Nonlinear finite-element analyses of concrete frame corners

A research project is currently being conducted to evaluate a new reinforcement detailing in frame corners in civil defense shelters where all reinforcement bars are spliced within the frame corner. As part of this, full-scale frame corners subjected to negative bending moment were tested and analyzed using the nonlinear finite-element program DIANA. A concrete material model based on nonlinear fracture mechanics to take cracking into account and plasticity models for concrete in compression and reinforcement steel were used. An interface model accounted for the bond-slip relation between reinforcement and surrounding concrete. Parameters that varied in the study were reinforcement detailing, reinforcement ratio, the effects of the weakness of the construction joint, and the interaction between reinforcement and concrete. Tests and finite-element analyses support the idea that the new reinforcement detailing is appropriate to use. Furthermore, it was found that the effect on the maximum load capacity of different bond-slip relations, the weakness of the construction joint, and incorrect positioning of the reinforcement bars in the corner were negligible.