Optimal design of hybrid steel-SMA reinforced concrete beam in fire

Research shows that a hybrid steel-shape memory alloy (SMA) reinforced concrete beam is able to prolong the fire resistance of the beam in terms of its bending capacity and deflection when compared with a steel-reinforced concrete beam with similar strength. While steel strength deteriorates as its temperature increases, SMA makes up for the lost strength by its ability to strengthen at high temperatures. However, the gain in strength by SMA reaches a peak at a critical temperature, at about 300oC, beyond which its strength starts to decrease. Therefore, to satisfy the fire resistance requirement for the design of a reinforced concrete beam, it is important that the time to reach the critical temperature should be delayed for as long as possible. This is usually achieved by increasing the axis distance of both the steel and SMA bars from the concrete surface. In doing so, the moment arm of the reinforcements from the neutral axis and hence their contribution to strength at high temperatures will be reduced. This paper describes the design of a hybrid steel-SMA reinforced concrete beam and the method to obtain the optimal positions of both the steel and SMA reinforcements so as to maximise the strength of the beam in fire