The link frame model (LFM), a tool for the seismic analysis of timber frame buildings considering system effects

Abstract

This article proposes a model that makes possible the seismic analysis of timber frame multistory buildings in general-purpose software. The model is entitled link frame model (LFM) and shows the following advantages in comparison to previous models: (1) it can model shearwalls only with frame elements and links with errors close to 0% with respect to analytical code models such as e.g. the special design provisions for wind and seismic (SDPWS); (2) for seismic analysis, both the static analysis method and the modal spectral analysis method can be used, in addition to the gravitational analysis; (3) the computation of the natural period shows deviations close to 0% in comparison with eigenvalues and eigenvectors; (4) it can be implemented in general purpose structural analysis software such as e.g. ETABS or SAP2000; and (5) building system effects, i.e. interaction of shearwalls with other assemblies, can optionally be captured if assigning the proper diaphragm out-of-plane flexural stiffness. Given the great impact of this last aspect in practical design, and the lack of its research, this paper does not only present the model and validation itself, but also analyzes the consequences of considering system effects in a representative case study building. The analysis demonstrates that the average shearwall tension (uplift) of regular buildings can decrease by 80% if considering system effects, which could make timber buildings much more cost competitive in seismic countries.