Dynamic Response of Unbonded Post-tensioned Concrete Walls for Seismic Resilient Structures

Abstract

The research in this thesis was conducted with the primary aim of advancing the current state of knowledge of unbonded Post-Tensioned (PT) precast concrete rocking walls. Emphasis was placed on systematically investigating both the static and dynamic experimental response of Single Rocking Wall (SRW) and Precast Wall with End Columns (PreWEC) systems. Using the experimental data generated, simple numerical modelling techniques were investigated and the Direct Displacement Based Design (DDBD) process was verified. The experimental programme consisted of component tests on modified energy dissipating Oconnectors and pseudo-static cyclic, snap back, and shake table testing on a selection of SRW and PreWEC systems. The unique experimental investigation into the cyclic response of an improved O-connector confirmed the suitability of the O-connector as a cost effective energy dissipater that is able to demonstrate stable hysteretic behaviour while being easy to install and replace. The focus of the wall tests was on assessing the general wall response and design, the influence of the O-connectors on the wall panel, initial stiffness and fundamental frequency, equivalent viscous damping and residual drifts from different loading types. During the wall tests only minor damage and negligible residual drifts were observed which confirmed the desirable seismic behaviour of SRW and PreWEC systems under both static and dynamic loads. An investigation was performed using a simple single degree of freedom numerical model to provide recommendations on appropriate damping schemes that are able to emulate the seismic response of SRW and PreWEC systems that were validated using the shake table test results. The numerical analyses indicated that good estimation of the seismic response could be attained when using 2% tangent stiffness proportional damping in combination with a hysteretic behaviour calibrated to the cyclic hysteresis. Lastly, an assessment of current methods used for determining the equivalent viscous damping for unbonded PT walls systems in the current DDBD framework was performed. A current method based on the weighted contribution of an unbonded PT only system and a purely dissipative system was found to produce good results when used with the proposed bilinear force-displacement idealisation based on an effective stiffness.