Experimental study on in-plane behavior of composite frame slabs and the influence of out-of-plane effect

This paper experimentally investigated the in-plane behavior of a steel-concrete composite frame slab under cyclic loading by considering the influence of the out-of-plane effect. A pure in-plane loading test and two in -plane loading tests of frame slabs with different out-of-plane loads were designed and conducted. Subse-quently, the test observations, load-displacement relationships, and shear and flexural deformation components were discussed to investigate the in-plane load resistance behaviors and failure mechanisms of the composite frame slabs with different out-of-plane loads. The experimental results of the pure in-plane loading test demonstrated an evident shear cracking concentration behavior and a pinching hysteretic curve associated with a typical shear-tension failure mode of the composite frame slab. Further, the in-plane loading test of the composite frame slab with small out-of-plane loads also exhibited a typical shear-tension failure mode, and thus had a load-displacement relationship similar to that of the pure in-plane loading test. In contrast, the in-plane loading test with large out-of-plane loads exhibited a horizontal shear failure mode, and thus exhibited a load-displacement curve with a more obvious pinching effect and significantly decreased ultimate load capacity. In addition, the influence of the out-of-plane loads on the in-plane stiffness of the composite frame slab was analyzed.