Impacts of Connection Stiffness on Moment Curvature in Cold-Formed Steel Design

Richardson, Jane

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Impacts of Connection Stiffness on Moment Curvature in Cold-Formed Steel Design

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Cold-formed steel (CFS) has risen in popularity in recent years as an alternative to structural steel. In essence, CFS is hot-rolled structural steel that is further rolled and processed at room temperature; this additional processing produces more finished and accurately sized members. When design considerations are taken into account, cold-formed steel members can be utilized beyond typical automotive and storage rack applications. Initially replacing the use of wooden studs in residential construction, this material has gradually been applied to wider structural engineering projects such as primary and secondary framing in low and mid-rise buildings. This work studied the impact of connection stiffness on the moment curvature of fastened CFS elements in free-standing structures. The mechanics of structural steel and CFS elements were established through a literature review followed by parametric investigations using case study models to explore the behavior of steel members and their associated influence on the system as a whole. The impacts of varying load conditions and the removal of redundant structural members were also examined to study the system's load path distribution prior to the application of detailed connections. Bolts and screws of comparable size were utilized in connection design and applied to the CFS models to investigate the performance of both types of fasteners based on their inherent differences in connection stiffness developed as a result of a screw’s increased exterior thread area compared to that of a bolt. The resulting moment-curvature relationships were noted for each connection and compared to the moment-curvature formulations defined by the Frye-Morris model for typical structural steel connections. It was found that the use of screwed fasteners in CFS construction could provide a more resilient design compared to those employing bolted fasteners. It was also found that the constructability of CFS structures could be improved when using screwed connections because this would eliminate the need to pre-punch holes in CFS members and reduce the number of elements required to fasten members together. Additionally, a modified version of the Frye-Morris model was suggested to expand its application to CFS structures with screwed connections.

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