Performance-based design of sheathed CFS buildings in seismic area Luigi Fiorino, Ornella Iuorio, Vincenzo Macillo, Raffaele Landolfo n University of Naples Federico II, Naples, Italy article info Available online 17 April 2012 Keywords: Behaviour factor Cold-formed steel Performance-based Residential buildings Sheathing-braced abstract The widely recognized structural performance provided by cold-formed steel (CFS) systems together with high levels of prefabrication, safety, durability and sustainability are spreading the CFS construc- tion systems all over the world. At the same time, the actual lack in European seismic design codes requires the development of specific design procedures for the application in seismic area. The seismic behaviour of CFS structures is characterized by the lateral response of shear walls. In particular, when the sheathing-design methodology is adopted, then the seismic behaviour is strongly influenced by the nonlinear response of sheathing-to-frame connections. In this paper a performance-based design methodology for the seismic design of sheathed CFS walls is proposed. The presented methodology is based on the results of an extensive parametric nonlinear dynamic study carried out on one story buildings by means of incremental dynamic analysis. Moreover, a multistep design procedure that allows all the main structural components to be defined in three steps is developed. In particular, a nonlinear dynamic (ND) nomograph for the assessment of the external screw spacing is presented in this work in order provide a new tool that upgrade the design procedure under investigation by the Authors in the last years. Finally the application of the proposed design methodology is verified through a case study. & 2012 Published by Elsevier Ltd. 1. Introduction Nowadays, the construction market offers a wide choice of structural typologies and the selection of technologies and pro- ducts to use for buildings is strongly influenced by economic costs and execution times. Besides, the construction system has to satisfy other fundamental requirements as safety, durability and eco-efficiency. From this perspective, the constructions made with cold-formed steel (CFS) structure combine successfully high structural performance with elevated quality level offering extre- mely competitive solutions, which satisfy the needs of very demanding customers [1]. The design of a CFS structure under horizontal loads can be carried out using two different approaches: ‘‘all-steel’’ design and ‘‘sheathing-braced’’ design. The first one considers only steel mem- bers as load carrying elements and the introduction of X or K bracing systems in the lateral resisting walls is required. The latter approach takes into account the resisting effect given by sheathing panels, usually wood or gypsum based. In this case, the system composed by sheathing, steel frame and fasteners represents the main seismic- force resisting system and the walls act as in-plane diaphragms. When the design is carried out according to the ‘‘sheathing-braced’’ approach, the advantages of choosing CFS solution are mainly due to the higher structural performance, with consequent material saving, which usually corresponds to ease of assembly, reduction of execu- tion times and lower costs [2]. Different approaches are available to estimate the lateral response of sheathed CFS shear walls: experimental, analytical and numerical methodologies. The experimental approach is based on full scale tests carried out on typical walls and it is frequently used. In fact, nominal shear strength design values provided by building codes [3] in tabulated form are based on experimental test results. Due to the required large number of test, it is clear that this approach is the most expensive one and, in addition, it can be used only when the wall characteristics (geometry and materials) are within the range of experimental results. In order to overcome the limitations of the experimental approach, finite element methods can be used to evaluate the shear response of sheathed CFS shear walls. Numerical models are usually calibrated on available experimental results and they can be used to simulate the structural response of walls having characteristics different from tested walls. As far as analytical approaches are concerned, approaches specifically developed for sheathed CFS walls are not present in literature. On the contrary, a large number of methods developed Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/tws Thin-Walled Structures 0263-8231/$ - see front matter & 2012 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.tws.2012.03.022 n Correspondence to: Department of Constructions and Mathematical Methods in Architecture University of Naples ‘‘Federico II’’ via Forno Vecchio, 36. 80134 Naples, Italy. Tel.: þ39 081 2538052; fax: þ39 081 2538989. E-mail addresses: lfiorino@unina.it (L. Fiorino), ornella.iuorio@unina.it (O. Iuorio), vincenzo.macillo@unina.it (V. Macillo), landolfo@unina.it (R. Landolfo). Thin-Walled Structures 61 (2012) 248–257