A sensitivity study regarding different CLT modeling assump tions and their influence on high-rise timber buildings - A sensitivity study regarding different CLT modeling assumptions and their influence on high-rise timber buildings

Abstract

The use of cross laminated timber (CLT) is steadily increasing due to its beneficial structural properties, but also due to the increased popularity of timber buildings in general. Timber elements, such as CLT, have a highly orthotropic behaviour that can be challenging to implement in finite element analysis, and the consequences of the orthotropic modeling could be more substantial for taller timber buildings. This thesis investigates different methods and assumptions regarding how CLT is modeled in FE-analysis, and which advantages or disadvantages certain modeling assumptions have in regards to results on both element level and system level. In this thesis, different modeling assumptions for CLT shell elements were analysed both as independent elements and as parts of a 10-storey, all timber, reference building. The reference building was created in the finite element program RFEM with the aim to replicate properties of an existing high-rise timber building, while still maintaining a relatively simple geometry. The stiffness parameters for the different modeling assumptions were extracted partly from recommendations and research, but they also include various simpli fications of existing assumptions. The stiffness properties related to out-of-plane shear are in general more complicated than other stiffness properties, and many inhomogeneous recommendations therefore exists. The out-of-plane shear stiffness parameter was therefore investigated more thoroughly. The modeling assumptions were applied to CLT slabs and to CLT shear walls to investigate the behaviour of the elements both when exposed to bending and in-plane shear. Different reduction factors were also included in the sensitivity study. The results show that many of the modeling assumptions yield similar results in regards to deflections and deformations in general, but certain simplified models show larger deviations. The reduction factor for in-plane shear that was investigated in the thesis resulted in large deformation differences in the sensitivity study. Based on the results from the analyses, a number of general recommendations and conclusions regarding how CLT shells should be modeled in FE-analysis are pre sented in the small-scale study and in the final chapter of this thesis.