Safety Assessment of Shear Strength Current Formulations for Composite Concrete Beams without Web Reinforcement

Abstract

[EN] Construction with precast concrete elements without web reinforcement and cast-in-place concrete on them to enhance the overall structure's integrity is a widespread practice in building construction. However as these composite elements' vertical shear strength has not been studied in-depth, a clear criterion about cast-in-place concrete's contribution to shear resistance is still a pending matter. The present study intends to reach practical conclusions about the shear strength assessment of composite concrete elements without web reinforcement. To do so, the shear strengths of 36 specimens, provided by existing shear formulations, were compared: 19 specimens tested by the authors, in which the existence of an interface between concretes, the cross-sectional shape and the concrete compressive strengths of the beam and slab were studied; and 17 specimens taken from a previous study about composite elements by Kim et al. (2016). The applied shear formulations were those of EC2-04, Draft 7 of EC2-20, fib MC-10, ACI 318-19 and the model proposed by Kim et al. (2016). Firstly, specimens' shear strength was calculated by considering that only the beam resisted shear. Secondly according to ACI 318-19 indications about assessing composite elements¿ shear strength, the entire composite element's effective depth was used considering the lower of the compressive strengths of the beam's and slab's concretes and the weighted average of the compressive strengths. Additionally,the entire effective depth and the beam's concrete compressive strength were used. Codes formulations were more precise when estimating the monolithic specimens' shear strengths than those of composites. Therefore, the development of an adapted methodology to assess these elements¿ shear strengths is needed. EC2-20 obtained the most accurate results and gave quite good estimations for composite elements when the entire effective depth and weighted average of the concretes compressive strengths were considered.