Hybrid Office Towers under Wind Loads - A Parametric Study of Dynamic Performance and Structural Stability

Abstract

As the demand for sustainable and space-efficient urban development increases, hybrid timber-concrete buildings offer an environmentally friendly alternative to conventional construction. However, due to timber’s high strength-to-weight ratio, these structures tend to be relatively light, making them more sensitive to wind-induced motion. This highlights the need for deeper investigation into their dynamic and structural behaviour to ensure both occupant comfort and safety in taller buildings. This thesis investigates the structural and dynamic performance of hybrid high-rise office buildings composed of timber and concrete, with a focus on wind-induced acceleration under the Serviceability Limit State and structural capacity under the Ultimate Limit State. Using a finite element model developed in FEM-Design, alongside hand calculations, the study analyses how different configurations, such as core thickness, core placement, concrete slab layout, and boundary conditions, affect the results. A parametric study was conducted on a 15-, 20-, and 25-storey timber-concrete hybrid building with a concrete core and cross-laminated timber slabs, where concrete was added either by thickening the core or additional concrete slabs at the top of the building. Core placement was also varied to assess its impact on stiffness and torsional response. For each configuration, eigenfrequencies, equivalent mass, and peak accelerations were calculated and compared against comfort criteria defined in SS-ISO 10137:2008. Structural capacity was verified through analysis based on Eurocode and the Swedish annex EKS 12. Wind-induced acceleration was the governing criterion in all cases. Adding concrete slabs at the top improved dynamic performance more effectively than increasing core thickness. While thicker cores helped with strength and stability, they were less efficient for improving comfort. Different core placements performed similarly overall. The most concrete-efficient strategy is to first use thick concrete slabs at the top of the building to improve comfort, followed by adding additional slabs if further improvement is needed. However, there is a point where adding more slabs becomes less effective than increasing core thickness, which then becomes the better option.