Solving the Problem of Short Column Effects in Masonry Infilled RC Frames: Numerical Investigations

In this study, the common issue related to the masonry infilled reinforced concrete (RC) frames under earthquake loading has been investigated. Namely, infilled RC frames are used in construction sector all over the world since they are easy and fast to construct. However, every medium to strong earthquake showed that this system is highly vulnerable to the seismic effects. Significant damage of infill walls, but also of the load carrying frame system demonstrates that stiff mortar connection between brittle masonry and highly deformable RC frames is not adequate. Damage of infilled RC frames lead to the high amounts of losses after earthquakes. Therefore, there is need to improve this behavior. Several problems caused by the infill/frame interaction have been investigated for decades and different approaches for modelling and improvement have been proposed. However, still there is no consensus on the modelling approach for infilled frames, as well none of the proposed solutions has not been accepted in practice. The most promising solution is to decouple infills from the frames and in this way diminishes negative effects of infill/frame interaction. This paper focuses on the short column effects, where infill walls increase shear forces in the columns, thus causing their damage. The numerical investigation of the short column effects on the traditional and decoupled infill has been presented. The analysis shows that the proposed decoupling system significantly improves the behavior of infilled RC frames. Infills are not activated by the frame deflection under earthquake loading and infills are not causing increase of forces in the surrounding frame. Results confirm that decoupled infills behave much better than traditional infills where contact between frame and infill has been achieved via mortar. Much higher in-plane drifts can be reached by using the decoupling INODIS system.