Research On The Calculating Method For The Strength Of Normal Cross Section Of Double Steel-Concrete Composite Continuous Beam

Double steel-concrete composite continuous beam is a new structural system born in 1980s. Besides the concrete roadway slab, there is a concrete bottom slab connected with the bottom steel flange through studs where the section suffers negative bending moment. In this way, the concrete slab helps to share the compress stress taken on by the bottom steel flange and web alone in the traditional steel-concrete composite continuous beam, so as to improve the stiffness and the bearing capacity of the beam. Therefore it is a reasonable and effective measure to improve the performance of the single-sided composite beam under negative moment. The calculating method for the strength of normal cross section of double steel-concrete composite continuous beam is researched, and some important conclusions are as followings:The calculating method for normal section strength of double composite beam is mainly researched in this dissertation. According to the deducing formula, the calculating method of normal section for the ultimate flexural capacity can be divided into elastic analysis method and plastic analysis method, and each is generalized respectively by considering or not considering slip and by considering full or partial shear connector. The calculating method for normal section of the ultimate shear capacity is analyzed under the circumstances of different tension ratio'r'. Also the calculating method of the inner force can be divided into elastic analysis and plastic analysis. In the elastic analysis method, the length of the cracked range for the concrete roadway slab of the negative moment areas of double composite continuous beam is calculated, as the length of the concrete bottom slab, and the computing chart of the deflection for double composite continuous beam, which can be used to calculate the inner forces in displacement method, are obtained. In the plastic analysis method, calculating equations of internal forces for the composite beam under two circumstances of uniformly-distributed load and concentrated load are obtained. According to the methods mentioned above, the ultimate load of double composite beam can be confirmed under the different conditions.Three pieces of double steel-concrete composite beam are tested under dead-load. The ultimate flexural capacity, the deflection and the strain and stress of the section of the composite beams are studied under the level of full shear connector, and compared with the theory results. The rationality of the calculating method for normal section strength is verified.A numerical study of double composite beam is conducted by means of the finite element program. The cracking of concrete, the nonlinear of concrete and steel, and bond-slip between reinforcement and concrete are taken into account in the analysis. The results from the finite element analysis show that the deflection and the bearing capacity of resisting moments of double-composite beam are improved by the concrete bottom slab, and there is a good agreement between theoretical analysis and the test results. Through the study, a deeper insight into the mechanical behaviors of double composite beam is gained, which is helpful to subsequent further research.