Experimental Evaluation of Negative Flexural Capacity of Composite Slabs Embedded with Truss Girders

In this study, a novel composite slab integrating truss girders was introduced. Flexural tests were conducted on a total of eight composite slab specimens to evaluate their negative flexural capacities. Based on the test results, the negative flexural behavior of the composite slabs was analyzed, including the development of catenary action, and the effects of truss girders and diagonally bent integrity reinforcements. All specimens showed satisfactory performance in terms of their flexural strength and stiffness and exhibited high ductility capacities. The test specimens did not show any noticeable degradation in flexural strength, and the tests were terminated due to the displacement stroke limitation of the actuator. Strain measurements clearly indicated an effective transition of the negative moment-resisting mechanism from flexural to catenary action at large deformations, causing the entire section to be subjected to tensile forces. The development of catenary action was the main reason for the high ductility observed in the specimens. The truss girders, although not spanning the entire width of the supporting beams, effectively enhanced the negative flexural strength of the composite slabs as their ends partially extended through the critical failure section. The effects of the truss girder were particularly notable in specimens supported by H-section beams, where the negative flexural strengths increased by about 10 –20%. Furthermore, diagonally bent integrity reinforcements, primarily introduced for ease of construction, were also found to effectively increase the negative flexural strength of the composite slabs by developing tensile forces when diagonal cracks developed in concrete sections.