SMA-Based Composites for Active Confinement of Masonry Columns

Although masonry is an extremely popular material in the building industry, it’s very weak in tension, as compared to its strength in compression. Smart pre-stressing of masonry with shape memory alloy is a promising solution to this limitation. The shape memory effect of SMA (Shape Memory Alloy) materials seems to be an innovative suitable solution for active strengthening of masonry structures. Strengthening masonry element with SMA wires and FRP (Fiber Reinforced Polymers) is possible in order to obtain permanent confining effect on the structural element even after the SMA activation. If pre-strained SMA wires are heated under constraint, actually, tensile stresses are produced in the wires, causing stress state on the surface of masonry element. Unconfined and passive confined masonry cylinders were tested for compressive strength and the results were compared to those of cylinders confined by SMA and FRP active confinement technique. This solution can improve the compressive strength and ductility of the columns due to the permanent confining effect of the SMA. Differently from others works, in the proposed concepts, the activation of SMA and the cross-linking of the matrix takes place simultaneously in order to achieve a final and durable effect. This work showed the potential of the proposed method to retrofit unreinforced masonry columns using SMA wires and FRP to protect them from earthquakes.