Strengthening and prestressing of bridge decks with ribbed iron-based shape memory alloy bars

Abstract

Given the increasing age of our built environment, including concrete structures, stakeholders in the construction industry require innovative and effective strengthening methods. In several studies and onsite applications, iron-based shape memory alloy (Fe-SMA) reinforcements have proven to be competitive alternatives to well-established materials. The objective of this investigation was to study the effectiveness of two different prestressed strengthening methods for concrete members in flexure using recently available ribbed Fe-SMA (“memory-steel”) bars. Reinforced concrete slabs similar to the cantilever extension of box-girder cross-sections were strengthened using only cementitious anchorages and subjected to quasi-static loading. The first strengthening method comprised the removal of the concrete cover and the installation of memory-steel bars with an additional mortar layer. The second strengthening method comprised the cutting of grooves in the concrete cover, followed by the installation of memory-steel bars with mortar (near-surface-mounted). The prestress was obtained via resistive heating of the memory-steel bars. The strengthened specimens exhibited highly improved cracking, yielding, and maintained ductility until ultimate concrete compression failure. Observations utilizing a digital image correlation system indicated a damage-free prestressing process and no premature failure of the strengthening reinforcement. Different analytical approaches were used to estimate the prestress.