Layout of cross braces on progressive collapse analysis of 3-D 12-story steel composite frame structures
In this paper, cross braces are implemented to mitigate the dynamic responses caused by column-remove scenarios of steel composite frames. To evaluate the effective of cross braces with different layout on enhancing the progressive collapse resisting capacity of the structures, alternative path method (APM) is performed on structural nonlinear dynamic history analysis. Firstly, a three-dimensional finite element model for 12-story steel composite frame structure is built with considering the contribution of the composite behavior of the floor system. Then, the FEM modeling method is verified by a progressive collapse test. Finally, a series of progressive collapse analyses on such model with different column-remove scenarios and layout of cross braces. The results show that the cross braces could mitigate the dynamic response caused by column failure in the affected bay, but no obvious mitigation were observed in the other bays. Cross braces blocked the horizontal development of structural progressive collapse for the structure with vertical layout of cross braces (SF-VB), which might aggravate the dynamic response of the affected bay though protected the residual structure. Cross braces layout at the top layer (TB) decreased the peak displacement of corner column failure mode above 50%, and was about 30% for the side column failure mode. The dynamic increase factor (DIF) of the most models was about 1.5, which demonstrated that the value given by the standards might result in some conservatism, but the DIF might closely to the given value for SF-VB. Such results provided basis information for progressive collapse prevention designs of such structural systems.
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