This thesis aims to find a new weld sizing criterion for the steel construction industry in New Zealand. Current standards, such as NZS 3404, ANSI/AISC 360-16, and Eurocode 3 use a factor of 0.6 to calculate weld capacity from the weld metal’s ultimate tensile strength (UTS). This difference between weld capacity and UTS is thought to have arisen from the need for a large factor of safety to ensure welds perform correctly during an earthquake. The events in Christchurch proved that this criterion was able to work as intended. Several papers have been published by P. Dong from University of Michigan, and alongside other researchers, they investigate a new definition of weld shear strength by using a traction stress-based method. This new method not only allows realistic angles of weld fracture to be investigated, but also different weld geometries such as partial penetration butt welds. Ongoing research at HERA is showing how this welding technique is a more economical option than larger fillet welds with similar performance. For this thesis a range of sample types were statically tested until failure. UTS of several weld metals was found and then compared with transverse shear results to see if 0.6 is indeed correct. It was found that if the results from the standardized transverse shear samples was used, this ratio could be increased to 1.0. But if the results from cruciform joint samples was used, which still load the weld in a transverse direction but with a higher stress concentration, required the ratio to be 0.8 for welds that could be welded with a single pass, and decreased further to 0.75 for large welds with 3 passes. Two types of partial penetration butt weld (PPBW) geometries were compared to a comparatively sized fillet weld. These tests showed the PPBWs were the best performers, with all PPBWs surviving testing compared to only 33% of fillet welds.
Courage has remained an elusive concept to define despite having been in the English lexicon for hundreds of years. The Canterbury earthquake sequence that began in 2010 provided a unique context in which to undertake research that would contribute to further conceptualisation of courage. This qualitative study was undertaken in Christchurch, New Zealand, with adults over the age of 70 who experienced the Canterbury earthquakes and continued to live in the Canterbury region. The population group was chosen because it is an under researched group in post-disaster environments, and one that offers valuable insights because of members' length and breadth of life experiences, and likely reminiscent and reflective life stage. A constructivist grounded theory approach was utilised, with data collected through semi-structured focus groups and individual key informant interviews. The common adverse experience of the participants initially discussed was the earthquakes, which was followed by exploration of courage in their other lived experiences. Through an inductive process of data analysis, conceptual categories were identified, which when further analysed and integrated, contributed to a definition of courage. The definition was subsequently discussed with social work professionals who had remained working in the Canterbury region after experiencing the earthquakes. From the examples and the actions described within these, a process model was developed to support the application of courage. The model includes five steps: recognising an adverse situation, making a conscious decision to act, accessing sources of motivation, mastering emotion and taking action. Defining and utilising courage can help people to face adversity associated with everyday life and ultimately supports self-actualisation and self-development. Recommendations from the study include teaching about courage within social work education, utilising the process model within supervision, intentionally involving older adults in emergency management planning and developing specific social work tasks in hospital settings following a disaster.
Several concrete cladding panels were damaged during the 2011 Christchurch Earthquakes in New Zealand. Damage included partial collapse of panels, rupture of joint sealants, cracking and corner crushing. Installation errors, faulty connections and inadequate detailing were also contributing factors to the damage. In New Zealand, two main issues are considered in order to accommodate story drifts in the design of precast cladding panels: 1) drift compatibility of tieback or push-pull connections and 2) drift compatibility of corner joints. Tieback connections restrain the panels in the out-of-plane direction while allowing in-plane translation with respect to the building frame. Tieback connections are either in the form of slots or oversized holes or ductile rods usually located at the top of the panels. Bearing connections are also provided at the bottom of panels to transfer gravity loads. At the corners of a building, a vertical joint gap, usually filled with sealants, is provided between the two panels on the two orthogonal sides to accommodate the relative movement. In cases where the joint gap is not sufficient to accommodate the relative movements, panels can collide, generating large forces and the likely failure of the connections. On the other hand, large gaps are aesthetically unpleasing. The current design standards appear to recognize these issues but then leave most of the design and detailing to the discretion of the designers. In the installation phase, the alignment of panels is one of the main challenges faced by installers (and/or contractors). Many prefer temporary props to guide, adjust and hold the panels in place whilst the bearing connections are welded. Moreover, heat generated from extensive welding can twist the steel components inducing undesirable local stresses in the panels. Therefore, the installation phase itself is time-consuming, costly and prone to errors. This paper investigates the performance of a novel panel system that is designed to accommodate lateral inter-story drift through a ‘rocking’ motion. In order to gauge the feasibility of the system, six 2m high precast concrete panels within a single-story steel frame structure have been tested under increasing levels of lateral cyclic drift at the University of Canterbury, New Zealand. Three different panel configurations are tested: 1) a panel with return cover and a flat panel at a corner under unidirectional loading, 2) Two adjacent flat panels under unidirectional loading, and 3) Two flat panels at another oblique corner under bidirectional loading. A vertical seismic joint of 25 mm, filled with one-stage joint sealant, is provided between two of the panels. The test results show the ability of the panels with ‘rocking’ connection details to accommodate larger lateral drifts whilst allowing for smaller vertical joints between panels at corners, quick alignment and easy placement of panels without involving extensive welding on site.
Eccentrically Braced Frames (EBFs) are a widely used seismic resisting structural steel system. Since their inception in the late 1970s, they have been a viable option with an available stiffness that is between simple braced systems and moment resisting systems. A similar concept, the linked column frame (LCF), uses shear links between two closely spaced columns. In both cases, the key component is the active link or the shear link, and this component is the objective of this study. The performance of high rise EBF buildings in the 2010 and 2011 Christchurch earthquakes was beyond that which was expected, especially considering the very high accelerations recorded. As the concrete high-rises were torn down, two EBF buildings remained standing and only required some structural repair. These events prompted a renewed interest in bolted shear links, as well as their performance. While some research into replaceable shear links had already been done (Mansour, 2011), the objectives of this study were to improve on the shear link itself, with the consideration that links built in the future are likely to be bolted. The main components of this study were to: 1. Reduce or eliminate the requirements for intermediate web stiffeners, as they were suspected of being detrimental to performance. Furthermore, any reduction in stiffening requirements is a direct fabrication cost saving. Links with low web aspect ratios were found to achieve exceptional ductilities when no stiffeners were included, prompting new design equations. 2. Ensure that the stresses in the ends of links are adequately transferred into the endplates without causing fractures. Although most of the experimental links had web doubler plates included, four had varied lengths of such doubler plates from 0.0 in. to 8.0 in. The link without any doubler plates performed to a similar level to its peers, and thus it is likely that links with quality end details may not need web doubler plates at all. 3. Evaluate the performance of a link with double sided stiffeners without the use of web welds, as opposed to conventional single sided, welded stiffeners. This link performed well, and web-weld-less double sided stiffeners may be an economical alternative to conventional stiffeners for deeper sections of links. 4. Evaluate the performance of a link with thin endplates that are made efficient with the use of gusset plates. This link performed to an acceptable level and provides evidence for a cost effective alternative to thick endplates, especially considering the high overstrength end moments in links, typically requiring 16-bolt connections. 5. Examine the potential use of an alternative EBF arrangement where the collector beam is over sized, and the link section is formed by cutting out parts of the beam's web. After running a series of finite element models each with a unique variation, a number of approximate design rules were derived such that future research could develop this idea further experimentally. 6. Ensure that during testing, the secondary elements (members that are not the shear link), do not yield and are not close to yielding. None of the instrumented elements experienced any unexpected yielding, however the concerns for high stresses in the collector beam panel zone during design were warranted. The use of an existing New Zealand design equation is recommended as an extra check for design codes worldwide. The above objectives were mainly conducted experimentally, except: the data set for item 1 was greatly expanded through the use of a calibrated numerical model which was then used in an extensive parametric study; item 5 was purely finite element based; and, a small parametric study was included for item 3 in an attempt to expand on the trends found there.
In order to provide information related to seismic vulnerability of non-ductile reinforced concrete (RC) frame buildings, and as a complementary investigation on innovative feasible retrofit solutions developed in the past six years at the University of Canterbury on pre-19170 reinforced concrete buildings, a frame building representative of older construction practice was tested on the shake table. The specimen, 1/2.5 scale, consists of two 3-storey 2-bay asymmetric frames in parallel, one interior and one exterior, jointed together by transverse beams and floor slabs. The as-built (benchmark) specimen was first tested under increasing ground motion amplitudes using records from Loma Prieta Earthquake (California, 1989) and suffered significant damage at the upper floor, most of it due to lap splices failure. As a consequence, in a second stage, the specimen was repaired and modified by removing the concrete in the lap splice region, welding the column longitudinal bars, replacing the removed concrete with structural mortar, and injecting cracks with epoxy resin. The modified as-built specimen was then tested using data recorded during Darfield (New Zealand, 2010) and Maule (Chile, 2010) Earthquakes, with whom the specimen showed remarkably different responses attributed to the main variation in frequency content and duration. In this contribution, the seismic performance of the three series of experiments are presented and compared.
High demolition rates were observed in New Zealand after the 2010-2011 Canterbury Earthquake Sequence despite the success of modern seismic design standards to achieve required performance objectives such as life safety and collapse prevention. Approximately 60% of the multi-storey reinforced concrete (RC) buildings in the Christchurch Central Business District were demolished after these earthquakes, even when only minor structural damage was present. Several factors influenced the decision of demolition instead of repair, one of them being the uncertainty of the seismic capacity of a damaged structure. To provide more insight into this topic, the investigation conducted in this thesis evaluated the residual capacity of moderately damaged RC walls and the effectiveness of repair techniques to restore the seismic performance of heavily damaged RC walls. The research outcome provided insights for developing guidelines for post-earthquake assessment of earthquake-damaged RC structures. The methodology used to conduct the investigation was through an experimental program divided into two phases. During the first phase, two walls were subjected to different types of pre-cyclic loading to represent the damaged condition from a prior earthquake, and a third wall represented a repair scenario with the damaged wall being repaired using epoxy injection and repair mortar after the pre-cyclic loading. Comparisons of these test walls to a control undamaged wall identified significant reductions in the stiffness of the damaged walls and a partial recovery in the wall stiffness achieved following epoxy injection. Visual damage that included distributed horizontal and diagonal cracks and spalling of the cover concrete did not affect the residual strength or displacement capacity of the walls. However, evidence of buckling of the longitudinal reinforcement during the pre-cyclic loading resulted in a slight reduction in strength recovery and a significant reduction in the displacement capacity of the damaged walls. Additional experimental programs from the literature were used to provide recommendations for modelling the response of moderately damaged RC walls and to identify a threshold that represented a potential reduction in the residual strength and displacement capacity of damaged RC walls in future earthquakes. The second phase of the experimental program conducted in this thesis addressed the replacement of concrete and reinforcing steel as repair techniques for heavily damaged RC walls. Two walls were repaired by replacing the damaged concrete and using welded connections to connect new reinforcing bars with existing bars. Different locations of the welded connections were investigated in the repaired walls to study the impact of these discontinuities at the critical section. No significant changes were observed in the stiffness, strength, and displacement capacity of the repaired walls compared to the benchmark undamaged wall. Differences in the local behaviour at the critical section were observed in one of the walls but did not impact the global response. The results of these two repaired walls were combined with other experimental programs found in the literature to assemble a database of repaired RC walls. Qualitative and quantitative analyses identified trends across various parameters, including wall types, damage before repair, and repair techniques implemented. The primary outcome of the database analysis was recommendations for concrete and reinforcing steel replacement to restore the strength and displacement capacity of heavily damaged RC walls.
This thesis is concerned with modelling rockfall parameters associated with cliff collapse debris and the resultant “ramp” that formed following the high peak ground acceleration (PGA) events of 22 February 2011 and 13 June 2011. The Christchurch suburb of Redcliffs, located at the base of the Port Hills on the northern side of Banks Peninsula, New Zealand, is comprised of Miocene-age volcanics with valley-floor infilling marine sediments. The area is dominated by basaltic lava flows of the Mt Pleasant Formation, which is a suite of rocks forming part of the Lyttelton Volcanic Group that were erupted 11.0-10.0Ma. Fresh exposure enabled the identification of a basaltic ignimbrite unit at the study site overlying an orange tuff unit that forms a marker horizon spanning the length of the field area. Prior to this thesis, basaltic ignimbrite on Banks Peninsula has not been recorded, so descriptions and interpretations of this unit are the first presented. Mapping of the cliff face by remote observation, and analysis of hand samples collected from the base of the debris slopes, has identified a very strong (>200MPa), columnar-jointed, welded unit, and a very weak (<5MPa), massive, so-called brecciated unit that together represent the end-member components of the basaltic ignimbrite. Geochemical analysis shows the welded unit is picrite basalt, and the brecciated unit is hawaiite, making both clearly distinguishable from the underlying trachyandesite tuff. RocFall™ 4.0 was used to model future rockfalls at Redcliffs. RocFall™ is a two-dimensional (2D), hybrid, probabilistic modelling programme for which topographical profile data is used to generate slope profiles. GNS Science collected the data used for slope profile input in March 2011. An initial sensitivity analysis proved the Terrestrial Laser Scan (TLS)-derived slope to be too detailed to show any results when the slope roughness parameter was tested. A simplified slope profile enabled slope roughness to be varied, however the resulting model did not correlate with field observations as well. By using slope profile data from March 2011, modelled rockfall behaviour has been calibrated with observed rockfall runout at Redcliffs in the 13 June 2011 event to create a more accurate rockfall model. The rockfall model was developed on a single slope profile (Section E), with the chosen model then applied to four other section lines (A-D) to test the accuracy of the model, and to assess future rockfall runout across a wider area. Results from Section Lines A, B, and E correlate very well with field observations, with <=5% runout exceeding the modelled slope, and maximum bounce height at the toe of the slope <=1m. This is considered to lie within observed limits given the expectation that talus slopes will act as a ramp on which modelled rocks travel further downslope. Section Lines C and D produced higher runout percentage values than the other three section lines (23% and 85% exceeding the base of the slope, respectively). Section D also has a much higher maximum bounce height at the toe of the slope (~8.0m above the slope compared to <=1.0m for the other four sections). Results from modelling of all sections shows the significance of the ratio between total cliff height (H) and horizontal slope distance (x), and of maximum drop height to the top of the talus (H*) and horizontal slope distance (x). H/x can be applied to the horizontal to vertical ratio (H:V) as used commonly to identify potential slope instability. Using the maximum value from modelling at Redcliffs, the future runout limit can be identified by applying a 1.4H:1V ratio to the remainder of the cliff face. Additionally, the H*/x parameter shows that when H*/x >=0.6, the percentage of rock runout passing the toe of the slope will exceed 5%. When H*/x >=0.75, the maximum bounce height at the toe of the slope can be far greater than when H*/x is below this threshold. Both of these parameters can be easily obtained, and can contribute valuable guideline data to inform future land-use planning decisions. This thesis project has demonstrated the applicability of a 2D probabilistic-based model (RocFall™ 4.0) to evaluate rockfall runout on the talus slope (or ramp) at the base of ~35-70m high cliff with a basaltic ignimbrite source. Limitations of the modelling programme have been identified, in particular difficulties with adjusting modelled roughness of the slope profile and the inability to consider fragmentation. The runout profile using RocFall™ has been successfully calibrated against actual profiles and some anomalous results have been identified.
To this extent, modern buildings generally demonstrated good resistance to collapse during the recent earthquakes in New Zealand. However, damage to non-structural elements (NSE) has been persistent during these events. NSEs include secondary systems or components attached to the floors, roofs, and walls of a building or industrial facility that are not explicitly designed to participate in the main vertical or lateral load-bearing mechanism of the structure. They play a major role in the operational and functional aspects of buildings and contribute a major portion of the building’s overall cost. Therefore, they are expected to accommodate the effects of seismic actions such as drifts and accelerations. Typical examples of NSEs include internal non-loadbearing partitions, suspended ceilings, sprinkler piping systems, architectural claddings, building contents, mechanical/electrical equipment, and furnishings. The main focus of this thesis is the drift sensitive NSEs: precast concrete cladding panels and internal partition walls. Even though most precast concrete cladding panels performed well from a life-safety point of view during recent earthquakes in NZ, some collapsed panels posed a significant threat to life safety. It is, therefore, important that the design and detailing of the panel-to-structure connections ensure that their strength and displacement capacity are adequate to meet the corresponding seismic demands, at least during design level earthquakes. In contrast, the partition wall is likely to get damaged and lose serviceability at a low inter-story drift unless designed to accommodate the relative deformations between them and the structure. Partition walls suffered wide-ranging damage such as screw failures, diagonal cracking, detachments to the gypsum linings, and anchorage failures during the 2011 Canterbury Earthquake Sequence in NZ. Therefore, the thesis is divided into two parts. Part I of the thesis focuses on developing novel low-damage precast concrete cladding panel connections, i.e. “rocking” connection details comprising vertically slotted steel embeds and weld plates. The low-damage seismic performance of novel “rocking” connection details is verified through experimental tests comprising uni-directional, bi-directional, and multi-storey scaled quasi-static cyclic tests. Comparison with the seismic performance of traditional panel connections reported in the literature demonstrated the system’s significantly improved seismic resilience. Furthermore, the finite element models of panel connections and sealants are developed in ABAQUS. The force-drift responses of the “rocking” panel system modelled in SAP2000 is compared with the experimental results to evaluate their accuracy and validity. Part II of the thesis focuses on a) understanding the seismic performance of traditional rigid timber-framed partition wall, b) development and verification of low-damage connections (i.e. “rocking” connection details comprising of dual-slot tracks), and c) seismic evaluation of partition walls with a novel “bracketed and slotted” connections (comprising of innovative fastener and plastic bracket named Flexibracket) under uni-directional and bidirectional quasi-static cyclic loadings. Moreover, parametric investigation of the partition walls was conducted through several experimental tests to understand better the pros and cons of the rocking connection details. The experimental results have confirmed that the implementation of the proposed low damage solutions of precast cladding panels and internal partition walls can significantly reduce their damage in a building.
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.
