Shake table test and numerical analyses of a thin-walled Cold-Formed Steel structure: Part 1 — Investigation of the structural skeleton without claddings

Abstract

CFS structures are classified as structures with low ductility. Due to this, they are not recommended for medium to high seismic areas. The paper presents the results of a complex experimental program coupled with numerical investigations on the behavior of Cold Formed Steel (CFS) structures under seismic actions. The scaled-down model skeleton was made of DX51D+Z C-shaped 89 × 41 × 12 × 1 mm steel elements connected by 4.8 × 16 mm self-tapping screws (STS) and 5.5 × 25 mm self-drilling screws (SDS). This structure represents a replica of constructive solutions for single-story or one or two-storey structures that are frequently met in South-Eastern Europe, including highly active seismic areas.The main purpose of the research program is to gather both quantitative and, more importantly, accurate information regarding structural response to dynamic actions characterized by input accelerations equal in amplitude to the maximum values specified in seismic design codes, up to PGA = 0.40 g. The damage of the joints and the reduction in the structural stiffness due to cyclic loads, such as the ones produced by earthquakes, change the structure’s eigen period and significantly influence the structure’s response to seismic actions. Larger gravitational loads lead to more extensive damage of the joints. The developed numerical model based on the experimentally determined connection axial rigidity can offer accurate results in terms of the fundamental frequency of vibration, relative accelerations and displacements. However, for a more accurate capturing of the local damages and onset of failure mechanisms, more complex numerical models are needed, which take into account non-linear material behavior.The results presented in this paper help to design these structures as only the skeleton and serve as a starting point for future research work aimed to assess the influence of the sheathing on the global response of CFS structures to seismic actions. Additionally, research in the direction of improved joints with better energy dissipation properties is also pursued by the authors.