Development of New Material Model for Reinforced Concrete under Plane Stress and its Application in the Modeling of Steel Frames with Reinforced Concrete Infill Walls

A rational, mechanics-based constitutive model for reinforced concrete in a state of plane stress is developed. The model accommodates the possibility of formation of multiple crack sets if the maximum tensile stress direction deviates by at least 30 degrees from existing crack orientations. Contribution of crack sliding/ opening motion to total strain is also taken into consideration. Reinforcing bars follow a linear elastic model with hardening as suggested by Menegotto and Pinto, with the modification that at crack interfaces the capacity of reinforcing bars to resist compression is reduced. Plain concrete follows a damage-based orthotropic material law. Stress-displacement relations at crack interfaces are modeled by simpler approximations of the Walraven's aggregate interlock principle formulas.;The panel model is implemented for 'mixed loading' and 'strain control' conditions. 'Mixed loading' refers to the case where normal stresses and shear strain are prescribed, and normal strains and shear stress are computed. 'Strain control' involves the specification of the three strain components from which the three stress components are derived. Shear stress-strain relations derived from the model display reasonably close comparisons with those of experiments. Cyclic axial and shear behavior of reinforced concrete panel are successfully modeled.;The material model for reinforced concrete under plane stress conditions is successfully implemented in the open source finite element program OpenSees (Open System for Earthquake Engineering Simulation). The tangent stiffness method for cracked and uncracked cases is employed. The material model is used to simulate reinforced concrete wall tests, and the results are found to be in acceptably close agreement with those of experiments.;The applicability of the material model in the simulation of steel frames with reinforced concrete infill walls is explored. Nonlinearity in steel frame is accounted for using the concentrated plasticity concept with the moment-rotation relation in accordance with the modified Ibarra-Krawinker model. Initially, a steel frame with partially restrained (PR) connections and a reinforced concrete infill wall tested at the University of Minnesota is modeled by assuming rigid beam-column connections. Comparison of total drift from the model with experiments indicates close agreement at earlier stages of loading. The frame was subsequently modeled accounting for the presence of PR connection. At earlier stages of loading, there is very little difference in response with respect to the fully restrained connection case. Convergence problems do not allow the modeling of steel frames with reinforced infill wall over the entire range of the experiment.