Stability and Dynamic Properties of Tall Timber Structures - A parametric study of the structural response due

Abstract

ABSTRACT The interest in building taller structures in timber is increasing in the building sector. However, the high strength-to-weight ratio of timber leads to a relatively light structure which is often associated with vibrations. The dynamic properties are essential in the design of tall timber structures, where wind-induced vibrations of the building in service state is addressed. The dynamic response is influenced by mass, stiffness and damping. These parameters influence the acceleration of the building which can be perceived as a discomfort for human occupancy. The aim is to find a structural concept that makes a taller structure than the usual today feasible. The objective is to make a parametric study and investigate how a multi-storey residential building of timber can be optimized with respect to dynamic wind loading. With a combination of numerical and analytical methods, accelerations are calculated and evaluated against the criteria for human comfort according to ISO 10137 and ISO 6897. An analytical calculation sheet is set up according to SS-EN-1991-1-4 and EKS 10 to define wind-induced acceleration. Starting from a beam-column structure with a central core, the effect of adding inner walls and exterior bracing is studied to see what limits the number of storeys for an open plan building. Analysis of the dynamic response due to wind shows the fundamental mode shape in torsion before exterior bracing is added. Results have shown that the structure can reach 5-storeys with inner walls of cross-laminated timber and 4-storeys with no walls. Moreover, it’s found that diagonal bracing in the facades improves the torsional stiffness significantly and the fundamental mode becomes a transversal mode. An outrigger bracing system has been found to be the most efficient, leading to a structure of 12-storeys. The parameters mass and stiffness are modified by adding concrete floors and assigning larger sections to the structure. Results show that the building can achieve 15-storeys with pure timber and 21-storeys when concrete floors are added. Secondary parametric action i.e. adding another outrigger generates a gain of one-storey and modifying the truss-work to steel gives a structure of 23-storeys.