Fiber-reinforced Polymer Shear Research Articles

Experimental study on shear performance of PET FRP-strengthened RC beams without stirrups

The shear behavior of simply supported RC beams strengthened with polyethylene terephthalate (PET) fiber-reinforced polymer (FRP) was studied in this paper. The test variables include strengthening schemes (i.e., U-wrapping and full-wrapping) and FRP reinforcement ratios. A comprehensive and meticulous investigation was conducted on the failure mode of RC beams, shear force-deflection curves, the development process of shear cracks, the evolution of FRP strain, and the interaction between FRP and concrete. The shear capacity and deformation were increased by 42.5–123.2% and −16.34–96.89% using the fully wrapped scheme, respectively. The improvement in shear capacity was 42.5–72.55% when the U-wrapped scheme was adopted. The PET FRP fully wrapped beams exhibited a type of ductile shear failure. The strain of PET FRP in the fully wrapped specimen exceeded 4% without fracture, ensuring the deformation capacity after the peak load. The shear deformation caused the increase in post-peak mid-span deflection. The U-wrapped specimens showed debonding failure, with the debonding strain of PET FRP being more than that of conventional FRP. Finally, six design guidelines for PET FRP shear contribution were evaluated for both U-wrapped and fully wrapped schemes.

Overcoming the brittleness of shear failure: A new FRP-RSC strengthening philosophy

Due to the linear elastic stress–strain behavior of carbon fiber reinforced polymer (CFRP), the ductility of CFRP shear-strengthened reinforced concrete (RC) beams will be significantly reduced. Compared with shear capacity enhancement, increasing the ductility of CFRP shear-strengthened RC members is a much more challenging task, and a satisfactory solution has yet to be found. This paper introduces a new methodology that combines the brittle fiber reinforced polymer (FRP) with ductile rubber support composite (RSC) to form the FRP-RSC strengthening system. The variable stiffness RSC can adjust the stiffness of the strengthening system, which is achieved by the changed shear transfer actions in FRP, transverse reinforcement and concrete. Eight specimens were tested to evaluate the effectiveness of the FRP-RSC strengthening method. Experimental tests demonstrated that the displacement ductility with this FRP-RSC technique was 2.15 times that of the conventional externally bonded (EB) FRP strengthening, reaching remarkably 5.24. The mechanisms for enhancements in ductility, deformability and shear capacity were revealed. Poor matches were observed between the predicted FRP shear strength contribution (Vf) per existing models and test data. A new model that can predict Vf of FRP-RSC strengthened RC beams was developed, and better agreements between predictions and experimental results were obtained.

The Efficiency of Using Machine Learning Techniques in Fiber-Reinforced-Polymer Applications in Structural Engineering

Sustainable solutions in the building construction industry have emerged as a new method for retrofitting applications in the last two decades. Fiber-reinforced polymers (FRPs) have garnered much attention among researchers for improving reinforced concrete (RC) structures. The existing design guidelines for FRP-strengthened RC members were developed using empirical methods that are based on specific databases, limiting the accuracy of the predicted results. Therefore, the use of innovative and efficient prediction tools to predict the behavior of FRP-strengthened RC members has become essential. During the last few years, efforts have been progressively focused on the use of machine learning (ML) as a feasible and effective technique for solving various structural engineering problems. Its capability to predict the behavior of complex nonlinear structural systems while considering a wide range of parameters offers a distinctive opportunity to make the behavior of RC members more predictable and accurate. This paper aims to evaluate the current state of using various ML algorithms in RC members strengthened with FRP to enable researchers to determine the capabilities of current solutions as well as to find research gaps to carry out more research to bridge revealed knowledge and practice gaps. Scopus databases were searched using predefined standards. The search revealed ninety-six articles published between 2016 and 2023. Consequently, these articles were analyzed for ML applications in the field of FRP retrofitting, including flexural and shear strengthening of RC beams, flexural strengthening of slabs, confinement and compressive strength of columns, and FRP bond strength. The results reveal that 32% of the reviewed studies focused on the application of ML techniques to the flexural and shear strengthening of RC beams, 32% on the confinement and compressive strength of columns, 6.5% on the flexural strengthening of slabs, 22% on FRP bond strength, 6.5% on materials, and 1% on beam–column joints. This research also revealed that the application of various ML algorithms has shown a significant improvement in resistance prediction accuracy as compared with the existing empirical solutions. Supervised learning techniques were the most favorable learning method due to their good generalization, interpretability, adaptability, and predictive efficiency. In addition, the selection of suitable ML algorithms and optimization techniques is found to be mainly dictated by the nature of the problem and the characteristics of the dataset. Nonetheless, selecting the most appropriate ML model and optimization algorithm for each specific application remains a challenge, given that each algorithm is developed with different principles and methodologies.

Reliability-based design of FRP shear strengthened reinforced concrete Beams: Guidelines assessment and calibration

Possessing a more complicated mechanism and catastrophic brittle collapse mode, it is necessary to investigate the reliability level of design guidelines for concrete structures shear strengthened with fiber reinforced polymer (FRP). In this paper, six guidelines have been appraised based on the philosophy of load and resistance factor design approach. First, the model error of shear capacity prediction was identified. Subsequently, the reliability index was estimated, followed by the calibration of FRP design factors and a comparison of the design economy. The results show that: (1) For U-jacketing and fully wrapping, the Chinese guideline is the most accurate. For side bonding, both Chinese and American guidelines show a satisfying prediction. (2) The reliability index for U-jacketing is generally larger than that for side bonding and smaller than fully wrapping. (3) The Australian guideline provides the largest reliability indexes for U-jacketing and side bonding, while the British guideline provides the largest reliability indexes for fully wrapping. (4) Besides the reliability level, the design economy also relies on the sensitivity of β to design factors. For U-jacketing, CIDAR shows the best economy, followed by CSA and fib. For fully wrapping, TR shows the best economy, followed by CIDAR and ACI for βT < 3.5.

Feasibility Study on the Effect of FRP Shear Reinforcements on the Behaviour of FRP-Reinforced Concrete Deep Beams

Unlike steel reinforcements in concrete, Fiber Reinforced Polymer (FRP) materials are light and free from corrosion. Therefore, FRP materials are increasingly being used in structural engineering as a replacement for steel reinforcements. While the use of FRP bars as longitudinal reinforcements in concrete deep beams has been studied somewhat widely, their use and effectiveness as web reinforcements are not well studied. In this study, the effect of the FRP web reinforcements on the behaviour and strength of FRP-reinforced concrete deep beams were investigated in an experimental study. Four glass fiber-reinforced concrete (RC) simply supported deep beam specimens were tested under a concentrated load with different shear span-to-depth ratios and web reinforcement ratios. The behaviour of the deep beams was described in terms of load–deflection behaviour, crack developments, strain in FRP reinforcements, and failure modes. The experimental investigation emphasized the significance of web reinforcements in determining the reinforced concrete deep beam behaviour, such as mid-span deflection, crack breadth, failure modes, and ultimate strengths. Furthermore, to predict the behavior of deep beams, numerical Finite Element models using Abaqus software were created. The present test results were compared to those predicted using the Finite Element models. This investigation shows that web reinforcement is quite important for FRP-RC deep beams to achieve a robust behaviour by enhancing its capacity and deformability.

Shear strengthening of RC beams with NSM FRP. II: Assessment of strength models

The application of near-surface mounted (NSM) fiber-reinforced polymer (FRP) for shear strengthening of RC beams has attracted abundant research in the past few decades, and a number of strength models for predicting the contribution of NSM FRPs to the shear capacity of strengthened beam have been proposed. In the first of these two companion papers, a total of 12 strength models of NSM FRP shear strengthened RC beams collected from the existing literature have been comprehensively reviewed, while the present paper aims to provide an objective assessment of these models. To this end, the experimental results of 196 RC beams strengthened in shear with NSM FRP bars/strips are collected from the existing literature, as the database for the assessment. The comparisons between the experimental results and predictions by these strength models reveal that the existing strength models all fail to give accurate predictions. The reasons for the inaccurate predictions of these models are also analyzed.

Shear strengthening of RC beams with NSM FRP. I: Review of strength models

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper.

Shear behavior of concrete beams reinforced with closed-type winding glass fiber-reinforced polymer stirrups

Conventional pultruded fiber-reinforced polymer (FRP) rod stirrups are susceptible to premature bent corner rupture and bond slip failure of overlapping legs. This research proposed a new type FRP shear reinforcement, closed-type winding GFRP (CW-GFRP) stirrups, featuring a fully closed rectangular cross-section. CW-GFRP stirrups completely avoided slip and significantly improved the strength of bent portion of stirrups. To investigate the feasibility of using CW-GFRP stirrups as shear reinforcement, shear test of 8 concrete beams reinforced with conventional pultruded stirrups and CW-GFRP stirrups was conducted. The beams were 300 mm deep and 150 mm wide, and their shear span ratio were 2.07. The effect of the material of stirrups, the spacing of stirrups, and the width of CW-GFRP stirrups were investigated. The test results showed that pultruded stirrups exhibited bond slip failure, in contrast, CW-GFRP stirrups reinforced beams prevented this failure and showed enhanced stiffness, narrower shear crack width and 1.09–1.12 times higher shear capacity. The splitting failure typical of CW-GFRP stirrups was reported, and a smaller stirrups width is expected to avoid splitting and generate greater strain at ultimate. It can be concluded that the new type of CW-GFRP stirrups is an optimized form of FRP shear reinforcement to supersede conventional pultruded stirrups. Strut-and-tie models based on ACI 318-19 and CSA S806-14 were used to predict the shear strength and produced a safe but relatively accurate prediction.

Re-evaluation of shear contribution of CFRP and GFRP sheets in concrete beams post-tensioned with unbonded tendons

Contemporary design guidelines for the shear resistance of post-tensioned concrete (PC) beams retrofitted with fibre reinforced polymer (FRP) sheets are developed from the results of reinforced concrete (RC) beams. The accuracy of these guidelines for calculating the shear resistance of PC beams wrapped with FRP sheets is still questionable due to the difference in the shear behaviour of RC vs PC beams. The effects of the essential factors (e.g. tendon profile and anchorage system) on the shear resistance of PC beams have not been sufficiently studied, particularly for unbonded post-tensioned concrete (UPC) beams. This study presents an experimental investigation on the shear behaviour of UPC T-beams and the shear contribution of CFRP/GFRP sheets. The experiment consisted of 26 large-scale UPC T-beams with various factors including the tendon profile (harped or straight), concrete strength, FRP anchors, CFRP vs GFRP sheets, and various wrapping configurations. The experimental results showed that CFRP/GFRP sheets increased the shear resistance of UPC beams by 4–26%, which was much lower than that in RC beams. In comparison with the UPC beams with straight tendons, those with harped tendons exhibited a reduction in the shear contribution of CFRP/GFRP sheets (approximately 40%) and showed a more ductile failure mode with an improvement of the beam deformation (up to 2.3 times). FRP anchorage systems significantly enhanced the FRP shear contribution and energy absorption increased by 88% and 42% regarding those without anchors, respectively. Besides, it was observed from the test data that the widely-used method to determine the experimental shear contribution of FRP sheets in PC beams based on the difference between the shear resistance of strengthened and unstrengthened beams was inappropriate because it failed to consider the interactions between FPR sheets and other shear components, i.e. concrete and stirrups. Meanwhile, the experimental shear contribution of FRP sheets is recommended to be determined from the actual strain data of the FRP sheets across the main shear crack.

Comparative analysis of design guidelines for FRP contribution to shear capacity of strengthened RC beams

In the past few years, strengthening and retrofitting of reinforced concrete (RC) structures using externally bonded (EB) fiber-reinforced polymers (FRP) laminates has been deemed as a promising rehabilitation technique. Structural applications of FRP include flexural and shear strengthening of RC beams and confinement of columns. Many guidelines and standards were developed to predict the contribution of FRP to the strength of structural members. For shear strengthening applications, in particular, most of the design guidelines tend to underestimate the capacity of the strengthened members, whereas other models provide unsafe predictions. The accuracy of the models is dependent on many factors, such as but not limited to the wrapping scheme, amount of internal shear reinforcement, shear crack angle, concrete compressive strength, number of FRP layers, and FRP type. For this purpose, this paper focuses on comparing and evaluating the accuracy of the available FRP shear design guidelines. The design standards that are considered in this study are the ACI440.2R-17, CSA-S806.12 (R2017), fib bulletin 90, and TR55. The accuracy of the design models was assessed against an experimental database collected from the literature. The database included RC beams externally strengthened in shear with different FRP types, configurations, and wrapping schemes. In addition, the database included strengthened beams with varying types of anchors. Results showed that most design codes provide reasonable predictions to the FRP shear strength in case of U-wraps. However, the guidelines are significantly conservative in case of complete wraps and anchored specimens. Overall, the ACI440.2R-17 and TR55 predictions are very conservative while fib bulletin 90 and CSA-S806.12 predictions are accurate and can be safely used to design FRP shear strengthened members.

Punching shear strength of interior concrete slab-column connections reinforced with FRP flexural and shear reinforcement

To predict the punching shear strength of interior reinforced concrete (RC) slab-column connections using fiber reinforced polymer (FRP) bars as flexural and shear reinforcement, an analytical study was performed. Based on the punching shear failure mechanism of FRP-RC slab-column connections, a design method was proposed addressing the features of FRP reinforcement. For an accurate strength prediction, the depth of compression zone was evaluated by a modified approach, formulas for the effective strain and strength contribution of FRP shear reinforcement were proposed, and the effects of the size, aspect ratio, and load eccentricity were included. For verification, predictions by the proposed method were compared with existing test results for FRP-RC slab-column connection specimens with or without FRP shear reinforcement and subjected to concentric or eccentric load, and the accuracy and reliability of the proposed method were thoroughly examined by comparing with the current design codes and existing models. The comparisons showed that the proposed method best matched with the various test results consistently for all design parameters. To give an insight into the design of FRP-RC slab-column connections, the effects of various design parameters on the punching shear strength were also analyzed in detail.

Shear Capacity Model with Variable Orientation of Concrete Stress Field for RC Beams Strengthened by FRP with Different Inclinations

A design-oriented analytical model able to evaluate the shear capacity of reinforced concrete (RC) beams strengthened with fiber-reinforced polymer (FRP) sheets or strips oriented in any direction is proposed. The formulation of the model is based on the variable-inclination stress-field approach, aiming to extend the provisions of current European standards to beams strengthened in shear using FRP. The main novelty of the model lies in taking into account the possible different inclination of steel stirrup and FRP reinforcement in determining the orientation of a compressed concrete stress field, and in shear strength evaluation, overcoming the approximation of the known models with variable inclination of the concrete strut in the assessment of concrete strut capacity, in which the value that has to be assigned to the shear reinforcement direction is not defined, that is, either that of the steel stirrup or the external FRP reinforcement. The proposed model is able to take into account different steel stirrup and external FRP shear reinforcement orientation in assessing the reduction of the steel transverse reinforcement efficiency due to the brittle failure of the composite and also as a function of the effective composite to yielding steel strain ratio. Moreover, regarding the former aspect, a simplified approximate procedure is proposed for solving the drawbacks related to verifying compressed concrete strength in the suggested method of application of code models for RC beams strengthened by means of FRP reinforcement inclined with a different slope from the pre-existing steel stirrup. Complete and U-shaped schemes are considered. The effectiveness of the proposed model adopting different relations for assessment of the FRP effective strains proposed in the literature is investigated, differentiating them by shape of the cross section and by the possible presence of fiber-anchoring devices. The shear capacity predicted by the model and those obtained using international codes and literature models are compared against the experimental results, proving that the proposed model is the most effective in predicting the shear strength when considering specimens having steel stirrups and FRP shear reinforcement arranged with different inclinations.

Composite behaviour of wide sandwich panels with thin high performance recycled aggregate concrete wythes with fibre reinforced polymer shear connectors

ABSTRACT The traditional means of using precast concrete sandwich panels are restrictive in terms of applications, where thick wythes result in heavy panels which are often unsuitable in retrofitting domestic and commercial buildings. As concrete sandwich panel technology has evolved to make it more widely accessible, recent research work has demonstrated that it is possible to achieve thermally efficient partial composite action within a thin wythe panel provided non-conductive shear connectors are used. This paper examines high performance recycled aggregate concrete in heavily insulated non-load-bearing panels for retrofitting domestic and commercial buildings. A series of concrete mixes were tested to develop one which would be more sustainable than the widely accepted standard mixes for wythes. Different 220 mm thick concrete sandwich panels were tested consisting of 20 mm thick fibre-reinforced recycled aggregate concrete wythes and a 180 mm layer of XPS insulation. Unconnected and shear connected panels were tested in flexure in a displacement control test. The effects of composite action and post-cracking toughness were examined and it was concluded that a shear connected panel comprising sustainable thin recycled aggregate concrete wythes enclosing a thick layer of insulation is a feasible product to use for light high-performance sandwich panels.

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.

Influence of CFRP Strand Sheet on Flexural Strengthening of Reinforced Concrete Beam

Fiber Reinforced Polymer (FRP) composites in the form of laminates and fabrics are installed on reinforced concrete members, using externally bonded (EB) techniques for strengthening. However, the utilisation of capacity of FRP composites is limited due to debonding observed in the strengthening system, due to FRP and concrete interfacial shear stress. Carbon fiber reinforced polymer (CFRP), in a new form of strand sheets were recently developed and have not been adequately investigated upon. These strands are less than 1.0 mm in diameter is woven with thread to obtain the desired width of the sheet. Such strand sheets are likely to have enhanced bond strengths due to the gaps between the strands that increase the surface available for bonding with the adhesive compared to laminates. This paper presents details of an experimental investigation of the influence of CFRP strand sheets on the flexural performance of CFRP strengthened reinforced concrete (RC) beams. In the experimental study, RC beams strengthened with CFRP strand sheets and lami-nates, were tested under four-point bending and compared with an un-strengthened specimen. The main parameter varied was the elastic modulus of the CFRP strand sheet and width ratio (wf /b) of high strength CFRP strand sheets. The relative contribution of the CFRP strand sheets to the bending moment capacity was observed to be significantly higher than that in the case of the CFRP laminate. The failure mode was observed to change from debonding to concrete cover separation with an increase in width ratio. The rupture was observed as the failure mode in the specimens strengthened with high modulus CFRP strand sheets. As a result, an increase in the bending-moment capacity and ductility of the beams was also observed. Based on the observed failure modes, models for predicting the mechanical behaviour of various systems were assessed.

Experimental study on flexural shear strengthening effect on low-strength RC beams by using FRP grid and ECC

This paper investigates the shear behaviour of reinforced concrete (RC) beams by using engineered cementitious composite (ECC) and fibre reinforced polymer (FRP) grid as a composite reinforcement layer. A total of seven RC beams, including one control beam and six strengthened beams, were tested to reveal their shear behaviour and strengthening effect. The test variables in the experiments included different reinforcement amounts of FRP grids and shear span ratios of RC beams. As a result, the shear strengthening effect of the FRP grid-ECC layer for RC beams is obvious. However, the strengthening effect of the specimen with two-layer FRP grids did not perform better due to premature debonding. Furthermore, through regression analysis on the experimental data, a formula is proposed to predict the angle of the critical inclined cracks in RC beams strengthened with ECC-FRP grids.

State-of-the-art review of anchored FRP shear-strengthened RC beams: A study of influencing factors

Several anchorage techniques have been proposed in the literature to delay or prevent the debonding failure mode and to upgrade and restore the capacity of externally bonded (EB) fiber-reinforced polymers (FRPs) shear-strengthened beams in a U-wrapping scheme, such as NSM, FRP extension, FRP insertion, horizontal FRP, FRP patch, FRP rope, FRP spike, metallic anchors, and combined anchors. Although the advantages of these anchorage techniques have been acknowledged by researchers, their effectiveness in enhancing FRP shear contribution is controversial. The present study is a state-of-the-art review of experimental tests that were carried out to investigate the effectiveness of anchorage techniques for FRP shear-strengthened beams. The various anchorage techniques are evaluated in terms of FRP shear strength and FRP strain based on the parameters that have a major influence on the behavior of FRP shear-strengthened beams. Furthermore, strength models for FRP shear-strengthened beams provided in various design guidelines are used to predict FRP shear strength compared to experimental results. The significance of the present findings with respect to FRP shear contribution is discussed.

FRP shear contribution prediction for U-wrapped RC T-beams using a soft computing tool

The reinforced concrete (RC) T-beam is relatively stronger in shear than the rectangular RC beam, represents the most realistic condition and has more implications in the construction industry. However, no study encompassing a large number of results of tests conducted on the RC T-beams externally shear strengthened with fiber-reinforced polymer (FRP) has been found. Therefore, the current study targets to calculate the contribution of externally bonded FRP towards the shear capacity of RC T-beams by means of a soft computing tool i.e. adaptive neuro-fuzzy inference system (ANFIS). A total of 148 sets of data collected from the literature and used for the training and testing of the ANFIS model. A comparative study between the ANFIS predictions and the obtained experimental outcomes has revealed that the ANFIS forecasts are in fine agreement with the experimental outcomes. Additionally, evaluation of the efficacy of the current ANFIS model has been done by comparing the ANFIS predictions with the predictions of seven broadly utilized design guidelines. On the basis of the comparison of different performance measures, it has been deduced that the efficacy of the current ANFIS model is superior to the considered design guidelines. A parametric study has also been done to explore the impact of the combined effect of the two input parameters on the FRP shear contribution.

Experimental Analysis of Shear Resisting Mechanisms in FRP RC Beams with Shear Reinforcement

Owing to the unique mechanical characteristics and lack of plasticity of fiber-reinforced polymers (FRPs), relatively large strains can develop in FRP reinforced concrete (RC) elements at ultimate limit states and this can lead to different relative contributions of concrete and shear reinforcement to the total element's shear capacity. This paper examines the development and relative contribution of the main shear resisting mechanisms in concrete beams with different overall depths and reinforced with longitudinal and transversal FRP reinforcement. Complementary strain measurements obtained from digital image correlation (DIC) and strain gauges are presented and discussed thoroughly. Although current FRP shear design approaches rely on the assumption that the contributions of concrete and shear reinforcement are constant up to failure, their relative magnitude is found to vary with increasing crack width. The experimental results indicate that, when minimum shear reinforcement is provided, current shear models based on a fixed truss angle approach tend to overestimate the contribution of concrete and underestimate the contribution of shear reinforcement. The use of a variable angle truss model, along with an appropriate reduction in the contribution of concrete, would lead to a more reliable estimate of the main shear resisting mechanisms and optimal design of the required amount of shear reinforcement.

A comparative study of different methods to calculate degrees of composite action for insulated concrete sandwich panels

Precast concrete sandwich wall panels consist of two outer wythes of precast concrete separated by a middle layer of insulation. In recent years, Fiber-Reinforced Polymer (FRP) shear connectors have been increasingly used since they have lower thermal conductivity compared to traditional steel shear connectors, which can significantly reduce thermal bridging. However, FRP shear connectors have lower stiffness, resulting in partial Degree of Composite Action (DCA), which is an important parameter to describe the structural behavior of the panels. Different methods have been proposed to calculate DCAs, including displacement method, strain method, and load method. This paper will compare and evaluate the effectiveness of these methods. A bending test was conducted on a full size of 7 m × 3 m, precast, prestressed insulated concrete sandwich panel with FRP shear connectors. A non-linear Finite Element (FE) model is created, where good correlations can be achieved between the test and FE results. The FE model is further employed to conduct a parametric study by varying the stiffness of the shear connectors. DCAs for different stiffnesses are calculated using the aforementioned three methods and the applicability and limitation of each method are investigated.