The Research About Working Together Of Cast-in-place Floor And Frame Beam

In the housing structure design, reinforced concrete frame structure is morecommonly used in structural system. Because of its economy and applicability, thestructural system still has a good development in the future of building in our country. Inall previous earthquakes, particularly, in the huge magnitude8.0earthquake, whichoccurred in Wenchuan of Sichuan province of China, most of frame buildings haveperformed the damage of "strong beam-weak column". How to make building structures tomeet the requirements of "strong column-weak beam", is an important research questionsneeding to resolve.In practical engineering, using cast-in-place floor to make frame beam and plate into aintegral part, greatly enhanced the ability of working together of them. In present structuraldesign, in order to consider the contribution of cast-in-place floor on the beam’s stiffness,the beam bending stiffness is usually multiplied by an amplification factor, withoutconsidering the effect of plate’s thickness, span, which result in unreasonable ofstructural design. At the same time, the reinforcement obtained by considering thecontribution of cast-in-place floor on frame beam’s stiffness is fully lay in the beam, andthe reinforcement of the plate is calculated separately. The design will make thereinforcement in the section of frame beam more than what it need actually, which improvethe cross-section flexural capacity.Large-scale finite element analysis software ANSYS and ETABS is applied in thisarticle. In this paper, through elastic analysis and calculation of many frame models, finallygets the rigidity amplification coefficient of center beam α中=1.9040+1.5481h f/h, inaccordance with standard practice, gets the rigidity amplifieation eoefficient of edge beamα边=(α中+1)/2。For an engineering example, according to the formula of the rigidity amplifieationeoefficient of frame beam obtained through analysis, calculate stiffness coefficient which isconsistent with the thickness of floor and span, then design the structure according to thestandard. Modify the model by reducing the reinforcement in the section of frame beam.Comparing the relationship between top-storey displacement and basal shearing force, thedevelopment of plastic hinge of the original design, which is obtained from the pushover analysis of the original structure, this paper’s structure and fixed structure, we can getconclusions:(1) magnifying the stiffness of the frame beam after fully considering thecontribution of cast-in-place floor on the beam’s stiffness, takes limited effect in satifyingthe "strong column-weak beam" of constructional design;(2) reducing the reinforcement inthe section of frame beam can greatly improve the ductility of the overall structure. This isan important reason to achieve the requirement for fortification against earthquakeof"strong column-weak beam".In the end of this article, some prospect is proposed about the stiffness amplificationfactor of beam and the research of reducing the reinforcement of frame beam.