Shear strengthening of reinforced concrete beams with carbon fiber reinforced polymer (CFRP) under fatigue and sustained loading applications

Four specimens were tested to evaluate the shear performance of beams with carbon fiber reinforced polymer (CFRP) laminates and CFRP anchors under fatigue and sustained loading applications. The specimens consisted of 24-in. deep T-beams that were constructed and tested at Phil M. Ferguson Structural Engineering Laboratory at the University of Texas at Austin. The specimens were strengthened in shear with CFRP laminates anchored with CFRP anchors. One end of each specimen was strengthened using bonded CFRP laminates while the other end was strengthened using unbonded CFRP laminates. Two specimens were used for fatigue testing and two were used for sustained load testing. For each set of tests, one specimen was strengthened using CFRP laminates prior to cracking and one specimen was strengthened using CFRP laminates following the initial cracking of the specimen. The CFRP laminates showed no signs of deteriorations in strength during fatigue testing, with only small increases in strain occurring in the CFRP laminates during testing. After fatigue loading was completed, the specimens were monotonically loaded to failure. The failure loads were 5 to 15% lower than beams that were not subjected to fatigue loading. Sustained load tests were subjected to a constant midpoint load based on service load requirements for a period of 217 days. CFRP laminates performed well during sustained loading. CFRP strains increased slightly throughout testing, but no signs of deterioration were observed. For both types of tests, specimens strengthened using bonded CFRP laminates demonstrated an increased stiffness resulting in smaller crack widths and lower strains in the internal steel. These benefits were not as great in specimens strengthened after the initial cracking of the specimen.