The Research For Analysis Method Of Time Effects In Steel And Concrete Composite Structures

Steel-concrete composite structures with a combination of significant technical and social benefits, which has the advantages of both steel structures and concrete structures, are in increasingly widespread application in recent years. Under sustained load, there will be gradual development of strain in concrete caused by creep and shrinkage, but steel don't has such characteristic. The difference between steel and concrete in long-term performance causes increases in deformation and curvature, redistribution of stress and internal actions, even redistribution of inner force in statically indeterminate structures. In bridges and other large complex structures, the effects caused by creep and shrinkage will be relatively more serious. So it is necessary to consider time effects in structural designs.A number of alternative methods for the inclusion of the time-dependent effects of creep and shrinkage are studied, and a new method is presented. Against the characteristic of composite beams, this papers analysed time-dependent behaviors of simple-supported beams and the effects in rigidity and stress, which is caused by creep, shrinkage and the slip of shear connectors. A method for time-dependent effects in continuous composite beams is also presented, which is called time-dependent rigidity method. On the basis of previous research, a program is compiled to calculate time effect in composite structures. A great deal of calculation was carried to verify the method and program.The stress in the top of steel beam increases remarkably, which may threaten the local stability in the web. In three typical codes, it is the most accurate to calculate the general time effects to use CEB-FIP(1990) method, CEB-FIP(1978) method fit the calculation in early time, and ACI-209(1982) is best for the calculation in the final time.