Modeling Shear-Flexure Interaction in Reinforced Concrete Elements Subjected to Cyclic Lateral Loading

This paper presents a beam-column fiber element able to describe the interaction between the bending moment and the axial and shear forces in reinforced concrete (RC) elements subjected to cyclic loading. In RC elements, shear forces are due to many complex interacting mechanisms, involving a significant part of the volume of the element; in this work, however, these are considered in an independent way and are modeled mainly at a cross section level. This strategy aims to reduce the computational effort in view of the application to seismic problems. In the proposed enhanced fiber element, stiffness-based, which adopts the Timoshenko beam theory, shear and flexural behavior are linked by means of kinematical assumptions. Different from standard fiber elements, the cross-sectional fibers take, for the purpose of computing the flexural sectional response, the direction of the compressive principal stress and hence are not parallel to the element longitudinal axis. This peculiar formulation accounts for the contributions to shear strength due to both the arch action and the inclined thrust-line developing in squat elements. In addition, The other important shear resisting mechanism of the so-called Mörsch’s truss is explicitly modeled by considering both a tension and a compression stress field inside the concrete below the neutral axis. These stress fields are modeled by comprising into the Mörsch’s truss analogy both a tension and a compression concrete diagonal. This modeling choice solves the problems related to the choice of the active compressive diagonal in standard Mörsch’s trusses when subjected to cyclic or seismic loading, and allows for adopting only one truss for cyclic loading. The nonlinear behavior of materials is described by means of appropriate constitutive relations for which the critical implementation issues are high-lighted. The proposed element has been validated by comparison with selected experimental results. The overall performance shows that the element is able to reasonably represent the experimental response in test cases strongly influenced by shear. A limited number of elements is required and an outstanding computational efficiency has been detected.