A hybrid steel-shape memory alloy reinforced concrete beam design for optimum fire resistance capacity

In structural design for reinforced concrete beams in fire, the traditional way to satisfy the fire resistance requirements is to provide adequate concrete cover, or axis distance, to the steel reinforcements. The purpose is to reduce the rate of temperature rise in the steel reinforcements, in which strength deteriorates with rising temperature. Past research shows that a shape memory alloy (SMA) reinforced concrete beam is able to increase both the strength and stiffness of the beam when the temperature in the SMA increases. However, the gain in strength by SMA at rising temperature reaches a peak at a critical temperature, about 300(circle) C, beyond which its strength starts to decrease. At present there is no guidance for the design of hybrid steel-SMA reinforced concrete beams to obtain the optimal recovery stress as required by the fire resistance level. This paper describes a conceptual design of a hybrid steel-SMA reinforced concrete beam and the process to obtain the optimal position of the SMA reinforcements in the cross-section so as to maximise the strength of the beam in fire. This research is a world first to use this concept for structural fire protection of concrete beams.