Structural Behavior Of RC And PC Beam-Column Sub-Assemblage Subjected To Progressive Collapse

Progressive collapse is a catastrophic event which is initiated by the failure of vertical load-carrying members and causing a chain reaction leading to the partial or complete collapse of the structure.Such an event might be triggered by the fire,explosions or sudden impact to load-carrying members.After the loss of a load-bearing element,the excessive load must be taken by the adjacent structural members to prevent such progressive collapse.This study starts with review of the of some of the classical examples of the progressive collapse and its types.Resisting mechanisms of progressive collapse are discussed with the deficiency in the recent design methods and improved design strategies are presented.Also,the analysis procedure for the progressive collapse of reinforced concrete(RC)frame structures in the codified provisions is presented.A comprehensive review is provided on the researches on compressive arch action(CAA),catenary action(CA)of RC and precast concrete(PC)structures.New approach for the numerical simulations of the experimental works on RC beam-column substructures subjected to quasi-static loading conditions available in the literature is presented by using finite element software package ABAQUS.Previous research studies show that RC and PC frame structures under a column removal scenario can develop arching action at small displacements while catenary resistance during the large displacement stage to prevent progressive collapse,if proper axial restraints are provided.For RC frame,this study presents finite element(FE)models to understand the structural behavior of it subjected to column removal scenario.First of all,FE models are validated against the experimental results available in the literature.RC beam-column substructures consist of a middle column joint,two side columns and two-span beam.Good agreements are found for all the FE models developed in this study.The procedure and the methodology for developing the finite element model are well documented in the literature.First of all,two models were developed to investigate the effects of rotational capacity based on the geometrical detailing.Furthermore,three FE models were developed to investigate the effects of exterior,corner and interior column removal scenarios on progressive collapse resistance.Also,FE model investigating the effects of multi-column removal scenario and the story effect on the collapse resistance are presented in this study.At the end,parametric analysis was conducted by varying the beam longitudinal reinforcement ratio,concrete compressive strength,and beam section depth.After detailed FE modeling of RC frame substructures,it is concluded that the amount of development of CAA and CA is highly dependent on the rotational capacity at the beam-column joints.Among the exterior,interior and corner column removal scenarios,the corner column removal is concluded to be the most critical one since the substructure could not develop resistance capacity beyond the flexural stage.The results of the multi-column removal scenario show that the collapse resistance of the structure is reduced considerably with the increasing number of columns removed while increasing the number of stories increase the collapse resistance mechanism at the same time.However,the presence of an increasing number of bays,adjacent to the column removal side contribute to the CAA of the beam,but the ultimate strength during the catenary stage remains unaffected.Furthermore,results of parametric analysis show that with the increase in the beam longitudinal reinforcement ratio,the initial stiffness of the beam,CAA and CA is increased.While an increase in the concrete compression strength and beam section depth significantly increase the initial stiffness and CAA while they do not significantly increase CA.For PC frame,primarily effect of horizontal restraints on two one-third-scale2 story 2-span beam-column sub frame was investigated experimentally and numerically it was found that the failure of PC frame was dominated by the pull out of side joints and load-carrying capacity was significantly affected by the horizontal restraints.