Fatigue behavior of externally bonded steel fiber reinforced polymer (SFRP) for retrofit of reinforced concrete

Steel fiber reinforced polymer (SFRP) strips comprised of multiple high-strength wires have been introduced into the repertoire of the structural engineer in recent years. The deleterious effects of fatigue loading on FRP-to-concrete bond have been identified in previous studies by the author; therefore the effect of fatigue loading on the bond behavior of SFRP is investigated. Four large-scale beam specimens (4.9 m long) having externally bonded SFRP retrofits are tested. These specimens are paired with unretrofit and CFRP-retrofit companion specimens allowing a number of direct comparisons to be made. Of the SFRP specimens, one is tested in monotonic loading to failure while the remaining three are tested at various fatigue load levels ranging from service load level to an extreme load level. Service load fatigue is cycled for 2 million cycles and the specimen is then tested monotonically to failure to assess the effects of fatigue conditioning on the ultimate performance of the beam. Extreme loading is selected to result in fatigue-induced failure of the internal reinforcing steel.