Experimental study on the shear strength of reinforced concrete composite T-shaped beams with web reinforcement

Abstract

The current increasing use of precast concrete elements and cast-in-place concrete slabs, namely concrete composite elements, in construction requires a better understanding of their behaviour in shear. In this work, 19 T-shaped composite and monolithic specimens failing in shear were experimentally tested. Their results were compared to study the influence on the shear strength of: the flange width, the presence of an interface between concretes and the strength of the concretes of both beam and slab. The shear transfer mechanisms were analysed by adapting to these specimens a mechanical model previously proposed by the authors for rectangular composite beams. It was concluded that: the composite specimens’ shear strength did not increase with widening flange width when the specimens showed an extended interface cracking, but increased when their crack pattern was similar to that of the monolithic specimens; the presence of an interface decreased the shear strength; the slab’s concrete compressive strength modified the composite specimens’ shear strength when the slab failed in shear, but not when the slab failed in bending or when the interface failed. The shear formulations of EC2, MC-10 Level III and ACI 318–19 gave good estimations when using the weighted average of the compressive strengths of the beam and slab concretes, similarly to those obtained with the proposed model. From the experimental results, the improvement of the interface shear strength of composite beams is proposed as a practical recommendation for increasing their shear strength. At the same time, the slab width and the slab’s concrete strength could be increased with the same purpose. This work experimental findings and the adaptation of the mechanical model to T-shaped beams lay the groundwork for a future development of a shear design and assessment formulation for concrete composite elements.