The Effect Of Slab On "Strong Column-weak Beam" Failure Mechanism Of RC Frame Structure

It has been required that the RC frame structure must realize “strong column-weak beam” failure mechanism under seismic action in Chinese seismic code.But according to the damage of frame structures destroyed in earthquake in recent years,it is found that the damage of columns in frame structures,which is designed by the method in Chinese code,is much more serious and even causes structural collapse.Referring to considerable literatures related to seismic damage analysis of frame structures,it is found that the strengthen effect of the effective slab flange width and the steel bars in slab on beams are the main reasons why “strong columnweak beam” failure mechanism is not observed in earthquake.But the research on axially constraint of beams,the magnification of shear force in columns and the constraint of the whole frame structure is still at an early stage.Therefore,more research on the effect of slab on the failure mechanism of frame structure is needed.In order to figure out the influence of slab on “strong column-weak beam” failure mechanism of frame structure and offer suggestions for improving seismic design of frame structures,the major research work and achievement of this thesis includes:(1)The axial deformation data of RC beam in cyclic loading test at home and abroad is collected to find the reason why beam elongates axially subjected to horizontal cyclic loading.The axial confinement of the beam caused by slab and column in the frame structure increases due to the axial elongation of the beam.The axial elongation of RC beam in the test is simulated using Perform-3D.The simulation results show that the traditional plastic hinge model can not simulate the shear behavior of the beam well,and can not accurately simulate the axial elongation of the beam.(2)Four RC frame structure models,which are without slab and with slab but different slab reinforcement ratio,are established using Abaqus.The effect of slab and slab reinforcement ratio on axial force,axial deformation,cross-sectional stiffness,ultimate flexural capacity of beams and shearing force of columns are discussed in detail to figure out the influence of slab on “strong column-weak beam” failure mechanism.The results show that the slab increases the axial force of the beam,enhancing the cross-section stiffness and flexural capacity of the beam.In addition,the shear force of the column increases due to the presence of the slab.(3)According to the influence of slab on frame structure,the suggestions on adjusting the design moment and shearing force of columns are proposed.Two sets of frame structures with different axial compression ratio of columns are designed by the method in Chinese code and the improved method respectively.The order of steel bars yielding in beam and column and the stress distribution of all the steel bars are compared between the two sets of frame structures.The comparison results show that the frame structure models designed by the improved design method can realize the "strong column-weak beam" failure mechanism.The reliability of the proposed suggestions on seismic design of frame structure is guaranteed.