Effective Widthfor Steel-Light Weight Concrete Composite Girders

Abstract

The current research program presents both experimental and numerical studiesto investigate the efficiency of using lightweight concrete (LWC) slabs in steel-concrete composite (SCC) beams and compares their behaviour with the normal weight concrete (NWC) slabs. In this respect, eight composite beams with channel shear connectors were tested in four-point bending to study the effects of concrete type and slab width, steel beam section, shear connector spacing and beam span on the behaviour of the composite beams. Two numerical models (Model 1 and Model 2) were developed to investigate the effects of a wider range of parameters on the behaviour of SCC beams connected to either LWC or NWC slabs. Model 1 used the concepts of strain comptability and force equilibrium, while model 2 adopted the nonlinear finite element analysis using ABAQUS 6.10. Both models were verified against the experimental results and showed good agreement with the test data. A total of 222 SCC beams were theoretically analyzed to develop design guidelines for such beams. Both the experimental and numerical studies showed that lightweight concrete can effectively be used in lieu of normal weight concrete to achieve a reduction of 22% in the slab weight with amarginal reduction in both yielding and ultimate loading capacities of the composite beams. The findings of this study have shown that the effective slab width relies on the load value. Therefore, the effective slab width for ultimate limit state calculations should be different from that used for serviceability limit states. It was also found that the size of the steel beam expressed by its slenderness ratio (L/rs) affects the value of the effective slab width. Steel beams with small slenderness ratios utilize wider portions of concrete slabs. Moreover, using LWC allows a considerable reduction in the number of required shear connectors without affecting the stiffness of the composite beams.In addition, it was observed that the slip value at the steel-concrete interface affects the effective moment of inertia of the composite beams, even if full composite action is achieved.Finally, design equations are proposed to accurately calculate the effective concrete widths at service and ultimate load. Also, design equations are provided to calculate the expected slip at the steel-concrete interface. The influence of the slip value between the concrete slab and steel section on the effective moment of inertia is also considered in this study.