Research In The Carrying Capacity Of The Simply Supported Composite Beam Of Steel And Concrete

Composite beams of steel and concrete are new type structures in which the steel and the concrete are integrated by connectors to take advantage of the respective properties of tension and compression. As they have merits of both steel structures and concrete structures, notable benefit of technology and economics have been achieved. Though composite beams have been applied and researched extensively, it is not enough in investigating the carrying capacity especially of the vertical shear of cross-section with respect to reinforced concrete structures and steel structures. The method to the cross-sectional carrying capacity in our Steel Structure Design Code has been established following the foreign countries mainly and combining our own practice without considering the concrete haunch in calculating the moment of resistance and the whole concrete portion in calculating the resistance to vertical shear. Such simplification is conservative for composite beams with haunches especially with deep haunches.In this paper, in the light of above-mentioned problem research in the mechanism of shear failure is done first, and then a new method is proposed through theoretical analysis based on properties of the composite beam. In the elastic analysis of composite beams, the concept of changing section is given up and formulas to the resistance in elastic state are deduced from composite beam's own cross-section, in which account is taken of concrete haunch. Influences of sectional dimension and material strength are also analyzed. In the elasto-plastic analysis, it is proposed that the composite beam arrives at the ultimate limit states of capacity when the stain of the outside edge of the cross-section reaches the ultimate stain. The formulas to the moment of resistance on the action of the pure moment and to the resisting shear considering the contribution of the concrete haunch on the action of the pure shear are then given. The method to the capacity at the mutual action of moment and shear is analyzed emphatically. The rule of judging whether thebeam is failure is suggested. The steps of calculating the capacity of the composite beam are concluded according to the theory proposed in the chapter, and the material methods are presented at such three states of the simply supported composite beam as applied two point loads, single point load, and uniform distributed load. A program is also worked out for the application of the algorithm proposed in the chapter to practice. The results from the elastic method and the elasto-plastic method presented in the paper agree better with test results than those from changing-section method and simple plastic method, and it is more superior in calculating the resistance to shear for the proposed methods.Designers can also benefit from the theory and algorithm introduced in this paper.