The dynamic behaviour of reinforced-concrete bridge piers subjected to New Zealand seismicity.

This thesis is concerned with the behaviour of slender, circular, reinforced-concrete bridge piers in earthquake conditions. The behaviour of the constituent materials and the pier member as a whole were investigated. A literature review of the cyclic stress-strain behaviour of reinforcing steel at quasi-static and dynamic strain rates is given. A test program to test the behaviour of the grades of reinforcing steel produced in New Zealand was conducted an analytical stress-strain model is proposed. A critical literature review of proposed analytical models for unconfined and confined concrete is given as well as the effects of dynamic strain rates. Various conclusions and recommendations are reported. Methods for assessing the ductility capacity and ductility demand of piers are discussed. A review of some proposed methods for designing the confinement steel in the plastic-hinge region of a pier is given. A programme in which fourteen one-sixth scale model bridge piers were tested to destruction on a shake table was carried out. The effects of pier slenderness, the axial-load level, base motion, base fixity, and low-level shaking were investigated. The results of these tests were used to investigate the ability of analytical models which were developed from the observed behaviour of quasi-static test specimens to predict the behaviour and the response of piers subjected to base excitations. It was found that the general pier behaviour can be predicted satisfactorily although the pier strength and stiffness are increased by the dynamic strain rates. The general response can be predicted satisfactorily by inelastic time-history analyses but the peak response is poorly predicted by both inelastic time-history analyses and spectral analyses. The modes of failure of the piers are investigated and the effect of buckling causing the fracture of the longitudinal steel is discussed. The effect of axial-load level and pier slenderness on the length of the plastic hinge is discussed