Column seismic shear load distribution in a seven-story multi-bay concrete frame

摘要

Earthquake-resistant buildings are intended to resist earthquake motions through ductile inelastic response of the seismic force-resisting system, and the design of special reinforced concrete moment frames (SMFs) requires the consideration of both strength and stiffness. SMFs are proportioned and detailed to allow for extensive inelastic deformations, and most frames are designed using elastic (or modified elastic) two-dimensional finite element analysis (FEA) models. However, the concrete columns' stiffnesses are significantly affected by varying axial loads caused by frame overturning. In the research presented here, a three-dimensional, nonlinear finite element analysis (3D-FEA) model is incorporated that includes eight-node solid elements for concrete material and two-dimensional beam elements for steel reinforcement. Concrete-column shear load distribution will be presented using 3D-FEA and will be compared to typical two-dimensional methods, and while it is widely known that columns loaded in axial compression are stronger than columns in axial tension, the compressive columns have an increased stiffness, which changes the proportionality of the shear load distribution within the concrete frame. In the case of moment frames, the increase in stiffness in compressive columns exceeds the augmentation in column strength so that the net effect is that the higher compressive columns are the most susceptible to shear loads.