Fiber-reinforced Polymer Wrapping Research Articles

Strengthening of heat-damaged steel fiber-reinforced concrete using CFRP composites: Experimental study and analytical modeling

Retrofitting concrete with fiber-reinforced polymer (FRP) wrap has been considered as an effective method to compensate for the loss of the compressive strength of the concrete at an elevated temperature. This paper presents a study on the axial compressive behavior of heat-damaged steel fiber-reinforced concrete strengthened with carbon FRP (CFRP) wraps. To this effect, steel fibers were added to two concrete mixtures with volume fractions of 0.5% and 1%. The effect of full and partial wrapping with CFRP composites on the compressive behavior of the heated concrete was examined. A stress–strain model was also proposed to predict the behavior of CFRP-confined post heated steel fiber-reinforced concrete. It was found that heated concrete wrapped with CFRP layers exhibits a higher compressive strength, peak axial strain, maximum volumetric strain, toughness and relative energy absorption than that of unwrapped concrete. The results also showed that the exposure of concrete to the heat leads to a slight decrease in the ascending and descending slopes of the axial stress–strain relationship. The comparison between the model predictions and experimental results revealed that the proposed model accurately predicts the axial stress-axial strain and axial stress-lateral strain of the heated concrete. These results are promising and demonstrate the benefits of full and partial FRP wrapping in the development of high-performance structural members subjected to an elevated temperature.

Large-Scale FRP-Confined Rectangular RC Columns with Section Curvilinearization under Axial Compression

A novel technique to improve the effectiveness of fiber-reinforced polymer (FRP) confinement for strengthening rectangular reinforced concrete (RC) columns is to implement section curvilinearization (SC) before FRP wrapping. In this SC technique, the four flat sides of a rectangular column are transformed into slightly curved sides, which increases the sectional size only slightly but can significantly enhance the FRP confinement effectiveness. However, existing research on curvilinearized square/rectangular columns (CSCs or CRCs) (particularly on CRCs) is very limited and has been conducted using small-scale specimens. To this end, the first-ever experimental program of axial compression tests on large-scale FRP-confined CRCs was recently carried out, and the results are presented in this paper. The experimental program covered the rise-to-span ratio of the curved sides, the corner radius ratio, and the sectional aspect ratio as the key test variables. The experimental results show that the slope of the linear second segment of the stress–strain curve of FRP-confined concrete in a CRC is much larger than that of the corresponding column without SC, demonstrating the effectiveness of the SC technique. On the basis of the present test results, an evaluation of the accuracy of the only stress–strain model for FRP-confined concrete in CRCs available at the time of conducting the present study is reported.

Buckling Behavior of Non-Retrofitted and FRP-Retrofitted Steel CHS T-Joints

This paper aims to investigate the buckling behavior of circular hollow section (CHS) T-joints in retrofitted and non-retrofitted states under axial brace compressive loading. For this purpose, two types of analysis are carried out. The first one is evaluating the critical buckling load in various tubular joints, and the other one is investigating the post-buckling behavior after each buckling mode. More than 180 CHS T-joints with various normalized geometric properties were numerically modeled in non-retrofitted state to compute their governing buckling mode, i.e., chord ovalization, brace local, or global buckling. Then three joints with different buckling modes were selected to be retrofitted by fiber-reinforced polymer (FRP) patches to illustrate the improving effect of the FRP wrapping on the post-buckling performance of the retrofitted joints. In addition, FRP composite failures were investigated. The results indicate that the FRP retrofitting is able to prevent the brace local buckling, and that matrix failure is the most common composite failure in the retrofitted joints.

Effect of Composite Fiber Panels and Basalt-Based Fiber Reinforced Polymer Wrapping on the Seismic Behavior of Square Reinforced Concrete Columns

Effect of Composite Fiber Panels and Basalt-Based Fiber Reinforced Polymer Wrapping on the Seismic Behavior of Square Reinforced Concrete Columns

Buckling behavior of cross laminated poplar timber columns using various performance improvement techniques

In present times, cross-laminated timber (CLT) has become a product of global interest. Utilization of locally available timber (having low strength, moderately low stiffness, and high shrinkage issues) in CLT with improvement techniques has proven to be cost-effective with environment-friendly features. In this study, various performance improvement techniques have been used for enhancing the strength parameters in long columns made from a timber specie (Poplar) found in abundance in the Kashmir region of India. Poplar used in the cross-laminated form with different binding/wrapping techniques viz. bolted, wrapped cold steel, single helix carbon fiber reinforced polymer (FRP), and double helix carbon FRP wrapping, have been fabricated and tested. The results indicate that laminating the slender CLT columns with a single FRP helix, increases the strength by about 35%, and this improvement can go as high as 50%, provided double helix FRP is adopted.

Investigational study on Influence of Fiber Reinforced Polymer Wrapping on Concentrically Loaded Concrete Column

The aim of research work to study the column with varying dimension and parameter. Along with wrapping of the column. The study has been made on axial load, axial deflection and lateral deflection. There 18 specimens have been casted and testing is done. Such as 300mm height and 150mm diameter column of six numbers, 450mm height and 150mm diameter columns of six numbers, 600mm height and 150mm diameter columns of six numbers. The 300mm height of the columns has been fully wrapped with 0-degree orientation of one-layer thickness, fully wrapped with 45-degree orientation of one-layer thickness, partially wrapped with 0-degree orientation of double-layers thickness, partially wrapped with 45-degree orientation of double layers thickness, fully wrapped with 45-degree orientation of double layers thickness and one number of unwrapped concrete columns. The 450mm height of the columns has been fully wrapped with 0-degree orientation of one-layer thickness, fully wrapped with 45-degree orientation of one-layer thickness, partially wrapped with 0-degree orientation of double-layers thickness, partially wrapped with 45-degree orientation of double layers thickness, fully wrapped with 45-degree orientation of double layers thickness and one number of unwrapped concrete column. The 600mm height of the columns has been fully wrapped with 0-degree orientation of one-layer thickness, fully wrapped with 45-degree orientation of one-layer thickness, partially wrapped with 0-degree orientation of double-layers thickness, partially wrapped with 45-degree orientation of double layers thickness, fully wrapped with 45-degree orientation of double layers thickness and one number of unwrapped concrete column. The specimens have been tested and corresponding results are obtained.

Effect of Shape Modification on the Performance of Cfrp Confined Square Concrete Columns: A Review

Now a days fiber-reinforced polymer (FRP) confinement is one of the most important techniques used for the strengthening and repairing of concrete structures. In the case of columns, the square/rectangular columns show less effectiveness towards FRP confinement compared with circular columns due to their flat sides and sharp corners. So the strengthening of square/rectangular columns needs more attention than circular columns. The performance of square/rectangular columns can be improved by modifying the shape of columns before FRP wrapping. The researches show that varying the corner radius of non-circular columns improves the confinement area and thereby increase the confinement efficiency of FRP. Recently, curvilinearization technique was developed in which slightly curved sides are provided to existing square/rectangular sections before application of FRP. Circularization is also another shape modification method in which the existing square columns are modifying into circular sections by using segmental concrete covers before the FRP wrapping process. This paper mainly deals with these shape modification techniques in the carbon-fiber-reinforced polymer (CFRP) confined square columns.

Analytical study on torsional behavior of concrete beams strengthened with fiber reinforced polymer laminates using softened truss model

This study aimed at evaluating the torsional capacity of reinforced concrete (RC) beams externally wrapped with fiber reinforced polymer (FRP) materials. An analytical model was described and used as a new computational procedure based on the softened truss model (STM) to predict the torsional behavior of RC beams strengthened with FRP. The proposed analytical model was validated with the existing experimental data for rectangular sections strengthened with FRP materials and considering torque-twist relationship and crack pattern at failure. The confined concrete behavior, in the case of FRP wrapping, was considered in the constitutive laws of concrete in the model. Then, an efficient algorithm was developed in MATLAB environment to accomplish the analysis, solve the appropriate equations, and calculate the torsional moment and angle of twist at all points. The parametric study considered the effect of effective fiber strain to reach a better prediction for the full torsional behavior. The model was able to predict the torsional behavior of the RC beams strengthened with FRP materials before and after cracking stages with reasonable accuracy.

Dynamic performance of concrete columns retrofitted with FRP using segment pressure technique

For RC columns exposed to blast loads, fibre reinforced polymer (FRP) is employed to examine its effectiveness in strengthening the concrete structure against blast load. It should be noted that no systematic studies could be found in the literature to derive pressure and impulse (P-I) diagram for FRP retrofitted RC columns. Therefore, the objective of this research is to develop finite element model to provide data for use in the development of P-I diagram that can be used to mitigate blast hazards and predict damage in RC columns retrofitted with FRP. In this study, various strengthening scheme performed against blast loads numerically by running computer simulations using the commercial software LS-DYNA. Validation of the models is performed based on the blast field test to investigate the accuracy of model simulations to present the behaviour of the models. The research compared the structural behaviour of an un-strengthened RC column with various column strengthened with different FRP wrap thickness, strength and arrangement. The results of the simulations showed that strengthening with FRP is an effective way to increase the blast resistance capacity of columns. This information would allow the designer to identify the critical location for placing blast barriers for protection purpose.

Ductility Behaviour of Rectangular Compression Members Retrofitted by Modified Technique of FRP Wrapping

This paper presents an experimental investigation on ductility behaviour of reinforced concrete compression members, rectangular in cross section, modified to elliptical shape in cross section by bonding precast segment covers followed by Carbon Fiber Reinforced Polymer wrapping (CFRP) under concentric and eccentric loading conditions. Eighteen reinforced concrete rectangular compression members of size 100mm×150mm in cross section and 300mm in height were prepared using normal-strength concrete. Reinforcement ratio was kept at minimum, to simulate compression members that need retrofitting. Out of eighteen specimens, nine specimens were converted to elliptical shape in cross section. From nine remaining rectangular specimens, three specimens retained as it is without wrapping FRP and designated as Group1, remaining six specimens were wrapped with one and two layers of CFRP and designated as Group2. Out of nine elliptical specimens, three specimens were retained as it is without wrapping FRP and designated as Group3, remaining six elliptical specimens were wrapped with one and two layers of CFRP and designated as Group4. Specimens were tested upto failure under monotonic axial compression with concentric and eccentric load conditions. From the experimental results, it is observed that rectangular compression members shape modified to ellipse in cross section and then wrapped with CFRP show outstanding increase in the ultimate load carrying capacity which may be due to increased cross sectional area and effective confinement of FRP wrapping. As the number of layers of CFRP increases the ultimate load carrying capacity increases. With increase in eccentricity, the ultimate loads of the compression members were found to be decreased. Elliptical specimens wrapped with one and two layers of CFRP reported exponential increase in deformation ductility under concentric load condition and considerable increase under eccentric load condition compared to rectangular specimens wrapped with CFRP.

Impact Testing of Reinforced Concrete Beams Shear- Strengthened with Fiber-Reinforced Polymer Wraps

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Experimental investigation of rectangular concrete-filled fiber reinforced polymer (FRP)-steel composite tube columns for various corner radii

To study the compressive behavior of rectangular concrete-filled fiber reinforced polymer (FRP)-steel composite tube (CFCT) columns, twenty-nine specimens were tested under compression loading in five series based on the corner radius. The variables are the corner radius of cross-section, the number of layers of FRP and the type of FRP wrapping. The experimental results revealed that the FRP wrapping may effectively suppress the local buckling for the steel tubes prior to FRP rupturing. The FRP fractures occurred at the corners in the middle of the specimens or at the longitudinal weld seams due to local stress concentrations. The stress–strain curves are influenced significantly by the corner radii for the rectangular CFCT columns. As the corner radius is increased, the linear ascending or descending slopes after the peak points of the stress–strain curve is generally enhanced, and a descending curve can be transformedinto an ascending curve. For a given FRP confinement, the ultimate strength increased with increasing corner radius. Based on the experimental results and collected test data, a unified model with a simple and unified expression for predicting ultimate axial strength considering the shape and corner radius of the cross-section was proposed for the CFCT columns.

RC frame structures retrofitted by FRP-wrapping: A model for columns under axial loading and cyclic bending

Abstract In order to mitigate the seismic risk of existing RC frame structures not designed with seismic criteria, a widespread strengthening strategy is based on increasing strength and ductility of RC columns by means of Fiber Reinforced Polymer wrapping. The existing models for RC cross-sections wrapped by FRP sheets were developed principally considering pure axial loads with uniform confinement pressure. In seismic areas, RC columns are instead usually subjected to axial load and cyclic bending. In the present work, in order to consider the effective loading conditions, an iterative cyclic model for square RC cross-sections wrapped by composite FRP sheets subjected to axial force and cyclic bending is proposed. The model considers the strain gradient-effect over the cross-section due to the bending loads that change significantly the confinement level of RC cross-section. Moreover, the model has been validated by comparing the numerical outcomes with various cyclic experimental results. The model has been also implemented in an open-source software with distributed plasticity finite elements in order to perform pushover analyses of an existing RC frame structure with different retrofitting strategies to improve the ductility of the columns for lateral forces.

Strength Characteristics of Concrete Specimen Wrapped With Glass Fiber Reinforced Polymer

Glass Fiber Reinforced Polymer (GFRP) is one of a relatively new class of composite material. These materials are manufactured from a combination of fibers and resins. These composite materials have proven to be efficient and economical for the development of new structures and the repair of deteriorating structures in civil engineering. One of the important reasons for the use of GFRP composite materials is because of its superior mechanical properties. These mechanical properties includes impact resistance, strength, stiffness, flexibility and also its enhanced ability to carry loads. In construction industry, in order to meet the advanced infrastructure requirements, new innovative technologies and materials are being introduced. Also any new technology or material has its own limitations but to meet the new requirements, new technologies and materials have to be invented and put to use. With structures becoming old and increasing bar corrosion, old buildings have to be retrofitted with additional materials to increase their durability and life. For strengthening and retrofitting of concrete structures confinement with FRP has various applications. In this project concrete specimens are wrapped with glass fibre reinforced polymers to study the effect of confinement in the strength of specimens. For wrapping bi-directional and uni-directional glass fibre reinforced polymer mats are used. During the uni-directional glass fibre reinforced polymer wrapping, it is wrapped in both horizontal and vertical directions. The fiber used in this paper is bi-directional fibre. To find the effect of wrapping, specimens are wrapped in one rotation and two rotations.

Compressive behavior of circular and square concrete column externally confined by different types of basalt fiber–reinforced polymer

This article studies the compressive behavior of concrete columns confined by different basalt fiber–reinforced polymers. A total of 30 columns were divided into 10 groups according to section shapes (circular and square), basalt fiber–reinforced polymer types (unidirectional basalt fiber–reinforced polymer, bidirectional basalt fiber–reinforced polymer, and hybrid basalt fiber–reinforced polymer/carbon fiber–reinforced polymers), and number of layers (0, 1, and 2). The test results showed that the compressive strengths of confined specimens increased by 20%–71% for circular columns and by 23%–41% for square columns. Similarly, the ultimate strains improved by 49%–296% for circular specimens and by 45%–145% for square specimens. The two-layer basalt fiber–reinforced polymer jacket had the best confinement effect, whereas the confining effect of bidirectional basalt fiber–reinforced polymer wrapping was relatively lower than that of unidirectional basalt fiber–reinforced polymer wrapping. Moreover, both the strength and ultimate strain of confined concrete improved with increasing number of basalt fiber–reinforced polymer layers. Finite element numerical models were also developed and verified by experimental results, and then the stress distributions of basalt fiber–reinforced polymer jackets and cross-sectional concrete were presented. Based on the test results and experimental data from several existing studies, modified strength and ultimate strain models were further developed for basalt fiber–reinforced polymer-confined circular and square columns.

Strengthening of deficient reinforced concrete columns subjected to concentric and eccentric loads

In this research, different techniques of repair of deficient reinforced concrete columns are compared. These include carbon fiber–reinforced polymer sheets, steel jackets, and reinforced concrete jackets. The experimental investigation includes testing of 16 deficient columns of dimensions 150 × 150 × 800 mm subjected to concentric and eccentric loading up to failure. Two main variables are considered: the load eccentricity and the strengthening technique. The experimental results showed that the three strengthening techniques used in this research significantly improved the ultimate load carrying capacity in all cases of loading. Also, in the two cases of concentric loading and big eccentricity of 150 mm, carbon fiber–reinforced polymer wrapping achieved the highest ductility and absorbed energy capacity. In addition, strengthening with reinforced concrete jacket improved the initial stiffness and toughness. The cracking load, ultimate load, and ductility of the deficient columns after strengthening were experimentally recorded and compared. The results can help the structural engineer to consider the most efficient method of repair for such columns.

Nonlinear Dynamic Response of a RC Frame for Different Structural Conditions Including the Effect of FE Model Updating

After destructive events such as earthquakes, attempts have generally been made to repair and strengthen structures using such methods as filling cracks by injection, wrapping structural elements with fiber-reinforced polymer (FRP). These applications can allow the recovery of lost structural performance. In this paper, the aim was to investigate the structural performance of an RC frame under different conditions—undamaged, damaged, repaired, and strengthened—by comparing results of nonlinear dynamic analyses. In addition, finite-element (FE) model updating effects were investigated in the case of the undamaged condition. To this end, an RC frame model was first constructed in the laboratory, and then, the model was damaged by lateral forces, repaired with epoxy injection, and lastly strengthened by wrapping with FRP. To obtain the dynamic characteristics of the RC frame under the different conditions, ambient vibration tests were performed for each condition. The FE model of the RC frame, obtained through global and local model updating using the ambient vibration test results, was modeled to achieve the nonlinear dynamic analyses. The results of the analyses were presented in the form of maximum displacements, principal stresses, and strains with contours diagrams. The maximum displacement increased significantly (133%) with the degree of damage, sharply decreased with the repaired (32%), and strengthened (36%) applications. The maximum and minimum principal stresses decreased by 24% and 35%, respectively, with the damaged condition. In addition, maximum differences between the undamaged and strengthened conditions were calculated as 17% for the maximum principal stress and 38% for the minimum principal stress. Findings indicated that the epoxy injection with FRP wrapping eliminates effect of the damage and recovers the model’s performance to its initial state. In addition, it is demonstrated in this paper that the updating procedure considerably changes the dynamic analysis results.

Axial\u2013Flexural Interaction in FRP-Wrapped RC Columns

The study reported herein aims at investigating the behavior of medium-scale circular reinforced concrete columns wrapped with fiber reinforced polymer (FRP) sheets under concentric and eccentric axial loads. The experimental program was devised to assess the effects of loading conditions, absence/presence of an FRP jacket as well as the FRP wrapping system. To achieve the study objectives, four column groups were tested under axial compression at 0, 25, 50 and 65 mm loading eccentricities corresponding to eccentricity-to-diameter ratios of 0, 0.13, 0.26 and 0.34, respectively. Specimens in a fifth group were tested in pure bending simulating axial compression at infinite loading eccentricities. Three column subcategories were tested under each of the 5 loading eccentricities: unwrapped; wrapped with one ply of hoop FRP sheets; and wrapped with two FRP plies with fibers oriented at 0 and 90° to the longitudinal column axis thereby providing externally-bonded longitudinal reinforcement and hoop confinement, respectively. Tests confirmed that FRP confinement enhances the axial–flexural column resistance even at large eccentricities that exceed the balanced state of unconfined columns. Although axial column resistance decreased with increasing bending moments, relative enhancements (25–35%) in axial resistance provided by FRP confinement were found to be more significant under eccentric loading than in pure compression. Compared to hoop FRP-confined columns, using additional longitudinal sheets resulted in minor (7–9%) but stable enhancements in axial resistance that were unaffected by the increase in loading eccentricity. The FRP hoop wraps had a minor effect on the flexural resistance of specimens tested in pure bending but managed to double their resistance when combined with the externally-bonded longitudinal FRP sheets. Finally, three stress–strain models of FRP-confined concrete were used in conventional section analysis to assess the axial–flexural interaction in the FRP-jacketed columns. Strength predictions made using the stress–strain model proposed in ACI 440.2R-17 design guidelines did not agree with the test results of the eccentrically-loaded columns and underestimated the moment resistance at a given axial force even when considering higher confinement ratios than those permitted by the guidelines. Strength predictions made using eccentricity-dependent stress–strain models showed better results especially when accounting for the increase in ultimate axial strains under eccentric loading.

Evaluation for RC Column Confined Partially with Externally FRP Wrapping Sheet Using Nonlinear FE Analysis

Little research has been carried out in validating, fiber reinforced polymer (FRP) concrete strengthened column and the effective using partial wrapping. Also the effect of several parameter on strengthen column using the partial wrapping sheet of desired width and thickness around column have not been found out. To this end, a nonlinear 3D finite element model has been developed in current study for CFRP strengthened reinforced concrete column to simulate the behavior accompanied by the effect of partial wrapping with emphasis on load capacity and failure mode. The finite element simulation of CFRP strengthened RC columns is performed using commercial finite element program ABAQUS. Modelling was conducted on reinforced concrete columns with dimensions of 160 x 250 x 960 mm. The finite element model incorporates the nonlinear material behavior of concrete, bilinear stress-strain curve of steel and linear elastic behavior of CFRP material. The concrete was modeled using a plastic damage model. The performance of the FE model was studied by simulating experimental columns from the literature. The load, and strain of CFRP obtained from the FE study were compared with the corresponding experimental results. The FEM results agreed well with the experiments. In addition, to enhance our understanding of the behavior of strengthened reinforced concrete column capacity using partial wrapping the effect of changing the spacing between the CFRP sheets and number of layers were examined. The increase number of layers and decrease spacing give a higher ultimate load capacity, and delay the failure.

An experimental study on strengthening of RC column with GFRP

Abstract This study investigates on the introduction of Glass Fiber Reinforced Polymer wrap (GFRP) on the existing concrete element. For this study the concrete specimens of cube, cylinder and column are cast in a concrete grade of M40 and the structural behavior of RC column retrofitted with GFRP wraps are investigated including the Compressive strength, split tensile strength, load deflection behavior, ultimate load carrying capacity etc. The properties of concrete with GFRP sheet wrapping was compared to the conventional concrete. From the study, it was concluded that there is considerable improvements in the load carrying capacity due to GFRP wrapping.