Study on the mechanical properties of integrated sleeve mortise and tenon steel–wood composite joints

This paper focuses on the application status and technical challenges of steel–timber composite joints in building structures, proposing and validating an innovative steel sleeve reinforcement connection technology. Through monotonic loading tests and finite element simulations, the performance of unreinforced joints and steel sleeve reinforced beam–column joints was analyzed. The study found that unreinforced joints are prone to crushing deformation or even failure at the mortise and tenon under bending moment, whereas joints reinforced with steel sleeves not only significantly enhance load-bearing capacity but also exhibit excellent initial rigidity characteristics. The failure mode mainly involves crack propagation at the edge of the steel plate and tearing of the wood, yet the overall structure remains intact. Furthermore, finite element simulations showed that for joints without sleeves, stress concentration areas are located at the upper and lower ends of the tenon, with compressive and tensile stresses distributed along the grain direction of the beam. Conversely, in joints reinforced with steel sleeves, the stresses on column sleeves and bolts are negligible. For beam sleeves, the regions with higher strain concentrate around the welded stiffeners and particularly around bolt holes. Based on the aforementioned test results and finite element analysis, further investigation was conducted into the impact of varying the length, thickness, and bolt diameter of beam sleeves on the mechanical properties of a new integrated sleeve mortise-and-tenon steel–timber composite beam–column joint. The research indicates that moderately increasing sleeve thickness can improve the joint’s seismic resistance, while being too thick or too thin is detrimental to its performance, with 3 mm sleeve thickness being optimal. An appropriate sleeve length enhances the joint’s seismic performance, with approximately 250 mm being the ideal length. Additionally, an appropriate bolt diameter is crucial for preventing internal damage to the joint; a bolt diameter of about 10 mm is most suitable under current conditions, effectively avoiding damage and plastic deformation due to insufficient or excessive stiffness, thereby optimizing the joint’s seismic performance.