Research On The Effect Of Cast-in-place Slab On The Seismic Performance Of Reinforced Concrete Frame Structure

Existed earthquake disaster investigations have shown that under the earthquake action,lots of plastic hinges appeared at the column end firstly in reinforced concrete frame structures,and the ultimate failure form of frame was closer to the “strong beam and weak column” mode,which was contrary with the “strong column and weak beam” mode required by the Chinese seismic code.Numerous experimental and theoretical research results from home and abroad have shown that the failure to reasonably simulate the effect of cast-in-place slab on the mechanical performance of the frame structure in practical design is one of the main reason.In the RC frame structure,the cast-in-place slab and the adjacent frame beam are overall poured to form a collaborative force mechanism,which increases the overall lateral stiffness of the frame structure and the flexural bearing capacity of the frame beam end,thereby changing the ultimate yield mechanism of the RC frame structure,which poses a great threat to the safety performance of the structure under the action of earthquake.Therefore,there is important practical significance to comprehensively research the effect of cast-in-place slab on the seismic performance of RC frame structure and summarize the suggested improved structural design methods,both for further improving the deficiencies of the existing theories and for the design reference of actual structures.Based on a large number of related literature from home and abroad,ABAQUS finite element software is used to establish three sets of RC frame structure models with cast-in-place slab,without slab and without slab but with additional slab mass.The effect of cast-in-place slab on seismic performance of RC frame structure is systematically studied by two methods of modal analysis and pushover analysis.The main research contents and conclusions are as follows:(1)Based on the results of modal analysis and pushover analysis,the contribution of cast-in-place slab to increase the lateral stiffness of RC frame structure is researched under the effect of different slab thickness,beam height,increasing coefficient of column end bending moment and slab reinforcement ratio.The structural lateral stiffness increasing coefficient is used to evaluate the effect of the cast-in-place slab on the structural stiffness.And finally,the empirical formulas of thelateral stiffness increasing coefficient based on the model parameters are given by regression analysis.(2)Based on the results of pushover analysis,the effect of cast-in-place slab on the deformation of RC frame structure,the tension and compression damage of concrete and the tensile reinforcement stress of beam end and column end is researched,at the same time the reinforcement stress distribution of the cast-in-place slab and its influencing factors are analyzed.The results show that the flexural bearing capacity of the frame beam end is strengthen because of the existence of the cast-in-place slab,causing the column end to yield before the beam end,which is not conductive to the realization of the ideal yield mechanism of “strong column and weak beam”.(3)The effective flange width of the beam end of each model is calculated and the effect of different model parameters on the value of the effective flange width of the beam end is analyzed.And finally,a simplified method for determining the effective flange width of the beam end is proposed,and some suggestions for improving the seismic design of RC frame structure also are proposed.