An analytical method to calculate temperatures of components of reverse channel connection to concrete filled steel section under fire conditions

• Proposed analytical model is based on Lumped Capacitance Method.
• Equivalent two-dimensional section factors are proposed for connection components.
• Overall fire gas emissivity for calculating connection temperature is εf=0.6.
• Heat transfer at steel/concrete interface is calculated by regression equations.
• Model is checked against results of extensive numerical simulations and fire tests.

The paper describes the development of an analytical model for calculating the temperatures of different components of reverse channel connections to concrete filled steel tubular sections. The proposed analytical model is based on the Lumped Capacitance Method and includes the calculation of the quantity of heat transferred at the interface between the steel tube and the concrete core. For unprotected connections, the connection is divided into two regions. One part of the connection is almost unaffected by the presence of the concrete core, on the contrary, temperature of the second part of the connection is significantly affected by the heat transfer at the steel/concrete interface. For protected connections, the entire connection is assumed to have the same temperature. Equivalent two-dimensional section factors are proposed for these connection parts. The analytical model is developed based on the results of extensive parametric studies under standard and different parametric fire conditions and validated against fire test results. The proposed analytical method is applicable to both fire protected and unprotected connections, including both the heating and cooling periods of the fire attack, and incorporating the effects of in-fill concrete.