Progressive Collapse Research Of Steel Frame Structures Based On The Alternate Path Method

Recently, with the improvement of national economic strength and technical level, the steel structure is widely used in tall building structure. The progressive collapse may be induced when the structure is subjected to accidental loads(fire, explosion or impact, etc.) in the service life, which will result the heavy losses of life and property. So, it has important theory meaning and engineering value to study the mechanism of the progressive collapse and resistance measures of progressive collapse for the steel structure.The alternate path method was employed to analyze the effect of eccentric braces on the resistance performance of progressive collapse for steel frame structure, and the stability problems of steel frame structures in the process of progressive collapse analysis was studied, the main contents are as follows:1)Two finite element models of steel frame, corresponding to unbraced frame and eccentrically braced frame separately, were built with the ANSYS10.0 software. The alternate path method was employed to analyze them through nonlinear static analysis(Pushdown analysis) and nonlinear dynamic analysis respectively. After the failure of the side and middle columns, the effect of eccentric braces on the resistance performance of progressive collapse for steel frame structure is investigated.2)Results of nonlinear static analysis showed that the vertical displacements of failed column, the rotation of the plastic hinge of the beam end above the failed column, the number of plastic hinges when the structure collapsed were significantly reduced after the eccentric braces were set. However, the vertical ultimate bearing capacity of structure was not improved obviously.3)The transient unloading method considering the initial state was employed to perform the dynamic nonlinear analysis for the steel frame structure, the corresponding loading time and unloading time were determined by calculating, the comparison of the results from nonlinear static analysis and from nonlinear dynamic analysis showed that a constant dynamic amplification factor(DAF) equal to 2.0 in the code would be conservative. It was suggested that the dynamic amplification factor for the unbraced frame and the eccentrically braced frame should be 1.4 and 1.2 separately.4)It was preliminary investigated that if the integral instability of the structure and the instability of individual components during the process of the yielding-type progressive collapse. The finite element models of 10-storey planar steel frame were built with the software ANSYS10.0. The load of the yielding-type beam mode was determined through the nonlinear static analysis. The load of integral instability of structure was determined by the eigenvalue analysis and nonlinear buckling analysis after the column-removal. The stability of beam and columns adjacent to the removed column were checked. Results indicated that the global instability did not occur before the yielding-type beam mode collapse was induced, but the instability of the beam and columns adjacent to the failed column could be occurred, which would caused the progressive collapse of the structure.