Following the devastation of the Canterbury earthquake sequence a unique opportunity exists to rebuild and restructure the city of Christchurch, ensuring that its infrastructure is constructed better than before and is innovative. By installing an integrated grid of modern sensor technologies into concrete structures during the rebuild of the Christchurch CBD, the aim is to develop a network of self-monitored ‘digital buildings’. A diverse range of data will be recorded, potentially including parameters such as concrete stresses, strains, thermal deformations, acoustics and the monitoring of corrosion of reinforcement bars. This procedure will allow an on-going complete assessment of the structure’s performance and service life, both before and after seismic activity. The data generated from the embedded and surface mounted sensors will be analysed to allow an innovative and real-time health monitoring solution where structural integrity is continuously known. This indication of building performance will allow the structure to alert owners, engineers and asset managers of developing problems prior to failure thresholds being reached. A range of potential sensor technologies for monitoring the performance of existing and newly constructed concrete buildings is discussed. A description of monitoring work conducted on existing buildings during the July 2013 Cook Strait earthquake sequence is included, along with details of current work that investigates the performance of sensing technologies for detecting crack formation in concrete specimens. The potential market for managing the real-time health of installed infrastructure is huge. Civil structures all over the world require regular visual inspections in order to determine their structural integrity. The information recorded during the Christchurch rebuild will generate crucial data sets that will be beneficial in understanding the behaviour of concrete over the complete life cycle of the structure, from construction through to operation and building repairs until the time of failure. VoR - Version of Record
The sequence of earthquakes that has greatly affected Christchurch and Canterbury since September 2010 has again demonstrated the need for seismic retrofit of heritage unreinforced masonry buildings. Commencing in April 2011, the damage to unreinforced stone masonry buildings in Christchurch was assessed and recorded with the primary objective being to document the seismic performance of these structures, recognising that they constitute an important component of New Zealand’s heritage architecture. A damage statistics database was compiled by combining the results of safety evaluation placarding and post-earthquake inspections, and it was determined that the damage observed was consistent with observations previously made on the seismic performance of stone masonry structures in large earthquakes. Details are also given on typical building characteristics and on failure modes observed. Suggestions on appropriate seismic retrofit and remediation techniques are presented, in relation also to strengthening interventions that are typical for similar unreinforced stone masonry structures in Europe.
Churches are an important part of New Zealand's historical and architectural heritage. Various earthquakes around the world have highlighted the significant seismic vulnerability of religious buildings, with the extensive damage that occurred to stone and clay-brick unreinforced masonry churches after the 2010-2011 Canterbury earthquakes emphasising the necessity to better understand this structural type. Consequently, a country-wide inventory of unreinforced masonry churches is here identified. After a bibliographic and archival investigation, and a 10 000 km field trip, it is estimated that currently 297 unreinforced masonry churches are present throughout New Zealand, excluding 12 churches demolished in Christchurch because of heavy damage sustained during the Canterbury earthquake sequence. The compiled database includes general information about the buildings, their architectural features and structural characteristics, and any architectural and structural transformations that have occurred in the past. Statistics about the occurrence of each feature are provided and preliminary interpretations of their role on seismic vulnerability are discussed. The list of identified churches is reported in annexes, supporting their identification and providing their address.
The Canterbury earthquake series of 2010/2011 has turned the city of Christchurch into a full scale natural laboratory testing the structural and non-structural response of buildings under moderate to very severe earthquake shaking. The lessons learned from this, which have come at great cost socially and economically, are extremely valuable in increasing our understanding of whole building performance in severe earthquakes. Given current initiatives underway on both sides of the Tasman towards developing joint Australasian steel and composite steel/concrete design and construction standards that would span a very wide range of geological conditions and seismic zones, these lessons are relevant to both countries. This paper focusses on the performance of steel framed buildings in Christchurch city, with greatest emphasis on multi-storey buildings, but also covering single storey steel framed buildings and light steel framed housing. It addresses such issues as the magnitude and structural impact of the earthquake series, importance of good detailing, lack of observed column base hinging, the excellent performance of composite floors and it will briefly cover research underway to quantify some of these effects for use in design.
Following the devastating 1931 Hawke's Bay earthquake, buildings in Napier and surrounding areas in the Hawke's Bay region were rebuilt in a comparatively homogenous structural and architectural style comprising the region's famous Art Deco stock. These interwar buildings are most often composed of reinforced concrete two-way space frames, and although they have comparatively ductile detailing for their date of construction, are often expected to be brittle, earthquake-prone buildings in preliminary seismic assessments. Furthermore, the likelihood of global collapse of an RC building during a design-level earthquake became an issue warranting particular attention following the collapse of multiple RC buildings in the February 22, 2011 Christchurch earthquake. Those who value the architectural heritage and future use of these iconic Art Deco buildings - including building owners, tenants, and city officials, among others - must consider how they can be best preserved and utilized functionally given the especially pressing implications of relevant safety, regulatory, and economic factors. This study was intended to provide information on the seismic hazard, geometric weaknesses, collapse hazards, material properties, structural detailing, empirically based vulnerability, and recommended analysis approaches particular to Art Deco buildings in Hawke's Bay as a resource for professional structural engineers tasked with seismic assessments and retrofit designs for these buildings. The observed satisfactory performance of similar low-rise, ostensibly brittle RC buildings in other earthquakes and the examination of the structural redundancy and expected column drift capacities in these buildings, led to the conclusion that the seismic capacity of these buildings is generally underrated in simple, force-based assessments.
Quick and reliable assessment of the condition of bridges in a transportation network after an earthquake can greatly assist immediate post-disaster response and long-term recovery. However, experience shows that available resources, such as qualified inspectors and engineers, will typically be stretched for such tasks. Structural health monitoring (SHM) systems can therefore make a real difference in this context. SHM, however, needs to be deployed in a strategic manner and integrated into the overall disaster response plans and actions to maximize its benefits. This study presents, in its first part, a framework of how this can be achieved. Since it will not be feasible, or indeed necessary, to use SHM on every bridge, it is necessary to prioritize bridges within individual networks for SHM deployment. A methodology for such prioritization based on structural and geotechnical seismic risks affecting bridges and their importance within a network is proposed in the second part. An example using the methodology application to selected bridges in the medium-sized transportation network of Wellington, New Zealand is provided. The third part of the paper is concerned with using monitoring data for quick assessment of bridge condition and damage after an earthquake. Depending on the bridge risk profile, it is envisaged that data will be obtained from either local or national seismic monitoring arrays or SHM systems installed on bridges. A method using artificial neural networks is proposed for using data from a seismic array to infer key ground motion parameters at an arbitrary bridges site. The methodology is applied to seismic data collected in Christchurch, New Zealand. Finally, how such ground motion parameters can be used in bridge damage and condition assessment is outlined. AM - Accepted manuscript
The Christchurch region of New Zealand experienced a series of major earthquakes and aftershocks between September 2010 and June 2011 which caused severe damage to the city’s infrastructure. The performance of tilt-up precast concrete buildings was investigated and initial observations are presented here. In general, tilt-up buildings performed well during all three major earthquakes, with mostly only minor, repairable damage occurring. For the in-plane loading direction, both loadbearing and cladding panels behaved exceptionally well, with no significant damage or failure observed in panels and their connections. A limited number of connection failures occurred due to large out-of-plane panel inertia forces. In several buildings, the connections between the panel and the internal structural frame appeared to be the weakest link, lacking in both strength and ductility. This weakness in the out-of-plane load path should be prevented in future designs.
Test results are presented for wall-diaphragm plate anchor connections that were axially loaded to rupture. These connection samples were extracted post-earthquake by sorting through the demolition debris from unreinforced masonry (URM) buildings damaged in the Christchurch earthquakes. Unfortunately the number of samples available for testing was small due to the difficulties associated with sample collection in an environment of continuing aftershocks and extensive demolition activity, when personal safety combined with commercial activity involving large demolition machinery were imperatives that inhibited more extensive sample collection for research purposes. Nevertheless, the presented data is expected to be of assistance to structural engineers undertaking seismic assessment of URM buildings that have existing wall-diaphragm anchor plate connections installed, where it may be necessary to estimate the capacity of the existing connection as an important parameter linked with determining the current seismic capacity of the building and therefore influencing the decision regarding whether supplementary connections should be installed.
The Christchurch earthquakes have highlighted the importance of low-damage structural systems for minimising the economic impacts caused by destructive earthquakes. Post-tensioned precast concrete walls have been shown to provide superior seismic resistance to conventional concrete construction by minimising structural damage and residual drifts through the use of a controlled rocking mechanism. The structural response of unbonded post-tensioned precast concrete wall systems, with and without additional energy dissipating elements, were investigated by means of pseudo-static cyclic, snap back and forced vibration testing with shake table testing to be completed. Two types of post-tensioned rocking wall system were investigated; a single unbonded post-tensioned precast concrete wall or Single Rocking Wall (SRW) and a system consisting of a Precast Wall with End Columns (PreWEC). The equivalent viscous damping (EVD) was evaluated using both the pseudo-static cyclic and snap back test data for all wall configurations. The PreWEC configurations showed an increase in EVD during the snap back tests in comparison to the cyclic test response. In contrast the SRW showed lower EVD during the snap back tests in comparison to the SRW cyclic test response. Despite residual drifts measured during the pseudo-static cyclic tests, negligible residual drift was measured following the snap back tests, highlighting the dynamic shake-down that occurs during the free vibration decay. Overall, the experimental tests provided definitive examples of the behaviour of posttensioned wall systems and validated their superior performance compared to reinforced concrete construction when subjected to large lateral drifts.
Perimeter Moment resisting steel frames (PMRSFs) are a commonly used seismic resisting system, placed around the perimeter of the building for maximum torsional stiffness. They are typically designed as “strong column weak beam” systems with fixed column bases. When subjected to severe earthquake demand, sufficient to push the beams into the inelastic range, it is expected that plastic hinging at the column bases will occur. However, the response of PMRSF systems to the severe 2010/2011 Christchurch earthquake series did not generate column base hinging in systems which exhibited beam yielding.
In the aftermath of the 2010-2011 Canterbury earthquakes in New Zealand, the residual capacity and reparability of damaged reinforced concrete (RC) structures was an issue pertinent to building owners, insurers, and structural engineers. Three precast RC moment-resisting frame specimens were extracted during the demolition of the Clarendon Tower in Christchurch after sustaining earthquake damage. These specimens were subjected to quasi-static cyclic testing as part of a research program to determine the reparability of the building. It was concluded that the precast RC frames were able to be repaired and retrofitted to an enhanced strength capacity with no observed reduction in displacement capacity, although the frames with “shear-ductile” detailing exhibited less displacement ductility capacity and energy dissipation capacity than the more conventionally detailed RC frames. Furthermore, the cyclic test results from the earthquake-damaged RC frames were used to verify the predicted inelastic demands applied to the specimens during the 2010-2011 Canterbury earthquakes. https://www.concrete.org/publications/acistructuraljournal.aspx
Between September 4, 2010 and December 23, 2011, a series of earthquakes struck the South Island of New Zealand including the city of Christchurch producing heavy damage. During the strongest shaking, the unreinforced masonry (URM) building stock in Christchurch was subjected to seismic loading equal to approximately 150-200% of code values. Post-earthquake reconnaissance suggested numerous failures of adhesive anchors used for retrofit connection of roof and floor diaphragms to masonry walls. A team of researchers from the Universities of Auckland (NZ) and Minnesota (USA) conducted a field investigation on the performance of new adhesive anchors installed in existing masonry walls. Variables included adhesive type, anchor diameter, embedment length, anchor inclination, and masonry quality. Buildings were selected that had been slated for demolition but which featured exterior walls that had not been damaged. A summary of the deformation response measured during the field tests are presented. AM - Accepted Manuscript
The research presented in this thesis investigated the environmental impacts of structural design decisions across the life of buildings located in seismic regions. In particular, the impacts of expected earthquake damage were incorporated into a traditional life cycle assessment (LCA) using a probabilistic method, and links between sustainable and resilient design were established for a range of case-study buildings designed for different seismic performance objectives. These links were quantified using a metric herein referred to as the seismic carbon risk, which represents the expected environmental impacts and resource use indicators associated with earthquake damage during buildings’ life. The research was broken into three distinct parts: (1) a city-level evaluation of the environmental impacts of demolitions following the 2010/2011 Canterbury earthquake sequence in New Zealand, (2) the development of a probabilistic framework to incorporate earthquake damage into LCA, and (3) using case-study buildings to establish links between sustainable and resilient design. The first phase of the research focused on the environmental impacts of demolitions in Christchurch, New Zealand following the 2010/2011 Canterbury Earthquake Sequence. This large case study was used to investigate the environmental impact of the demolition of concrete buildings considering the embodied carbon and waste stream distribution. The embodied carbon was considered here as kilograms of CO2 equivalent that occurs on production, construction, and waste management stage. The results clearly demonstrated the significant environmental impacts that can result from moderate and large earthquakes in urban areas, and the importance of including environmental considerations when making post-earthquake demolition decisions. The next phase of the work introduced a framework for incorporating the impacts of expected earthquake damage based on a probabilistic approach into traditional LCA to allow for a comparison of seismic design decisions using a carbon lens. Here, in addition to initial construction impacts, the seismic carbon risk was quantified, including the impacts of seismic repair activities and total loss scenarios assuming reconstruction in case of non-reparability. A process-based LCA was performed to obtain the environmental consequence functions associated with structural and non-structural repair activities for multiple environmental indicators. In the final phase of the work, multiple case-study buildings were used to investigate the seismic consequences of different structural design decisions for buildings in seismic regions. Here, two case-study buildings were designed to multiple performance objectives, and the upfront carbon costs, and well as the seismic carbon risk across the building life were compared. The buildings were evaluated using the framework established in phase 2, and the results demonstrated that the seismic carbon risk can significantly be reduced with only minimal changes to the upfront carbon for buildings designed for a higher base shear or with seismic protective systems. This provided valuable insight into the links between resilient and sustainable design decisions. Finally, the results and observations from the work across the three phases of research described above were used to inform a discussion on important assumptions and topics that need to be considered when quantifying the environmental impacts of earthquake damage on buildings. These include: selection of a non-repairable threshold (e.g. a value beyond which a building would be demolished rather than repaired), the time value of carbon (e.g. when in the building life the carbon is released), the changing carbon intensity of structural materials over time, and the consideration of deterministic vs. probabilistic results. Each of these topics was explored in some detail to provide a clear pathway for future work in this area.
On 14 November 2016 a magnitude Mw 7.8 earthquake struck the upper South Island of New Zealand with effects also being observed in the capital city, Wellington. The affected area has low population density but is the largest wine production region in New Zealand and also hosts the main national highway and railway routes connecting the country’s three largest cities of Auckland, Wellington and Christchurch, with Marlborough Port in Picton providing connection between the South and North Islands. These transport facilities sustained substantial earthquake related damage, causing major disruptions. Thousands of landslides and multiple new faults were counted in the area. The winery facilities and a large number of commercial buildings and building components (including brick masonry veneers, historic masonry construction, and chimneys), sustained damage due to the strong vertical and horizontal acceleration. Presented herein are field observations undertaken the day immediately after the earthquake, with the aim to document earthquake damage and assess access to the affected area.
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.
Micro - electro - mechanical system (MEMS) based accelerometers are now frequently used in many different parts of our day - to - day lives. It is also increasingly being used for structural testing applications. Researchers have had res ervation of using these devices as they are relatively untested, but now with the wider adoption, it provides a much cheaper and more versatile tool for structural engineering researchers. A number of damaged buildings in the Christchurch Central Business District (CBD) were instrumented with a number of low - cost MEMS accelerometers after the major Christchurch earthquakes. The accelerometers captured extremely high quality building response data as the buildings experienced thousands of aftershocks. This d ata set was amongst one of only a handful of data set s available around the world which provides building response data subjected to real ground motion. Furthermore, due to technological advances, a much larger than usual number of accelerometers has been deployed making the data set one of the most comprehensive available. This data set is utilised to extract modal parameters of the buildings. This paper summarises the operating requirements and preference for using such accelerometers for experimental mod al analysis. The challenges for adapting MEMS based devices for successful modal parameters identification are also discussed.
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.
Case study unreinforced masonry (URM) buildings that were seismically retrofitted prior to the 2010/11 Canterbury earthquake sequence and exhibited successful performance during these earthquakes are presented herein. Selected buildings were divided into the following categories based on size and complexity: (1) simple, single storey box type buildings (i.e. electrical substations), (2) common and simple commercial buildings, and (3) large and complex clay brick and stone URM buildings. The retrofitted case study URM buildings were evaluated based on overall structural seismic performance as well as the categories of initial seismic design, heritage preservation, architectural appeal, and cost. Detailed observations of 4 representative case study buildings and a summary of findings are reported herein. http://db.nzsee.org.nz/2017/Orals.htm
This thesis investigates life-safety risk in earthquakes. The first component of the thesis utilises a dataset of earthquake injuries and deaths from recent earthquakes in New Zealand to identify cause, context, and risk factors of injury and death in the 2011 MW6.3 Christchurch earthquake and 2016 MW7.8 Kaikōura earthquake. Results show that nearly all deaths occurred from being hit by structural elements from buildings, while most injuries were caused by falls, strains and being hit by contents or non-structural elements. Statistical analysis of injured cases compared to an uninjured control group found that age, gender, building damage, shaking intensity, and behaviour during shaking were the most significant risk factors for injury during these earthquakes. The second part of the thesis uses the empirical findings from the first section to develop two tools for managing life-safety risk in earthquakes. The first tool is a casualty estimation model for health system and emergency response planning. An existing casualty model used in New Zealand was validated against observed data from the 2011 Christchurch earthquake and found to underestimate moderate and severe injuries by an order of magnitude. The model was then updated to include human behaviour such as protective actions, falls and strain type injuries that are dependent on shaking intensity, as well as injuries and deaths outside buildings. These improvements resulted in a closer fit to observed casualties for the 2011 Christchurch earthquake. The second tool that was developed is a framework to set seismic loading standards for design based on fatality risk targets. The proposed framework extends the risk-targeted hazard method, by moving beyond collapse risk targets, to fatality risk targets for individuals in buildings and societal risk in cities. The framework also includes treatment of epistemic uncertainty in seismic hazard to allow this uncertainty to be used in risk-based decision making. The framework is demonstrated by showing how the current New Zealand loading standards could be revised to achieve uniform life-safety risk across the country and how the introduction of a new loading factor can reduce risk aggregation in cities. Not on Alma, moved and emailed. 1/02/2023 ce
Unrestrained unreinforced clay brick masonry (URM) parapets are found atop a large number of vintage URM buildings. Parapets are typically non-structural cantilevered wall elements that form a fire barrier and in most cases form decorative and ornamental features of vintage URM buildings. Parapets are considered to be one of the most vulnerable elements that are prone to out-of-plane collapse when subjected to earthquake induced shaking. An in-depth analysis of the damage database collected following the 2010/2011 Canterbury earthquakes was performed to obtain information about the distribution, characteristics and observed performance of both the as-built and retrofitted parapets in the Christchurch region. Results, statistical interpretation and implications are presented herein. http://www.aees.org.au/downloads/conference-papers/2015-2/
Axial elongation of reinforced concrete (RC) plastic hinges has previously been observed in a range of laboratory experiments, and more recently was observed in several Christchurch buildings following the 2010/2011 Canterbury earthquakes. Axial restraint to plastic hinges is provided by adjacent structural components such as floors as the plastic hinges elongate, which can significantly alter the performance of the plastic hinge and potentially invalidate the capacity design strength hierarchy of the building. Coupling beams in coupled wall systems are particularly susceptible to axial restraint effects due to their importance in the strength hierarchy, the high ductility demands that they experience, and the large stiffness of bounding walls. From computational modelling it has been found that ignoring axial restraint effects when designing coupled walls can result in significantly increased strength, reduced ductility and reduced energy dissipation capacity. The complexity of the topic merits further research to better account for realistic restraint effects when designing coupled walls.
Five years after the devastating series of earthquakes in Christchurch, New Zealand, the structural engineering community is now focussing on low damage design by either proactively reducing the possibility of significant damage to primary steel members (i.e. developing seismic resisting systems that will deliver a high damage threshold in severe earthquakes) or by improved detailing of the primary steel members for rapid replacement. This paper presents a development of Eccentrically Braced Frames (EBFs) with replaceable active links. It uses the bolted flange- and web splicing concept to connect the active link to the collector beam or column. Finite element analyses have been performed to investigate the behaviour and reliability of EBFs with this new type replaceable active link. The results show a stable hysteretic behaviour and more significantly easier replacement of the damaged active link in comparison with conventional EBFs.
The Catholic Cathedral of the Blessed Sacrament is a category 1 listed heritage building constructed largely of unreinforced stone masonry, and was significantly damaged in the recent Canterbury earthquakes. The building experienced ground shaking in excess of its capacity leading to block failures and partial collapse of parts of the building, which left the building standing but still posing a significant hazard. In this paper we discuss the approach to securing the building, and the interaction of the structural, heritage and safety demands involved in a dynamic seismic risk environment. We briefly cover the types of failures observed and the behaviour of the structure, and investigate the performance of both strengthened and un-strengthened parts of the building. Seismic strengthening options are investigated at a conceptual level. We draw conclusions as to how the building performed in the earthquakes, comment on the effectiveness of the strengthening and securing work and discuss the potential seismic strengthening methods.
The 2011, 6.3 magnitude Christchurch earthquake in New Zealand caused considerable structural damage. It is believed that this event has now resulted in demolition of about 65-70% of the building stock in the Central Business District (CBD), significantly crippling economic activities in the city of Christchurch. A major concern raised from this event was adequacy of the current seismic design practice adopted for reinforced concrete walls due to their poor performance in modern buildings. The relatively short-duration earthquake motion implied that the observed wall damage occurred in a brittle manner despite adopting a ductile design philosophy. This paper presents the lessons learned from the observed wall damage in the context of current state of knowledge in the following areas: concentrating longitudinal reinforcement in wall end regions; determining wall thickness to prevent out-of-plane wall buckling; avoiding lap splices in plastic hinge zones; and quantifying minimum vertical reinforcement. http://www.2eceesistanbul.org/
The paper proposes a simple method for quick post-earthquake assessment of damage and condition of a stock of bridges in a transportation network using seismic data recorded by a strong motion array. The first part of the paper is concerned with using existing free field strong motion recorders to predict peak ground acceleration (PGA) at an arbitrary bridge site. Two methods are developed using artificial neural networks (a single network and a committee of neural networks) considering influential parameters, such as seismic magnitude, hypocentral depth and epicentral distance. The efficiency of the proposed method is explored using actual strong motion records from the devastating 2010 Darfield and 2011 Christchurch earthquakes in New Zealand. In the second part, two simple ideas are outlined how to infer the likely damage to a bridge using either the predicted PGA and seismic design spectrum, or a broader set of seismic metrics, structural parameters and damage indices.
The susceptibility of precast hollow-core floors to sustain critical damage during an earthquake is now well-recognized throughout the structural engineering community in New Zealand. The lack of shear reinforcement in these floor units is one of the primary reasons causing issues with the seismic performance of these floors. Recent research has revealed that the unreinforced webs of these floor units can crack at drift demands as low as 0.6%. Such observation indicates that potentially many of the existing building stock incorporating hollow-core flooring systems in cities of relatively high seismic activity (e.g. Wellington and Christchurch) that probably have already experienced a level of shaking higher than 0.6% drift in previous earthquakes might already have their floor units cracked. However, there is little information available to reliably quantify the residual gravity load-carrying capacity of cracked hollow-core floor units, highlighting the need to understand the post-cracking behavior of hollow-core floor units to better quantify the extent of the risk that cracked hollow-core floor units pose.
The current seismic design practice for reinforced concrete (RC) walls has been drawn into question following the Canterbury earthquakes. An overview of current research being undertaken at the University of Auckland into the seismic behaviour of RC walls is presented. The main objectives of this research project are to understand the observed performance of several walls in Christchurch, quantify the seismic loads on RC walls, and developed improved design procedures for RC walls that will assist in revisions to NZS 3101. A database summarising of the performance of RC wall buildings in the Christchurch CBD was collated to identify damage modes and case-study buildings. A detailed investigation is underway to verify the seismic performance of lightly reinforced concrete walls and an experimental setup has been developed to subject RC wall specimen to loading that is representative of a multi-storey building. Numerical modelling is being used to understand the observed performance of several case-study RC walls buildings in Christchurch. Of particular interest is the influence that interactions between walls and other structural elements have on the seismic response of buildings and the loads generated on RC walls.
The Catholic Cathedral is classified as a category 1 listed heritage building constructed largely of unreinforced stone masonry, and was significantly damaged in the recent Canterbury earthquakes of 2010 and 2011. In the 2010 event the building presented slight to moderta damage, meanwhile in the 2011 one experienced ground shaking in excess of its capacity leading to block failures and partial collapse of parts of the building, which left the building standing but still posing a significant hazard. In this paper we discuss the approach to develop the earthquake analysis of the building by 3D numerical simulations, and the results are compared/calibrated with the observed damage of the 2010 earthquake. Very accurate records were obtained during both earthquakes due to a record station located least than 80 m of distance from the building and used in the simulations. Moreover it is included in the model the soil structure interaction because it was observed that the ground and foundation played an important role on the seismic behavior of the structure. A very good agreement was found between the real observed damage and the nonlinear dynamic simulations described trough inelastic deformation (cracking) and building´s performance.
During the Christchurch earthquake of February 2011, several midrise buildings of Reinforced Concrete Masonry (RCM) construction achieved performance levels in the range of life safety to near collapse levels. These buildings were subjected to seismic demands higher than the building code requirements of the time and higher than the current New Zealand Loadings Standard (NZS-1170.5:2004). Structural damage to these buildings has been documented and is currently being studied to establish lessons to be learned from their performance and how to incorporate these lessons into future RCM design and construction practices. This paper presents a case study of a six story RCM building deemed to have reached the near collapse performance level. The RCM walls on the 2nd floor failed due to toe crushing reducing the building’s lateral resistance in the east-west direction. A nonlinear dynamic analysis on a 3D model was conducted to simulate the development of the governing failure mechanism. Preliminary analysis results show that the damaged walls were initially under large compression forces from gravity loads which caused increase in their lateral strength and reduced their ductility. After toe crushing failure developed, axial instability of the model was prevented by a redistribution of gravity loads.
There is very little research on total house strength that includes contributions of non-structural elements. This testing programme provides inclusive stiffness and response data for five houses of varying ages. These light timber framed houses in Christchurch, New Zealand had minor earthquake damage from the 2011 earthquakes and were lateral load tested on site to determine their strength and/or stiffness, and to identify damage thresholds. Dynamic characteristics including natural periods, which ranged from 0.14 to 0.29s were also investigated. Two houses were quasi-statically loaded up to approximately 130kN above the foundation in one direction. Another unidirectional test was undertaken on a slab-on-grade two-storey house, which was also snapback tested. Two other houses were tested using cyclic quasi-static loading, and between cycles snapback tests were undertaken to identify the natural period of each house, including foundation and damage effects. A more detailed dynamic analysis on one of the houses provided important information on seismic safety levels of post-quake houses with respect to different hazard levels in the Christchurch area. While compared to New Zealand Building Standards all tested houses had an excess of strength, damage is a significant consideration in earthquake resilience and was observed in all of the houses. http://www.aees.org.au/downloads/conference-papers/2015-2/
