Fundamental vibration period of cross laminated timber structures – CLT dynamics

This project aims to address knowledge gaps in the dynamic properties of cross-laminated timber (CLT). With support from the Federal Office for the Environment (FOEN), a timber-framed test building is being constructed in stages in Vauffelin on which earthquake-protection measurements will be carried out. A series of static and dynamic tests will be performed on the four-storey building using steel cables. The results will provide engineers with a reliable basis for calculating the dynamic properties of cross-laminated timber.

Factsheet

  • Lead department School of Architecture, Wood and Civil Engineering
  • Institute Institute for Timber Construction, Structures and Architecture
  • Research unit Earthquake Engineering
  • Duration (planned) 15.11.2019 - 31.12.2021
  • Project management Prof. Martin Geiser
  • Head of project Prof. Martin Geiser
  • Project staff Urs Oberbach
  • Partner BAFU

Background

The fundamental vibration period T1 is one of the key parameters in earthquake engineering. Various methods can be used to calculate it, but their results sometimes diverge significantly, creating a great element of uncertainty when it comes to realistically estimating the fundamental vibration period. This knowledge gap means engineers face a dilemma in terms of meeting the need for safety and cost-effectiveness. The revised norm SIA 261:2020 – with significantly shorter fundamental periods (TC) and higher soil parameters (S) – exacerbates this problem.

Procedure

The core element of the project is the construction of a four-storey test building on a scale of 1:1 which will provide a temporary solution for the testing period and will then be demolished. The test building’s dimensions are 4m x 5m, which is roughly equivalent to a quarter of a single-family house. It will be a shell construction, but the dimensions and the bracing system represent realistic conditions. The bracing system is regular, but differs in the x and y axes to enable analysis of the frame effect.

Results

The evaluations and experimental analysis aim to provide practising engineers with a realistic and clear basis for estimating the fundamental vibration period in multi-storey CLT structures or timber-framed buildings with CLT bracing. The validity of the general assumption of 5% damping in CLT structures will also be tested.

Being able to realistically estimate the dynamic properties will allow engineers to optimally design and calculate the bracing system, meeting the requirement for both earthquake protection and cost-effectiveness.