Research On Damage Index Based On Energy Dissipation Capacity And Seismic Design Method Of RC Members

In the performance-based seismic design method,the realization of the structural performance levels need to be quantified by damage index,the rationality of the damage index depends on the uniformity between the damage description and the damage mechanism of the structure,that is,whether the index can comprehensively reflect the influence of the amplitude,duration and spectrum characteristics of the ground motion on the structure,it also depends on the convenience of the damage index,that is,whether the index can establish a direct quantitative relationship with the design parameters(ductility coefficient,yield load,and reinforcement conditions,etc.)of the structure,which is convenient for guiding structural design.The damage index can be divided into three aspects:(a)degradation-based damage index,(b)deformation-based damage index,and(c)energy-based damage index.The degradation-based damage index corresponds to the physical indicators,and the damage is defined according to the changes of the structural characteristics before and after the ground motion,but the relationship between the damage index and design parameters(ductility coefficient,yield load,and reinforcement conditions)was not established,which is not convenient for guiding the design.The deformation-based damage index considers that the damage of the structure is caused by the maximum elastic-plastic deformation exceeding a certain threshold.The index considers the influence of amplitude and spectral characteristics,but it is difficult to effectively consider the influence of the duration on the structure.The energy-based damage index can fully reflect the influence of earthquake action(amplitude,frequency spectrum and duration)on the structure.The widely accepted energy-based damage index is the Park-Ang damage index,which includes the deformation damage term and the energy dissipation damage term.It can explain the influence of the ground motion(amplitude,frequency spectrum,and duration)on the structure,and the relationship between the Park-Ang damage index and design parameters is established,which makes the seismic design based on the damage target possible.However,the coupling relationship between deformation damage term and energy dissipation damage term was not explained,and the influence of variable amplitude displacement cycle on damage development process was not considered.To accommodate for these shortcomings,scholars have performed many revisions on the determination of on the damage index,which are of great significance for perfecting the damage index.However,these revisions do not touch on the influence of the variable amplitude displacement history on the damage development,which causes the verification of the revised damage index to lack sufficient theoretical support.Therefore,the energy-based damage index needs to be researched systematicallyBased on the National Natural Science Foundation Project "quantitative research on damage of RC frame structure based on the non-stationary energy characteristics of seismic wave(50908022)",this paper focuses on the decay law of energy dissipation capacity of RC members under earthquake action,and the research work is carried out from the following aspects:(1)18 RC members under the stable variable amplitude displacement cycle and 4 RC members under the random variable amplitude displacement cycle are tested,and the influence of displacement history,stirrup ratio and reinforcement ratio on the energy dissipation capacity of RC members is studied;(2)It is found that the energy dissipation capacity of half-cycle for RC member is determined by the maximum displacement history and the cumulative energy dissipation,that is,the energy dissipation capacity is controlled by the maximum displacement history and the cumulative energy dissipation.The relationship between structural design parameters and energy dissipation capacity is established.On the basis,a method for estimating the energy dissipation capacity of RC members is proposed;(3)Based on the estimation method of the energy dissipation capacity of RC members under the variable amplitude displacement cycle,the damage quantification index of RC members based on the energy dissipation capacity is proposed.9 RC members are tested under variable amplitude displacement cycle,and the damage development process is recorded in detail to discuss the performance classification criteria;(4)The damage quantitative index of energy dissipation capacity can provide unified performance classification criteria for reinforced concrete members under random variable amplitude displacement cycles,and the performance classification criteria for the damage quantitative index of the energy dissipation capacity degradation Dk are proposed,where a damage quantification index in the range of 0<Dk<0.4 corresponds to the nondamaged stage,a damage quantification index in the range of 0.4<Dk?0.6 and 0.6<Dk?0.7 corresponds to the mild damage stage and the moderate damage stage,respectively,a damage quantification index in the range of 0.7<Dk<0.8 corresponds to the severe damage stage,and a damage quantification index in the range of 0.8<Dk?1 corresponds to the destruction stage;(5)The damage quantitative index of energy dissipation capacity is related to cantilever length,stirrup ratio,yield load,yield displacement,ductility coefficient,period,mass,peak acceleration(PGA),peak velocity(PGV)and seismic duration.In the seismic design method,the cross-section and longitudinal reinforcement are related to yield load,yield displacement,ductility coefficient and cantilever length;The period is related to mass;The seismic parameters are related to PGA,PGV and seismic duration.Therefore,when the section,longitudinal reinforcement,period and seismic parameters are determined,the relationship between the the damage quantitative index of energy dissipation capacity and the stirrup ratio is established.The quantitative index of energy dissipation capacity damage is defined as the performance design target of RC members at the end of earthquake action,when the performance design target is determined,the stirrup ratio can be obtained.On this basis,the seismic design method of RC members based on the damage quantitative index of energy dissipation capacity is proposed,and the calculation method of each parameter is illustrated by an example;(6)Comparison of the design results of stirrup ratio based on the damage quantitative index and the design results of stirrup ratio based on the code for seismic design of buildings,and the influence of stirrup ratio based on the damage quantitative index under different period conditions and different seismic fortification intensity conditions is discussed.