Fire Resistance Of Multi-Layer Concrete Filled Square Steel Tubular Column And Steel-Concrete Composite Beam Frame

Abstract:This thesis presents shell-solid elaborate finite element analyses of fire resistance of concrete filled square steel tubular column(CFST) and steel-concrete composite beam(SCB) frame with three spans and three stories, and the mechanical behavior of concrete-filled double circular steel tubular stub column(CFDT) under axial loaded. In the analyses model, steel beam and steel column use shell element, concrete use solid element, steel stud use beam element, steel bar use truss element, and the restriction of steel tube to concrete and the bond-slip performance of SCB were considered during analysis under high temperature. The main contents are listed as follows:(1) Based on ABAQUS finite element analysis, using the right high temperature material thermal parameters and thermo-mechanical coupling constitutive relation, the mechanical behavior of CFST and interaction between steel tube and concrete under high temperature were analyzed. The temperature field and fire-resistance performance of CFST and single steel-concrete composite beam frame under different fire conditions were also analyzed. The calculated results were verified with test results.(2) Two models of CFST and SCB frame with three spans and three stories are designed, one is equal spans, the other is unequal spans. Using the right finite modeling method, the temperature field and fire-resistance performance were analyzed. By changing the load and the protective layer thickness of columns, two different failure modes of the frame were obtained, and through the analysis of internal force and deformation of frame failure modes, the effects of span on fire resistance performance were discussed.(3) Using the same boundary conditions of fire, the difference of fire resistance performance of frame columns and fixed single columns, frame beams and fixed single beams were studied and discussed.(4) The finite element method was used to analyze the influence of stub columns of axial stress and perimeter stress of internal to external steel tube, and the axial stress of internal to external concrete. The influences of significant parameters, such as internal to external diameter ratio of steel tube, internal to external steel ratio of steel tube, and strength of concrete on bearing capacity of the stub columns was discussed. Based on this, simplified formula of ultimate bearing capacity of the CFDT was proposed.