Evalution On Seismic Damage Of Hollow-section Piers And Study Ofseismic Performance Indexs

Compared with solid-section piers,hollow-section piers have many advantages,such as small section,light weight,large stiffness,good mechanical performance and saving masonry materials,which have been widely used in highway and railway bridge construction.Especially in the western of China where seismic activities are frequent,the hollow-section piers are widely used and popularized.Quantifying the damage status of structure accurately is the basis of ensuring the seismic performance goals of structures,also is the principal research content based on the theory of the seismic performance.Being able to quantify the damage level of components quickly and effectively under the action of earthquake load,and then timely adopt accurate reinforcement strategy or repair plan,are crucial to ensure the smooth rescue and relief after the earthquake,and also have a far-reaching impact on post-disaster reconstruction,recovery of production,and revitalization of the economy.How to apply reasonable and effective methods to clarify the damage mechanism of the hollow-section pier and quantitatively describe the damage degree of the hollow-section pier under the action of earthquake are of great importance to the seismic design and damage assessment of the pier.Therefore,based on the experimental results of 14 rectangular hollow-section piers and 5 round-end hollow-section piers,the damage characteristics,failure mechanism,the damage to the component(strength degradation,stiffness degradation and the residual displacement)were analyzed systemly.Classification of performance level of hollow-section pier and the performance target quantification of each damage component were studied deeply.the applicability of the existing damage model to seismic damage assessment of rectangular and round-end hollow-section piers were discussed in detail.The main contents and results are as follows:(1)It can be seen from the test that all hollow-section piers have experienced the process of micro-crack on concrete surface,longitudinal reinforcement yield,initial spalling of protective layer concrete,large area spalling of protective layer,longitudinal reinforcement buckling or concrete collapse.Before yielding,the damage is mainly manifested as the increase and expansion of horizontal cracks in concrete;after yielding,the damage is mainly manifested as the increase of horizontal main crack width in the plastic hinge area and the formation and expansion of oblique cracks.For rectangular hollow-section piers,the ultimate failure state is mostly the concrete collapse at the bottom of the piers,for the round-end hollow-section piers,most of the pier bottom hollow chamfer concrete damage is the most serious.And then author analyzed the influence of design parameters on the crack width of each component.(2)On the basis of summarizing various hollow pier hysteresis curve of hollow-section piers,the damage components,such as strength degradation,stiffness degradation and residual displacement,were analyzed and studied.At the same time,the influence of various influencing parameters(shear span ratio,stirrup ratio,longitudinal reinforcement ratio and axial pressure ratio)on each damage component was further analyzed.At last,based on the strength degradation coefficient,stiffness degradation coefficient and residual displacement coefficient of each component,the relation between the damage components and displacement ductility ratio of rectangular hollow pier and circular hollow pier was fitted respectively.(3)Combining with the characteristics of component damage and damage development,on the basis of component of crack width,compressive strain of concrete,steel bar strain,then thesis defines the rectangular hollow pier and circular hollow pier's five performance levels: basic condition,slight damage,moderate damage,severe injury,close to collapse,and defines the corresponding five gear damage state evaluation results: fully operational,normal operation,limited operation,stop operation,loss of operation.On this basis,thesis quantified the damage components at each performance level.(4)Based on the performance level division standard of hollow-section pier,refer to the damage index range of different damage levels proposed by various scholars,combined with the experimental phenomenon and the development process of hollow pier damage,the thesis proposed damage index ranges corresponding to five performance levels,then selected 14 double parameters damage models which are more representative,and then calculated the damage evolution curve of each pier under different load levels and studied the applicability of the models for the earthquake damage assessment of hollow pier combined the results of the test.It is found that for the rectangular hollow-section pier and the round-end hollow-section pier,Zeng Wuhua's formula can reasonably reflect the damage situation of components in the whole test process,which is consistent with the actual damage degree of components.Therefore,Zeng Wuhua model is the preferred method for seismic damage assessment of the rectangular hollow-section pier and the round-end hollow-section pier.