Seismic Sidesway Collapse Riliability Analysis Of RC Frame Structures And Probabilistic Assessment Of COF

The collapse of buildings structures under strong earthquake motions is the mainreason for economic loss and human casualties, therefore, seismic collapse performanceassessment of structures as well as more reasonable design methods to resist seismic col-lapse are becoming more and more important. The great Wenchuan earthquake indicatesthat, even the buildings structures designed according to the current seismic design codewould have possibilities of collapse when encountered unpredicted rare or even very rareearthquakes. It was also observed in the Wenchuan earthquake that a lot lof reinforcedconcrete (RC) frame designed according to the criteria “strong-column-weak-beam(SCWB)” didn’t fail in accordance with the anticipated failure modes. Considering theabove situations, the refined analysis of collapse modes and reliability for RC framestructures under earthquakes, as well as the scientific evaluation of column overdesignfacfors (COF) in SCWB will be of great theoretical importance and practical values. Theglobal collapse modes of structures under earthquakes generally can be categorized intotwo kinds: sidesway incremental collapse (or sidesway collapse for short), and verticalprogressive collapse. In this thesis, only the former is selected as the research object,which is defined as the global dynamic instability of structures due to excessive intersto-ry deformations with the increase of applied loads. The main contents are as follows:Firstly, three RC frame buildings with three, five and nine storyes are designed ac-cording to the current seismic design code. These structures are all modeled in the plat-form OpenSees. The nonlinear static analysis is performed for these structures based onpushover analysis (POA) method, and the sidesway collapse resistant performance indi-ces including overstrength factor and ductility factors are obtained through the pushovercurves. The nonlinear dynamic analysis is implemented for the structures by using theIDA method. The collapse probabilities are obtained by a statistical method based on fre-quency counting, and then the collapse fragilities based on strong motion intensity arebuilt up. Through the collapse fragility curves, a sidesway collapse resistant safety evalu-tion index, i.e., the collapse margin ratio (CMR) is acquired.Secondly, some representative failure modes for sidesway collapse of RC framestructures are analyzed, and seven typical sidesway collapse modes are identified. Theprobabilistic seismic demand anlaysis (PSDA) method for global structures is applied tostructural members, and the probabilistic seismic demand models (PSDMs) are built forstructural members. In addition, the probabilistic seismic capacity models (PSCMs) forstructural members are established based on the prediction equations in the current codesand research achievements at home and abroad. Based on the above PSDMs and PSCMs, the limit state equations are setup, and then the conditional failure probabilities of struc-tural members are obtained. By using system reliability methods, the seismic fragilityanalysis is executed for each representative failure mode. Combined with the results ofprobabilistic seismic hazard analysis (PSHA) of the building sites, the annual failureprobabilities corresponding to each representative collapse mode are gotten.Thirdly, the global reliability for the sidesway collapse of RC frame structures underearthquakes is analyzed. The maximum interstory drift angle (ISDA) of structures is cho-sen as the global performance parameter, and the multiple strip method is utilized to runthe global probabilistic seismic demand analysis. Through global PSDA, the medians andlogarithmic standard deviations of ISDA demands of structures under different intensityof earthquake strong motions are obtained. In addition, the medians and logarithmicstandard deviations of ISDA capacities of structures are gotten by using IDA. By meansof the first order reliability method (FORM), the probabilities for sidesway collapse ofstructures under different intensity of earthquake strong motions are obtained. Further-more, the analysis results via the above three methods are compared.Lastly, on the basis of sidesway collapse reliability analysis of structures, the proba-bilistic evaluation is carried out for the COFs which is comonly used in seismic designcriteria SCWB of structures. The reliability anlaysis method based on representative fail-ure modes is firstly used to analyzed the failure probabilities of structures design accord-ing to different COF values, and the effective intervals for COF of the beam-mode con-trolled failure mode. And then, the demand and capacity factor method (DCFM) is usedto assess the seismic performance of structures with different COFs by taking the capaci-ty demand ratio (CDR) and the confidence probability as performance indicators. Takinguse of the confidence probability as90%for collapse prevention performance level inFEMA355f for reference, the effective intervals for COFs of the combined-mode con-trolled failure modes are obtained.