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Research papers, The University of Auckland Library

The Canterbury earthquakes in New Zealand caused significant damage to a number of reinforced concrete (RC) walls and subsequent research that has been conducted to investigate the design provisions for lightly reinforced RC walls and precast concrete wall connection details is presented. A combination of numerical modelling and large-scale tests were conducted to investigate the seismic behaviour of lightly RC walls. The model and test results confirmed the observed behaviour of an RC wall building in Christchurch that exhibited a single flexural crack and also raised questions regarding the ability of current minimum reinforcement requirements to prevent the concentration of inelastic deformation at a small number of flexural cracks. These findings have led to changes to the minimum vertical reinforcement limits for RC walls in in the Concrete Structures Standard (NZS 3101:2006), with increased vertical reinforcement required in the end region of ductile RC walls. An additional series of wall tests were conducted to investigate the seismic behaviour of panel-to-foundation connections in singly reinforced precast concrete panels that often lack robustness. Both in-plane and out-of-plane panel tests were conducted to assess both grouted connections and dowel connections that use shallow embedded inserts. The initial test results have confirmed some of the previously identified vulnerabilities and tests are ongoing to refine the connection designs. http://www.aees.org.au/downloads/conference-papers/2015-2/

Research Papers, Lincoln University

The urban environment influences the way people live and shape their everyday lives, and microclimate sensitive design can enhance the use of urban streets and public spaces. Innovative approaches to urban microclimate design will become more important as the world’s population becomes ever more urban, and climate change generates more variability and extremes in urban microclimatic conditions. However, established methods of investigation based upon conventions drawn from building services research and framed by physiological concepts of thermal comfort may fail to capture the social dynamics of urban activity and their interrelationship with microclimate. This research investigates the relationship between microclimate and urban culture in Christchurch, New Zealand, based upon the concept of urban comfort. Urban comfort is defined as the socio-cultural (therefore collective) adaptation to microclimate due to satisfaction with the urban environment. It involves consideration of a combination of human thermal comfort requirements and adaptive comfort circumstances, preferences and strategies. A main methodological challenge was to investigate urban comfort in a city undergoing rapid physical change following a series of major earthquakes (2010-2011), and that also has a strongly seasonal climate which accentuates microclimatic variability. The field investigation had to be suitable for rapidly changing settings as buildings were demolished and rebuilt, and be able to capture data relevant to a cycle of seasons. These local circumstances meant that Christchurch was valuable as an example of a city facing rapid and unpredictable change. An interpretive, integrative, and adaptive research strategy that combined qualitative social science methods with biophysical measures was adopted. The results are based upon participant observation, 86 in-depth interviews with Christchurch residents, and microclimate data measurements. The interviews were carried out in a variety of urban settings including established urban settings (places sustaining relatively little damage) and emerging urban settings (those requiring rebuilding) during 2011-2013. Results of this research show that urban comfort depends on adaptive strategies which in turn depend on culture. Adaptive strategies identified through the data analysis show a strong connection between natural and built landscapes, combined with the regional outdoor culture, the Garden City identity and the connections between rural and urban landscapes. The results also highlight that thermal comfort is an important but insufficient indicator of good microclimate design, as social and cultural values are important influences on climate experience and adaptation. Interpretive research is needed to fully understand urban comfort and to provide urban microclimate design solutions to enhance the use of public open spaces in cities undergoing change.

Research papers, University of Canterbury Library

This thesis addresses the topic of local bond behaviour in RC structures. The mechanism of bond refers to the composite action between deformed steel reinforcing bars and the surrounding concrete. Bond behaviour is an open research topic with a wide scope, particularly because bond it is such a fundamental concept to structural engineers. However, despite many bond-related research findings having wide applications, the primary contribution of this research is an experimental evaluation of the prominent features of local bond behaviour and the associated implications for the seismic performance of RC structures. The findings presented in this thesis attempt to address some structural engineering recommendations made by the Canterbury Earthquakes Royal Commission following the 2010-2011 Canterbury (New Zealand) earthquake sequence. A chapter of this thesis discusses the structural behaviour of flexure-dominated RC wall structures with an insufficient quantity of longitudinal reinforcement, among other in situ conditions, that causes material damage to predominantly occur at a single crack plane. In this particular case, the extent of concrete damage and bond deterioration adjacent to the crack plane will influence the ductility capacity that is effectively provided by the reinforcing steel. As a consequence of these in situ conditions, some lightly reinforced wall buildings in Christchurch lost their structural integrity due to brittle fracture of the longitudinal reinforcement. With these concerning post-earthquake observations in mind, there is the underlying intention that this thesis presents experimental evidence of bond behaviour that allows structural engineers to re-assess their confidence levels for the ability of lightly reinforced concrete structures to achieve the life-safety seismic performance objective the ultimate limit state. Three chapters of this thesis are devoted to the experimental work that was conducted as the main contribution of this research. Critical details of the experimental design, bond testing method and test programme are reported. The bond stress-slip relationship was studied through 75 bond pull-out tests. In order to measure the maximum local bond strength, all bond tests were carried out on deformed reinforcing bars that did not yield as the embedded bond length was relatively short. Bond test results have been presented in two separate chapters in which 48 monotonic bond tests and 27 cyclic bond tests are presented. Permutations of the experiments include the loading rate, cyclic loading history, concrete strength (25 to 70 MPa), concrete age, cover thickness, bar diameter (16 and 20 mm), embedded length, and position of the embedded bond region within the specimen (close or far away to the free surface). The parametric study showed that the concrete strength significantly influences the maximum bond strength and that it is reasonable to normalise the bond stress by the square-root of the concrete compressive strength, √(f'c). The generalised monotonic bond behaviour is described within. An important outcome of the research is that the measured bond strength and stiffness was higher than stated by the bond stress-slip relationship in the fib Model Code 2010. To account for these observed differences, an alternative model is proposed for the local monotonic bond stress-slip relationship. Cyclic bond tests showed a significant proportion of the total bond degradation occurs after the loading cycle in the peak bond strength range, which is when bond slip has exceeded 0.5 mm. Subsequent loading to constant slip values showed a linear relationship between the amount of bond strength degradation and the log of the number of cycles that were applied. To a greater extent, the cyclic bond deterioration depends on the bond slip range, regardless of whether the applied load cycling is half- or fully-reversed. The observed bond deterioration and hysteretic energy dissipated during cyclic loading was found to agree reasonably well between these cyclic tests with different loading protocols. The cyclic bond deterioration was also found to be reasonably consistent exponential damage models found in the literature. This research concluded that the deformed reinforcing bars used in NZ construction, embedded in moderate to high strength concrete, are able to develop high local bond stresses that are mobilised by a small amount of local bond slip. Although the relative rib geometry was not varied within this experimental programme, a general conclusion of this thesis is that deformed bars currently available in NZ have a relative rib bearing area that is comparatively higher than the test bars used in previous international research. From the parametric study it was found that the maximum monotonic bond strength is significant enhanced by dynamic loading rates. Experimental evidence of high bond strength and initial bond stiffness generally suggests that only a small amount of local bond slip that can occur when the deformed test bar was subjected to large tension forces. Minimal bond slip and bond damage limits the effective yielding length that is available for the reinforcing steel to distribute inelastic material strains. Consequently, the potential for brittle fracture of the reinforcement may be a more problematic and widespread issue than is apparent to structural engineers. This research has provided information that improve the reliability of engineering predictions (with respect to ductility capacity) of maximum crack widths and the extent of bond deterioration that might occur in RC structures during seismic actions.

Research papers, University of Canterbury Library

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.

Research papers, University of Canterbury Library

This study explores the impact post-earthquake images from Christchurch, New Zealand inserted into a task requiring sustained attention or vigilance have on performance, selfreports of task-focus, and cerebra activity using functional near-infrared spectroscopy (fNIRS). The images represent the current state of Christchurch; a city struggling to recover from devastating earthquakes that peaked in February, 2011, killing 185 people, injuring hundreds more and causing widespread and massive damage to infrastructure, land and building in the region. Crowdsourcing was used to gather a series of positive and negative photos from greater Christchurch to be employed in the subsequent experiment. Seventy-one Christchurch resident participants (51 women, 20 men) then took part in a vigilance task with the sourced images embedded to assess possible cognitive disruptions. Participants were randomly assigned to one of three conditions: embedded positive pictures, embedded negative pictures, or embedded scrambled image controls. Task performance was assessed with signal detection theory metrics of sensitivity A’ and β’’. Individuals viewing the positive images, relating to progress, rebuild, or aesthetic aspects within the city, were overall more conservative or less willing to respond than those in the other conditions. In addition, positive condition individuals reported lower task focus, when compared to those in the control condition. However, indicators of cerebral activity (fNIRS) did not differ significantly between the experimental groups. These results combined, suggest that mind wandering events may be being generated when exposed to positive post-earthquake images. This finding fits with recent research which indicates that mind-wandering or day dreaming tends to be positive and future oriented. While positive recovery images may initiate internal thoughts, this could actually prove problematic in contexts in which external attention is required. While the actual environment, of course, needs to recover, support agencies may want to be careful with employing positive recovery imagery in contexts where people actually should be paying attention to something else, like operating a vehicle or machinery.