Structural Stressing State Analysis Of Plane Steel Frame Under Progressive Collapse Scenario

When the frame structure is subjected to accidental load,it may suffer from the failure of a local structural component,which leads to disproportionate damage to the whole structure compared to the initial failure.And such mechanical behavior of the frame structure is characterized by the term “progressive collapse”.Based on the structural stressing state theory,this paper investigates the characteristics of the structural working behavior of a plane steel frame model under the progressive collapse scenario by both experimental modelling model output and finite element analysis.The main achievements of this paper are as follows:The structural stressing state is modelled by the generalized strain energy density(GSED)sum.With an innovative application of the Mann-Kendall criterion to the GSED sum-load curve,the structural stressing state leap load P is distinguished and characterized as the threshold of the structural catenary phase.And the corresponding working characteristics is revealed by prosing the parameters of sectional curvature,shearing force,axial force,joint rotation,and average sectional strain,etc.By applying the M-K criterion to the characteristic segment of the GSED sum-F curve after load P,the second leap load Q of the structural stressing state is distinguished.Q is characterized as the start of the “plastic platform” stage of the structure.The corresponding working characteristics are embodied in the platforms of the curvature changing trend and joint rotations.Besides,some clues of new energy growth points of the structure during the later loading stage are given.By proposing the maximum shear strain and the rotation angle of the principal strain direction,the shear deformation characteristics of the structure in the catenary stage and the plastic platform stage are observed.It is revealed that the total shear deformation of concrete filled steel tubular(CFST)composite section is not consistent with the local shear deformation of the outer steel tube surface.With the help of the ABAQUS finite element simulation,the rationality of the mutation loads of the structural stressing state and the validity of the M-K criterion are verified.From a perspective of the internal forces,the mechanical behavior features of the structure in different working stages are investigated.From the point of view of energy,the coordinative working performance between different materials of the columns are analyzed.