Extended sandwich model for reinforced concrete slabs: Shear strength without transverse reinforcement

In this paper, the description of the shear strength of orthogonally reinforced concrete slabs without transverse reinforcement by the newly developed extended sandwich model is presented. Based on a sandwich model, the slab element is subdivided into two cover elements and a core element, respectively; while the covers are subjected to in-plane forces only, the core has to resist to the transverse shear forces. Rotating, stress free cracks as well as tension stiffening effects according to the cracked membrane model are considered in the sandwich covers. Unlike to the covers, crack faces in the core are assumed to be able to transfer shear stresses by aggregate interlock. The fixed crack faces stand perpendicular to the slab plane, whereas the crack orientation relative to the slab plane is defined by the crack pattern of the covers. The influences of a deviation of the principal shear and moment direction from the direction of the in-plane reinforcement as well as of the slab thickness on the shear strength of slabs without transverse reinforcement are presented. Verifications against experimental data from beam and slab tests generally show a good agreement. Experimental evidence relating to size effects as well as deviations of the principal shear and moment direction from the in-plane reinforcement direction is confirmed.