Fire response of externally stiffened steel I-beam-to-CHS welded connections: A numerical modelling

• Effects of different parameters on the connection stiffness in fire are studied.
• Thickening of the diaphragms is provided clear advance on the connection stiffness.
• Introducing a joint can has a superior improvement on the connection behaviour.
• A low stress utilization ratio in the connection avoids premature stiffness loss.

Considering the likelihood of the fire accidents in the offshore oil platforms, an insight to the behaviour of I-shape beam-to-CHS column connections at elevated temperature is essential for proper fire design of the platforms. The connection constitutes an important structural element in the topside of an offshore platform. As a consequence of fire, the mechanical properties of the steel material decreases, the structure starts to demonstrate a non-linear behaviour. This paper reports the results of a numerical study on the response of this type of connection at elevated temperature. A non-linear coupled mechanical–thermal finite element model has been used for this purpose. The model has first been validated against experimental results from a series of small-scale fire tests on this type of connection carried out previously by the authors. A reasonable agreement has been obtained between the experimental results and the numerical predictions. The numerical model has then been used to simulate the fire response of a number of full-scale I-shape beam-to-CHS column connections in existing offshore platforms. Effects of parameters such as the magnitude of the superimposed load, axial stress in the column, the stiffeners' contribution to the rotational stiffness of these connections at elevated temperatures are studied.