Influence of the concrete mechanical properties on the efficacy of the shear strengthening intervention on RC beams by NSM technique

The occurrence of a failure mode, different from debonding, consisting on the detachment, from the beam core, of “two concrete lateral walls” containing the glued laminates, highlights the paramount importance of concrete mechanical properties on the effectiveness of NSM shear strengthening technique. A new mechanical-analytical interpretation of the phenomenon affecting the ultimate behaviour of RC beams NSM-strengthened in shear is presented along with the main findings. This approach takes into account the possibility that the shear strengthening contribution of the NSM laminates can be limited by the three following failure modes: debonding, concrete tensile fracture and laminates’ tensile rupture. The interaction between laminates can be also accounted for. The proposed mechanical interpretation of the NSM laminates behaviour can be extended to NSM rods.Fundação para a Ciência e a Tecnologia (FCT) - programa “CUTINSHEAR - Performance assessment of an innovative structural FRP strengthening technique using an integrated system based on optical fiber sensors” s, POCTI/ECM/59033/2004. This work has been partially carried out under the program “Dipartimento di Protezione Civile – Consorzio RELUIS”, signed on 2005-07-11 (n. 540), Research Line 8, whose financial support is greatly appreciatePrograma “Dipartimento di Protezione Civile – Consorzio RELUIS” nº 540Research Line 8Empreiteiros CasaisS&P®Secil (Unibetão, Braga)Degussa

Theoretical model and computacional procedure to evaluate the NSM FRP strips shear strength contribution to a RC beam

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Due to complex phenomena, such as: a) interaction between forces transferred through bond to the surrounding concrete and the concrete fracture, and b) interaction among adjacent strips, the NSM FRP strip constitutive law is largely different than the linear elastic one characterizing the FRP behavior in tension. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results, and its predictions are also compared with those obtained by a recently developed more sophisticated model.Fundação para a Ciência e a Tecnologia (FCT) - CUTINEMO - Carbon fiber laminates applied according to the near surface mounted technique to increase the flexural resistance to negative moments of continuous reinforced concrete structures” (PTDC/ECM/73099/2006

NSM FRP strips shear strength contribution to a RC beam : a design procedure

This paper presents a closed-form procedure to evaluate the shear strength contribution provided to a Reinforced Concrete (RC) beam by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips. This procedure is based on the evaluation of: a) the constitutive law of the average-available-bond-length NSM FRP strip effectively crossing the shear crack and b) the maximum effective capacity it can attain during the loading process of the strengthened beam. Due to complex phenomena, such as: a) interaction between forces transferred through bond to the surrounding concrete and concrete fracture, and b) interaction among adjacent strips, the NSM FRP strip constitutive law is largely different than the linear elastic one characterizing the FRP behavior in tension. Once the constitutive law of the average-available-bond-length NSM strip is reliably known, its maximum effective capacity can be determined by imposing a coherent kinematic mechanism. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by a recently developed more sophisticated model.(undefined

A new approach for modelling the NSM shear strengthening contribution in reinforced concrete beams

Empreiteiros CasaisDegussa PortugalSecil (Unibetão, Braga)S&P®Fundação para a Ciência e a Tecnologia (FCT) - POCTI/ECM/59033/200

Mechanical model to simulate the NSM FRP strips shear strength contribution to RC beams

A three dimensional mechanical model has been recently developed to simulate the Near Sur-face Mounted (NSM) Fibre Reinforced Polymer (FRP) strips shear strength contribution to Reinforced Con-crete (RC) beams throughout the entire loading process, as function of the Critical Diagonal Crack (CDC) opening angle. It was developed by fulfilling equilibrium, kinematic compatibility and constitutive laws of both intervening materials and bond between them. It takes into consideration all of possible failure modes that can affect the behaviour, at ultimate, of a single NSM strip, namely: loss of bond (debonding), semi-conical concrete tensile fracture, rupture of the strip itself and a mixed shallow-semi-cone-plus-debonding failure. Besides, it allows the interaction among adjacent strips to be accounted for. The numerical results, in terms of both shear strength contribution and predicted cracking scenario are presented and compared with experimental evidence regarding some of the most recent experimental programs. From that comparison, a satisfactory level of prediction accuracy, regardless of the main parameters such as concrete mechanical prop-erties, amount and inclination of strips, arises. The main findings, as well as the influence of some of the main intervening parameters, are shown.The authors of the present work wish to acknowledge the support provided by the Empreiteiros Casais, S&P.., degussa.. Portugal, and Secil (Unibetao, Braga).The study reported in this paper forms a part of the research program SmartReinforcement Carbon fibre laminates for the strengthening and monitoring of reinforced concrete structures supported by ADI-IDEIA, Project n.. 13-05-04-FDR-00031. This work was also carried out under the auspices of the Italian DPC-ReLuis Project (repertory n. 540), Research Line 8, whose financial support is greatly appreciated

Three dimensional mechanical model for simulating the NSM FRP strips shear strength contribution to RC beams

Shear strengthening of Reinforced Concrete (RC) beams by means of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips is an emerging technique for structural rehabilitation that is gaining increasing interest in the FRP community mainly because of some advantages it provides with respect to the better consolidated technique of the Externally Bonded Reinforcement (EBR). Those advantages encompass, mainly, a better exploitation of material and a higher protection against vandalism along with a relative faster applicability. Yet, the behavior of such NSM FRP strips is extremely complex, as can be gathered by experimental evidence, due to the complex geometry, the non linear mechanical properties of bond, and the scatter affecting the concrete tensile properties along with their non-linearity. In an attempt to provide valuable contribution to a better understanding of their behavior, a three dimensional mechanical model for simulating the shear strength contribution provided by a system of NSM FRPs to a RC beam throughout the loading process was recently developed. Its upgraded version is herein presented along with the main findings. It correctly interprets the experimental evidence taking into account complex phenomena such as the interaction between bond transferred force and concrete fracture along with the interaction between adjacent strips.The authors of the present work wish to acknowledge the support provided by the "Empreiteiros Casais", S&P(R), degussa (R) Portugal, and Secil (Unibetao, Braga). The study reported in this paper forms a part of the research program "SmartReinforcement - Carbon fibre laminates for the strengthening and monitoring of reinforced concrete structures" supported by ADI-IDEIA, Project no. 13-05-04-FDR-00031. Also, this work was carried out under the auspices of the Italian DPC-ReLuis Project (repertory no. 540), Research Line 8, whose financial support is greatly appreciated

Shear strengthening of RC beams by means of NSM laminates : experimental evidence and predictive models

Relatório 06-DEC/E-1

Analytical modelling strategy for predicting the NSM FRP strips contribution for RC beams shear strength

Shear strengthening of RC beams by means of FRP strips glued by a structural adhesive into thin shallow slits cut in the cover of the web lateral faces, is becoming a popular technique. Nonetheless, many aspects related to the mechanical behaviour and relevant failure modes still need to be clarified. A recent experimental-analytical investigation has demonstrated that, besides debonding and tensile rupture of the strip, the semi-conical tensile fracture of concrete surrounding the strip should be considered among the possible failure modes. A comprehensive analytical model for predicting the NSM strips contribution to the shear strength of RC beams was also developed. Despite its consistency with experimental results, that model had room for improvements. The upgraded version of that analytical model is herein presented and appraised on the basis of some among the most recent experimental results. This appraisal shows the high level of accuracy and potentialities of that modelling strategy arise

Design formula to evaluate the NSM FRP strips shear strength contribution to a RC beam

This paper presents the closing step of a synthesis process aiming at deriving, from a previously developed more complex model, a simple design formula to evaluate the shear strength contribution provided by a system of Near Surface Mounted (NSM) Fiber Reinforced Polymer (FRP) strips to a Reinforced Concrete (RC) beam. The self-contained and ready-to-implement set of analytical equations and logical operations is presented along with the main underlying physical-mechanical principles and assumptions. The formulation proposed is appraised against some of the most recent experimental results and its predictions are also compared with those obtained by the two previous and more sophisticated versions of the same modeling strategy. Monte Carlo simulations are carried out in order to appraise the sensitivity of the NSM shear strength contribution prediction to the value assumed by the input parameters.Fundação para a Ciência e a Tecnologia (FCT

Shear strengthening of RC beams by means of NSM FRP strips : constitutive law of a single strip

The need to provide a rational explanation to the observed peculiar failure mode affecting the behaviour, at ultimate, of a Reinforced Concrete (RC) beam strengthened in shear by Near Surface Mounted (NSM) Fibre Reinforced Polymer (FRP) strips, led the authors to develop a comprehensive numerical model for simulating the NSM shear strength contribution to RC beams throughout the entire loading process as function of the Critical Diagonal Crack (CDC) opening angle. That model was respectful of equilibrium, ki-nematic compatibility and constitutive laws. Despite its high level of prediction accuracy, taking into account all of the possible failure modes, as well as the interaction among adjacent strips, that model resulted rela-tively complex to be easily implemented in a practitioners-addressed building regulations code. Yet, it can be conveniently simplified into a more user-friendly and closed-form design formula. Crucial point of that sim-plification is the development of a reliable constitutive analytical law providing the single strip strength as function of the imposed end slip. This paper presents the modelling strategy adopted to determine that consti-tutive law, as well as its final analytical expression.The authors of the present work wish to acknowledge the support provided by the Empreiteiros Casais, S&P.., degussa.. Portugal, and Secil (Unibetao, Braga). The study reported in this paper forms a part of the research program SmartReinforcement Carbon fibre laminates for the strengthening and monitoring of reinforced concrete structures supported by ADI-IDEIA, Project no 13-05-04-FDR-00031. This work was also carried out under the auspices of the Italian DPC-ReLuis Project (repertory n. 540), Research Line 8, whose financial support is greatly appreciated