Fundamental Period of Timber Structures

In seismic design, the fundamental period of a building is a key parameter for assessing earthquake actions. Due to modeling uncertainties and simplifications, especially in timber structures, verifying the plausibility of calculated periods is crucial. Accurate determination is essential: overestimated periods can underestimate seismic forces in force-based design, while underestimated periods may lead to overly conservative and costly bracing systems. Thus, it's a matter of balancing safety and cost-effectiveness. Since 2023, the research project "Guideline for Determining the Fundamental Period of Timber Buildings" has been conducting Ambient Vibration Tests (AVT) on approximately 50 timber or timber-hybrid buildings. For about half of these, a comparison is made between spatial structural models and correctly interpreted AVT results. The aim is to establish a reliable basis for both determining and validating the fundamental period of timber buildings. Preliminary results indicate that calculated periods from structural models are often too high. This discrepancy is largely due to unaccounted stiffness contributions from secondary seismic and non-structural elements, as well as other influences like dynamic effects, spatial interaction, and minor damage in the elastic range. These factors are actively studied within the project. Ultimately, the project will deliver a practical guideline for engineers, combining interpreted measurement data and model results. This will support more accurate assessments of fundamental periods, reducing uncertainty and helping achieve more balanced seismic designs for timber buildings.