Experimental Behavior of CFRP Strap–Strengthened RC Beams Subjected to Sustained Loads

RC beams strengthened with transverse prestressed unbonded carbon fiber–reinforced polymer (CFRP) straps have shown substantial increases in shear capacity when subjected to short-term static loading. However, understanding the time-dependent behavior is a further prerequisite in order to better evaluate this strengthening technique and its engineering applications. This paper presents time-dependent experimental results from an unstrengthened RC beam and four RC beams strengthened with CFRP straps. The parameters considered include the concrete strength, applied load level, and prestress level in the CFRP straps. The beams were subjected to sustained loads that were fixed percentages of the short-term failure load. To investigate the development of the external concrete strains, the internal steel shear link strains, the strap strains, and the shear crack patterns, the beams were monitored over a period of about 320 days. The long-term beam deformations were also recorded and decomposed into bending and shear components. Compared with an equivalent unstrengthened beam, the presence of the CFRP straps reduced the proportion of the shear deflection. However, in the strengthened beams the shear proportions of the total midspan deflection were still 24%–28%, which were not negligible. An analysis using a Mohr’s circle of strain confirmed that the long-term tensile behavior in the shear span appears to dominate the development of the shear deformation.