Vector Form Intrinsic Finite-Element Analysis of Steel Frames with Semirigid Joints

This study uses the vector form intrinsic finite-element (VFIFE) method to investigate the inelastic large deflection behavior of steel frames with semirigid joints. The structural connections are modeled by the two-node, multidegree-of-freedom spring system and dummy element with stiffness but without actual mass and length. The proposed model is first verified by comparing its numerical solutions with the published results. The various structural behaviors, such as the bifurcation instability, the snap-through buckling, and the inelastic structural response with beam element fracture, are then fully studied. The numerical results show that the semirigid joint reduces the global stiffness of structure. Therefore, as expected, the simplified rigid joint will over estimate the loading capacity of the structure. The fracture analysis of the multi span frame shows that when the beam fractures, the structure elements would absorb more energy and thus, the reduction ratio of loading capacity after beam fracture is smaller than that of single-span frame. In addition, the loss of loading capacity is more obvious when the beams fracture in the lower story. DOI: 10.1061/(ASCE)ST.1943-541X.0000485. (C) 2012 American Society of Civil Engineers.