An elasticity- and fracture mechanics-based model for composite timber I-joists with openings in the web

Abstract

Timber I-joists with plywood or oriented strand board web and solid (or engineered) wood flanges combine a lightweight design with exceptional strength and stiffness. Nevertheless, the structural behaviour of the I-joists are significantly influenced by the presence, shape, size, and location of the openings in the web, which is the focus of this study. A prescribed shear distribution along the flange-web interface and a suitable Airy stress function are adopted to satisfy the boundary conditions on the edges of the web. An analytical model for the full stress field in the web is derived and validated by 2D finite element (FE) simulations. The difference in the magnitude of the maximum stresses obtained from the analytical and FE models is less than 10 % even for the large openings (up to 90 % of the web’s depth). Different failure criteria (in the framework of direct strength and fracture mechanics) are used in conjunction with the analytical stress field to predict the failure mode and the load-carrying capacity of the I-joists. The direct strength approach grossly underestimated the peak loads; however, the failure loads obtained from the fracture mechanics-based approach showed a good correlation with the test data available in the literature.