Across-Wind and Torsional Response of Tall Mass Timber Buildings: Semi-Empirical Equations for Structural Design

Across- and torsional-aerodynamic wind loads on buildings are complex phenomena to predict analytically. Existing prediction equations in building codes and literature were empirically developed based on wind tunnel tests. These tests only considered tall buildings constructed with conventional materials such as concrete and steel due to the assumption that the design of mid-rise buildings is not governed by across- and torsional-wind loads. However, tall mass timber buildings with heights equivalent to mid-rise concrete and steel buildings are prone to wind-induced oscillations because of their lightweight and low lateral stiffness. Hence, designers need to ensure that across-wind and torsional responses are controlled to uphold occupants’ comfort and maintain building serviceability. The existing empirical across and torsional-wind load prediction equations may not be applicable to tall mass timber buildings due to the height ranges considered in their development. In this paper, we first assessed the applicability of the existing equations by comparing their prediction with wind tunnel test data representing the height and plan aspect ratios of tall mass timber buildings. Significant discrepancies are observed in the predicted and experimental across-wind forces and torsional moment coefficients. The mismatches are more pronounced for buildings shorter than 96 m in height and those with large side ratios. Therefore, new semi-empirical equations are developed based on 18 wind tunnel experiment datasets. Comparisons between the proposed equations and experimental data demonstrate an improved match. The newly proposed equations provide a reference for the preliminary structural design of wind-excited tall mass timber buildings.