Tension Stiffening of Reinforced Concrete Shear Elements Strengthened with Externally Bonded FRP Sheets (original) (raw)
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Materials
Based on the characterization of the bond between Fiber-Reinforced Polymer (FRP) bars and concrete, the structural behavior of cracked Glass-FRP (GFRP)-Reinforced Concrete (RC) tensile elements is studied in this paper. Simulations in which different bond-slip laws between both materials (FRP reinforcement and concrete) were used to analyze the effect of GFRP bar bond performance on the load transfer process and how it affects the load-mean strain curve, the distribution of reinforcement strain, the distribution of slip between reinforcement and concrete, and the tension stiffening effect. Additionally, a parametric study on the effect of materials (concrete grade, modulus of elasticity of the reinforcing bar, surface configuration, and reinforcement ratio) on the load-mean strain curve and the tension stiffening effect was also performed. Results from a previous experimental program, in combination with additional results obtained from Finite Element Analysis (FEA), were used to de...
Tension Stiffening and Cracking Behavior of Glass Fiber-Reinforced Polymer-Reinforced Concrete
ACI Structural Journal, 2017
In this study, 60 large-scale specimens—52 glass fiber-reinforced polymer (GFRP) reinforced concrete and eight steel-reinforced concrete—were tested under uniaxial tension to investigate tension stiffening and cracking behavior of GFRP-reinforced normal- and high-strength concretes. The test parameters included bar type, bar diameter, reinforcement ratio, and concrete strength. Tension stiffening was found to be independent of concrete strength, bar diameter, and reinforcement ratio when shrinkage was included in the analysis of the member response. The final stabilized crack spacing was found to decrease with an increase in reinforcement ratio and concrete strength, and a decrease of bar diameter. The current code provisions and guidelines—namely, ACI 440.1R-06 and CEB-FIP Model Code 2010—were found to significantly overestimate tension stiffening in GFRP-reinforced specimens. A new tension stiffening model was therefore developed that provided better simulation of the test data. The CEB-FIP 1978 model for crack spacing was modified for GFRP-reinforced members.
Tension stiffening behavior of GFRP-reinforced concrete
Synopsis: Synopsis: Synopsis: Synopsis: This paper presents an experimental study into the structural response of Glass Fiber Reinforced Polymers Reinforced Concrete (GFRP-RC) tension members. The influence of concrete strength, reinforcement ratio and bar diameter on tension stiffening is investigated by testing elements in direct tension. Using bars specially manufactured with internal strain gauges, typical strain patterns occurring between cracks during direct tension tests were measured and bond stresses derived, thereby obtaining the information for modeling tension stiffening behavior of GFRP-RC. An increase in the tension stiffening behavior with decrease in reinforcement ratio and increase in concrete strength was observed. No appreciable change in tension stiffening was recorded with changes in bar diameter at constant reinforcement ratio. This paper also discusses the limitations that may be encountered in modifying current models to represent the tension stiffening effect of GFRP-RC.
Modeling of the Behavior of Concrete Tension Members Reinforced with FRP Rods
2003
The paper is devoted to the analysis of cracking and deformability of concrete tension members reinforced with fiber-reinforced polymer (FRP) rods. A theoretical nonlinear model, derived from a cracking analysis founded on slip and bond stresses, is adopted for evaluating the crack width, crack spacing, and elongation of tension members. The procedure takes into account the local bond-slip law, experimentally determined by means of pullout tests, and allows us to evaluate the influence of tensile stiffening. The analysis is performed with considering all parameters influencing the behavior of tension members, such as the concrete strength, the kind of FRP rebars, the surface treatment of FRP rebars, and the concrete cover thickness. The theoretical predictions are compared with available experimental results, obtained on cylindrical concrete specimens reinforced with carbon FRP (CFRP) rods, and with predictions of the traditional models usually adopted for design purposes.
Composite Structures, 2011
Due to their different mechanical properties, cracking and deformability behaviour of FRP reinforced concrete (FRP RC) members is quite different from traditional steel reinforced concrete (SRC) having great incidence on their serviceability design. This paper presents and discusses the results of an experimental programme concerning concrete tension members reinforced with glass fibre reinforced polymer (GFRP) bars. The main aim of the study is to evaluate the response of GFRP reinforced concrete (GFRP RC) tension members in terms of cracking and deformations. The results show the dependence of load-deformation response and crack spacing on the reinforcement ratio. The experimental results are compared to prediction models from codes and guidelines (ACI and Eurocode 2) and the suitability of the different approaches for predicting the behaviour of tensile members is analysed and discussed.
Micromechanical modeling of tension stiffening in FRP-strengthened concrete elements
Journal of Composite Materials, 2018
This article presents a micromodeling computational framework for simulating the tensile response and tension-stiffening behavior of fiber reinforced polymer–strengthened reinforced concrete elements. The total response of strengthened elements is computed based on the local stress transfer mechanisms at the crack plane including concrete bridging stress, reinforcing bars stress, FRP stress, and the bond stresses at the bars-to-concrete and fiber reinforced polymer-to-concrete interfaces. The developed model provides the possibility of calculating the average response of fiber reinforced polymer, reinforcing bars, and concrete as well as the crack spacing and crack widths. The model, after validation with experimental results, is used for a systematic parameter study and development of micromechanics-based relations for calculating the crack spacing, fiber reinforced polymer critical ratio, debonding strength, and effective bond length. Constitutive models are also proposed for conc...
2009
This paper presents numerical simulation of the tension behaviour of reinforced concrete (RC) members strengthened with externally bonded carbon fiber sheets (CFS) by using two dimensional (2D) rigid body spring model (RBSM). A non-linear RC model strengthened with CFS with bond-slip relations to model the concrete, steel reinforcement interface and concrete, externally bonded CFS interface, and simple models for bond deterioration due to cracking was embedded in the RBSM code that was developed by the authors. Comparison between the RBSM prediction and experimental results shows good agreement. The CFS has shown significant change in the bond stress and average stress of steel reinforcing bar and concrete. In addition the CFS has reduced the crack spacing and gave good crack width control.
Contribution of Externally Bonded FRP to Shear Capacity of RC Flexural Members
Journal of Composites for Construction, 1998
Fiber reinforced polymer (FRP) materials are continuing to show great promise for use in strengthening reinforced concrete (RC) structures. These materials are an excellent option for use as external reinforcing because of their light weight, resistance to corrosion, and high strength. Externally bonded FRP sheets have been used to increase moment capacity of flexural members and to improve confinement in compression members.
The Role of the Bond on the Structural Behaviour of Flexural FRP Reinforced Concrete Members
2005
The paper focuses on the bond between fibre-reinforced polymer (FRP) reinforcements and concrete including its modelling (local bond-slip law) and influence on the structural behaviour of FRP reinforced concrete members. The analysis, both theoretical and experimental, refers to flexural concrete beams upgraded by externally bonded FRP sheets, considering different bonding systems such as the commonly used resin-FRP system and novel bonding technologies (near surface mounted system, cementitious-FRP system). The structural behaviour of strengthened beams is analyzed by means of a non linear model derived from a cracking analysis based on slip and bond stress. By using some bond-slip models, the performances of beams under service conditions (cracking, deformability) are evaluated varying parameters governing the FRP-to-concrete bond behaviour. Results of the analysis furnish useful information to find interface bonding systems which can offer suitable bond characteristics to optimize the performances of FRP reinforced concrete members.
Influence of FRP Axial Rigidity on FRP-Concrete Bond Behaviour : An Analytical Study
Advances in Structural Engineering, 2009
Bond behaviour between externally bonded Fiber Reinforced Polymer (FRP) strengthening and concrete supports is essential in shear and flexural applications, in order to transfer stress between concrete and external reinforcement, and influences the nominal capacity of the structural element. In the majority of cases, constitutive models τ-s (shear/bond stress-slip) available in the literature, are not directly calibrated with experimental results, partly due to the difficulty of obtaining τ-s diagrams experimentally. This paper aims at improving knowledge of bond behaviour between FRP and concrete, and presents a critical review of the principal bond-slip models currently available in the literature and a new proposal calibrated on the basis of experimental τ-s diagrams, taking into account the influence of FRP strengthening rigidity. A new expression for interfacial fracture energy is also proposed and validated with experimental results.