Investigation On Seismic Fragility Analysis Of RC Frame Structures Accounting For Ground Motion Duration

Amplitude,frequency and duration are the key characteristics of earthquake that influence structural response.But pseudo acceleration response spectra which could quantify the amplitude and frequency of event is only used in current structural design and fragility assessment.For the problem,this study evaluated the need to consider ground motion duration in seismic fragility analysis,and proposed strategy to explicitly consider the effect of duration in the assessment.Three reinforced concrete frame structures with varying heights were employed as study case,and Open Sees was used to simulate the seismic response of structures under short and long duration ground motion records.Fragility analysis and performance assessment were than conduct to evaluate the influence of duration.Analysis results indicate that ground motion duration has far-reaching influence on vulnerability.Compared with short duration ground motion,long duration ground motion can enhance structural damage risk over 50%,which can also increase vulnerability indices and decrease margin ratios.Duration has significant influence on structural damage risk.It is necessary to explicitly consider ground motion duration during the seismic fragility analysis.Based on the probability statistics and artificial neural networks,various strategies are proposed to explicitly consider duration in the analysis procedures,and the effect of different duration characteristics on analysis results was further compared:1)The stripe-cloud approach was proposed to investigate the influence of ground motion duration on seismic fragility of structures.Vector intensity measure?IM?of ground motion,IM=[IM₁,IM₂],IM was introduced.First,IM₁ is used to perform time-history analysis of structures based on stripe method,and IM₂ which relates to ground motion duration is used to discretize the statistical results of the time-history analysis.Then cloud method is adopted further to establish the probabilistic seismic demand models for structures which can consider the influence of ground motion duration reasonably.The results demonstrate that stripe-cloud method dramatically increases the correlation between seismic intensity measures and structural damage measures,but also improves the reliability of the probabilistic seismic demand models of structures.Vector IM can effectively consider the effect of duration on seismic fragility analysis.Long-duration ground motion can cause severer damage at lower intensity levels comparing to short-duration ground motion.It is necessary to explicitly consider the effect of ground motion duration in seismic fragility analysis.The influence of ground motion duration on the seismic fragility analysis results is also related to the IM selected.Energy-related IMs can consider the influence of duration appropriately.2)Comprehensive scalar intensity measures can also provide variety information of ground motion.This study selected P_a,P_v,PGA,PGV,SI_H as sub-variables,and Canonical Correlational Analysis?CCA?was adopted to combine them linearly for comprehensive measure IM_CCA.The contribution rate of each sub-variable was also conducted.The results reflect that IM_CCA can effectively consider duration and has good effectiveness.3)A fragility analysis based on BP neural network was proposed.Vector IM related to duration was introduced,then the BP neural network was used to predict structural seismic requirements.And fragility analysis was conducted to obtain fragility surface which considered effect of ground motion duration.The results show that the approach allows BP neural network to replace the linear regression analysis,and the data form is flexible,which reduces the trouble of applying vector-type strength indicators in fragility analysis and considers the effect of ground motion duration effectively;the influence of ground motion duration on seismic fragility analysis is related to seismic intensity levels,duration can dramatically influence the structural damage risk in high intensity levels;the effect of ground motion duration is also related to characteristics of structures.