Fiber-reinforced Polymer Reinforcement Ratio Research Articles

Parametric investigation of continuous beams strengthened with near surface mounted FRP bars

This study evaluates the near surface mounted fiber-reinforced polymer (FRP) reinforcement technique for strengthening continuous reinforced concrete beams. A three-dimensional finite element model was developed and validated with a recent experimental study. The model incorporates robust features, including concrete nonlinear behavior, debonding and slipping of FRP bars, and various failures. It was able to capture the ultimate load (Pu) with maximum deviation of 7%, beam’s load–deflection curves, load–strain responses in rebar and concrete, and various failure modes. A parametric study was conducted and showed that failure mode changes from concrete shear to FRP bar debonding at concrete compressive strength fc’of 20–30 MPa, with a 26–52% increase in Pu relative to the un-strengthened beam. Varying the hogging/sagging FRP reinforcement ratio (ρh/ρs) from zero to 2.0 results in a 39% increase in Pu and a change of failure mode. A value of 1.5 is recommended for ρh/ρs. Also, the synergistic effects of NSM FRP and internal steel reinforcements were studied. An FRP bar length in the hogging and sagging zones of 80% the beam span was found to be sufficient to mitigate debonding and thus is recommended. Pu did not vary significantly with the span ratio for two-span continuous beams. A design expression for the debonding strain in FRP bars based on the American Concrete Institute design guide was assessed and a further refined model is developed.

RC beams strengthened in shear with FRP-Reinforced UHPC overlay: An experimental and numerical study

In this study, a hybrid strengthening technique consisting of ultra-high performance concrete (UHPC) overlay reinforced by fiber reinforced polymer (FRP) bars is proposed to strengthen reinforced concrete (RC) beams in shear. Eleven beams, five of which are physical samples tested under static load, and the other six are virtual ones derived from a robust finite element (FE) analysis, are used to assess the effectiveness of this retrofitting technique. Several parameters are examined, namely overlay thickness, overlay configuration (continuous vs. discontinuous), FRP reinforcement ratio in the overlay, and type of FRP rebar (Glass-FRP vs. Carbon-FRP). Results showed that the system was very effective in increasing the beam capacity (Pu) and altering the failure mode from shear to flexure. Increasing the overlay thickness (toverlay) from 0 to 30 mm for plain and FRP-reinforced overlays results in a significant increase in Pu of 76–117%, compared to the control beam. Using discontinuous UHPC strips, although does not alter the shear failure, results in 89% increase in Pu. Reinforcing the overlay with GFRP and CFRP bars results in reducing the overlay thickness needed to shift the failure mode from shear to flexure. The energy absorption index, which is a measure of ductility, of the strengthened specimens was 4.0 to 6.9 times that of the control beam. FRP bars resulted in 11–25% increase in energy absorption compared to plain overlays, with GFRP showing more ductility than CFRP. An analytical procedure is also included and used to predict Pu from modifying existing code equations to include the contribution of UHPC overlay to shear.

Numerical Investigation of Axial Force–Bending Moment Interaction for FRP-Confined Reinforced Concrete Columns with Internal Steel Transverse Reinforcement

Externally bonded fiber-reinforced polymer (FRP) laminates are widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can increase the axial and bending moment capacities of these columns through a confinement mechanism. The confinement produced by FRP laminates acts in addition to that exerted by the internal transverse steel, although the latter is often neglected in current design standards and guidelines. In this study, a recently developed FRP-and-steel-confined concrete constitutive model was employed to numerically investigate the axial force–bending moment interaction for FRP-confined RC columns modeled using finite-element (FE) analysis. The proposed model was first validated against experimental data available in the literature and then used to quantify, through an extensive parametric study, the effects of transverse steel confinement, FRP strength, FRP stiffness, FRP reinforcement ratio, column diameter, concrete compressive strength, and load eccentricity ratio on the strength of FRP-confined RC columns subject to combined axial compression and bending moment. It was found that the internal steel confinement can substantially enhance the strength of these columns, especially for low concrete compressive strengths, large cross sections, and small eccentricities. When design code provisions limiting concrete and FRP deformations were considered for eccentrically loaded columns, the contribution of the steel confinement increased for increasing FRP reinforcement ratio. Based on the parametric study results, this investigation proposed an extension to eccentric axial compression of two relative confinement coefficients, which were previously developed to describe the contribution of transverse steel confinement to the peak strength of FRP-confined RC columns subject to pure compression.

Comparison of the Prediction of Effective Moment of Inertia of FRP Rebar-Reinforced Concrete by an Optimization Algorithm.

FRP (fiber-reinforced polymer)-reinforced concrete members have larger deflection than reinforced concrete members because of the low modulus of elasticity of the FRP bar. In this paper, we proposed a new effective moment of inertia equation to predict the deflection of FRP-reinforced concrete members based on the harmony search algorithm. The harmony search algorithm is used to optimize a function that minimizes the error between the deflection value of the experimental result and the deflection value expected from the specimen's specifications. In the experimental part, four GFRP (Glass Fiber-Reinforced Polymer)- and BFRP (Basalt Fiber-Reinforced Polymer)-reinforced concrete slab specimens were manufactured and tested. FRP-reinforced concrete slabs were reinforced with GFRP and BFRP rebars on spiral rib surfaces. The effects of the FRP reinforcement ratio and balanced reinforcement ratio (ρf/ρfb), the moment of inertia of the transformed cracked section and the gross moment of inertia (Icr/Ig), and the cracking moment and the maximum service load moment (Mcr/Ma) on the effective moment of inertia have been considered. The experimental results and predicted results of the flexural testing of concrete slabs reinforced with FRP rebars were compared, and the experimental results were in good agreement with the calculated values using the proposed effective moment of inertia equation.

Assessment of punching shear strength of FRP-RC slab-column connections using machine learning algorithms

Recently, the use of fiber-reinforced polymer (FRP) bars replacing steel reinforcement has been widely applied to overcome the corrosion issue, particularly concrete slab-column connections using FRP bars as flexural reinforcement (FRP-RC slabs). However, experimental studies showed that the use of FRP differentiates the punching shear behavior from steel-RC slabs. Various methods have been proposed to predict the punching shear strength of FRP-RC slabs, but existing design equations need improvement because their accuracy is low with wide scatteredness. Thus, this study aims at pioneering the application of machine learning (ML) algorithms for the prediction of the punching shear strength of FRP-C slabs without shear reinforcement. For this purpose, an experimental database with 104 specimens was compiled, with the input variables of the shear span-to-effective depth ratio, column perimeter-to-effective depth ratio, effective slab depth, concrete compressive strength, FRP reinforcement ratio, and ultimate tensile strength and elastic modulus of FRP. Three ML algorithms, including support vector regression (SVR), random forest (RF), and extreme gradient boosting (XGBoost), were evaluated for the application. To develop the ML-based models, a grid search method with a 5-fold cross-validation approach was used in the training process to determine the optimal hyperparameters. The performance of the ML-based models was estimated using various statistical estimators and compared with the current design codes and existing models. The comparisons showed that all three ML-based models could accurately predict the punching shear strength of the FRP-RC slabs without any significant and evident bias with the input variables. The XGBoost-based model displayed the best prediction with the coefficient of determination (R2) of 0.962, the root mean square error (RMSE) of 0.061 MN, mean absolute error (MAE) of 0.035 MN, and mean absolute percent error (MAPE) of 8.931% for testing dataset. The correlation coefficient, feature score, and sensitive analysis for the input variables indicated that the effective slab depth has the most substantial influence on the prediction performance. The prediction by the XGBoost-based model was more accurate and robust than that by the SVR- and RF-based models, current design codes, and existing models. These analysis results proved that the XGboost-based model can be used in the design and evaluation of FRP-RC slabs reliably and precisely.

A Method for Calculating Cracking Moment of FRP Reinforced Concrete Beam

This paper presents an analytical method for calculating the cracking moment of concrete beams reinforced with fiber reinforced polymer (FRP) bars, which considers the non-linear behavior of concrete in the tension zone and the contribution of FRP reinforcement. Theoretical cracking moments obtained by the proposed method were verified with the experimental results and the theoretical results calculated according to ACI 440.1R-15. The comparison results show good agreement between theoretical and experimental data. A parametric study on the effect of longitudinal FRP reinforcement ratio and elastic modulus of FRP on the cracking moment of FRP reinforced concrete beams also were done by using the proposed method. The parametric study results show that both longitudinal reinforcement and modulus of elasticity of FRP significantly affect the cracking moment of FRP reinforced concrete beams. Moreover, parametric study results also clarify the weakness of ACI 440.1R-15 in determining the cracking moment of concrete beams reinforced with a large amount of FRP reinforcement ratio and with high modulus of elasticity of FRP.

Investigation of ANN architecture for predicting shear strength of fiber reinforcement bars concrete beams.

In this paper, an extensive simulation program is conducted to find out the optimal ANN model to predict the shear strength of fiber-reinforced polymer (FRP) concrete beams containing both flexural and shear reinforcements. For acquiring this purpose, an experimental database containing 125 samples is collected from the literature and used to find the best architecture of ANN. In this database, the input variables consist of 9 inputs, such as the ratio of the beam width, the effective depth, the shear span to the effective depth, the compressive strength of concrete, the longitudinal FRP reinforcement ratio, the modulus of elasticity of longitudinal FRP reinforcement, the FRP shear reinforcement ratio, the tensile strength of FRP shear reinforcement, the modulus of elasticity of FRP shear reinforcement. Thereafter, the selection of the appropriate architecture of ANN model is performed and evaluated by common statistical measurements. The results show that the optimal ANN model is a highly efficient predictor of the shear strength of FRP concrete beams with a maximum R2 value of 0.9634 on the training part and an R2 of 0.9577 on the testing part, using the best architecture. In addition, a sensitivity analysis using the optimal ANN model over 500 Monte Carlo simulations is performed to interpret the influence of reinforcement type on the stability and accuracy of ANN model in predicting shear strength. The results of this investigation could facilitate and enhance the use of ANN model in different real-world problems in the field of civil engineering.

Numerical investigation of FRP-confined short square RC columns

Finite element (FE) simulation of confined RC columns is a complex task, as it involves the precise representation of a concrete material model that could express the volumetric change of concrete under a triaxial state of stress. The problem of confining RC columns using fiber-reinforced polymer (FRP) is more complex. This is due to the passive nature of FRP containment. Recently, the concrete damage plasticity (CDP) model available in an FE software product (ABAQUS) has been widely used to represent RC columns subjected to axial loading. The present paper aims to calibrate the concrete dilatancy angle and viscoplastic regularization parameters in the CDP model for the applications of square RC columns confined with FRP sheets. Ten experimental FRP-confined RC column specimens are incorporated in the calibration. In addition, a parametric study is investigated, including 96 cases, to obtain the influence of various design variables on the ratio between the confined to unconfined concrete compressive strength (fcc/fc). Four design variables are considered (i.e., the corner radius, concrete compressive strength, FRP reinforcement ratio, and cross-sectional size of columns). The study also focuses on assessing the reliability of four design codes: ACI-440, ECP-208, CSA-S806 and FIB-Bulletin-14. The numerical results show that a viscoplastic regularization with a fixed value equal to 0.0005 could provide accurate behavior. Nevertheless, the dilation angle cannot be considered a fixed value and should be related to the confinement degree coefficient Cd, which depends on the cross-sectional geometrical and FRP properties. Among the four considered design codes, ACI-440 and ECP-208 provide more accurate behavior than CSA-S806 and FIB-Bulletin-14.

Critical shear crack theory-based punching shear model for FRP-reinforced concrete slabs

Owing to their high strength-to-weight ratio, superior corrosion resistance, and convenience in manufacture, fiber-reinforced polymer (FRP) bars can be used as a good alternative to steel bars to solve the durability issue in reinforced concrete (RC) structures, especially for seawater sea-sand concrete. In this paper, a theoretical model for predicting the punching shear strength of FRP-RC slabs is developed. In this model, the punching shear strength is determined by the intersection of capacity and demanding curve of FRP-RC slabs. The capacity curve is employed based on critical shear crack theory, while the demand curve is derived with the help of a simplified tri-linear moment-curvature relationship. After the validity of the proposed model is verified with experimental data collected from the literature, the effects of concrete strength, loading area, FRP reinforcement ratio, and effective depth of concrete slabs are evaluated quantitatively.

Prediction model for the flexural strength of steel fiber reinforced concrete beams with fiber-reinforced polymer bars under repeated loading

This study investigates the flexural performance of steel fiber reinforced concrete (SFRC) beams with fiber-reinforced polymer (FRP) bars under repeated loading. Fourteen beams with dimensions of 150 mm × 300 mm × 2100 mm were cast and tested via a four-point bending test. The effects of the FRP reinforcement ratio, type of reinforcement, concrete strength, steel fiber shape, and steel fiber volume fraction on the failure mode, cracking moment, skeleton curve, deflection, strength degradation, and flexural strength of the beams were investigated. The test results revealed two different failure modes for the SFRC beams reinforced with FRP bars, including compression failure and tensile failure. The flexural strength of the beams decreased as the number of load cycles increased under the same deflection. A higher FRP reinforcement ratio, concrete strength, and steel fiber volume fraction enhanced the flexural strength of the beams and decreased the deflection. Finally, the flexural strength test results were compared with several different prediction models. The ACI 440.1R-15, CSA S806-12, and GB 50608–2010 models underestimated the flexural strength of the beams, while the proposed prediction model, which based on the equivalent force block, provided more accurate prediction results.

Flexural Capacity and Deflection of Fiber-Reinforced Lightweight Aggregate Concrete Beams Reinforced with GFRP Bars

Adding fibers is highly effective to enhance the deflection and ductility of fiber-reinforced polymer (FRP)-reinforced beams. In this study, the stress and strain conditions of FRP-reinforced lightweight aggregate concrete (LWC) beams with and without fibers at ultimate load level were specified. Based on the sectional analyses, alternative equations to predict the balanced reinforcement ratio and flexural capacity for beams failed by balanced failure and concrete crushing were established. A rational equation for estimating the short-term stiffness of FRP–LWC beams at service-load levels was suggested based on Zhu’s model. In addition, the contribution of the steel fibers on the short-term stiffness was quantified incorporating the effects of FRP reinforcement ratio. The proposed short-term stiffness model was validated with measured deflections from an experimental database for fiber-reinforced normal weight concrete (FNWC) beams reinforced with FRP bars. Furthermore, six glass fiber-reinforced polymer (GFRP)-reinforced LWC beams with and without steel fibers were tested under four-point bending. Based on the test results, the proposed models and procedures according to current design codes ACI 440.1R, ISIS-M03, GB 50608, and CSA S806 were linked together by comparing their predictions. The results showed that increasing the reinforcement ratio and adding steel fibers decreased the strain of the FRP bars. The flexural capacity of the LWC beams with and without steel fibers was generally underestimated by the design codes, while the proposed model provided accurate ultimate moment predictions. Moreover, the proposed short-term stiffness model yielded reasonable estimations of deflection for both steel fiber-reinforced lightweight aggregate concrete (SFLWC) and FNWC beams.

Finite element simulation of RC beams under flexure strengthened with different layouts of externally bonded fiber reinforced polymer (FRP) sheets

DOI: 10.7764/RDLC.17.3.383 Current research work is aimed to numerically simulate the failure behavior of Fiber Reinforced Polymer (FRP) strengthened reinforced concrete beams having different FRP reinforcement ratios. Required objectives are achieved by performing a series of bending tests on RC beams carrying different FRP layout and FRP reinforcement ratio. Tested beams were numerically simulated by using a Finite Element Method based computer package. The layouts of the FRP strengthening were decided based upon the FRP reinforcement ratios ranging from fully wrapped beams to the beams having significantly lower FRP reinforcement ratios. Tests results are presented in the form of load-deflection curves for all of the beams and a comparison of different beam strengthening schemes is also presented. Failure patterns of RC beams strengthened with different layouts of externally bonded FRP sheets were also compared. Results of flexural tests on twelve beams specimens and numerical simulation have indicated that CFRP and GFRP can significantly increase the bending and shear strength of retrofitted beams. However, the use of higher FRP reinforcement ratios to get higher strength increment is not advisable as epoxy properties and concrete surface quality plays a vital role to increase flexural and shear strength.

Numerical study of steel-to-FRP reinforcement ratio as a design-tool controlling the lateral response of SFRC beam-column joints

This study proposes both steel and fiber-reinforced polymer (FRP) composites as main reinforcement for modern reinforced concrete (RC) moment-resisting frame (MRF) structures. A detailed three-dimensional finite element model (3D FEM), which takes into account the material and geometric nonlinearity and the bond behavior of steel and glass FRP (GFRP) reinforcement, was created and validated against the available experimental results. 54 cases covering several combinations of steel-to-GFRP reinforcements and design scenarios (under and over reinforced design scenarios) were studied. The analysis results of steel-FRP reinforced concrete (SFRC) joints pointed to the ratio between the effective FRP reinforcement ratio and the balanced FRP reinforcement ratio (the normalized reinforcement ratio) as the main design tool that can be adopted to achieve a predefined seismic behavior. Moreover, a definition is given to the lower and upper limits of the normalized ratio. Design recommendations regarding the controllability of the serviceability state, the post-yielding state, the ultimate state, and the residual strength of SFRC joints through an appropriate design for the steel-to-FRP mixing ratio are drawn. Ultimately, a mechanical model describing the behavior of SFCR joints with different steel-to-FRP reinforcement ratios is introduced based on the general behaviors of the simulated joints.

Behavior and Design Aspects of FRP-Strengthened URM Walls under Out-of-Plane Loading

AbstractThe use of externally bonded fiber-reinforced polymer (FRP) composites for upgrading the out-of-plane flexural resistance of unreinforced masonry (URM) walls is experimentally and analytically investigated in this study. A total of six hollow concrete block walls were tested to failure using an airbag and a reaction frame to obtain a uniform load on the wall. The masonry walls were placed horizontally and tested as one-way slabs with span direction perpendicular to the bed joints. The first wall was left unstrengthened to be used as control specimen; the other five walls were strengthened using different schemes of externally attached glass-fiber-reinforced polymer (GFRP) sheets. The main parameters studied experimentally were FRP reinforcement ratio and stiffness. In addition to the experimental program, an analytical model was developed to predict the ultimate moment capacity of the URM walls. The procedure outlined in standard guidelines was also utilized to compute the flexural capacity of wal...

Seismic response of PP-band and FRP retrofitted house models under shake table testing

Current research work presents the seismic response of brick masonry houses retrofitted by different composite materials under dynamic shake table tests. Tests were performed on 1:4 scaled unreinforced masonry (URM), Polypropylene (PP-band) retrofitted, Glass Fiber Reinforced Polymer (FRP) retrofitted and FRP+PP-band retrofitted house models. A minimum reinforcement ratio of FRP was selected to use with PP-band as FRP+PP-band composite. Results show that URM is highly brittle and can hardly withstand an ordinary ground motion, whereas PP-band retrofitting has increased the ability of URM houses to withstand a severe ground motion with intense cracking and separation of wall segments. However, despite no collapses, PP-band retrofitted house model had lost its serviceability when subjected to strong input ground motion. Unlike PP-band, FRP retrofitted houses were collapsed suddenly without giving any warning with respect to ductility and energy dissipation. The sudden failure of FRP houses is attributed to very low FRP reinforcement ratio (0.0006), as it is an expensive material and its sole use in higher amounts would result in significant increase of retrofitting costs. Results show that a potential use of FRP in combination with PP-band is a good alternative as it significantly enhances the shear capacity, energy dissipation as well as the ductility of URM masonry structure at a very low retrofitting costs.

Intermediate crack-induced debonding analysis for RC beams strengthened with FRP plates

This paper presents the analysis of intermediate crack-induced (IC) debonding failure loads for reinforced concrete (RC) beams strengthened with adhesively-bonded fiber-reinforced polymer (FRP) plates or sheets. The analysis consists of the energy release and simple ACI methods. In the energy release method, a fracture criterion is employed to predict the debonding loads. The interfacial fracture energy that indicates the resistance to debonding is related to the bond-slip relationships obtained from the shear test of FRP-toconcrete bonded joints. The section analysis that considers the effect of concrete‟s tension stiffening is employed to develop the moment-curvature relationships of the FRP-strengthened sections. In the ACI method, the onset of debonding is assumed when the FRP strain reaches the debonding strain limit. The tension stiffening effect is neglected in developing a moment-curvature relationship. For a comparison purpose, both methods are used to numerically investigate the effects of relevant parameters on the IC debonding failure loads. The results show that the debonding failure load generally increases as the concrete compressive strength, FRP reinforcement ratio, FRP elastic modulus and steel reinforcement ratio increase.

Modeling of Flexural Behavior and Punching Shear of Concrete Bridge Decks with FRP Stay-in-Place Forms Using the Theory of Plates

A robust analytical model for predicting full response and ultimate load of concrete bridge decks constructed with fiber-reinforced polymer (FRP) stay-in-place (SIP) structural forms is presented. It adopts the plate theory to establish surface deflections, while incorporating concrete nonlinearity in compression and cracking in tension, as well as the degree of bond between the FRP SIP form and the concrete. The model accounts for various boundary conditions at the edges of the deck in both directions, including both finite and infinite width in the direction of traffic, and either fixed or hinged conditions in the other direction, depending on the connection to the support girders. A punching shear failure criterion was incorporated to predict the ultimate load. The model was validated against a large experimental database, and reasonable agreement was observed. The average percent difference in ultimate loads was 5.5%. The model was then used in a parametric study to assess the FRP reinforcement ratio in terms of the FRP plate thickness, the width of the deck parallel to traffic, and the span of the deck, which is the girder spacing. It was shown that reducing the FRP reinforcement ratio from 10.7 to 2.7% results in about a 20% reduction in punching shear ultimate load. The ultimate loads obtained for decks with (width/span) aspect ratios of 2.73, 1.33, 0.87, and 0.55 were 100, 94, 83, and 73%, respectively, of the ultimate load of the real condition of infinite width. Finally, the punching shear load decreased by about 18% as the deck span-to-depth ratio increased from 10 to 16.5.

Effect of longitudinal CFRP strengthening on the shear resistance of reinforced concrete beams

The flexural strengthening by external bonding of fiber reinforced polymer (FRP) to the tension face of reinforced concrete (RC) beams has proven to play similar role as that of the internal longitudinal reinforcement in increasing flexural strength and stiffness of the beams. Internal longitudinal reinforcement is also known to influence the shear strength of RC beams particularly the concrete shear strength component Vc. However, the effect of longitudinal FRP strengthening on Vc of RC beams has not yet been investigated. It is well established that Vc of flexural members can be reliably quantified from shear tests on beams without shear reinforcement. Therefore, RC beams without stirrups were constructed and strengthened with carbon FRP (CFRP) reinforcement to assess the effect of longitudinal strengthening on the shear strength of the beams. The study included five strengthened beams and two unstrengthened beams; all were tested under three-point bending. The test results indicated that the shear strength of the strengthened beams increased over that of the unstrengthened beams. The strength increase was up to 35%. The beneficial effect of the longitudinal strengthening was accounted for by considering the FRP reinforcement ratio in addition to the steel reinforcement ratio. Both reinforcement ratios were combined together in an equivalent reinforcement ratio accounting for the difference in the modulus of elasticity of the two materials. The equivalent reinforcement ratio was introduced in the conventional design methods for steel-reinforced beams to assess the shear strength of the strengthened beams. The experimental shear strength of the test beams were compared with the predictions of the modified design methods and good agreement was found.

Axial Capacity of Circular Concrete Columns Reinforced with GFRP Bars and Spirals

AbstractSeveral codes and design guidelines are now available for the design of concrete structures reinforced with fiber-reinforced polymer (FRP) bars under flexural and shear loads. Yet, because of a lack of research, North American codes and design guidelines do not recommend using FRP bars as longitudinal reinforcement in columns to resist compressive stresses. This paper reports on 12 full-scale circular reinforced concrete (RC) columns that were tested under concentric axial loads. The columns were reinforced with longitudinal glass FRP (GFRP) bars and newly developed GFRP spirals. The 300-mm diameter columns were designed according to code requirements. The test parameters included reinforcement type (GFRP versus steel); longitudinal FRP reinforcement ratio; and the volumetric ratios, diameters, and spacing of spiral reinforcement. The test results indicated that the GFRP and steel RC columns behaved in a similar manner. The average load carried by the longitudinal GFRP bars ranged between 5% and 1...

Elliptical and circular FRP-confined concrete sections: A Mohr–Coulomb analytical model

An analytical stress–strain model is developed for predicting the compressive behavior of elliptical and circular fiber reinforced polymer (FRP)-confined concrete members. The model is based on a diagonal Poisson’s ratio formulation expressed as a function of the mechanical properties of the unconfined concrete and confining FRP jacket, the geometry of the concrete section, and the extent of internal damage in the confined concrete core. A Mohr–Coulomb yield criterion is introduced for analysis of the compressive behavior of confined concrete. Equilibrium and strain compatibility are used to obtain the ultimate compressive strength and strain of elliptical and circular FRP-confined concrete sections as a function of the effective confining stiffness of the FRP jacket. A simplified expression is derived for the FRP reinforcement ratio which precludes strain softening in elliptical and circular FRP-confined concrete sections.