Effect of Structural Redundancy on Progressive Collapse Resistance Enhancement in RC Frame Structures

Progressive collapse of building structures is a field of research that has received considerable attention all over the world. Moreover, the vulnerability of conventional reinforced concrete (RC) frame buildings to structural failure triggered by the loss of key elements has been noted during recent years. Various guidelines such as unified facilities criteria (UFC) recommend that distinctive structural characteristics should be considered in the initial steps of structural design, so as to mitigate progressive collapse possibility of structures. Such guidelines state that including these features will provide for a significantly more robust structure and decrease the probability of progressive collapse while facing an uncommon loading situation. The structural redundancy index is among those features that can help the structural system to maintain its stability during abnormal loadings. It should be noted that, however, most provisions regarding progressive collapse in different guidelines include a general statement on alternative load paths, and there is rather non explicit mention of redundancy in such guidelines. In other words, the exact influence of this structural characteristic on progressive collapse is not clearly defined. This research highlights the importance of considering structural redundancy effects on progressive collapse of RC frame buildings and provides systematically identified information to better understand the way redundancy affects continuous collapse of structures. For this purpose, 16 finite-element models of RC moment resisting frames with different structural configurations were designed according to the provisions of ACI-318 and modeled in OpenSees. Subsequently, several damage scenarios (both in plan and elevation) were investigated to identify the ability of structures to resist progressive collapse under different circumstances. Numerical results were then compared and the effect of redundancy on progressive collapse of RC structures was clearly quantified. Finally, several predictive graphs were proposed to estimate the response of RC frame structures under progressive collapse.