A near-surface-mounted (NSM) technique using fiber-reinforced polymer (FRP) reinforcement increases the load-bearing capacity and stiffness of reinforced-concrete (RC) beams and delays the yielding moment. In those cases, the verification of serviceability limit states becomes necessary to guarantee functionality and protection of steel reinforcement. At present, there is a lack of provisions for the crack width prediction, mainly because of the scarceness of experimental data. This work presents the results of an experimental program aiming at studying the effect of different NSM reinforcement arrangements on the midspan deflection, crack spacing, and crack width of NSM FRP RC beams. One RC beam and 11 NSM FRP RC beams were tested under a four-point bending configuration up to failure. Carbon- and glass-FRP rods were used. It was found that NSM FRP reinforcement provides an effective reduction in deflection, crack width, and spacing. Larger crack formation phases were observed in all strengthened specimens. Moreover, crack width decreases with the increase of the NSM FRP reinforcement ratio. Finally, cracks at the bottom of the beam are around 11%–25% wider than at the height of the steel internal reinforcement.

This paper aims to evaluate the influence of relatively high service temperatures (near or beyond the glass transition temperature (T_g) of epoxy adhesive) on the flexural performance and end debonding phenomenon in near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened, reinforced concrete (RC) beams. To this end, an experimental program consisting of 24 beams (divided into four groups) was performed, where different parameters was combined (i.e., service temperature, steel reinforcement ratio, CFRP ratio, and concrete compressive strength). In addition, the effect of the testing temperature on the end debonding phenomenon was investigated with an analytical procedure according to fib Bulletin 90, and the predictions were compared to experimental results. Taking specimens tested at 20 °C as a reference, no considerable change was observed in the ultimate load of the specimens tested below 60 °C (being in the range of epoxy T_g), and all specimens failed by FRP rupture. On the other hand, the increase in testing temperature up to 70 and 85 °C was followed by a decrease in the capacity of the strengthened beams and a change in failure mode, moving from FRP rupture to end debonding and concrete crushing. The analytical procedure successfully predicted the occurrence of premature end debonding failure and demonstrated that the effect of temperature on the mechanical properties of materials can be a key factor when predicting the premature end debonding in a NSM joint.

This paper presents a study of the effect of high service temperature (near or beyond glass transition temperature (T_g) of structural epoxy adhesive) on the behavior of near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP)-strengthened reinforced concrete (RC) beams. The study includes experimental work as well as analytical and numerical analysis. To this end, fourteen beams have been tested up to failure in two different series. In series 1, specimens with three different CFRP areas have been tested at two different temperatures (i.e., 20 and 40 °C). In series 2, and with the aim of evaluating the effect of higher temperatures, only one CFRP area was tested under four different temperatures (i.e., 20, 60, 70, and 85 °C). Experimental results are evaluated in terms of load–deflections, failure modes, and bond performance. Furthermore, the experimental load–deflection curves are satisfactorily compared to both analytical predictions and finite element (FE) numerical simulations. In both cases, shrinkage and temperature effects on the short-term response of flexural elements have been accounted for. No significant reduction in stiffness and ultimate load was observed for specimens being tested up to 60 °C (in the range of epoxy T_g), showing FRP rupture failure in all of them. For specimens under 70 and 85 °C, the failure mode changed from FRP rupture to FRP end debonding and concrete crushing, respectively.