Experimental and analytical investigation of cold-formed steel floor trusses under gravity loading

Dizdar, Çağan
Cold-Formed Steel structures are getting increasingly popular in the market with their economic and short construction duration advantages. One of the most common floor system used in CFS buildings utilizes trusses made of CFS members. Despite their increasing use, behavior of CFS floor trusses has been the subject of very limited research. The governing failure mode of these structures under gravity loading is usually local buckling of compression chord elements. Therefore, a reliable design of such structures requires accurate determination of force effects and realistic estimation of CFS member capacities. The current study aims at investigating the validity of analysis assumptions and design techniques currently used for CFS floor trusses. Effect of parameters, such as connection detail at diagonal-chord joints, number of fasteners used at each diagonal-chord connection, CFS member thickness and the presence of OSB sheathing plate were studied as part of the experimental program. The focus of the study was twofold: truss stiffness and truss load capacity. Truss stiffness was studied in relation to the stiffness of diagonal-chord connections. With the incorporation of joint axial flexibility, the truss stiffness predictions were observed to accurately represent the measured response. In regards to the accurate determination of truss load capacity, both the normal force and bending moment effects on chord members were considered. Experimental and numerical results indicate the presence of significant bending effect on truss chord members. A simple procedure was established in order to quantify this effect and determine the value of chord bending moment. In the proposed procedure maximum bending moment occurred on truss chord members was calculated using imaginary loading, which was determined based on truss midspan deflection. The normal force and bending moment effects on chord members were considered together with the corresponding capacities determined based on the code provisions. Truss load capacities obtained through this procedure were observed to accurately represent the measured capacities.