Infrastructure Engineering - Theses
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ItemSite-Specific Ground Motions for Dynamic Analyses in Regions of Lower Seismicity( 2022)Site-specific dynamic analyses of structures have many advantages over traditional code spectrum procedures in regions of lower seismicity. The prime reason is that the site-specific response spectra and accelerograms are more realistic representations of earthquake actions for a structure located on a unique construction site. Developing site-specific ground motions requires a comprehensive understanding of regional seismic hazard analyses, soil condition analyses and site response analyses. Guidelines or facilities for performing site-specific dynamic analyses in accordance with the design code are unavailable to engineering practitioners in Australia. The primary objective of this thesis is to develop a computationally effective method to generate response spectra and accelerograms for site-specific dynamic analysis in intraplate regions of lower seismicity, with a focus on the Southeastern Australia (SEA) region. Based on the proposed method, this thesis provides suites of ground motions in compliance with the Australian standard for direct engineering applications. The conditional mean spectrum (CMS) methodology was first reviewed and its challenges for application in intraplate regions were overcome by employing a diversity of ground motion prediction expressions (GMPEs) and the uniform seismicity model. Three different schemes using a weighted averaging of candidate GMPEs were adopted, and a comparison of predictions demonstrated only minor differences confirming the robustness of the modelling. The constructed CMS were targeted for sourcing ground motions to define seismic hazard at the bedrock level. The bedrock motions were amplified through soil column models to simulate site amplification effects. Subsoil information retrieved from multiple borehole records from the same site was sampled to construct soil column models to achieve conservative estimations of soil amplification ratio at the fundamental period of vibration of the structure to account for resonance. The sampling process involves closed-form expressions for determining the shear strain profile in a soil column considering degradation in the shear modulus of the soil in seismic conditions. The applications of resultant site-specific response spectra and accelerograms, following a ground motion selection scheme proposed by the author, were demonstrated with nonlinear time history analysis for structural design and multiple stripe analysis for risk assessment. This thesis is concluded with three outcomes: (1) a ground motion database for site-specific seismic design based on twenty sites that typify subsoil profiles in SEA, (2) an online program at https://quakeadvice.org/ for generating ground motions with user-defined borehole information, and (3) suites of ground motions for risk assessment of structures following the multiple stripe analysis method.
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ItemPerformance of steel framed domestic structures subjected to earthquake loads( 1997)This thesis investigates the performance of cold formed steel framed domestic structures subjected to earthquake loads. These structures generally include one and two storey houses, comprising steel wall framing, exterior veneer cladding and internal lining. The dynamic, non-linear performance of such structures during earthquakes is simplified to static linear behaviour for design purposes using the structural response modification factor, Rµ. This factor is defined as the product of the structural ductility reduction factor, Rµ, and the over-strength of the system, Ω. This thesis develops a rigorous technique for the determination of Rµ and the application of this technique is demonstrated for a proprietary framing system. This is achieved using novel non-linear, transient dynamic finite element models of these structures subjected to earthquake loads. The model parameters are estimated from unique experiments conducted on representative structures using a shaking table. It is shown that the framing system considered is non-ductile (ie Rµ≈1). This result directly contradicts the assumed ductile behaviour of these framing systems as specified in the Australian earthquake loading standard, AS 1170.4. The significance of this is that current design practices are unconservative and therefore underestimate the earthquake loads on these structures.
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ItemEarthquake design and analysis of tall reinforced concrete chimneys( 2000)Current codes of practice for the design of tall concrete chimneys provide conservative aseismic design guidelines in high seismic regions. A lack of experimental data related to the cyclic behaviour of chimney structures to severe earthquake excitation has resulted in the assumption that such structures are brittle and must be designed in the elastic range. This design approach results in expensive structures and is not consistent with the design philosophy commonly adopted for general structure which permits some inelastic response at the ultimate limit state event. A research program funded by the CICIND organisation has been undertaken to investigate the inelastic cyclic behaviour of tall reinforce concrete chimneys using both experimental and analytical techniques to determine whether the behaviour is brittle or ductile. The research has been divided into three parts; (a) overview of earthquake ground motions, review of the earthquake response of structures and review of chimney design code provisions, (b) detailed description of experimental research examining the cyclic behaviour of chimney sections and (c) development of an aseismic design and analysis procedure for reinforced concrete chimneys including code recommendations. (For complete synopsis open document)
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ItemA new refined approach to the formulation of the earthquake-resistant design regulations for torsionally coupled multistorey buildings( 1989)This thesis presents a detailed parametric study of the elastic earthquake response of torsionally coupled single and multi storey buildings using a probabilistic approach. The aim is to validate the findings of previous deterministic studies, to assess the empirical design procedures stipulated by the current provisions of building codes, and to critically appraise the alternative design recommendations made by the earlier deterministic studies. The structural models are idealised by a discrete parameter prismatic shear beam model which is representative of low to moderately high rise frame-type buildings. The earthquake horizontal ground motion is modeled as a Gaussian, zero mean, stationary random process that is fully characterised by a probabilistic ground acceleration power spectrum. The first and second order statistical parameters defining such a spectrum are derived from an ensemble of 68 actual earthquake motions recorded in the west coast of the U.S.A. A new procedure called the Intensity Correlated Probabilistic Power Spectrum Method (ICPPSM) is developed. This procedure uses the standard random vibration and extreme value theories, and the new concept of the intensity correlated probabilistic power spectrum to compute the mean peak structural responses. Based on the numerical results obtained from the probabilistic approach, a more rational three-step formulation to the codified seismic torsional provisions is proposed to allow for the coupling effects in the design of multi storey buildings.
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ItemSeismic performance of concrete beam-slab-column systems constructed with a re-usable sheet metal formwork system( 2007)This report describes an investigation of seismic performance of a ribbed slab system constructed with an innovative re-usable sheet metal formwork system. Experimental results from quasi-static cyclic lateral load tests on half-scale reinforced concrete interior beam-slab-column subassemblages are presented. The test specimen was detailed according to the Australian code (AS 3600) without any special provision for seismicity. This specimen was tested up to a drift ratio of 4.0 %. Some reinforcement detailing problems were identified from the first test. The damaged specimen was then rectified using Carbon Fibre Reinforced Polymer (CFRPs), considering detailing deficiencies identified in the first test. The repaired test specimen was tested under a lateral cyclic load as per the original test arrangement up to a drift level of 4%. The performance of the repaired specimen showed significant improvement with respect to the level of damage and strength degradation. The results of the rectified specimen indicate that the use of CFRPs may offer a viable retrofit/repair strategy in the case of damaged structures, where this damage may be significant. Two finite element analysis models were created and results of the first test were used to calibrate the FE model. The second FE model was used to obtain detail information about stress and strain behaviour of various components of the beam-column subassemblage and to check the overall performance before carrying out expensive lab tests. It was concluded that finite element modelling predictions were reliable and could be used to obtain more information compared to conventional type laboratory tests. Time-history analyses show that the revised detailing is suitable to withstand very large earthquakes without significant structural damage.