Experimental Investigation On Seismic Performance Of RC Hollow Piers

Compared with solid columns in same external size, hollow piers offer the advantages of high bending and torsional stiffness, significant reductions in the volume of materials and large reductions in dead load as well as in seismic inertia force, consequently become widely used in high-pier bridge structures. In the mountainous western China, several intense earthquakes have been triggered in decade years, and the seismic safety of high-pier bridge is facing serious challenges. Proper seismic design approach are required to ensure the structural capacity satisfy the demand of future intense earthquakes. However, there is no special design approach for the hollow-pier structures in various national codes such that the practical design of hollow pier is often based on the seismic methodology of solid pier. Therefore, it is necessary to deepen investigation on the seismic performance of hollow bridge piers.In order to update and develop seismic design theory and approach of hollow piers, test observation, theoretical analysis and simulation technique were executed to distinguish the characters between solid pier and hollow piers. The design parameters were studied comparatively to find their effects on the seismic properties of the pier. The detail contents are as follows.1) Summary on research history about seismic performance experiment of hollow piers was finished according to archive review. The problems to be faced and study purpose were determined for the current experimental investigation.2) According to the motivation of this thesis,9 pier solid-section and hollow-section reinforced concrete specimens were designed. The semi-static test was executed.3) According to observation, the author described the appearance and evolution of cracks, peeling and spalling of cover concrete and the progress of bearing capacity.4) The hysteretic properties, dissipative capacity and curvature distribution along the pier height were compared among various specimens. Discussion was made about the effects of stirrup ratio and longitudinal reinforcement ratio on ductile performance and equivalent length of plastic hinge of solid pier and hollow pier. Comparative study was implemented on equivalent length of plastic hinge based upon the formulations in national codes or existing archives. The appropriate equation of equivalent length of plastic hinge was recommended for hollow-section piers.5) A numerical simulation based on the fiber element of Opensees was carried out with Mander confined concrete model and fatigue-fracture steel model being used. The applicability of this kind of simulation was researched for hollow piers.The main conclusions could be obtained accordance with the forgoing experimental observation, theoretical analysis and FEM simulation.1) The failure mode of both solid pier and hollow pier are flexural failure in the pseudo-static testing, and they share the same rule of crack extension:at small amplitudes of deformation new crack will emerge with the increasing of deformation, at the larger amplitudes of deformation the width of cracks in the region of plastic hinge formed at the bottom of pier will increase other than the emergence of new crack.2) The hysteresis loop of both solid pier and hollow pier follows an inverse S-shape. Increasing longitudinal reinforcement ratio can improve the energy dissipation ability of both solid pier and hollow pier greatly. Increasing stirrup ratio can improve the energy dissipation ability of solid pier to some extent, but has little effect on that of hollow pier.3) The solid pier and hollow pier share the same rule of the distribution of curvature along pier:before the yielding of the specimens a linear distribution of curvature along the pier was observed, after the yielding only the curvature in the region of pier bottom continued increasing with the increase of deformation of pier specimens, the other part had little increasing.4) longitudinal reinforcement ratio (or diameter of the bars) have a greater effects on the equivalent length of plastic hinge, stirrup ratio has little effect on the equivalent length of plastic hinge of hollow piers, but effect solid pier in certain extent.5) By comparing calculation models of plastic hinge length based on the prediction of the displacement at pier top, the conclusion could be given that Paulay-Priestley model, Eurocode8 model and Caltrans model can make a more accurate result respectively, Berry model and Japanese code model are more conservative. The approach in Guidelines for Seismic Design of Highway Bridges will lead to a medium plastic hinge length compared with the above two methods.The numerical simulation, based on Mander confined concrete model and fatigue-fracture steel model, have a good simulation to the process of the test, and reappears all mechanical properties of the specimens in the loading procedure.6) The numerical simulation, based on Mander confined concrete model and fatigue-fracture steel model, have a good simulation to the process of the test, and reappears all mechanical properties of the specimens in the loading procedure.