| The progressive collapse is caused by the initial local failture.Then the initial local failture extends from the member to the member,and eventually leads to the collapse of partial structure or the collapse of the integral structure.That is,the ultimate failure state of the structure is not proportional to the initial failture of the structure.There will be serious casualties and economic losses in the event of the progressive collapse.Currently,the researchers at home and abroad have conducted more adequate studies of the progressive collapse machanism and progressive collapse resistance performance of frame structures.However,the researches on the progressive collapse of the slab-column structures are not sufficient,and the researches on the progressive collapse of the unbonded prestressed concrete slab-column structures are rarely seen in the literature.Based on this,this paper mainly carried out the following work:(1)A finite element model of a one-story 2x2 bay slab-column structure under the initial failure condition of the interior column was established.Then the progressive collapse analysis was carried out using the nonlinear static pushdown method.And the finite element modeling method developed in this paper was verified by comparing to the existing experimental results.(2)A finite element model of a eight-story 2x3 bay slab-column structure was established,the unbonded prestresses of which were distributed in strips in both longitudinal and transverse directions.Then the nonlinear static pushdown analysis of progressive collapse mechanism and progressive collapse resistance performance were carried out under the initial failure condition of the long side middle column,short side middle column,comer column and interior column,respectively.Based on this,the effects of the location of the removed columns,the storey in which the column was removed,and the distribution of the unbonded prestresses were further studied.The results showed that the unbonded prestressed slab-column structures would experience the elastic action,elasto-plastic action,catenary action and ultimate stage before the progressive collapse occured in all of the column failure conditions.The effect of the location of the removed columns on the progressive collapse resistance performance of the unbonded prestressed slab-column structures under all of the column failure conditions mainly depended on the number of alternative load path and the application range of the uniform load(specifically,the amplified static load in this paper).And the higher the storey in which the column was removed,the better the progressive collapse resistance performance of the slab-column structures.Besides,the progressive collapse resistance performance of slab-column structures with unbonded prestresses banded close to column strip was the highest..The progressive collapse resistance performance of the slab-column structures in all of the column failture conditions could be improved significantly by increasing the amount of the unbonded prestresses distributed on the column strip of the slab and the amount of the reinforcement distributed on the core areas of the column strip and middle strip of the slab.(3)Considering that the slab-column connections were prone to punching failture,a finite element model of a one-story 2x3 bay slab-column structure was established,the unbonded prestresses of which were distributed in strips in both longitudinal and transverse directions.Then the nonlinear static pushdown analysis of progressive collapse mechanism and progressive collapse resistance performance were carried out under the initial failure condition of the slab-column connection right above the long side middle coumn,short side middle column,corner column and interior column,respectively.The results showed that the unbonded prestressed slab-column structures would experience the elastic action,elasto-plastic action,catenary action and ultimate stage before the progressive collapse occured in all of the slab-column connection failure conditions.And the progressive collapse resistance performance of the slab-column structures in all of the slab-column connection failture conditions could be improved significantly by increasing the amount of the unbonded prestresses distributed on the column strip of the slab and the amount of the reinforcement distributed on the core areas of the column strip and middle strip of the slab.Additionally,the slab-column structures were prone to progressive collapse under the condition of slab-column connection failture than under the condition of column failture.Therefore,the progressive collapse resistance performance of the slab-column structures could be improved effectively by enhancing the punching resistance of the slab-column connection. |
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