An experimental program was carried out to investigate the effect of the prestressed Near Surface Mounted (NSM) Carbon Fiber Reinforced Polymer (CFRP) laminates on the behavior of reinforced concrete (RC) slabs. Four RC slabs were tested, a reference slab (without CFRP), and three slabs flexurally strengthened using NSM CFRP laminates with different prestress level of the ultimate tensile strength of the CFRP: 0%, 20% and 40%. The experimental program is described and the main results are presented and analyzed in terms of the structural behavior of the RC slabs, failure modes and performance of the NSM technique with prestressed CFRP laminates. The results show that prestressing CFRP laminates with NSM technique is an effective solution to increase cracking, service, yielding and maximum loads of RC slabs failing in bending. By applying 20% of prestressed NSM CFRP laminates, the service and ultimate loads have increased, respectively, 55% and 136%, when the corresponding values of the reference slab are taken for comparison purposes, while 119% and 152% were the increase when applying 40% of prestressed laminates. A numerical strategy was used to evaluate the load-deflection of the tested RC slabs, and a good agreement between experimental and numerical results was obtained.

a b s t r a c tThe effectiveness of the Near Surface Mounted (NSM) technique with prestressed CFRP (carbon fiber reinforced polymer) laminates for the flexural strengthening of reinforced concrete (RC) slabs of low strength concrete was assessed. Four RC slabs were tested, a reference slab (without CFRP), and three slabs flexurally strengthened using NSM CFRP laminates with different prestress level of the ultimate tensile strength of the CFRP: 0%, 20% and 40%. The experimental program is described and the main results are presented and analyzed in terms of the structural behavior of the RC slabs, failure modes and performance of the NSM technique with prestressed CFRP laminates. The results show that prestressing CFRP laminates with NSM technique is an effective technology to increase cracking, service, yielding and maximum loads of RC slabs made by low strength concrete. By applying NSM CFRP laminates prestressed at 20%, the cracking, service and maximum loads have increased, respectively, 258%, 123% and 125%, when the corresponding values of the reference slab are taken for comparison purposes, while 400%, 190% and 134% were the increase when applying laminates prestressed at 40%. Using available experimental results obtained with the same test setup, but using RC slabs of higher strength concrete, it can be concluded that as minimum is the concrete strength as more effective is the NSM technique with prestressed CFRP laminates in terms of serviceability limit states. A numerical strategy was used to evaluate the load-deflection of the tested RC slabs and to highlight the influence of the percentage of CFRP, the percentage of tensile longitudinal bars and the elasticity modulus of the CFRP on the effectiveness of the NSM technique with prestressed CFRP laminates for the flexural strengthening of RC slabs, by performing a parametric study.

The efficacy of the NSM technique using prestressed CFRP laminates for the flexural strengthening of RC slabs was assessed experimentally. The results obtained indicated that the application of NSM CFRP laminates with a certain level of prestress is a suitable strategy to increase the load-carrying capacity of slabs in terms of service limit state (SLS) conditions. The higher is the CFRP prestressed level the larger is the performance of the NSM technique in the improvement of the behavior of the slabs at SLS conditions, but the deflection at the maximum load of the slabs decreased with the increase of the prestress level. The prestressed NSM CFRP laminates were more effective in the slabs with the lower concrete strength class, mainly at SLS conditions. The increase of the percentage of the flexural reinforcement had a detrimental effect on the performance of prestressed NSM CFRP laminates. An analytical formulation was developed for predicting the cracking, yielding and maximum loads of RC slabs flexurally strengthened with prestressed NSM CFRP laminates and a very good predictive performance was obtained. An upper limit is proposed for the prestress level for ensuring a compromise of ductility and strengthening effectiveness of this type of structural elements.

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A B S T R A C T R I~ S U M I~The paper reports on data acquired during 700 days of monitoring a widened reinforced concrete underbridge. The deck was monitored before, during and after widening and both portions of the deck, existing and new, were instrumented. Concrete strains were monitored by means of embedment and surface Vibrating Wire strain Gauges (VWG).Predicted creep, shrinkage, thermal and settlement strains were evaluated by means of a finite element analysis. The creep and shrinkage factors used were those from the simplified form of the B3 model [1]. Good agreement between calculated and measured longterm strains was observed at almost all gauge positions.From the analysis carried out, it was found that the stresses from the time dependent phenomena of creep, shrinkage and temperature, combined with those from the settlement of abutments, were greater than the magnitude of stresses obtained from the design live load.