Timber structures hold aesthetic value that seamlessly blends the architect’s idea and the natural environment. Hence, there is a global surge in use of engineered wood products as sustainable structural components for both residential and commercial buildings. At present, the demand for intricate and taller structures has pushed engineers to innovate and develop more effective wood products and structural systems that can withstand larger loads without any structural failures or serviceability issues. Cross Laminated Timber (CLT) presents one option of innovative product that can be used in efficient structural systems in residential and commercial applications. CLT buildings can be constructed using either platform-type or balloon-type method. In balloon approach, the CLT walls are continuous for the entire height of the building and the floor panels are attached to the walls at each floor. This method has several advantages with respect to the platform-type one, such as use of larger panels, reducing the number of connections, and avoiding accumulation of compression perpendicular to grain stresses in the lower floors, thus presents itself as a viable solution for high-rise buildings.
While significant amount of research is available for platform-type CLT systems, virtually no research information is available for balloon-type walls. Canada-based Building Systems Group researchers form FPInnovations: Dr. Zhiyong Chen and Dr. Marjan Popovski have developed two mechanics-based analytical models (rigid- and elastic-base models) for predicting the deflection and resistance of balloon-type CLT shear walls. The elastic-base model can predict the potential crushing occurring at the bottom of the wall. Their work is currently published in the research journal, Engineering Structures.
The Canadian scientists developed the analytical models based on engineering principles and mechanics. The models can predict the deflection and resistance of balloon-type CLT shear walls under lateral loads, with consideration of the vertical load. The analytical models were validated against in-house test results of four balloon-type CLT shear walls in two configurations tested under monotonic or cyclic loads. The verified analytical models were used to investigate the influence of vertical load, wall aspect ratio, and properties of vertical joints on the structural performance of the balloon-type CLT shear walls.
The authors reported that the performance of the balloon-type CLT shear walls can be influenced by the behaviour of the bottom part of the wall that can experience some crushing. It was also reported that the lateral stiffness and resistance of the balloon-type CLT shear walls increased with an increase in vertical load applied to the walls, while it decreased with an increase in the wall aspect ratio (height to length). Overall, the results from the parametric analysis, first of its kind in the world, gave a valuable insight into the structural behavior of the balloon-type CLT shear walls.
In summary, the Chen-Popovski study presented two new analytical models: rigid- and elastic-base model, that can predict the deflection and resistance of the balloon-type shear walls. The developed analytical models were validated against results from full-scale tests on single and coupled CLT shear walls conducted at FPInnovations. The influence of specific parameters on the structural performance of balloon-type CLT shear walls was investigated using the verified elastic-base model. In a statement to Advances in Engineering the authors of the study highlighted that the developed analytical models can be used by researchers and engineers to predict the structural performance of balloon-type CLT shear walls.
Zhiyong Chen, Marjan Popovski. Mechanics-based analytical models for balloon-type cross-laminated timber (CLT) shear walls under lateral loads. Engineering Structures, volume 208 (2020) 109916.