Challenges and solutions in the design of a 10 storey CLT building

This paper has presented an overview of the structural challenges and solutions during the design of a tall CLT building currently under construction in Sydney. The ten storey structure was an all timber CLT structure, with structural steel balconies, on a concrete podium. In contrast to typical CLT structures such as single storey residential dwellings and small multi-storey multi-residential buildings, this building has an irregular and very large floor plan, requiring additional care in the design of both the gravity and lateral load resisting systems. Understanding of the system displacements is crucial in the design of any structure, and paramount in the design of a tall timber building. For this reason, computer modelling was used to understand load paths and interactions within the structure. The modelling of individual fasteners or connections consumes significant computational cost and time, so equivalent springs were used to calibrate cantilever members within the 3D Etabs model. An equivalent truss model was used to understand floor load path sand to ensure diaphragm actions. During the analysis, it was noted that dual system action, common to hybrid reinforced concrete structures, was being displayed by the numerical model. Although this assisted the structuralperformance, careful design consideration wasrequired to ensure the stresses created by this actioncould be resisted by the structural members. Forexample, while it is possible to transfer stress wheredoors are cut within the CLT panel, it is difficult tocreate the required moment connection across gluelaminated lintels.Significant material savings were made by alteringthe thicknesses of panels, both up the height of thebuilding and across the floor plate, which created anadditional challenge during detailing with notches andcuts being required to enable the use of hold downbrackets. Additional design consideration was alsorequired around door lintels where the cumulativeintroduction of concentrated loading up the 10 storeybuilding placed significant compressive load on theCLT panels.As with any lightweight flooring solution, the useof long span CLT floor requires rigorous analysis toidentify potential vibration issues. Finite elementanalysis was performed to check performance againstcode levels.Close collaboration between the members of theTrans-Tasman design team was key in ensuring thesuccessful design of what will be one of Australia’smost exciting timber buildings.