| Reinforced concrete slab-column structure,as the name implies,structural system consists of just slabs and columns.Because its structural system contained two-way slabs supported directly on columns without using beams,also know as flat-slab buildings.Reinforced concrete slab-column structure is widely used in such constructions as multistory factory buildings,warehouses,garage or other public buildings because of its engineering advantages,say,simple and unobstructed space,flexibility in room layout,saving in storey height,and shorter construction time.Slab-column connections are regarded as most weak zones with complex stress distribution because it's vulnerable to punching shear failure.Punching shear failure is a brittle failure,which occurs with almost no warning signs.The inner force redistribution will emerge in order to achieve a new stable equilibrium after connections failure,the load carried by the failure connections would redistribute to other adjacent connections.When load increased suddenly,adjacent connections will emerge in punching failure one after another because of without enough alternative load path or strength reserve,and finally caused partial or total collapse of structures.Recently,structures collapse accidents due to punching shear failure has serious impact on human casualties and economy.These accidets revealed some shortcomings in codes of practice and the essential of reconsidering punching provision.Therefore,it should be essential to study the collapse resistant capacity and post-punching behavior which can help adopting reasonable structural mesures to avoid or delay progressive collapse.The designers hoped that the slab-column structures have the alternative load path under the accidental actions to deliver load to more adjacent connections similar to the catenary action of longitudinal reinforcement in the traditional frame structure.Therefore,design codes placed a certain amount of continuous bottom reinforced steelbars through the column which was called"integrity reinforcements".It is provided to give the failure connection some residual strength after punching shear failure.This theme is provided to a new structural measure point at the behaviors of reinforced concreteslab-column structure aimed at avoiding its progressive collapse,namely"Diagonal Integrity Reinforcements".The following research is carried out in this theme:1.This paper carried out nonlinear finite-element analysis of loading process and stress state of slab-column connections,based on the test.The results show that the finite-element analysis predicted results accord well with the test results.Moreover,this paper revaled the stress distribution and the formation process of alternate laod path by analysing the stress state of whole loading process.2.After carried out the analysis of punching shear behavior of slab-column connections,slab is provided the diagonal integrity reinforcements with different reinforcement ratio to analize penetration resistance behavior of slab-column connections by using ABAQUS.Finally,the results has show that the relation curve between reinforcement ratio diagonal integrity reinforcements and penetration capacity.3.Based on the yield line forms of the slab,the bearing capacity of the slab is calculated according to the yield line theory of the slab.According to the exsit test parameters of slab-column structure,the finite element model respectively on the slab column structure in side column or middle column failure after the collapse of the process is established.The calculation results and the actual results were compared and discussed the collapse patterns and the max principal stressto reveals the characteristics of acceptance of plate column structure which can be used to simulate and calculate the progressive collapse resistance of slab column structure and provides the reference for the design of slab column structures. |
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