Strengthening of steel beams using iron-based shape memory alloy (Fe-SMA) strips

The current study presents a retrofit system, which can be used for strengthening of steel bridge beams using (un-bonded) mechanically-anchored iron-based shape memory alloy (Fe-SMA, ‘memory-steel’) strips. After anchoring, the Fe-SMA strips are activated by a heating and a subsequent cooling process. The anchorage system can simultaneously hold two strips (each with 50-mm width and 1.5-mm thickness) and transfer their prestressing force to the steel beam at the strip ends. The system is based on friction and does not introduce any damage to the parent metallic substrate. Owing to the so-called ‘shape memory effect’ (SME) of the alloy, the strips are prestressed after activation by heating up to a defined maximum temperature. After strengthening, the beam was statically loaded up to 60% of its yield capacity. Finally, in order to examine efficiency of the proposed SMA-strengthening solution, the steel beam was subjected to cyclic loading. The results of the static tests demonstrated the positive effects of the prestressed Fe-SMA strips on reducing tensile stresses in the beam bottom flange. Furthermore, the evolution of the prestress level in the strips during the fatigue loading was studied. The presented experimental study on the strengthened steel beam shows the effectiveness of un-bonded Fe-SMA strips as a retrofitting technique to enhance the static and fatigue performance of metallic bridge girders.