Experimental Investigation On Seismic Performance Of Plastic Hinge Region Of Rectangular Hollow-section Concrete Piers

Hollow pier is endowed with cavity body,which is a chosable way to reduce the weight of solid pier to lightweight member.Compared with the solid piers with the same external size,hollow piers have the advantages of saving masonry material,decreasing structural weight and seismic inertia force to some extent,which could be helpful of protecting the overall safety of the bridge.Therefore,hollow piers are applied widely in large-span bridges,especially in the western region of China,where lies numberous mountains and valleys.The piers usually have plastic hinge zone that can absorb and dissipate a large amount of seismic energy in the process of formation.Therefore,it is very important to accurately predict the mechanical behavior of the plastic hinge region of the pier,including researches on concrete damage,confined concrete effect and length of equivalent plastic hinge.In order to study the seismic performance of the plastic hinge region of rectangular hollow piers,the pseudo-static test results of seven rectangular hollow piers are carried out.The damage incubation and evolution of the plastic hinge zone are observed.The effects of design parameters on the seismic performance of hollow piers are comparatively analized.And the applicability of the related models is also discussed.The complete research contents are as follows.1)The quasi-static tests of seven rectangular hollow piers with different design parameters(aspect ratio,longitudinal reinforcement ratio and stirrup ratio)are performed out,which covers test setup,test plan program and loading protocol.2)According to the stress mechanism and deformation in the plastic hinge area of tested piers,the damage state and damage path are described,including the appearance and expansion of the cracks,the spalling and crushing of the concrete,and the buckling and fracture of the longitudinal rebars.3)The hysteresis curves,the skeleton curves,and the moment-curvature curves on the bottom section of the piers are portrayed.The curvature distribution along the pier body and energy dissipation capacity are analyzed.The ductility seismic performance is studied.4)The typical calculation models of the equivalent plastic hinge length at home and abroad are summarized and classified,and the applicability of each calculation model to the 7 rectangular hollow piers is discussed.5)The experimental datas of equivalent plastic hinge length of 37 hollow piers in literature are collected.The influence factors are analyzed,including geometric size,axial compression ratio,longitudinal reinforcement,concrete compressive strength and stirrup rate,which aims to bring forward the applicable model of hollow piers.6)The five typical concrete constitutive models at home and abroad are summarized and analyzed.According to the results of the stirrup strain and the numerical simulation results via OpenSEES,the confined concrete effect in plastic hinge area is qualitatively described.The applicability of each model to core concrete in plastic hinge area of the hollow piers is discussed in view of peak stress and peak strain.According to the results of the above experimental and numerical analysis,the following conclusions are acquired:1)The failure type of the seven rectangular hollow piers is typical bending failure.In a certain region at the bottom of piers,the number of cracks is more concentrated,the width of the crack is wider,the concrete of the protective layer is spalled severely,and the longitudinal reinforcement is seriously buckled and fractured.As a result,the plastic hinge area is remarkably formed.2)It is found that the ductility of the piers with high aspect ratio is better.Although the volumetric stirrup ratio has little influence on the improvement of strength,it does have great impact on the energy dissipation capacity within a certain range.The longitudinal reinforcement ratio can improve the ductility and strength of the piers to a certain extent.3)The curvature distribution along the pier body is as follows: the curvature is small and almost linear distribution before the equivalent yielding.Then curvature quickly increases in the plastic hinge region,which remarks better energy dissipation.4)The calculated results of Telemachos,Eurocode8 and Gao Zhenshi agree well with the experimental results.These three models can be applied to evaluate the equivalent plastic hinge length of rectangular hollow piers with similar design parameters.5)Based on the test datas of 37 hollow piers,the modified Paulay-Priestley model is put forward which is applicable for calculation of the equivalent plastic hinge length for hollow piers,as well as checked by other nine tested hollow piers and OpenSEES numerical simulation.6)Based on the test datas of stirrups strain and OpenSEES simulation results,the confined concrete effect of rectangular hollow piers in the plastic hinge region is meticulously analyzed.Five typical constitutive models are compared in terms of the peak stress and peak strain of concrete.The Saatcioglu-Razvi model is in agreement with the experimental results.