The Effect Of Concrete Slabs On The Flexural Rigidity And Torsional Rigidity Of RC Frame Beams

Cast-in-situ RC beam-slab floor system is the one which is the most widely used at present. It has great effect on the safety and economy of the structure. Beams and slabs of cast-in-situ RC floor system are integrated and act on each other. And they bear the loads and produce coordinate deformation together. But in the methods of designing the cast-in-situ RC floor system under the gravity load, beams and slabs are divided practically. For the slabs designing, beam is deemed as fixed hinge support. on other hand, engineers introduce the rigidity amplification coefficient and the torque reduction coefficient to take account of influential effect which is slabs imposing on beams, then calculate internal force distribution of the slabs individually.In this paper, finite element analysis software ETABS are used to analyze which factor control the influential effect of the slab toward the rigidity of beam in Cast-in-situ RC beam-slab floor system. From the beginning of the basic beam-slab floor unite, model is abundant and analysis is deepen step by step. This paper obtain the essential factor which is the beam-to-slab relative stiffness, and the beam-to-slab relative stiffness determined by elastic modulus of the material,span length and section dimension of the component and the arrangement of the secondary beam, But most important factor is the structure form. Concretely speaking, it's the position of this beam and the adjacent beams. Finally, rigidity adjustment coefficient of the waffle slab system and the ribbed floor are formed table and the feasibility is verified by practical engineering. In this paper, ETABS are used to analyze the torque reduction coefficient of the beam by building the analysis model. The results show that the torque of the beam is reduced to 50% because of the torsional rigidity influenced by poured concrete slab. According to different structure form, the torque reduction coefficient is different. And Research improve the design of beam and slab in cast-in-situ RC floor system , which help to avoid safety hidden trouble and stop wasting, then make the design of floor system more safe. reasonable and economic, and the performance of structure system more effective.