Application of Shape Memory Alloy and CFRP Strips for Active Flexural Strengthening of RC Beams

Abstract

Prestressing concrete has become over the years a well-known technique to improve the serviceability and ultimate state of reinforced concrete members. New prestressing systems involving relatively new materials such as carbon composites or memory steel are highly demanded especially for the active strengthening of existing structures. This paper presents experimental tests of RC beams that were retrofitted with two prestressing systems using carbon fibre reinforced polymer (CFRP) or iron-based shape memory alloys (FeSMA) strips. For both applied techniques, the strips have comparable axial stiffness and prestressing force and were externally applied, unbonded and end-anchored. Prestressing of CFRP strips was performed using a hydraulic jack whereas FeSMA was activated upon heating using a gas burner. All beams were tested under four-point bending. The actively strengthened beams exhibited improved behavior at the serviceability stage including 80% greater cracking load and higher initial stiffness compared to the reference beam. The ultimate load capacity of CFRP beams was about 20% higher than FeSMA beams. It was caused by the premature failure of anchorage observed in case of FeSMA beams while CFRP beams failed due to the crushing of concrete with some signs of damage to the anchorage.