Experimental study on seismic performance of infilled frames with improved flexible connection

This study examines the seismic performance of infilled frames with improved flexible connections (IFC), addressing limitations of conventional flexible connections (FC) recommended by Chinese seismic design codes. In-plane (IP) and out-of-plane (OOP) quasi-static tests were conducted on both IFC and FC infilled frames to evaluate and compare their bi-directional seismic behavior. Additional OOP tests on IFC infills were performed to establish performance levels. Finite element simulations were developed to reproduce the IP and OOP responses, and were validated against experimental hysteresis behaviors and damage patterns to explore underlying damage mechanisms further. Results demonstrate that IFC infills utilizing basalt fiber grid (BFG) tie-belts provide superior in-plane decoupling and out-of-plane stability compared to FC infills, especially for autoclaved aerated concrete (AAC) masonry. Under bi-directional loading, FC infills exhibited reduced OOP capacity due to prior in-plane damage, revealing potential vulnerabilities of conventional steel reinforcement connections. The proposed IFC system effectively mitigates these vulnerabilities and achieves enhanced IP capacity objectives and OOP performance, offering a robust solution for improving the seismic resilience of infilled frame structures. • The Improved Flexible Connection for AAC block infilled frames (IFC infilled frames) has been proposed, realizing in-plane infill-frame movement decoupling and facilitating infills' out-of-plane arcing mechanism during earthquakes. • In-plane quasi-static tests and out-of-plane quasi-static tests with prior in-plane damage were conducted for IFC infilled frames to study their bi-directional seismic performance. • Out-of-plane quasi-static tests were conducted on IFC infilled frames to determine their out-of-plane performance levels.