A finite element model is also developed using ABAQUS to simulate the structural dynamic responses. The rocking column system proposed in this paper is shown to produce resilient design with quick repair or replacement.
Environmental stress and disturbance can affect the structure and functioning of marine ecosystems by altering their physical, chemical and biological features. In estuaries, benthic invertebrate communities play important roles in structuring sediments, influencing primary production and biogeochemical flux, and occupying key food web positions. Stress and disturbance can reduce species diversity, richness and abundance, with ecological theory predicting that biodiversity will be at its lowest soon after a disturbance with assemblages dominated by opportunistic species. The Avon-Heathcote Estuary in Christchurch New Zealand has provided a novel opportunity to examine the effects of stress, in the form of eutrophication, and disturbance, in the form of cataclysmic earthquake events, on the structure and functioning of an estuarine ecosystem. For more than 50 years, large quantities (up to 500,000m3/day) of treated wastewater were released into this estuary but in March 2010 this was diverted to an ocean outfall, thereby reducing the nutrient loading by around 90% to the estuary. This study was therefore initially focussed on the reversal of eutrophication and consequent effects on food web structure in the estuary as it responded to lower nutrients. In 2011, however, Christchurch was struck with a series of large earthquakes that greatly changed the estuary. Massive amounts of liquefied sediments, covering up to 65% of the estuary floor, were forced up from deep below the estuary, the estuary was tilted by up to a 50cm rise on one side and a corresponding drop on the other, and large quantities of raw sewage from broken wastewater infrastructure entered the estuary for up to nine months. This study was therefore a test of the potentially synergistic effects of nutrient reduction and earthquake disturbance on invertebrate communities, associated habitats and food web dynamics. Because there was considerable site-to-site heterogeneity in the estuary, the sites in this study were selected to represent a eutrophication gradient from relatively “clean” (where the influence of tidal flows was high) to highly impacted (near the historical discharge site). The study was structured around these sites, with components before the wastewater diversion, after the diversion but before the earthquakes, and after the earthquakes. The eutrophication gradient was reflected in the composition and isotopic chemistry of primary producer and invertebrate communities and the characteristics of sediments across the sample sites. Sites closest to the former wastewater discharge pipe were the most eutrophic and had cohesive organic -rich, fine sediments and relatively depauperate communities dominated by the opportunistic taxa Capitellidae. The less-impacted sites had coarser, sandier sediments with fewer pollutants and far less organic matter than at the eutrophic sites, relatively high diversity and lower abundances of micro- and macro-algae. Sewage-derived nitrogen had became incorporated into the estuarine food web at the eutrophic sites, starting at the base of the food chain with benthic microalgae (BMA), which were found to use mostly sediment-derived nitrogen. Stable isotopic analysis showed that δ13C and δ15N values of most food sources and consumers varied spatially, temporally and in relation to the diversion of wastewater, whereas the earthquakes did not appear to affect the overall estuarine food web structure. This was seen particularly at the most eutrophic site, where isotopic signatures became more similar to the cleaner sites over two-and-a-half years after the diversion. New sediments (liquefaction) produced by the earthquakes were found to be coarser, have lower concentrations of heavy metals and less organic matter than old (existing) sediments. They also had fewer macroinvertebrate inhabitants initially after the earthquakes but most areas recovered to pre-earthquake abundance and diversity within two years. Field experiments showed that there were higher amounts of primary production and lower amounts of nutrient efflux from new sediments at the eutrophic sites after the earthquakes. Primary production was highest in new sediments due to the increased photosynthetic efficiency of BMA resulting from the increased permeability of new sediments allowing increased light penetration, enhanced vertical migration of BMA and the enhanced transport of oxygen and nutrients. The reduced efflux of NH4-N in new sediments indicated that the capping of a large portion of eutrophic old sediments with new sediments had reduced the release of legacy nutrients (originating from the historical discharge) from the sediments to the overlying water. Laboratory experiments using an array of species and old and new sediments showed that invertebrates altered levels of primary production and nutrient flux but effects varied among species. The mud snail Amphibola crenata and mud crab Austrohelice crassa were found to reduce primary production and BMA biomass through the consumption of BMA (both species) and its burial from bioturbation and the construction of burrows (Austrohelice). In contrast, the cockle Austrovenus stutchburyi did not significantly affect primary production and BMA biomass. These results show that changes in the structure of invertebrate communities resulting from disturbances can also have consequences for the functioning of the system. The major conclusions of this study were that the wastewater diversion had a major effect on food web dynamics and that the large quantities of clean and unpolluted new sediments introduced to the estuary during the earthquakes altered the recovery trajectory of the estuary, accelerating it at least throughout the duration of this study. This was largely through the ‘capping’ effect of the new liquefied, coarser-grained sediments as they dissipated across the estuary and covered much of the old organic-rich eutrophic sediments. For all aspects of this study, the largest changes occurred at the most eutrophic sites; however, the surrounding habitats were important as they provided the context for recovery of the estuary, particularly because of the very strong influence of sediments, their biogeochemistry, microalgal and macroalgal dynamics. There have been few studies documenting system level responses to eutrophication amelioration and to the best on my knowledge there are no other published studies examining the impacts of large earthquakes on benthic communities in an estuarine ecosystem. This research gives valuable insight and advancements in the scientific understanding of the effects that eutrophication recovery and large-scale disturbances can have on the ecology of a soft-sediment ecosystem.
Oblique-convergent plate collision between the Pacific and Australian plates across the South Island has resulted in shallow, upper crustal earthquake activity and ground surface deformation. In particular the Porters Pass - Amberley Fault Zone displays a complex hybrid zone of anastomosing dextral strike-slip and thrust/reverse faulting which includes the thrust/reverse Lees Valley Fault Zone and associated basin deformation. There is a knowledge gap with respect to the paleoseismicity of many of the faults in this region including the Lees Valley Fault Zone. This study aimed to investigate the earthquake history of the fault at a selected location and the structural and geomorphic development of the Lees Valley Fault Zone and eastern rangefront. This was investigated through extensive structural and geomorphic mapping, GPS field surveying, vertical aerial photo interpretation, analysis of Digital Elevation Models, paleoseismic trenching and optically stimulated luminescence dating. This thesis used a published model for tectonic geomorphology development of mountain rangefronts to understand the development of Lees Valley. Rangefront geomorphology is investigated through analysis of features such as rangefront sinuosity and faceted spurs and indicates the recently active and episodic nature of the uplifted rangefront. Analysis of fault discontinuity, fault splays, distribution of displacement, fault deformation zone and limited exposure of bedrock provided insight into the complex structure of the fault zone. These observations revealed preserved, earlier rangefronts, abandoned and uplifted within the eastern ranges, indicating a basinward shift in focus of faulting and an imbricate thrust wedge development propagating into the footwall of the fault zone and along the eastern ranges of Lees Valley. Fault scarp deformation analysis indicated multiple events have produced the deformation present preserved by the active fault trace in the northern valley. Vertical deformation along this scarp varied with a maximum of 11.5 m and an average of 5 m. Field mapping revealed fan surfaces of various ages have been offset and deformed, likely during the Holocene, based on expected relative surface ages. Geomorphic and structural mapping highlighted the effect of cross-cutting and inherited structures on the Lees Valley Fault, resulting in a step-over development in the centre of the eastern range-bounding trace. Paleoseismic trenching provided evidence of at least two earthquakes, which were constrained to post 21.6 ± 2.3 ka by optically stimulated luminescence dating. Single event displacements (1.48 ± 0.08 m), surface rupture earthquake magnitudes (Mw 6.7 ± 0.1, with potential to produce ≥ 7.0), and a minimum recurrence interval (3.6 ± 0.3 ka) indicated the Lees Valley Fault is an active structure capable of producing significant earthquake events. Results from this study indicate that the Lees Valley Fault Zone accommodates an important component of the Porters Pass - Amberley Fault Zone deformation and confirms the fault as a source of potentially damaging, peak ground accelerations in the Canterbury region. Remnants of previous rangefronts indicate a thrust wedge development of the Lees Valley Fault Zone and associated ranges that can potentially be used as a model of development for other thrust-fault bounded basins.
Between 2010 and 2011, Canterbury experienced a series of four large earthquake events with associated aftershocks which caused widespread damage to residential and commercial infrastructure. Fine grained and uncompacted alluvial soils, typical to the Canterbury outwash plains, were exposed to high peak ground acceleration (PGA) during these events. This rapid increase in PGA induced cyclic strain softening and liquefaction in the saturated, near surface alluvial soils. Extensive research into understanding the response of soils in Canterbury to dynamic loading has since occurred. The Earthquake Commission (EQC), the Ministry of Business and Employment (MBIE), and the Christchurch City Council (CCC) have quantified the potential hazards associated with future seismic events. Theses bodies have tested numerous ground improvement design methods, and subsequently are at the forefront of the Canterbury recovery and rebuild process. Deep Soil Mixing (DSM) has been proven as a viable ground improvement foundation method used to enhance in situ soils by increasing stiffness and positively altering in situ soil characteristics. However, current industry practice for confirming the effectiveness of the DSM method involves specific laboratory and absolute soil test methods associated with the mixed column element itself. Currently, the response of the soil around the columns to DSM installation is poorly understood. This research aims to understand and quantify the effects of DSM columns on near surface alluvial soils between the DSM columns though the implementation of standardised empirical soil test methods. These soil strength properties and ground improvement changes have been investigated using shear wave velocity (Vs), soil behaviour and density response methods. The results of the three different empirical tests indicated a consistent improvement within the ground around the DSM columns in sandier soils. By contrast, cohesive silty soils portrayed less of a consistent response to DSM, although still recorded increases. Generally, within the tests completed 50 mm from the column edge, the soil response indicated a deterioration to DSM. This is likely to be a result of the destruction of the soil fabric as the stress and strain of DSM is applied to the un‐mixed in situ soils. The results suggest that during the installation of DSM columns, a positive ground effect occurs in a similar way to other methods of ground improvement. However, further research, including additional testing following this empirical method, laboratory testing and finite 2D and 3D modelling, would be useful to quantify, in detail, how in situ soils respond and how practitioners should consider these test results in their designs. This thesis begins to evaluate how alluvial soils tend to respond to DSM. Conducting more testing on the research site, on other sites in Christchurch, and around the world, would provide a more complete data set to confirm the results of this research and enable further evaluation. Completing this additional research could help geotechnical DSM practitioners to use standardised empirical test methods to measure and confirm ground improvement rather than using existing test methods in future DSM projects. Further, demonstrating the effectiveness of empirical test methods in a DSM context is likely to enable more cost effective and efficient testing of DSM columns in future geotechnical projects.
“One of the most basic and fundamental questions in urban master planning and building regulations is ‘how to secure common access to sun, light and fresh air?” (Stromann-Andersen & Sattrup, 2011). Daylighting and natural ventilation can have significant benefits in office buildings. Both of these ‘passive’ strategies have been found to reduce artificial lighting and air-conditioning energy consumption by as much as 80% (Ministry for the Environment, 2008); (Brager, et al., 2007). Access to daylight and fresh air can also be credited with improved occupant comfort and health, which can lead to a reduction of employee absenteeism and an increase of productivity (Sustainability Victoria, 2008). In the rebuild of Christchurch central city, following the earthquakes of 2010 and 2011, Cantabrians have expressed a desire for a low-rise, sustainable city, with open spaces and high performance buildings (Christchurch City Council, 2011). With over 80% of the central city being demolished, a unique opportunity to readdress urban form and create a city that provides all buildings with access to daylight and fresh air exists. But a major barrier to wide-spread adoption of passive buildings in New Zealand is their dependence on void space to deliver daylight and fresh air – void space which could otherwise be valuable built floor space. Currently, urban planning regulations in Christchurch prioritize density, allowing and even encouraging low performance compact buildings. Considering this issue of density, this thesis aimed to determine which urban form and building design changes would have the greatest effect on building performance in Central City Christchurch. The research proposed and parametrically tested modifications of the current compact urban form model, as well as passive building design elements. Proposed changes were assessed in three areas: energy consumption, indoor comfort and density. Three computer programs were used: EnergyPlus was the primary tool, simulating energy consumption and thermal comfort. Radiance/Daysim was used to provide robust daylighting calculations and analysis. UrbaWind enabled detailed consideration of the urban wind environment for reliable natural ventilation predictions. Results found that, through a porous urban form and utilization of daylight and fresh air via simple windows, energy consumption could be reduced as much as 50% in buildings. With automatic modulation of windows and lighting, thermal and visual comfort could be maintained naturally for the majority of the occupied year. Separation of buildings by as little as 2m enabled significant energy improvements while having only minimal impact on individual property and city densities. Findings indicated that with minor alterations to current urban planning laws, all buildings could have common access to daylight and fresh air, enabling them to operate naturally, increasing energy efficiency and resilience.
Non-structural elements (NSEs) have frequently proven to contribute to significant losses sustained from earthquakes in the form of damage, downtime, injury and death. In New Zealand (NZ), the 2010 and 2011 Canterbury Earthquake Sequence (CES), the 2013 Seddon and Cook Strait earthquake sequence and the 2016 Kaikoura earthquake were major milestones in this regard as significant damage to building NSEs both highlighted and further reinforced the importance of NSE seismic performance to the resilience of urban centres. Extensive damage in suspended ceilings, partition walls, façades and building services following the CES was reported to be partly due to erroneous seismic design or installation or caused by intervening elements. Moreover, the low-damage solutions developed for structural systems sometimes allow for relatively large inter-story drifts -compared to conventional designs- which may not have been considered in the seismic design of NSEs. Having observed these shortcomings, this study on suspended ceilings was carried out with five main goals: i) Understanding the seismic performance of the system commonly used in NZ; ii) Understanding the transfer of seismic design actions through different suspended ceiling components, iii) Investigating potential low-damage solutions; iii) Evaluating the compatibility of the current ceiling system with other low-damage NSEs; and iv) Investigating the application of numerical analysis to simulate the response of ceiling systems. The first phase of the study followed a joint research work between the University of Canterbury (UC) in NZ, and the Politecnico Di Milano, in Italy. The experimental ceiling component fragility curves obtained in this existing study were employed to produce analytical fragility curves for a perimeter-fixed ceiling of a given size and weight, with grid acceleration as the intensity measure. The validity of the method was proven through comparisons between this proposed analytical approach with the recommended procedures in proprietary products design guidelines, as well as experimental fragility curves from other studies. For application to engineering design practice, and using fragility curves for a range of ceiling lengths and weights, design curves were produced for estimating the allowable grid lengths for a given demand level. In the second phase of this study, three specimens of perimeter-fixed ceilings were tested on a shake table under both sinusoidal and random floor motion input. The experiments considered the relationship between the floor acceleration, acceleration of the ceiling grid, the axial force induced in the grid members, and the effect of boundary conditions on the transfer of these axial forces. A direct correlation was observed between the axial force (recorded via load cells) and the horizontal acceleration measured on the ceiling grid. Moreover, the amplification of floor acceleration, as transferred through ceiling components, was examined and found (in several tests) to be greater than the recommended factor for the design of ceilings provided in the NZ earthquake loadings standard NZS1170.5. However, this amplification was found to be influenced by the pounding interactions between the ceiling grid members and the tiles, and this amplification diminished considerably when the high frequency content was filtered out from the output time histories. The experiments ended with damage in the ceiling grid connection at an axial force similar to the capacity of these joints previously measured through static tests in phase one. The observation of common forms of damage in ceilings in earthquakes triggered the monotonic experiments carried out in the third phase of this research with the objective of investigating a simple and easily applicable mitigation strategy for existing or new suspended ceilings. The tests focused on the possibility of using proprietary cross-shaped clip elements ordinarily used to provide seismic gap as a strengthening solution for the weak components of a ceiling. The results showed that the solution was effective under both tension and compression loads through increasing load bearing capacity and ductility in grid connections. The feasibility of a novel type of suspended ceiling called fully-floating ceiling system was investigated through shaking table tests in the next phase of this study with the main goal of isolating the ceiling from the surrounding structure; thereby arresting the transfer of associated seismic forces from the structure to the ceiling. The fully-floating ceiling specimen was freely hung from the floor above lacking any lateral bracing and connections with the perimeter. Throughout different tests, a satisfactory agreement between the fully-floating ceiling response and simple pendulum theory was demonstrated. The addition of isolation material in perimeter gaps was found effective in inducing extra damping and protecting the ceiling from pounding impact; resulting in much reduced ceiling displacements and accelerations. The only form of damage observed throughout the random floor motion tests and the sinusoidal tests was a panel dislodgement observed in a test due to successive poundings between the ceiling specimen and the surrounding beams at resonant frequencies. Partition walls as the first effective NSE in direct interaction with ceilings were the topic of the final experimental phase. Low-damage drywall partitions proposed in a previous study in the UC were tested with two common forms of suspended ceiling: braced and perimeter-fixed. The experiments investigated the in-plane and out-of-plane performance of the low-damage drywall partitions, as well as displacement compatibility between these walls and the suspended ceilings. In the braced ceiling experiment, where no connection was made between ceiling grids and surrounding walls no damage in the grid system or partitions was observed. However, at high drift values panel dislodgement was observed on corners of the ceiling where the free ends of grids were not restrained against spreading. This could be prevented by framing the grid ends using a perimeter angle that is riveted only to the grid members while keeping sufficient clearance from the perimeter walls. In the next set of tests with the perimeter-fixed ceiling, no damage was observed in the ceiling system or the drywalls. Based on the results of the experiments it was concluded that the tested ceiling had enough flexibility to accommodate the relative displacement between two perpendicular walls up to the inter-storey drifts achieved. The experiments on perimeter-fixed ceilings were followed by numerical simulations of the performance of these ceilings in a finite element model developed in the structural analysis software, SAP2000. This model was relatively simple and easy to develop and was able to replicate the experimental results to a reasonable degree. Filtering was applied to the experimental output to exclude the effect of high frequency noise and tile-grid impact. The developed model generally simulated the acceleration responses well but underestimated the peak ceiling grid accelerations. This was possibly because the peak values in time histories were affected by impact occurring at very short periods. The model overestimated the axial forces in ceiling grids which was assumed to be caused by the initial assumptions made about the tributary area or constant acceleration associated with each grid line in the direction of excitation. Otherwise, the overall success of the numerical modelling in replicating the experimental results implies that numerical modelling using conventional structural analysis software could be used in engineering practice to analyse alternative ceiling geometries proposed for application to varying structural systems. This however, needs to be confirmed through similar analyses on other ceiling examples from existing instrumented buildings during real earthquakes. As the concluding part of this research the final phase addressed the issues raised following the review of existing ceiling standards and guidelines. The applicability of the research findings to current practice and their implications were discussed. Finally, an example was provided for the design of a suspended ceiling utilising the new knowledge acquired in this research.
This dissertation addresses a diverse range of topics in the physics-based broadband ground motion simulation, with a focus on New Zealand applications. In particular the following topics are addressed: the methodology and computational implementation of a New Zealand Velocity Model for broadband ground motion simulation; generalised parametric functions and spatial correlations for seismic velocities in the Canterbury, New Zealand region from surface-wave-based site characterisation; and ground motion simulations of Hope Fault earthquakes. The paragraphs below outline each contribution in more detail. A necessary component in physics-based ground motion simulation is a 3D model which details the seismic velocities in the region of interest. Here a velocity model construction methodology, its computational implementation, and application in the construction of a New Zealand velocity model for use in physics-based broadband ground motion simulation are presented. The methodology utilises multiple datasets spanning different length scales, which is enabled via the use of modular sub-regions, geologic surfaces, and parametric representations of crustal velocity. A number of efficiency-related workflows to decrease the overall computational construction time are employed, while maintaining the flexibility and extensibility to incorporate additional datasets and re- fined velocity parameterizations as they become available. The model comprises explicit representations of the Canterbury, Wellington, Nelson-Tasman, Kaikoura, Marlborough, Waiau, Hanmer and Cheviot sedimentary basins embedded within a regional travel-time tomography-based velocity model for the shallow crust and provides the means to conduct ground motion simulations throughout New Zealand for the first time. Recently developed deep shear-wave velocity profiles in Canterbury enabled models that better characterise the velocity structure within geologic layers of the Canterbury sedimentary basin to be developed. Here the development of depth- and Vs30-dependent para-metric velocity and spatial correlation models to characterise shear-wave velocities within the geologic layers of the Canterbury sedimentary basin are presented. The models utilise data from 22 shear-wave velocity profiles of up to 2.5km depth (derived from surface wave analysis) juxtaposed with models which detail the three-dimensional structure of the geologic formations in the Canterbury sedimentary basin. Parametric velocity equations are presented for Fine Grained Sediments, Gravels, and Tertiary layer groupings. Spatial correlations were developed and applied to generate three-dimensional stochastic velocity perturbations. Collectively, these models enable seismic velocities to be realistically represented for applications such as 3D ground motion and site response simulations. Lastly the New Zealand velocity model is applied to simulate ground motions for a Mw7.51 rupture of the Hope Fault using a physics-based simulation methodology and a 3D crustal velocity model of New Zealand. The simulation methodology was validated for use in the region through comparison with observations for a suite of historic small magnitude earthquakes located proximal to the Hope Fault. Simulations are compared with conventionally utilised empirical ground motion models, with simulated peak ground velocities being notably higher in regions with modelled sedimentary basins. A sensitivity analysis was undertaken where the source characteristics of magnitude, stress parameter, hypocentre location and kinematic slip distribution were varied and an analysis of their effect on ground motion intensities is presented. It was found that the magnitude and stress parameter strongly influenced long and short period ground motion amplitudes, respectively. Ground motion intensities for the Hope Fault scenario are compared with the 2016 Kaikoura Mw7.8 earthquake, it was found that the Kaikoura earthquake produced stronger motions along the eastern South Island, while the Hope Fault scenario resulted in stronger motions immediately West of the near-fault region. The simulated ground motions for this scenario complement prior empirically-based estimates and are informative for mitigation and emergency planning purposes.
Cats all over the world hunt wild animals and can contribute to the extinction of threatened species. In New Zealand, around half of all households have at least one cat. When cats live close to a natural area, such as a wetland, they may have impacts on native species. A previous study on the movements and hunting behaviour of domestic (house) cats around the Travis Wetland, Christchurch, New Zealand during 2000-2001 raised concerns about the effects of cats on the local skink population, as skinks were a frequent prey item. My study is a comparison to the prior study, to determine if impacts have changed alongside changes in human populations in the area post-earthquake. The domestic cat population in the area was estimated by a household survey in March-April 2018. For a 6 month period from March-September 2018, 26 households recorded prey brought home by their 41 cats. During April-July 2018, 14 cats wore Global Positioning System (GPS) devices for 7 days each to track their movements. Skink abundance was measured with pitfall trapping over 20 days in February 2018. There were more households in the area in 2018 than there were in 2000, but the numbers of cats had decreased. In the 196 ha study area around Travis Wetland, the domestic cat population was estimated at 429 cats, down from the previous 494. Most of the cats were free roaming, but the majority had been desexed and many were mostly seen at home. A total of 42 prey items were reported from 26 households and 41 cats over 6 months. Of these, 62% were rodents, 26% were exotic birds, and 12% were native birds. There were no native skinks, other mammals, or other vertebrates such as fish and amphibians (invertebrates were not included in this study). Eight male and six female cats were tracked by GPS. Home range sizes for the 100% minimum convex polygons (MCPs) ranged from 1.34 to 9.68 ha (mean 4.09 ha, median 3.54 ha). There were 9/14 (64%) cats that entered the edge of the wetland. Males had significantly larger home range areas at night and in general compared with females. However, age and distance of the cat’s household to the wetland did not have a significant effect on home range size and there was no significant correlation between home range size and prey retrieved. In 20 days of skink trapping, 11 Oligosoma polychroma were caught. The estimated catch rate was not significantly different from an earlier study on skink abundance in Travis Wetland. The apparently low abundance of skinks may have been the result of successful wetland restoration creating less suitable skink habitat, or of other predators other than cats. In the future, increased education should be provided to the public about ways to increase wildlife in their area. This includes creating lizard friendly habitat in their gardens and increasing management for cats. Generally, only a few cats bring home prey often, and these select cats should be identified in initial surveys and included in further studies. In New Zealand, until management programmes can target all predators in urban areas, domestic cats could stay out at night and inside during the day to help decrease the abundance of rodents at night and reduce the number of birds and lizards caught during the day.
On the 22nd of February, 2011 the city of Christchurch, New Zealand was crippled by a colossal earthquake. 185 people were killed, thousands injured and what remained was a city left in destruction and ruin. Thousands of Christchurch properties and buildings were left damaged beyond repair and the rich historical architecture of the Canterbury region had suffered irreparably. This research will conduct an investigation into whether the use of mixed reality can aid in liberating Christchurch’s rich architectural heritage when applied to the context of destructed buildings within Christchurch. The aim of this thesis is to formulate a narrative around the embodiment of mixed reality when subjected to the fragmentary historical architecture of Christchurch. Mixed reality will aspire to act as the defining ligature that holds the past, present and future of Christchurch’s architectural heritage intact as if it is all part of the same continuum. This thesis will focus on the design of a memorial museum within a heavily damaged historical trust registered building due to the Christchurch earthquake. It is important and relevant to conceive the idea of such a design as history is what makes everything we know. The memories of the past, the being of the now and the projection of the future is the basis and fundamental imperative in honouring the city and people of Christchurch. Using the technologies of Mixed Reality and the realm of its counter parts the memorial museum will be a definitive proposition of desire in providing a psychological and physical understanding towards a better Christchurch, for the people of Christchurch. This thesis serves to explore the renovation possibilities of the Canterbury provincial council building in its destructed state to produce a memorial museum for the Christchurch earthquake. The design seeks to mummify the building in its raw state that sets and develops the narrative through the spaces. The design intervention is kept at a required minimum and in doing so manifests a concentrated eloquence to the derelict space. The interior architecture unlocks the expression of history and time encompassed within a destructive and industrialised architectural dialogue. History is the inhabitant of the building, and using the physical and virtual worlds it can be set free. This thesis informs a design for a museum in central Christchurch that celebrates and informs the public on past, present and future heritage aspects of Christchurch city. Using mixed reality technologies the spatial layout inside will be a direct effect of the mixed reality used and the exploration of the physical and digital heritage aspects of Christchurch. The use of technology in today’s world is so prevalent that incorporating it into a memorial museum for Christchurch would not only be interesting and exploratory but also offer a sense of pushing forward and striving beyond for a newer, fresher Christchurch. The memorial museum will showcase a range of different exhibitions that formulate around the devastating Christchurch earthquake. Using mixed reality technologies these exhibitions will dictate the spaces inside dependant on their various applications of mixed reality as a technology for architecture. Research will include; what the people of Canterbury are most dear to in regards to Christchurch’s historical environment; the use of mixed reality to visualise digital heritage, and the combination of the physical and digital to serve as an architectural mediation between what was, what is and what there could be.
A non-destructive hardness testing method has been developed to investigate the amount of plastic strain demand in steel elements subjected to cyclic loading. The focus of this research is on application to the active links of eccentrically braced frames (EBFs), which are a commonly used seismic-resisting system in modern steel framed buildings. The 2010/2011 Christchurch earthquake series, especially the very intense February 22 shaking, which was the first earthquake worldwide to push complete EBF systems fully into their inelastic state, generating a moderate to high level of plastic strain in EBF active links, for a range of buildings from 3 to 23 storeys in height. This raised two important questions: 1) what was the extent of plastic deformation in active links; and 2) what effect does that have to post-earthquake steel properties? This project comprised determining a robust relationship between hardness and plastic strain in order to be able to answer the first question and provide the necessary input into answering the second question. A non-destructive Leeb (portable) hardness tester (model TH170) has been used to measure the hardness, in order to determine the plastic strain, in hot rolled steel universal sections and steel plates. A bench top Rockwell B was used to compare and validated the hardness measured by the portable hardness tester. Hardness was measured from monotonically strained tensile test specimens to identify the relationship between hardness and plastic strain demand. Test results confirmed a good relationship between hardness and the amount of monotonically induced plastic strain. Surface roughness was identified as an important parameter in obtaining reliable hardness readings from a portable hardness reader. A proper surface preparation method was established by using three different cleaning methods, finished with hand sanding to achieve surface roughness coefficients sufficiently low not to distort the results. This work showed that a test surface roughness (Ra) is not more than 1.6 micron meter (μm) is required for accurate readings from the TH170 tester. A case study on an earthquake affected building was carried out to identify the relationship between hardness and amount of plastic strain demand in cyclically deformed active links. Hardness was carried out from active links shown visually to have been the most affected during one of the major earthquake events. Onsite hardness test results were then compared with laboratory hardness test results. A good relationship between hardness from onsite and laboratory was observed between the test methods; Rockwell B bench top and portable Leeb tester TH170. Manufacturing induced plastic strain in the top and bottom of the webs of hot rolled sections were discovered from this research, an important result which explains why visual effects of earthquake induced active link yielding (eg cracked or flaking paint) was typically more prevalent over the middle half depth of the active link. The extent of this was quantified. It was also evident that the hardness readings from the portable hardness tester are influenced by geometry, mass effects and rigidity of the links. The final experimental stage was application of the method to full scale cyclic inelastic tested nominally identical active links subjected to loading regimes comprising constant and variable plastic strain demands. The links were cyclically loaded to achieve different plastic strain level. A novel Digital Image Correlation (DIC) technique was incorporated during the tests of this scale, to confirm the level of plastic strain achieved. Tensile test specimens were water jet cut from cyclically deformed webs to analyse the level of plastic strain. Test results show clear evidence that cyclically deformed structural steel elements show good correlation between hardness and the amount of plastic strain demand. DIC method was found to be reliable and accurate to check the level of plastic strain within cyclically deformed structural steel elements.
The influence of nonlinear soil-foundation-structure interaction (SFSI) on the performance of multi-storey buildings during earthquake events has become increasingly important in earthquake resistant design. For buildings on shallow foundations, SFSI refers to nonlinear geometric effects associated with uplift of the foundation from the supporting soil as well as nonlinear soil deformation effects. These effects can potentially be beneficial for structural performance, reducing forces transmitted from ground shaking to the structure. However, there is also the potential consequence of residual settlement and rotation of the foundation. This Thesis investigates the influence of SFSI in the performance of multi-storey buildings on shallow foundations through earthquake observations, experimental testing, and development of spring-bed numerical models that can be incorporated into integrated earthquake resistant design procedures. Observations were made following the 22 February 2011 Christchurch Earthquake in New Zealand of a number of multi-storey buildings on shallow foundations that performed satisfactorily. This was predominantly the case in areas where shallow foundations, typically large raft foundations, were founded on competent gravel and where there was no significant manifestation of liquefaction at the ground surface. The properties of these buildings and the soils they are founded on directed experimental work that was conducted to investigate the mechanisms by which SFSI may have influenced the behaviour of these types of structure-foundation systems. Centrifuge experiments were undertaken at the University of Dundee, Scotland using a range of structure-foundation models and a layer of dense cohesionless soil to simulate the situation in Christchurch where multi-storey buildings on shallow foundations performed well. Three equivalent single degree of freedom (SDOF) models representing 3, 5, and 7 storey buildings with identical large raft foundations were subjected to a range of dynamic Ricker wavelet excitations and Christchurch Earthquake records to investigate the influence of SFSI on the response of the equivalent buildings. The experimental results show that nonlinear SFSI has a significant influence on structural response and overall foundation deformations, even though the large raft foundations on competent soil meant that there was a significant reserve of bearing capacity available and nonlinear deformations may have been considered to have had minimal effect. Uplift of the foundation from the supporting soil was observed across a wide range of input motion amplitudes and was particularly significant as the amplitude of motion increased. Permanent soil deformation represented by foundation settlement and residual rotation was also observed but mainly for the larger input motions. However, the absolute extent of uplift and permanent soil deformation was very small compared to the size of the foundation meaning the serviceability of the building would still likely be maintained during large earthquake events. Even so, the small extent of SFSI resulted in attenuation of the response of the structure as the equivalent period of vibration was lengthened and the equivalent damping in the system increased. The experimental work undertaken was used to validate and enhance numerical modelling techniques that are simple yet sophisticated and promote interaction between geotechnical and structural specialists involved in the design of multi-storey buildings. Spring-bed modelling techniques were utilised as they provide a balance between ease of use, and thus ease of interaction with structural specialists who have these techniques readily available in practice, and theoretically rigorous solutions. Fixed base and elastic spring-bed models showed they were unable to capture the behaviour of the structure-foundation models tested in the centrifuge experiments. SFSI spring-bed models were able to more accurately capture the behaviour but recommendations were proposed for the parameters used to define the springs so that the numerical models closely matched experimental results. From the spring-bed modelling and results of centrifuge experiments, an equivalent linear design procedure was proposed along with a procedure and recommendations for the implementation of nonlinear SFSI spring-bed models in practice. The combination of earthquake observations, experimental testing, and simplified numerical analysis has shown how SFSI is influential in the earthquake performance of multi-storey buildings on shallow foundations and should be incorporated into earthquake resistant design of these structures.
Previous earthquakes demonstrated destructive effects of soil-structure interaction on structural response. For example, in the 1970 Gediz earthquake in Turkey, part of a factory was demolished in a town 135 km from the epicentre, while no other buildings in the town were damaged. Subsequent investigations revealed that the fundamental period of vibration of the factory was approximately equal to that of the underlying soil. This alignment provided a resonance effect and led to collapse of the structure. Another dramatic example took place in Adapazari, during the 1999 Kocaeli earthquake where several foundations failed due to either bearing capacity exceedance or foundation uplifting, consequently, damaging the structure. Finally, the Christchurch 2012 earthquakes have shown that significant nonlinear action in the soil and soil-foundation interface can be expected due to high levels of seismic excitation and spectral acceleration. This nonlinearity, in turn, significantly influenced the response of the structure interacting with the soil-foundation underneath. Extensive research over more than 35 years has focused on the subject of seismic soil-structure interaction. However, since the response of soil-structure systems to seismic forces is extremely complex, burdened by uncertainties in system parameters and variability in ground motions, the role of soil-structure interaction on the structural response is still controversial. Conventional design procedures suggest that soil-structure interaction effects on the structural response can be conservatively ignored. However, more recent studies show that soil-structure interaction can be either beneficial or detrimental, depending on the soil-structure-earthquake scenarios considered. In view of the above mentioned issues, this research aims to utilise a comprehensive and systematic probabilistic methodology, as the most rational way, to quantify the effects of soil-structure interaction on the structural response considering both aleatory and epistemic uncertainties. The goal is achieved by examining the response of established rheological single-degree-of-freedom systems located on shallow-foundation and excited by ground motions with different spectral characteristics. In this regard, four main phases are followed. First, the effects of seismic soil-structure interaction on the response of structures with linear behaviour are investigated using a robust stochastic approach. Herein, the soil-foundation interface is modelled by an equivalent linear cone model. This phase is mainly considered to examine the influence of soil-structure interaction on the approach that has been adopted in the building codes for developing design spectrum and defining the seismic forces acting on the structure. Second, the effects of structural nonlinearity on the role of soil-structure interaction in modifying seismic structural response are studied. The same stochastic approach as phase 1 is followed, while three different types of structural force-deflection behaviour are examined. Third, a systematic fashion is carried out to look for any possible correlation between soil, structural, and system parameters and the degree of soil-structure interaction effects on the structural response. An attempt is made to identify the key parameters whose variation significantly affects the structural response. In addition, it is tried to define the critical range of variation of parameters of consequent. Finally, the impact of soil-foundation interface nonlinearity on the soil-structure interaction analysis is examined. In this regard, a newly developed macro-element covering both material and geometrical soil-foundation interface nonlinearity is implemented in a finite-element program Raumoko 3D. This model is then used in an extensive probabilistic simulation to compare the effects of linear and nonlinear soil-structure interaction on the structural response. This research is concluded by reviewing the current design guidelines incorporating soil-structure interaction effects in their design procedures. A discussion is then followed on the inadequacies of current procedures based on the outcomes of this study.
The increase of the world's population located near areas prone to natural disasters has given rise to new ‘mega risks’; the rebuild after disasters will test the governments’ capabilities to provide appropriate responses to protect the people and businesses. During the aftermath of the Christchurch earthquakes (2010-2012) that destroyed much of the inner city, the government of New Zealand set up a new partnership between the public and private sector to rebuild the city’s infrastructure. The new alliance, called SCIRT, used traditional risk management methods in the many construction projects. And, in hindsight, this was seen as one of the causes for some of the unanticipated problems. This study investigated the risk management practices in the post-disaster recovery to produce a specific risk management model that can be used effectively during future post-disaster situations. The aim was to develop a risk management guideline for more integrated risk management and fill the gap that arises when the traditional risk management framework is used in post-disaster situations. The study used the SCIRT alliance as a case study. The findings of the study are based on time and financial data from 100 rebuild projects, and from surveying and interviewing risk management professionals connected to the infrastructure recovery programme. The study focussed on post-disaster risk management in construction as a whole. It took into consideration the changes that happened to the people, the work and the environment due to the disaster. System thinking, and system dynamics techniques have been used due to the complexity of the recovery and to minimise the effect of unforeseen consequences. Based on an extensive literature review, the following methods were used to produce the model. The analytical hierarchical process and the relative importance index have been used to identify the critical risks inside the recovery project. System theory methods and quantitative graph theory have been used to investigate the dynamics of risks between the different management levels. Qualitative comparative analysis has been used to explore the critical success factors. And finally, causal loop diagrams combined with the grounded theory approach has been used to develop the model itself. The study identified that inexperienced staff, low management competency, poor communication, scope uncertainty, and non-alignment of the timing of strategic decisions with schedule demands, were the key risk factors in recovery projects. Among the critical risk groups, it was found that at a strategic management level, financial risks attracted the highest level of interest, as the client needs to secure funding. At both alliance-management and alliance-execution levels, the safety and environmental risks were given top priority due to a combination of high levels of emotional, reputational and media stresses. Risks arising from a lack of resources combined with the high volume of work and the concern that the cost could go out of control, alongside the aforementioned funding issues encouraged the client to create the recovery alliance model with large reputable construction organisations to lock in the recovery cost, at a time when the scope was still uncertain. This study found that building trust between all parties, clearer communication and a constant interactive flow of information, established a more working environment. Competent and clear allocation of risk management responsibilities, cultural shift, risk prioritisation, and staff training were crucial factors. Finally, the post-disaster risk management (PDRM) model can be described as an integrated risk management model that considers how the changes which happened to the environment, the people and their work, caused them to think differently to ease the complexity of the recovery projects. The model should be used as a guideline for recovery systems, especially after an earthquake, looking in detail at all the attributes and the concepts, which influence the risk management for more effective PDRM. The PDRM model is represented in Causal Loops Diagrams (CLD) in Figure 8.31 and based on 10 principles (Figure 8.32) and 26 concepts (Table 8.1) with its attributes.
The overarching goal of this dissertation is to improve predictive capabilities of geotechnical seismic site response analyses by incorporating additional salient physical phenomena that influence site effects. Specifically, multidimensional wave-propagation effects that are neglected in conventional 1D site response analyses are incorporated by: (1) combining results of 3D regional-scale simulations with 1D nonlinear wave-propagation site response analysis, and (2) modelling soil heterogeneity in 2D site response analyses using spatially-correlated random fields to perturb soil properties. A method to combine results from 3D hybrid physics-based ground motion simulations with site-specific nonlinear site response analyses was developed. The 3D simulations capture 3D ground motion phenomena on a regional scale, while the 1D nonlinear site response, which is informed by detailed site-specific soil characterization data, can capture site effects more rigorously. Simulations of 11 moderate-to-large earthquakes from the 2010-2011 Canterbury Earthquake Sequence (CES) at 20 strong motion stations (SMS) were used to validate simulations with observed ground motions. The predictions were compared to those from an empirically-based ground motion model (GMM), and from 3D simulations with simplified VS30- based site effects modelling. By comparing all predictions to observations at seismic recording stations, it was found that the 3D physics-based simulations can predict ground motions with comparable bias and uncertainty as the GMM, albeit, with significantly lower bias at long periods. Additionally, the explicit modelling of nonlinear site-response improves predictions significantly compared to the simplified VS30-based approach for soft-soil or atypical sites that exhibit exceptionally strong site effects. A method to account for the spatial variability of soils and wave scattering in 2D site response analyses was developed and validated against a database of vertical array sites in California. The inputs required to run the 2D analyses are nominally the same as those required for 1D analyses (except for spatial correlation parameters), enabling easier adoption in practice. The first step was to create the platform and workflow, and to perform a sensitivity study involving 5,400 2D model realizations to investigate the influence of random field input parameters on wave scattering and site response. Boundary conditions were carefully assessed to understand their effect on the modelled response and select appropriate assumptions for use on a 2D model with lateral heterogeneities. Multiple ground-motion intensity measures (IMs) were analyzed to quantify the influence from random field input parameters and boundary conditions. It was found that this method is capable of scattering seismic waves and creating spatially-varying ground motions at the ground surface. The redistribution of ground-motion energy across wider frequency bands, and the scattering attenuation of high-frequency waves in 2D analyses, resemble features observed in empirical transfer functions (ETFs) computed in other studies. The developed 2D method was subsequently extended to more complicated multi-layer soil profiles and applied to a database of 21 vertical array sites in California to test its appropriate- ness for future predictions. Again, different boundary condition and input motion assumptions were explored to extend the method to the in-situ conditions of a vertical array (with a sensor embedded in the soil). ETFs were compared to theoretical transfer functions (TTFs) from conventional 1D analyses and 2D analyses with heterogeneity. Residuals of transfer-function- based IMs, and IMs of surface ground motions, were also used as validation metrics. The spatial variability of transfer-function-based IMs was estimated from 2D models and compared to the event-to-event variability from ETFs. This method was found capable of significantly improving predictions of median ETF amplification factors, especially for sites that display higher event-to-event variability. For sites that are well represented by 1D methods, the 2D approach can underpredict amplification factors at higher modes, suggesting that the level of heterogeneity may be over-represented by the 2D random field models used in this study.
The Avon-Heathcote Estuary, located in Christchurch, New Zealand, experienced coseismic deformation as a result of the February 22nd 2011 Christchurch Earthquake. The deformation is reflected as subsidence in the northern area and uplift in the southern area of the Estuary, in addition to sand volcanoes which forced up sediment throughout the floor of the Estuary altering estuary bed height and tidal flow. The first part of the research involved quantifying the change in the modern benthic foraminifera distribution as a result of the coseismic deformation caused by the February 22nd 2011 earthquake. By analysing the taxa present immediately post deformation and then the taxa present 2 years post deformation a comparison of the benthic foraminifera distribution can be made of the pre and post deformation. Both the northern and the southern areas of the Estuary were sampled to establish whether foraminifera faunas migrated landward or seaward as a result of subsidence and uplift experienced in different areas. There was no statistical change in overall species distribution in the two year time period since the coseismic deformation occurred, however, there were some noticeable changes in foraminifera distribution at BSNS-Z3 showing a landward migration of taxa. The changes that were predicted to occur as a result of the deformation of the Estuary are taking longer than expected to show up in the foraminiferal record and a longer time period is needed to establish these changes. The second stage involved establishing the modern distribution of foraminifera at Settlers Reserve in the southern area of the Avon-Heathcote Estuary by detailed sampling along a 160 m transect. Foraminifera are sensitive to environmental parameters, tidal height, grainsize, pH and salinity were recorded to evaluate the effect these parameters have on distribution. Bray-Curtis two-way cluster analysis was primarily used to assess the distribution pattern of foraminifera. The modern foraminifera distribution is comparable to that of the modern day New Zealand brackish-water benthic foraminifera distribution and includes species not yet found in other studies of the Avon-Heathcote Estuary. Differences in sampling techniques and the restricted intertidal marshland area where the transect samples were collected account for some of the differences seen between this model and past foraminifera studies. xiii The final stage involved sampling a 2.20 m core collected from Settlers Reserve and using the modern foraminiferal distribution to establish a foraminiferal history of Settlers Reserve. As foraminifera are sensitive to tidal height they may record past coseismic deformation events and the core was used to ascertain whether record of past coseismic deformation is preserved in Settlers Reserve sediments. Sampling the core for foraminifera, grainsize, trace metals and carbon material helped to build a story of estuary development. Using the modern foraminiferal distribution and the tidal height information collected, a down core model of past tidal heights was established to determine past rates of change. Foraminifera are not well preserved throughout the core, however, a sudden relative rise in sea level is recorded between 0.25 m and 0.85 m. Using trace metal and isotope analysis to develop an age profile, this sea level rise is interpreted to record coseismic subsidence associated with a palaeoseismic event in the early 1900’s. Overall, although the Avon-Heathcote Estuary experienced clear coseismic deformation as a result of the 22nd of February 2011 earthquake, modern changes in foraminiferal distribution cannot yet be tracked, however, past seismic deformation is identified in a core. The modern transect describes the foraminifera distribution which identifies species that have not been identified in the Avon-Heathcote Estuary before. This thesis enhances the current knowledge of the Avon-Heathcote Estuary and is a baseline for future studies.
This report presents the simplified seismic assessment of a case study reinforced concrete (RC) building following the newly developed and refined NZSEE/MBIE guidelines on seismic assessment (NZSEE/MBIE, semi-final draft 26 October 2016). After an overview of the step-by-step ‘diagnostic’ process, including an holistic and qualitative description of the expected vulnerabilities and of the assessment strategy/methodology, focus is given, whilst not limited, to the implementation of a Detailed Seismic Assessment (DSA) (NZSEE/MBIE, 2016c). The DSA is intended to provide a more reliable and consistent outcome than what can be provided by an initial seismic assessment (ISA). In fact, while the Initial Seismic Assessment (ISA), of which the Initial Evaluation Procedure is only a part of, is the more natural and still recommended first step in the overall assessment process, it is mostly intended to be a coarse evaluation involving as few resources as reasonably possible. It is thus expected that an ISA will be followed by a Detailed Seismic Assessment (DSA) not only where the threshold of 33%NBS is not achieved but also where important decisions are intended that are reliant on the seismic status of the building. The use of %NBS (% New Building Standard) as a capacity/demand ratio to describe the result of the seismic assessment at all levels of assessment procedure (ISA through to DSA) is deliberate by the NZSEE/MBIE guidelines (Part A) (NZSEE/MBIE 2016a). The rating for the building needs only be based on the lowest level of assessment that is warranted for the particular circumstances. Discussion on how the %NBS rating is to be determined can be found in Section A3.3 (NZSEE/MBIE 2016a), and, more specifically, in Part B for the ISA (NZSEE/MBIE 2016b) and Part C for the DSA (NZSEE/MBIE 2016c). As per other international approaches, the DSA can be based on several analysis procedures to assess the structural behaviour (linear, nonlinear, static or dynamic, force or displacement-based). The significantly revamped NZSEE 2016 Seismic Assessment Guidelines strongly recommend the use of an analytical (basically ‘by hand’) method, referred to the Simple Lateral Mechanism Analysis (SLaMA) as a first phase of any other numerically-based analysis method. Significant effort has thus been dedicated to provide within the NZSEE 2016 guidelines (NZSEE/MBIE 2016c) a step-by-step description of the procedure, either in general terms (Chapter 2) or with specific reference to Reinforced Concrete Buildings (Chapter 5). More specifically, extract from the guidelines, NZSEE “recommend using the Simple Lateral Mechanism Analysis (SLaMA) procedure as a first step in any assessment. While SLaMA is essentially an analysis technique, it enables assessors to investigate (and present in a simple form) the potential contribution and interaction of a number of structural elements and their likely effect on the building’s global capacity. In some cases, the results of a SLaMA will only be indicative. However, it is expected that its use should help assessors achieve a more reliable outcome than if they only carried out a detailed analysis, especially if that analysis is limited to the elastic range For complex structural systems, a 3D dynamic analysis may be necessary to supplement the simplified nonlinear Simple Lateral Mechanism Analysis (SLaMA).” This report presents the development of a full design example for the the implementation of the SLaMA method on a case study buildings and a validation/comparison with a non-linear static (pushover) analysis. The step-by-step-procedure, summarized in Figure 1, will be herein demonstrated from a component level (beams, columns, wall elements) to a subassembly level (hierarchy of strength in a beam-column joint) and to a system level (frame, C-Wall) assuming initially a 2D behaviour of the key structural system, and then incorporating a by-hand 3D behaviour (torsional effects).
Landslides are significant hazards, especially in seismically-active mountainous regions, where shaking amplified by steep topography can result in widespread landsliding. These landslides present not only an acute hazard, but a chronic hazard that can last years-to-decades after the initial earthquake, causing recurring impacts. The Mw 7.8 Kaikōura earthquake caused more than 20,000 landslides throughout North Canterbury and resulted in significant damage to nationally significant infrastructure in the coastal transport corridor (CTC), isolating Kaikōura from the rest of New Zealand. In the years following, ongoing landsliding triggered by intense rainfall exacerbated the impacts and slowed the recovery process. However, while there is significant research on co-seismic landslides and their initial impacts in New Zealand, little research has explored the evolution of co-seismic landslides and how this hazard changes over time. This research maps landslides annually between 2013 and 2021 to evaluate the changes in pre-earthquake, co-seismic and post-earthquake rates of landsliding to determine how landslide hazard has changed over this time. In particular, the research explores how the number, area, and spatial distribution of landslides has changed since the earthquake, and whether post-earthquake mitigation works have in any way affected the long-term landslide hazard. Mapping of landslides was undertaken using open-source, medium resolution Landsat-8 and Sentinel-2 satellite imagery, with landslides identified visually and mapped as single polygons that capture both the source zone and deposit. Three study areas with differing levels of post-earthquake mitigation are compared: (i) the northern CTC, where the majority of mitigation was in the form of active debris removal; (ii) the southern CTC, where mitigation was primarily via passive protection measures; and (iii) Mount Fyffe, which has had no mitigation works since the earthquake. The results show that despite similar initial impacts during the earthquake, the rate of recovery in terms of landslide rates varies substantially across the three study areas. In Mount Fyffe, the number and area of landslides could take 45 and 22 years from 2021 respectively to return to pre-earthquake levels at the current rate. Comparatively, in the CTC, it could take just 5 years and 3-4 years from 2021 respectively. Notably, the fastest recovery in terms of landslide rates in the CTC was primarily located directly along the transport network, whereas what little recovery did occur in Mount Fyffe appeared to follow no particular pattern. Importantly, recovery rates in the northern CTC were notably higher than in the southern CTC, despite greater co-seismic impacts in the former. Combined, these results suggest the active, debris removal mitigation undertaken in the northern CTC may have had the effect of dramatically reducing the time for landslide rates to return to pre-earthquake levels. The role of slope angle and slope aspect were explored to evaluate if these observations could be driven by local differences in topography. The Mount Fyffe study area has higher slope angles than the CTC as a whole and landslides predominantly occurred on slightly steeper slopes than in the CTC. This may have contributed to the longer recovery times for landsliding in Mount Fyffe due to greater gravitational instability, however the observed variations are minor compared to the differences in recovery rates. In terms of slope aspect, landslides in Mount Fyffe preferentially occurred on north- and south-facing slopes whereas landslides in the CTC preferred the east- and south-facing slopes. The potential role of these differences in landslide recovery remains unclear but may be related to the propagation direction of the earthquake and the tracking direction of post-earthquake ex-tropical cyclones. Finally, landslides in the CTC are observed to be moving further away from the transport network and the number of landslides impacting the CTC decreased significantly since the earthquake. Nevertheless, the potential for further landslide reactivation remains. Therefore, despite the recovery in the CTC, it is clear that there is still risk of the transport network being impacted by further landsliding, at least for the next 3-5 yrs.
Coastal and river environments are exposed to a number of natural hazards that have the potential to negatively affect both human and natural environments. The purpose of this research is to explain that significant vulnerabilities to seismic hazards exist within coastal and river environments and that coasts and rivers, past and present, have played as significant a role as seismic, engineering or socio-economic factors in determining the impacts and recovery patterns of a city following a seismic hazard event. An interdisciplinary approach was used to investigate the vulnerability of coastal and river areas in the city of Christchurch, New Zealand, following the Canterbury Earthquake Sequence, which began on the 4th of September 2010. This information was used to identify the characteristics of coasts and rivers that make them more susceptible to earthquake induced hazards including liquefaction, lateral spreading, flooding, landslides and rock falls. The findings of this research are applicable to similar coastal and river environments elsewhere in the world where seismic hazards are also of significant concern. An interdisciplinary approach was used to document and analyse the coastal and river related effects of the Canterbury earthquake sequence on Christchurch city in order to derive transferable lessons that can be used to design less vulnerable urban communities and help to predict seismic vulnerabilities in other New Zealand and international urban coastal and river environments for the future. Methods used to document past and present features and earthquake impacts on coasts and rivers in Christchurch included using maps derived from Geographical Information Systems (GIS), photographs, analysis of interviews from coastal, river and engineering experts, and analysis of secondary data on seismicity, liquefaction potential, geology, and planning statutes. The Canterbury earthquake sequence had a significant effect on Christchurch, particularly around rivers and the coast. This was due to the susceptibility of rivers to lateral spreading and the susceptibility of the eastern Christchurch and estuarine environments to liquefaction. The collapse of river banks and the extensive cracking, tilting and subsidence that accompanied liquefaction, lateral spreading and rock falls caused damage to homes, roads, bridges and lifelines. This consequently blocked transportation routes, interrupted electricity and water lines, and damaged structures built in their path. This study found that there are a number of physical features of coastal and river environments from the past and the present that have induced vulnerabilities to earthquake hazards. The types of sediments found beneath eastern Christchurch are unconsolidated fine sands, silts, peats and gravels. Together with the high water tables located beneath the city, these deposits made the area particularly susceptible to liquefaction and liquefaction-induced lateral spreading, when an earthquake of sufficient size shook the ground. It was both past and present coastal and river processes that deposited the types of sediments that are easily liquefied during an earthquake. Eastern Christchurch was once a coastal and marine environment 6000 years ago when the shoreline reached about 6 km inland of its present day location, which deposited fine sand and silts over this area. The region was also exposed to large braided rivers and smaller spring fed rivers, both of which have laid down further fine sediments over the following thousands of years. A significant finding of this study is the recognition that the Canterbury earthquake sequence has exacerbated existing coastal and river hazards and that assessments and monitoring of these changes will be an important component of Christchurch’s future resilience to natural hazards. In addition, patterns of recovery following the Canterbury earthquakes are highlighted to show that coasts and rivers are again vulnerable to earthquakes through their ability to recovery. This city’s capacity to incorporate resilience into the recovery efforts is also highlighted in this study. Coastal and river areas have underlying physical characteristics that make them increasingly vulnerable to the effects of earthquake hazards, which have not typically been perceived as a ‘coastal’ or ‘river’ hazard. These findings enhance scientific and management understanding of the effects that earthquakes can have on coastal and river environments, an area of research that has had modest consideration to date. This understanding is important from a coastal and river hazard management perspective as concerns for increased human development around coastlines and river margins, with a high seismic risk, continue to grow.
The collapse of Redcliffs’ cliff in the 22 February 2011 and 13 June 2011 earthquakes were the first times ever a major failure incident occurred at Redcliffs in approximately 6000 years. This master’s thesis is a multidisciplinary engineering geological investigation sought to study these particular failure incidents, focusing on collecting the data necessary to explain the cause and effect of the cliff collapsing in the event of two major earthquakes. This study provides quantitative and qualitative data about the geotechnical attributes and engineering geological nature of the sea-cut cliff located at Redcliffs. Results from surveying the geology of Redcliffs show that the exposed lithology of the cliff face is a variably jointed rock body of welded and (relatively intact) unwelded ignimbrite, a predominantly massive unit of brecciated tuff, and a covering of wind-blown loess and soil deposit (commonly found throughout Canterbury) on top of the cliff. Moreover, detailing the external component of the slope profile shows that Redcliffs’ cliff is a 40 – 80 m cliff with two intersecting (NE and SE facing) slope aspects. The (remotely) measured geometry of the cliff face comprises of multiple outstanding gradients, averaging a slope angle of ~67 degrees (post-13 June 2011), where the steepest components are ~80 degrees, whereas the gentle sloping sections are ~44 degrees. The physical structure of Redcliffs’ cliff drastically changed after each collapse, whereby seismically induced alterations to the slope geometry resulted in material deposited on the talus at the base of the cliff. Prior to the first collapse, the variance of the gradient down the slope was minimal, with the SE Face being the most variable with up to three major gradients on one cross section. However, after each major collapse, the variability increased with more parts of the cliff face having more than one major gradient that is steeper or gentler than the remainder of the slope. The estimated volume of material lost as a result of the gradient changes was 28,267 m³ in February and 11,360 m³ in June 2011. In addition, surveys of the cliff top after the failure incidents revealed the development of fissures along the cliff edge. Monitoring 10 fissures over three months indicated that fissured by the cliff edge respond to intense seismicity (generally ≥ Mw 4) by widening. Redcliffs’ cliff collapsed on two separate occasions as a result of an accumulated amount of damage of the rock masses in the cliff (caused by weathering and erosion over time), and two Mw 6.2 trigger earthquakes which shook the Redcliffs and the surrounding area at a Peak Ground Acceleration (PGA) estimated to be around 2 g. The results of the theoretical study suggests that PGA levels felt on-site during both instances of failure are the result of three major factors: source of the quake and the site affected; topographic amplification of the ground movement; the short distance between the source and the cliff for both fault ruptures; the focus of seismic energy in the direction of thrust faulting along a path that intercepts Redcliffs (and the Port Hills). Ultimately, failure on the NE and SE Faces of Redcliffs’ cliff was concluded to be global as every part of the exposed cliff face deposited a significant volume of material on the talus at the base of the cliff, with the exception of one section on the NE Face. The cliff collapses was a concurrent process that is a single (non-monotonic) event that operated as a complex series of (primarily) toppling rock falls, some sliding of blocks, and slumping of the soil mantle on top of the cliff. The first collapse had a mixture of equivalent continua slope movement of the heavily weathered / damaged surface of the cliff face, and discontinuous slope movement of the jointed inner slope (behind the heavily weathered surface); whereas the second collapse resulted in only discontinuous slope movement on account of the freshly exposed cliff face that had damage to the rock masses, in the form of old and (relatively) new discontinuous fractures, induced by earthquakes and aftershocks leading up to the point of failure.
