بررسي خرابي پيشرونده در قابهاي خمشي فولادي فضايي

In the present paper, progressive collapse and its main causes have been investigated. The approaches for reducing the risk of progressive collapse are event control, indirect design and direct design. Two basic means of direct design are local resistance design and alternate path method. Based on the studies undertaken on the progressive collapse behaviour of the structures, it has been demonstrated that the alternate path method is the most efficient and economical way for progressive collapse resistant design. Using this method, it is possible to assess the ability of structures against progressive collapse. In the present study, the progressive collapse behaviour of steel space frames has been investigated using alternate path method. The first step in the alternate path method is to find the vritical members in the structure, therefore three criteria for finding the critical members in steel space frames have been presented, namely, load carrying capacity criterion, strain energy criterion and stiffness criterion. It has been shown that the static alternate path analysis is only an approximate simulation of the progressive collapse phenomenon and this analysis is not adequate by itself. Consequently dynamic alternate path analyses must be undertaken to evaluate accurately the progressive collapse behaviour of the structures. Also in this study, the effects of strengthening grids on the behaviour of steel space frames have been evaluated. Finally, the obtained results from the alternate path analyses have been used to draw some important conclusions and to suggest some general recommendations for progressive collapse resistant design of steel space frames.