Numerical modeling of URM infill walls retrofitted with embedded reinforcing steel

Unreinforced masonry (URM) infill walls present a serious threat to communities in earthquake prone regions because they typically exhibit brittle and catastrophic failures. These failures have been observed in the aftermath of recent earthquakes such as the 2010 Haiti (Mw 7.0) and the 2010 Maule Chile (Mw 8.8). As the cost is typically the main hindrance to sesimically upgrading of these URM walls, there is a pressing need for developing cost-effective retrofit strategies. The main goal of this study is to propose a solution for seismic retrofit of URM infill walls by providing embedded horizontal and/or vertical reinforcing steel into pre-cut grooves. To investigate the feasibility of the proposed retrofitting technique, a nonlinear finite element model is developed which simulates the performance of the infill walls before and after retrofitting. In this study, the reinforced-concrete frame is modeled using smeared crack elements combined with interface models to capture opening of concrete cracks. The reinforcing steel is modeled using nonlinear truss elements and is placed in parallel with vertical and horizontal concrete interface elements. For the URM infill wall, the mortar joint is modeled with a zero-thickness cohesive interface element while the masonry unit is modeled with the combined smeared and discrete crack approaches. The reinforcing steel is modeled using nonlinear truss elements. The numerical results show that the ductility of the retrofitted walls may be enhanced with this retrofitting technique.