An investigation on force modification factors in cold-formed steel structures

Abstract

Cold-formed steel (CFS) structures are a new feature in the recently effectuated 2018 Turkish Seismic Code (TSC). Their seismic design philosophy and other regulations are described within the Code. In the scope of this thesis, the Force Modification Factors defined in the Code for CFS structures are examined. Experimental and analytical studies are carried out on a real-life CFS building to investigate if the defined coefficients are practically applicable. The building chosen for this study is a two-story twin-villa type of building in Enez (Edirne) region. An Ambient Vibration Test is implemented to obtain the characteristic modal periods of the building. Then the building is thoroughly modelled in computing environment as close to reality as possible. In order to analyze the nonlinear behavior of the structure, performance analysis is conducted and the results are evaluated. Two additional laboratory experiments are carried out to determine the important structural parameters used in the analysis. The samples used in the experiments are 2.40 m x 2.40 m shear walls with X-braces on both sides, and are sheathed (on both sides) with OSB panels in one and with gypsum panels in the other. In the experiments, the behavior of a standard wall panel with double X-braces and double sheathing is investigated generally. Also a mathematical relationship is determined for the connections between the bracing and the frame members. The results obtained from the performance analysis of the analytical model and the force modification factors given in the 2018 TSC are then compared. The objective of the studies conducted within the scope of this thesis is to come up with a concluding remark on whether the given factors are reliable enough in practice. Obviously, experimental and analytical studies carried out on only one building are not sufficient to compare the order of the factors. Here, the sole intent is to get a reasonable idea about the rank of these coefficients and to provide an insight for future works that aim to study the same subjects in more detail.