Experimental study of cold formed steel roof truss connections

Abstract

[EMBARGOED UNTIL 5/1/2024] Cold-formed steel (CFS) roof trusses are commonly used due to their cost effectiveness, reliability, and high stiffness to weight ratio. To increase the effectiveness of these widely used trusses, the overall research project aims at evaluating the response of CFS roof trusses under static and dynamic loads resulting from an external blast. Numerical simulations models of full-scale CFS roof trusses are performed and validated using fullscale CFS truss experiments in the lab and in the field. To improve the simulation predictions, the accurate response of the connections will need to be incorporated into the numerical models. Since connection related failures are common in such trusses, and to improve the understanding of the full-scale truss response, it is necessary to study the response, including failure modes, of such connections. Therefore, the objective of this thesis is to experimentally study the response of CFS truss connections of cold formed steel roof trusses. Material response, including modulus of elasticity, yield stress and strain, and ultimate stress and strain, were also evaluated in this thesis. The connection testing included the evaluation of connections with varying member types, number of screws, and screw spacing. The results included stiffness, deflection, and load capacities. Conclusions were made for several key subjects as follows. The cold rolling process results in changes to material properties that result in decreased ductility. Increasing the number of screws increases load capacity and stiffness. Decreased screw spacing causes a group concentration effect that reduces load and stiffness of the connection in proportion to number of screws. Connections exhibit bearing and tearing, tilting, pull-out, block shear and shearing of screws failures. The web member composing the end bearing connections had a drastic impact on the performance of the end bearing connection.