Strengthening of steel beams with adhesively bonded memory-steel strips

Abstract

This study entails the development of a non-destructive prestressed strengthening solution for steel beams using adhesively bonded memory-steel (also known as iron-based shape memory alloy, Fe-SMA) strips. The Fe-SMA strip is activated via heating and subsequent cooling to generate prestress, while the two ends of the Fe-SMA strip are adhesively bonded as anchorages. The behavior of the Fe-SMA-to-steel bonded joints was investigated through lap-shear tests, from which an effective bond length of approximately 120 mm was determined. Subsequently, a strengthening solution for a 5.3 m span steel I-beam was designed based on finite element analysis. A 4200 mm × 100 mm × 1.5 mm Fe-SMA strip was bonded to the bottom of the steel beam with a bond length of three times the effective bond length, and a two-step activation strategy using torches was proposed. Furthermore, the designed strengthening solution was experimentally tested. With activation to the target temperature of 240 °C, the Fe-SMA developed a prestress level of approximately 280 MPa. A series of static and fatigue four-point bending tests were conducted. After 3 million cycles of fatigue loading, no debonding or degradation was observed for the adhesively bonded Fe-SMA-strengthened specimen; this demonstrated the reliable performance of the strengthening solution under service loads.