Out-of-plane behavior and simplified modeling of reinforced masonry-infilled Chuan-dou timber frames

The masonry-infilled Chuan-dou timber frame is a conventional structural system widely used in non-engineered residential buildings in China’s seismic regions. However, these structures are highly vulnerable to out-of-plane (OOP) failure for the absence of an effective connection between the infills and frames. This study investigates the OOP response of structures with infills-to-frames reinforcement through full-scale testing and finite element (FE) modeling. Two reinforcement strategies were considered: infills-beam and infills-column retrofitting. The results reveal that reinforcement alters both the failure modes and resistance mechanisms. Infills-beam retrofitting leads to unidirectional bending failure governed by vertical arching and reinforcement contribution. Infills-column retrofitting promotes bidirectional bending failure, with vertical and horizontal arching actions working together with reinforcement. FE analysis revealed sustained force increases in embedded ties, nails, and steel clamps after infill cracking, highlighting the critical role of reinforcement following arching failure. And simplified predictive models were proposed based on two- and three-side support boundary conditions. These models incorporate vertical and horizontal arching effects and quantify the relative contributions of reinforcement. The predicted OOP capacities agree well with test results, with a maximum error below 10 %.