A Study On Progressive Collapse And Reliability Of Reinforced Concrete Frame Structures

In recent years,the rampant terrorism is rampant and major terrorist attacks have occurred.Since the "911" incident in the United States resulting in huge economic losses and casualties,the domestic and foreign academics have successively carried out the analysis of the progressive collapse about the structures which have local damages under accident events and the study of the method of resisting progressive collapse.Structural progressive collapse is a complex nonlinear behavior.It is necessary to analyze the whole process of structural collapse.At the same time,because there are many uncertain factors in the internal and external environment of the structure,the analysis of the continuous collapse capability of the structure based on the reliability method has become an important content of the present structural design.In order to study the progressive collapse capacity of RC frame structure and its influencing factors,a typical reinforced concrete frame structure is established.In this thesis,a study will be carried out in the following aspects(1)A 8 level RC frame fiber element model is established by OpenSees program.Based on the nonlinear static pushdown analysis method,the vertical progressive collapse analysis of a plane frame with di fferent failure conditions is carried out,and the force mechanism and the distribution of resistance distribution are studied after the local failure of the structure.It is found that there are different anti collapse mechanisms for damaged structures under different failure conditions.When the middle column at the bottom of the structure fails,the progressive collapse bearing capacity of the damaged structure is mainly provided by the beam mechanism and the catenary mechanism.The catenary mechanism is mainly formed by the development of the axial tension of the two layers of the bottom of the structure.When the bottom side column fails,the damage structure relies only on the beam mechanism to resist vertical progressive collapse,and the catenary mec hanism is not developed in the failure position.The bearing capacity of catenary mechanism in vertical collapse failure is higher than that provided by beam mechanism.(2)Establishing the critical state function of structural collapse,which based on vertical displacement response of damaged joints and vertical displacement of limit state of progressive collapse.A method based on stochastic finite element for calculating the overall reliability of damaged structures is presented.The principle and process of the three methods of reliability method(FORM、SORM and IS)are analyzed and compared.Reliability calculation and parameter sensitivity analysis of a 2 storey two span RC frame model are carried out.The importance of random parameters which affecting the progressive collapse of the structure is analyzed,and the relative importance of reinforcement material parameters and concrete material parameters in vertical collapse is analyzed.Analyzing and discussing The influence of lateral stiffness on random variables,which provides a way to reduce the risk of progressive collapse.(3)The progressive collapse resistance of damaged structures is evaluated and analyzed based on structural robustness.In the aspect of quantitative,the structural robustness index is quantified based on the overall structural reliability of the structure,and the structural robust index calculation method is established by the failure probability.The robustness of the different damage parts of the residual structure and the risk of continuous collapse are analyzed and compared.In the aspect of qualitative,the vulnerability curves of different structural design parameters(span,layer height and layer number)and different working conditions(side column and middle column)are established,and the influence factors of structural resistance to progressive collapse are studied and discussed.