Embedded Through‐Section (ETS) technique is a relatively recent shear strengthening strategy for reinforced concrete (RC) beams and consists of opening holes across the depth of the beam’s cross‐section, with the desired inclinations, where bars are introduced and are bonded to the concrete substrate with adhesive materials. To assess the effectiveness of this technique, a comprehensive experimental program composed of 14 RC beams was carried out, and the obtained results confirm the feasibility of the ETS method and revealed that: (i) inclined ETS strengthening bars were more effective than vertical ETS bars, and the shear capacity of the beams has increased with the decrease of the spacing between bars; (ii) brittle shear failure was converted in ductile flexural failure, and (iii) the contribution of the ETS strengthening bars for the beam shear resistance was limited by the concrete crushing or due to the yielding of the longitudinal reinforcement. The applicability of the ACI 318 (2008) and Eurocode 2 (2004) standard specifications for shear resistance was examined, and a good agreement between the experimental and analytical results was obtained.

This work presents and analysis the results of an ongoing research project on the use of the near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) laminates for the increase of the load carrying capacity of statically indeterminate (two spans) reinforced concrete (RC) slabs. The test program consisted of seventeen slab strips, grouped in two series that are different on the adopted strengthening scheme: H series, where H is the notation to identify the slabs strengthened with NSM CFRP laminates exclusively applied in the hogging region; HS series, where HS is the notation to identify the slabs strengthened with NSM CFRP laminates applied in both hogging and sagging regions. The program includes six unstrengthened reference RC slab strips, and eleven strengthened with CFRP NSM configurations designed to increase in 25% or 50% the load carrying capacity of the corresponding reference RC slabs. An extensive monitoring system was applied in the constituent materials, in the critical regions of the tested slabs, in order to collect information for the discussion about the effectiveness of NSM technique in terms of load carrying and moment redistribution capacity. The strengthening procedures adopted in the laboratory tests followed, as much as possible, the real strengthening practice for this type of interventions. The obtained results show that the proposed technique is able to increase significantly the load carrying capacity of statically indeterminate RC slabs, even for those with relatively high steel reinforcement ratios. The load carrying capacity of the strengthened slabs was limited by its shear capacity or by the detachment of the strengthened concrete cover layer. At failure of the strengthened slabs, the longitudinal steel bars at intermediate support (hogging region) and at loaded sections (sagging regions) have already yielded, and the deflection was quite large. However, for some strengthening configurations, the CFRP laminates led to a decrease of the moment redistribution capacity of the slabs. HIGHLIGHTS► Eleven slab strips flexurally strengthened with NSM CFRP laminates were tested.► Two different arrangements of CFRP laminates were applied in the slab strips. ► The increase of the load carrying and moment redistribution capacities was analyzed. ► The target increase of the load carrying capacity was attained for HS configurations. ► Some strengthening configurations led to a decrease of the moment redistribution capacity.

Recent experimental research has shown that Near Surface Mounted (NSM) technique has high potential to increase the load carrying capacity of continuous reinforced concrete (RC) slabs. This flexural strengthening technique is based on the installation of rectangular cross sectional carbon fibre reinforced polymer (CFRP) laminates into thin slits opened onto the top concrete cover at the intermediate supports and in the bottom concrete cover in the tensile zones. However, the linear-elastic behaviour of the CFRP laminates, and the possibility of occurring premature detachment of the concrete cover that includes these laminates can compromise, not only the flexural strengthening effectiveness of the NSM technique, but also the moment redistribution and the ductility performance of this type of structures. To evaluate the influence of the concrete strength class, the percentage of existing longitudinal tensile reinforcement and the percentage of CFRP on the strengthening effectiveness, moment redistribution capacity and ductility performance, a parametric study was carried out by executing material nonlinear analysis with a FEM-based computer program, which predictive performance was calibrated using the results of a previous experimental program.

To assess the effectiveness of the near surface mounted (NSM) technique, in terms of load carrying and moment redistribution capacities, for the flexural strengthening of continuous reinforced concrete (RC) slabs, an experimental program was carried out. The experimental program is composed of three series of three slab strips of two equal span length, in order to verify the possibility of increasing the negative (at the intermediate support region) resisting bending moment in 25% and 50% and maintaining moment redistribution levels of 15%, 30% and 45%. Though the flexural resistance of the NSM strengthened sections has exceeded the target values, the moment redistribution was relatively low, and the increase of the load carrying capacity of the strengthened slabs did not exceed 25%. This experimental program is analyzed to highlight the possibilities of NSM technique for statically indeterminate RC slabs in terms of flexural strengthening effectiveness, moment redistribution and ductility performance. Using a FEM-based computer program, which predictive performance was appraised using the obtained experimental results, a high effective NSM flexural strengthening strategy is proposed, capable of enhancing the slab's load carrying capacity and maintaining high levels of ductility.

Little is known about the behavior and durability of strengthening systems applied on concrete substrata and the possible loss of performance due to the degradation of the intervening materials by the structure’s natural aging process and exposure of the externally strengthened elements to aggressive environments. In this context, the present work presents an experimental analysis of the behavior of reinforced concrete beams strengthened with Carbon Fiber Reinforced Polymer (CFRP), applied according to the Externally Bonded Reinforcement (EBR) technique, maintained in a laboratory environment (indoor and protected) or exposed to weathering (outdoor exposure). In addition, specimens of the intervenient materials were also molded and exposed to the same environmental conditions as the beams. The results indicate that weather-exposed epoxy adhesives present reductions up to 70% in their mechanical properties after exposure, while the CFRP composite properties remain similar. It was also found that the strengthening system provided 50% and 28% increments in the load-carrying capacity and stiffness of the elements, respectively. However, the tests conducted after 6 months of weathering exposure showed a 10% reduction in the load-carrying capacity of the strengthened elements.