Two-way seismic behaviour of concrete frames with infill walls

The effects of masonry infill walls on the behaviour of reinforced concrete frames are often ignored in seismic engineering. A three-dimensional non-linear finite-element model is introduced in this paper to simulate in-plane and out-of-plane behaviour of masonry infilled reinforced concrete frames. It employs a surface-based cohesive contact model to capture the crack and slide failure mode of the infill wall mortar joints. Comparison with experimental data shows that the proposed numerical model provides good estimates of the strength, deformation and failure modes in both directions. Several two-way numerical tests are conducted to investigate the interaction of in-plane and out-of-plane responses. The tests include sequential out-of-plane and in-plane loading (and vice versa) as well as simultaneous application of both loadings. The results indicate that out-of-plane performance and in-plane strength are significantly decreased by the interaction of loadings in two directions. The out-of-plane loading causes the out-of-plane failure mode, which is often seen in past earthquake events, and before which the in-plane strength is not fully developed. A mathematical expression is proposed for engineering analysis.