Softening coefficient of reinforced concrete elements subjected to three-dimensional loads

Reinforced concrete structures are prone to fail under the effect of complex three-dimensional loading conditions. Accurate constitutive models for concrete under the effect of triaxial stresses are therefore necessary in order to predict the proper response. A strong interaction between in-plane and out-of-plane shear loads has been observed in experimental tests of concrete structures. This paper presents the derivation of concrete constitutive laws under the effect of triaxial stresses, in particular the softening coefficient, using the results of large-scale tests on representative concrete panels. The experimental testing of eight full-scale panel specimens is briefly described and the results are then used to derive analytical expressions for the softening coefficient under the effect of bi-directional shear. Finally, existing membrane shear theories are modified to take into consideration the effect of applied out-of-plane shear. The response of the tested panels proved to be accurately predicted using the new theory.