The Simplified Formula For Calculating The Deflection Of Steel-concrete Composite Beams And The Distortional Stability Analysis Of Its Negative Moment Zone

This paper is composed of two parts. The first part focuses on calculating the deflection of composite beam considering the slippage between the steel beam and concrete slab. The simplified formula was built and the results were compared with that of the experiment and the formula adopted by the nation regulation. The second part is about the examination on the stability of the compressed lower flange of the steel girder near the negative moment zone. The two parts are all based on the problems found in the design examples of several simply supported and continuous composite beams.Firstly, based on the content of chapter 11 of 《National Regulation of Steel Structure GB50017-2003》, two steel-concrete composite beams were designed. There were two parts of the design should be reconsidered: The deflection of the composite beam and the lateral stability of composite beams in the negative zone. The methods used in the examples were analyzed and the drawbacks were pointed out.Secondly, the differential equations considering the slippage effect were built with reference to the early related researches. The equation of the slippage was the same as that got from the energy differential method. The solution of equation was transformed to express the reduced stiffness ratio. Simplified formula was fitted with the result of national regulation and that of the experiment. It has the simple format and corrects the mistake of national regulation formula when the average stiffness is relatively small.Thirdly, the stress of the lower compressed flange is usually calculated by the Winkler Elastic Foundation Beam method. The stress result is not conservative compared with the result of FEM analysis. Assuming that the lateral displacement of the compressed flange and its rotation had the definite relationship, the critical stress was got and it fit well with the result of ANSYS. The different bound conditions, various moment distributions and the overall performances under combined normal force and moment were all analyzed afterwards. The ultimate stress got from the ANSYS considered the initial deformation and residual stress showed that the relation between the elastic critical stress and the ultimate stress could be expressed by the column B curve adopted by national regulation so the relative length-slenderness method was also applicable in this problem. As adding the transverse stiffer is such an important way to strengthen the beam, its impact on the composite beams was also investigated.