Thermally activated iron-based shape memory alloy for strengthening metallic girders

Abstract

The study presents a new retrofit solution for strengthening metallic I-girders. The retrofit system involves two iron-based shape memory alloy (Fe-SMA, 'memory-steel') strips (each with a width and thickness of 50 and 1.5 mm, respectively) that are mechanically anchored (using friction clamps) to the girders. The shape memory effect (SME) of the Fe-SMA material has been used to activate/prestress the strips by heating to a predefined temperature. The main advantage of the proposed SMA-retrofit system is that, unlike conventional systems, it can prestress itself without a need for heavy hydraulic jacks, which then results in a significant reduction of the required time, labor works and cost of prestressing process. In order to evaluate the efficiency of the proposed retrofit system, in this study, a series of static and fatigue four-point bending tests were performed on a 6.4-m SMA-retrofitted beam. Five static

Iron-based shape memory alloy (Fe-SMA) for fatigue strengthening of cracked steel bridge connections

“…The introduction of new materials, such as carbon-fiber reinforced polymers (CFRPs) and ironbased shape memory alloys (Fe-SMAs) with unique properties, overcomes the problems associated with conventional strengthening techniques [16][17][18][19][20][21]. The fatigue strengthening of various steel members with prestressed CFRP composites has already received considerable interest [18,20,[22][23][24], whereas steel strengthening with prestressed (activated) Fe-SMAs has only been recently introduced [16,21,25]. With respect to all strengthening attempts with prestressed CFRPs and Fe-SMAs, the latter is found to be considerably easier to prestress [16,25].…”

Heat-activated prestressing of NiTiNb shape memory alloy wires

“…The maximum recovery stress equal to 425 MPa was achieved by them at a pre-strain of 6.6%. Researchers for example, [13,[20][21][22][23] have investigated recovery stress in other types of SMAs also. Dommer & Andrewes [16] investigated recovery stress in NiTiNb SMA.…”

“…In the recent past a lot of research has been carried out on Fe-SMAs [19][20][21][22][23][24][25][26][27][28][29][30]. Fe-SMAs have started to gain popularity in the Civil Engineering due to their low cost and thus bears a good potential to be used in bulk.…”

Development of Mechanical Strengthening System for Bridge Connections Using Prestressed CFRP Rods

“…The PUR systems can be used for strengthening steel beams against flexural (Hosseini et al 2018c), buckling , and fatigue loading. These systems were successfully used for strengthening old steel bridge girders in Switzerland and Australia (Ghafoori et al 2018;Hosseini et al 2019a). More recently, a series of PUR systems has been developed for strengthening steel plates (Hosseini et al 2018b;Hosseini et al 2019b).…”

“…SMAs are a new class of structural materials that can be prestressed through an activation process that includes heating and cooling (Hosseini et al 2019c). The SMA-based PUR systems have been using for strengthening steel plates (Izadi et al 2018a;Izadi et al 2018b), girders (Fritsch et al 2019;Izadi et al 2019a) and connections (Izadi et al 2019b).…”