Reliability Analysis Of Steel-Concrete Composite Beams

According to the 《 The Design Codes of Steel structure (GB50017—2003)》, the reliability of steel-concrete composite beams under serviceability limited states and bearing capacity limited states is analyzed from point of the reliability theory.Firstly, the different in design express, the value of loads and factors of resistance between the new codes and the old is compared and the revised content about the steel-concrete beam in the codes is introduced.Secondly, the reliability index of steel-beams, concrete-slab and connect elements in the equation of limited states which is established according to the elastic and plastic design methods is computed in the cases of dead loads and live loads is the leading action separately and the whole analytic models of composite beams, i.e. the structural systems consisted of elements in series is put forward, and then the reliability index is worked out. In addition, the influence of elements on the index is discussed, which provide reference to the optimum design of the composite beams.Thirdly, considering the design parameters of composite beams as random variables, the probability nature of rigidity reduced factor is analyzed using probability theory and Monte-Carlo method, thus, the probability distribution function and characteristic number of rigidity reduced factor is calculated. Considering rigidity reduced factor as deterministic and random variables separately, the comparison analysis of reliability of the deflection expression corresponding different loads combination in current codes is performed. Two different expressions for the limited states equation of deflection are used. The results show that the reliability of deflection conforms to the suggestion value under serviceable states presented in ISO 2394: it is zero for reversible limited states and 1.5 for irreversible limited states.Lastly, based on the current codes, the reliability of crack width of concrete-slab in negative moment zone is analyzed, the influence of different load ratio, ratio of reinforcement and strength grades of materials on reliability of composite beams is studied All of these will provide a reference for design standards of composite beams.