published_or_final_version / Computer Science / Master / Master of Philosophy

Traditional seismic design philosophy for reinforced concrete seismic frame structures localises damage and inelastic deformation to regions of significant plasticity within the beam (plastic hinge zones) during a severe earthquake event. Collapse prevention of the frame is applied through capacity design methods, requiring the maximum expected flexural strength of the beam plastic hinges to be reliably assessed in order to design for, and ensure, the predominantly elastic flexural response of the columns in the frame. Previous experimental and numerical investigations have shown that significant and detrimental damage to the frame and floor system occurs due to the formation and elongation of ductile beam plastic hinges; requiring extensive post-earthquake repair or demolition with likely loss of function of the building. This poses significant economic consequences to occupiers of the building, as the time required to reinstate the integrity of the structural and non-structural building components is often lengthy. More importantly, it has been highlighted that the interaction between elongating ductile plastic hinges and the accompanying floor system enhances the flexural strength of the beam hinges, altering the distribution of forces in the seismic frame compared to that assumed during capacity design. Research has shown that the consideration of frame-floor interaction in current New Zealand design codes significantly underestimates the flexural strength enhancement of beam plastic hinges, threatening the hierarchy of strength and collapse prevention mechanisms employed in capacity design. Recent research has introduced change in the design philosophy of precast concrete seismic frames. Rather than designing for localised damage in the frame, unique Non-tearing (of the floor) connection details have been developed which provide a gap or slot between the end of the beam and column face and force connection rotation to occur about a shallow hinge located at the top of the beam, thereby avoiding the formation of plastic hinges and associated beam elongation effects altogether. Research investigations have shown that Non-tearing connections successfully minimise damage to the structural frame and floor, while providing seismic energy dissipation characteristics at least comparable to that of traditional reinforced concrete connections. In this research, the mechanics of different non-tearing connection arrangements were investigated and original theory introduced for the aspects of connection behaviour which diverged from fundamental reinforced concrete design. A variety of precast concrete non-tearing connection details were developed, with the design focus placed on economic and construction efficiency in order to encourage the rapid implementation of non-tearing connection technology into New Zealand construction industry. The performance of the developed connection details were explored and assessed experimentally and analytically. A two bay precast concrete frame with precast floor system was tested under a demanding reversed cyclic, quasi-static loading protocol using displacement control. The seismic response of the non-tearing connection details employed in the test frame successfully minimised damage to the frame and floor systems. Only minor repair of one primary crack at each connection between the floor diaphragm and supporting beam would be required after a design level earthquake. Issues encountered with buckling of the longitudinal reinforcement in the bottom of the beam reduced the connection performance at high levels of drift. However, detailing measures were successfully employed in successive tests which improved the drift capacity of the connections. Detailing improvements to enhance the seismic response of the developed non-tearing connections were recommended based observations from the frame test. Numerical analysis of the non-tearing connection details was performed using simple rotational and compound spring models, with the key features of the experimental response captured with excellent accuracy. The analytical models were constructed using engineering theory, rather than by calibration with experimental observations. The modelling assumptions and principles adopted in the analysis have been presented for use in design offices or future research programmes when designing and analysing seismic frames using non-tearing connections. This research successfully contributed to the development and progression of non-tearing frame technology. With further research and the refinement of construction details, non-tearing floor connections exhibit impressive potential for providing superior seismic safety, performance and efficiency in precast concrete seismic frame buildings.

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The interface normal behavior between Ottawa sand and concrete for static and cyclic loading has been studied using Cyclic Multi Degree-of-Freedom test device. The static force controlled test for the interface showed exponential relation between normal stress and strain during initial loading, hyperbolic relation during unloading and linear relation during reloading. A series of cyclic force controlled interface tests are described for normal behavior and the interface behavior is found to be a function of the applied initial normal stress, the amplitude of the stress and the number of loading cycles. The reloading modulus is shown to increase with number of loading cycle. Also, a series of combined normal (force controlled) and shear (displacement controlled) tests are described in which the shear stress for given amplitude of shear displacement is found to increase as normal stress and number of loading cycles increases. The results of the laboratory tests for normal behavior are used to determine the parameters to describe the interface stress-strain response. The model is shown to describe the hysteresis behavior of the interface as a function of amplitude of normal stress and number of loading cycles. The model is used to predict the results of cyclic normal tests and combined normal and shear tests, and was found to yield satisfactory results. The interface model is implemented in a 2D nonlinear soil-structure interaction finite element procedure. The finite element procedure is verified with respect to simple problems for which close form solution or laboratory results are available. The response of the force controlled cyclic test and combined normal and shear test is then predicted using the FE procedure and reasonable results are obtained. A pier foundation subjected to base displacement is then analysed for different combinations of soil and interface behavior. Computer results are qualitatively compared with displacement and contact stresses and the effect of including the interface behavior is identified with respect to debonding and rebonding of the interface. The results of this research have provided understanding of the cyclic behavior of sand-concrete interface subjected to normal and combined normal and shear loading. The interface behavior has been represented by simple mathematical model for which parameters can be easily determined from static and cyclic tests. The model is also defined for general loading to incorporate debonding and rebonding and it is easy to implement into a FE procedure.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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