Self-centering Precast Concrete Walls for Buildings in Regions with Low to High Seismicity

Abstract

Self-centering precast concrete walls that utilise unbonded post-tensioning (PT) can provide superior lateral load resistance to conventional concrete construction by minimising structural damage and residual drifts. This thesis investigates the application of both simple self-centering walls that are suitable for regions of low seismicity and more complex wall systems that are suitable for regions with moderate to high seismicity. A series of experimental tests confirmed the behaviour of individual unbonded PT concrete walls that had no specific confinement reinforcement in the compression toe. Individual PT walls are suitable for buildings located in regions of low seismicity, where the lateral drift demand is small and so extensive damage to the wall toe can be avoided. The nominal flexural strength can be used to easily design the wall, and an ultimate compressive strain in excess of 0.003 may be more suitable for PT walls. The results from both experimental tests and finite element analyses were used to quantify the strains in the wall toe and develop refined equations to accurately predict the unbonded tendon stresses and wall nominal flexural strength. Energy dissipating O-Connectors were designed for use in a self-centering wall system that consists of a Precast Wall with End Columns (PreWEC), and is suitable for regions of moderate to high seismicity. A finite element model was developed that accurately captured the cyclic behaviour of the PreWEC system that was observed during experimental testing. The PreWEC model was used to investigate the influence of several important design parameters, including the relative quantities of PT and energy dissipating connectors. Current design procedures that are used to ensure that self-centering is achieved were shown to be inaccurate. Analysis of the cyclic hysteresis behaviour of self-centering systems and dynamic time-history analyses were used to demonstrate how self-centering should be defined. The PreWEC system was used as an example to demonstrate that realistic residual drift limits could be satisfied following an earthquake using a simple design check that was developed. Lastly, the interaction between the self-centering wall and the surrounding structure was investigated. Detailed finite element and time-history analysis of a prototype building indicated the influence of the type of wall-to-floor connection that was incorporated into the building, and concluded that it is not sufficient to model the wall system in isolation.