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This paper investigates the seismic performance of a single storey moment resisting cold‐formed steel (CFS) portal frame through cyclic testing. Six monotonic and six cyclic tests were performed on three different section sizes of CFS portal frames. The portal frames were 3.2m long x 2.2m high and the CFS sections bolted with either perfect‐fit tolerance bolt holes (PTBH) or normal tolerance bolt holes (NTBH) connections. Connections with NTBH are standard in CFS, but connections with PTBH are often only used for short‐spanning frames. Results from the tests demonstrated that both PTBH and NTBH connections had stable hysteresis and good hysteretic energy dissipation capacity and ductility. On average, the NTBH connections performed better under cyclic loading in comparison to the PTBH connections (5.4% larger ductility and 22.3% increased energy dissipation). Strain gauge results show failure due to combined bending and bi‐moment stresses, of which the bi‐moment stress component accounted for 41% of the total longitudinal stresses at the section web. It should be noted that bi‐moment stresses are often incorrectly ignored by practitioners; the experimental test results thus show that by doing so the sections would fail at 59% of the design moment. [ABSTRACT FROM AUTHOR]

The true seismic performance of three full-scale, 2·2 m high by 3·2 m long, cold-formed steel (CFS), moment-resisting frame structures is investigated for the first time in this paper. In general, shear wall type CFS structures have performed well during earthquake events in the past; however, portal frame CFS type structures have not been investigated to any great degree. Limited cyclic testing of CFS moment-resisting connections/frames has shown the connections/frames perform well. However, these cyclic tests do not take account of inertia forces of the framing structural system. The seismic performance of CFS portal frames was investigated for the first time under true seismic loading using the hybrid test method. Results show that the frames perform well and under extreme loading fail through local buckling of the column section at the column-to-haunch connection. This failure mechanism needs to be prevented as it does not align with the strong column–weak beam design philosophy. [ABSTRACT FROM AUTHOR]

Highlights • Cyclic testing of cold-formed steel portal frames. • Perfect-fit and normal tolerance bolt hole connection types investigated. • Good seismic performance through ductility and energy dissipation capacity. • Normal tolerance bolt hole connection has greater ductility and energy dissipation capacity. • Bi-moment should be considered by designers as it is the second largest stress after major axis bending. Abstract This paper investigates the seismic performance of a single storey moment resisting cold-formed steel (CFS) portal frame through cyclic testing. Six monotonic and six cyclic tests were performed on three different section sizes of CFS. The portal frames were 3.2 m long × 2.2 m high and the CFS sections bolted with either perfect-fit tolerance bolt holes (PTBH) or normal tolerance bolt holes (NTBH) connections. Connections with NTBH are standard in CFS, but connections with PTBH are often only used for short-spanning frames. Results from the tests demonstrated that both PTBH and NTBH connections had stable hysteresis and good hysteretic energy dissipation capacity and ductility. On average, the NTBH connections performed better under cyclic loading in comparison to the PTBH connections (5.4% larger ductility and 22.3% increased energy dissipation). Strain gauge results show failure due to combined bending and bi-moment stresses, of which the bi-moment stress component accounted for 41% of the total longitudinal stresses at the section web. It should be noted that bi-moment stresses are often incorrectly ignored by practitioners; the experimental test results thus show that by doing so the sections would fail at 59% of the design moment. Initial failure was localised at the top of the column sections in the form of local buckling at the web-to-flange junction under compressive stresses. Several load cycles past the initial buckling stage led to a further reduction of steel ductility due to strain hardening and strain ageing leading to fracture of the steel in the section corners. The buckling/tearing failure in the columns would result in a reduced axial load carrying capacity. [ABSTRACT FROM AUTHOR]