Equivalent Load Amplification Factor And Fragility Analysis For Progressive Collapse Resistance Of Steel Frame

The safety of the structure has been the focus of the civil engineers. The traditional codes for structural design only consider normal load caused by such as weight of the structure, occupancy and environment. Some major structural collapse occurred in the past few decades, were not caused by normal load, but triggered by an initial local failure due to unexpected events, which resulted in redistribution of the load, and then led to the damage of the structure in a chain-reaction way if the load redistribution can not reach a new equilibrium. This phenomenon was also known as the progressive collapse. After the attack of September11, terrorist attacks occur frequently, resulting in loss of life and property as well as severe negative social impact, thus to mitigate the progressive collapse have become the hot topic of researchers. Based on existing research achievement, the following research works were conducted.(1)According to guideline GSA2003and DoD2010, the progressive collapse resistance of a steel frame structure was assessed and results from the static Pushdown analysis and nonlinear dynamic analysis were compared; considering the structure model with panel zone, the effect of panel zone deformation on progressive collapse resistance was discussed.(2)Employing steel frame structure, compare the performance indicators (the maximum vertical displacement, the maximum plastic hinge rotation and the sum of plastic hinge rotation) obtained from static pushdown and nonlinear dynamic analysis, defining the equivalent load amplification factor(ELAF). Taking into account the influence of the structural parameters (the yield strength and stiffness of the beam, gravity load and elastic modulus) on the ELAF, explore the relationship between the ELAF and the maximum plastic hinge rotation.(3)Resistance to progressive collapse was assessed considering the uncertainty of structural design variables such as yield strength, vertical live load, elastic modulus and damping ratio. The criteria of beam-end plastic hinge rotation were used to define the limit state of progressive collapse. Probability of exceeding the limit state for vertical displacement is calculated using Nataf transformation and point estimation corresponding to different vertical loads, and finally fragility curves of progressive collapse resistance were established.