Behavior of different bolted connection configurations in frames composed of cold-formed sections

Abstract

Rigid bolted cold-formed steel connections have been very popular for their better distribution of straining actions and for better full-filling serviceability requirements. However, the behavior of every single element in the connection as well as the interaction between them is not clear due to its complex behavior. A nonlinear finite element parametric study was conducted on the apex knee connection of a portal frame constructed with cold-formed back-to-back double-lipped C sections for both the rafter and the column. These back-to-back lipped C sections, connected by gusset plates are used as beam and column members. Only the webs of lipped C sections are connected to the connection gusset plates with bolts. The section flanges are not connected to the columns for ease of construction. The study focused on investigating the effect of different parameters on the ultimate capacity and the failure mode of the eave connection. Studied parameters include different bolt configurations, bolt diameters, gusset plate thickness, the bolt pre-tensioning force, and the edge distance. The effect of bolt bearing on the C-section web was considered in the calculation of the capacity of the connection. Five modes of failure were identified namely; lateral out-of-plane buckling of the gusset plate, local buckling of the connected section, bolt bearing of C-section web and the gusset plate, tearing of C-section web. It was observed that bearing failure is the dominant mode of failure. However, in some cases, the lateral-out-of-plane buckling of the gusset plate takes place and causes the premature failure of the connections at low values of applied loads. The local failure of the connected sections occurs at the ultimate loading phase. Several observations were found and some useful recommendations for optimum connection configuration are suggested. A simple interaction design procedure for special configuration to calculate the resistance of the joint connection under moment, shear, and normal forces based on the bolt bearing failure for different bolt pitches is proposed.