Identification of Modal Parameters of Multi-storey Timber Buildings from Ambient Vibration Tests

A growing number of tall timber buildings have been built across Europe and North America. The major challenge in the design of tall timber buildings is wind-induced vibration due to inherently low mass and flexibility, which makes them susceptible to low-level vibrations. Dynamic properties, such as modal parameters (natural frequencies and damping ratios), are important for accurate estimation of wind-induced response. This chapter presents the identification results of an ambient vibration testing campaign on five timber buildings, including the two tallest all-timber buildings in the world, Treet in Bergen and Mjøstårnet in Brumunddal, Norway. The two most common construction types: Cross-laminated timber (or mass timber) buildings and glue-laminated timber buildings were tested. The random decrement technique and frequency-domain decomposition method were used to identify and assess the amplitude dependence of modal properties. The results show that output-only modal analysis can be used for extracting natural frequencies of tall timber buildings. The results of the random decrement method show that modal properties exhibit amplitude-dependent behavior. Additionally, the aspects affecting the dynamic properties such as construction type and height of the building are discussed. The results of this chapter serve as a useful guideline for practicing engineers in designing tall timber buildings.