An engineering approach to evaluate stress concentrations at openings in CLT shear walls

Abstract

In the past decade, the construction of mass timber buildings made from sustainable cross-laminated timber (CLT) has increased significantly. However, openings such as doors or windows in CLT shear walls can substantially reduce their load-bearing capacity. Many design standards address this by neglecting wall segments with openings, leading to inefficient designs and inaccurate internal force distributions in CLT buildings. While current design standards provide guidance for wall sections without openings, they lack suitable approaches for geometries with discontinuities, where stress concentrations occur. To address this gap, we propose a fracture mechanics-based method to predict brittle failure at corners using 2D linear elastic finite element (FE) models. The method evaluates Mode I and Mode II energy release rates based on mean stresses and applies a mixed-mode fracture criterion. The modeling framework accounts for orthotropic material behavior, local mesh refinement around singularities, and nonlinear connection behavior. The models are validated against published experimental data, and the results show good agreement for both crack-driven and connection-driven failure cases. A sensitivity analysis with respect to key parameters influencing the total energy release rate confirms the robustness of the proposed approach. These findings support the method's applicability for practical design purposes and pave the way for its broader use in other timber engineering applications.