Debonding Sawtooth Analytical Model for SRG-Strengthened Joints Subjected to Direct Shear and Experimentally Tested

This paper presents a new and easy-to-use analytical model for the debonding of steel reinforce grout (SRG)-reinforced concrete specimens subjected to single lap shear tests. The non-linearity is concentrated at the interface between mortar and textile supposed linear elastic, assuming a perfect bond between the support – infinitely rigid and resistant – and mortar. The behavior at the interface, assumed discontinuous and multilinear, is characterized by a tangential stress-slip relationship consisting of four phases: three elastic perfectly brittle and one elastic perfectly ductile. A pseudo-linear hardening phase is observed experimentally in global force-displacement curves when detachment triggers, and consequently, it is essential to assume a non-zero residual tangential resistance at the interface. Admitting such assumptions, the slip at the interface between reinforcement and substrate can be described through a second order differential field equation which states closed form solutions, properly derived. This paper also proposes an implementation in a commercial finite element (FE) software, which discretizes the interface between mortar and steel cords by means of three in parallel cutoff bars, two of which are elastic perfectly brittle and one elastic perfectly ductile, using rigid beams for the connections and modelling SRG with elastic quadrilateral elements. Finally, the reliability of the proposed procedure and model is validated against experimental tests carried out by the authors using five SRG-strengthened specimens tested with direct shear test.