Steady- and transient-state response of cold-formed steel-to-steel screwed connections at elevated temperatures

Cold-formed steel-to-steel screwed connections serve as the primary connectors in cold-formed steel framings. Most previous investigations of screwed connections focused on the failure limit states at ambient temperature. This paper presents details on single-shear experiments of cold-formed steel-to-steel screwed connections at ambient and elevated temperatures. A total of 189 steady-state tests and 36 transient-state tests are conducted. Four types of failure modes were identified, and the failure mode of the screwed connection at elevated temperatures is established to be quite similar to that of the same screwed connection under the steady-state condition of below 100 °C. The minimum loaded edge distance of three times the nominal diameter of the screw in AISI S240-15 is shown to be adequate for the shear design of cold-formed steel-to-steel screwed connections at elevated temperatures. The influence of design parameters, such as the screw diameter, steel type and thickness, is discussed, and the differences of the test results obtained from both transient and steady-state test methods are compared. In addition, the expressions from Laboube and Sokols' investigation are verified to be suitable for considering the group effect of two screws on the shear strength of screwed connections at elevated temperatures. The tested shear strength of cold-formed steel-to-steel screwed connections is also compared with the current AISI specification at ambient and elevated temperatures, and a conservative prediction is provided by using the reduced material properties of the corresponding steel.