The Effects Of Slabon Strong Beam-Weak Column Failure Of RC Frame Structures

In Wenchuan earthquake and Yushu earthquake,many RC structures designed by current standardswere damaged in "strong column-weak beam" pattern which should be avoided in the structural seismic design,rather thanexpected "strong beam-weak column" pattern.The seismic damage has aroused high attention of researchers,and the related study has been developed by researchers.In this paper,based on the systematic summary of domestic and foreign related research,it is studied that the effects of floor slab on "strong beam-weak column" failure of RC frame structures from energy dissipationofstructuresand components,usage ratio of componentsand inter-story displacement anglemainly,and the main researches are shown as follows:1.The relevant provisions of different nations' standards for "strong column-weak beam" are compared and commented.The design idea on "strong column-weak beam" ofdifferent nations' standards is to raisemoment magnification factor of column end.The difference is shown that how to consider the influence of floor slab whenthedesign moment of beam end is calculated.Inone way,the bending moment of beam end is calculatedby original beam section,and the influence of floor slab is considered indirectly though improving moment magnification factor of column end;In the other way,the strengthening effect of floor slab on beamis converted into a certain range of slab participating in bending with beam,and the bending moment of beam end iscalculated by T-shaped section.2.Under different intensities of earthquake ground motion,it is studied thatthe impact of the floorslab on seismic response of RC frame structures.By simplifying both beam and slab into T-shaped beams with different effective flange widths,four analysis models are establishedand nonlinear seismic response analysesareconducted on the models.Though contrastiveanalysesin energy dissipationofstructures and components,usage ratio of components and inter-story displacement angle,it is found that:1)When the intensity ofground motion is not higher than the rare earthquake intensity of the original structure's fortification intensity,because of the strengthening effect of floor slab on beam,with the effective flange width of T-shapedbeamsincreasing,the plastic energy dissipation of the beams is reduced,while the plastic energy dissipation of the columns is not increased;the usageratios of the main bearing components(frame beams and frame columns)are generally decreased;the maximum inter-story displacementangleis reduced.2)When the intensity ofground motion ishigher than the rare earthquake intensity of the original structure's fortification intensity,because of the strengthening effect of floor slab on beam,with the effective flange width of T-shapedbeamsincreasing,the plastic energy dissipation of the beams is reduced,while the plastic energy dissipation of the columns is increased;generally the usageratio of the frame beamsis decreased and the usageratio of frame columns is improved(especially the bottom columns);the maximum inter-story displacement angle of the bottom layeris increased;and the possibility of "strong beam-weak column" failure isimproved.3.Modeled on front teaching building which collapsedin wenchuan earthquake in Xuankou Middle School,three analysis models are established:bare frame model,models that the effective flange widths of T-shaped beamsare calculated by American ACI specification and New Zealand NZS3101 specification respectively.And the effect of T-shaped beamon "strong beam-weak column" failureof RC frame structure is studied further.By comparing the flexural capacity of beams,it is discovered that the floor slab can significantly improve the negative flexural capacity of beam end and influence formation of "strong column-weak beam" mechanism.Throughcontrasting energy dissipationofstructures and components,usage ratio of components and inter-story displacement angle,it is found that the floor slabs improve the stiffness and strength of beams and reduces the energy dissipation of beams,while the inelastic energy dissipation and usage ratio of the bottom column and the maximum inter-story displacement angle of the bottom layerunder strong ground motion are increased;the bottom storyturn into weak story;the risk of collapse is increased;the possibility of "strong beam-weak column" failure isimproved.