Progressive Collapse Reliability Analysis For RC Frame Structures Under Earthquakes

Since the progressive collapse event of Ronan Point apartment in England dueto gas explosion in1968, especially since the “911” terrorist attack event whichcaused the collapse of World Trade Centers (WTC) in America in2001, the problemof progressive collapse of building structures has been becoming more and moresignificant in the community of civil engineering worldwide. For the present, theresearch on progressive collapse under abnormal loads mainly focuses on explosionsand impacts, while the problem of progreesive of building structures under strongearthquakes has been paid much less attention to. From another viewpoint, in thefield of structural reliability theory, the ultimate limit state (ULS) and theserviceability limit state (SLS) have been explored to many achievements, however,there has been much less research on the “third limit state”, i.e., progressive collapselimit state. In this thesis, two kinds of reinforced concrete frame buildings (one is aplane frame, the other is a space frame) are designed according to the currentseismic design code. And then, they are modeled in OpenSees to investigate theprogressive collapse limit state. Based on the deterministic and probabilisticprogressive collapse analysis, the reliability for progressive collapse limit state ismade a detailed study from the viewpoint of total probability theorem (TPT). Themain contents are as follows:Firstly, two reinforced concrete frame buildings (one is a plane frame, the otheris a space frame) are designed according to the current seismic design code. Andthen, they are modeled in OpenSees to implement the nonlinear finite elementanalysis. The nonlinear static pushover analysis is firstly applied to the plane frame,and then, the nonlinear static pushdown analysis as well as the nonlinear dynamicanalysis under the scenarios of column removal based on the alternative load pathapproach are performed for both plane and space frames. According to the nodedisplacements above the removed column, the maximum load factor that thedamaged structure could reach in pushdown analysis èas well as the change of theinternal forces of the adjacent components before and after the column removal, thereaction of the global structure caused by the failure of local parts is assessedqualitatively, through which the key elements are identified. Furthermore, the resultsfrom the plane model and the space one are compared quantitatively.Secondly, there is a very important yet difficult problem in the alternative pathapproach, that is, how to identify the key elements to be removed? In this thesis, anew method based on member reliability analysis of structures is proposed toidentify the key elements in structures. Two methods, namely, finite element reliability method (FERM), and random poshover analysis (RPOA) based on Latinhypercube sampling, are applied to implement the reliability analysis of structuralmembers for the two models respectively. Through the comparison of the reliabilityindices of structural members, the most propable members (MPM) of failure ofstructures under earthquakes are identified.Lastly, a random pushdown analysis approach is applied to the damagedstructures after the removal of key elements to implement the global reliabilityanalysis. For the case of scenario of column removal without considering thereasons of abnormal loads, the load factors of pushdown analysis are analyzedstatistically, and then the conditional reliability for the progressive collapse limitstate is calculated. For the case of global progressive collapse of structures underearthquakes, the failure probabilities of global progressive collapse of structures areobtained through the TPT via the convolution of seismic hazard, the conditionalfailure probabilities of the most probable members of failure, as well as theconditional global failure probability of the damage structures. It is demonstratedthrough the numerical analysis that the failure probability of progressive collapsefor the space RC frames designed according to the current seismic design code isvery small in the case of removal of just one column, and the code-conformingstructures have adequate robustness in satisfying the third seismic design criteria,i.e., no collapse of structures under the major earthquakes.