Glass Fiber Reinforced Polymer Strengthening Research Articles

An Experimental Study on the Effect of GFRP and CFRP Strengthening on the Static and Dynamic Behavior of R/C Beams Under Progressive Damage

This paper aims to investigate the effect of glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP) strengthening materials on the static and dynamic behavior of reinforced concrete (R/C) beams subjected to progressive damage. Four identical beams, each strengthened with either GFRP or CFRP, are tested under a cyclic quasi-static loading pattern. Impact hammer tests are performed for undamaged states and various damage levels of the beams. The dynamic test data are analyzed using the Enhanced Frequency Domain Decomposition (EFDD) method to estimate the dynamic characteristics of the beams. In this context, the first three vibration modes in both vertical and horizontal directions are considered. Strengthening is applied to both pre-damaged and undamaged beams, enabling a comparison of their performance before and after the strengthening procedure. Beams strengthened with CFRP exhibit a higher load-bearing capacity and stiffness but also fail at lower displacement levels compared to those strengthened with GFRP, which demonstrate more ductile behavior. Furthermore, the modal frequency ratios indicate that the first vibration mode is more sensitive to damage than the second and third modes. This study highlights the effectiveness of both strengthening materials in enhancing the structural performance of both undamaged and damaged beams.

Long-term performance of 15-year-old full-scale RC beams strengthened with EB FRP composites

Despite the well-known advantages of fiber-reinforced polymer (FRP) composites, concerns of the long-term performance of reinforced concrete (RC) structures strengthened with FRP composites have been an obstacle to the growing applications of FRP composites due to the lack of knowledge and scarce test data about long-term performances. Thus, the long-term performance of three 15-year-old full-scale (6.8 m long) RC beams was investigated in this study. A non-strengthened beam was served as a control specimen and two were strengthened with externally bonded (EB) glass FRP (GFRP) laminates. The three beams that had been left outside for exposure to harsh environmental conditions for over 15 years were tested under the typical three-point bending condition. It was found that the EB GFRP-strengthened RC beams were superior to the non-strengthened RC one from the standpoint of load-carrying capacity, initial stiffness, ductility, and toughness (energy absorption capacity), which indicates that the EB GFRP strengthening was still effective even over 15 years. Furthermore, the long-term effective tensile strength reduction of the GFRP composites due to the over 15-year exposure to the harsh environment was calculated to be 26.5 % in comparison with the design tensile strength, which is crucial information for the EB FRP strengthening technique.

Effectiveness of GFRP strengthening of normal and high strength fiber reinforced concrete after exposure to heating and cooling

Damage induced by fire is considered a serious threat to reinforced concrete structures during their useful lifetime. While concrete is a non-flammable material, its exposure to fire affects its stress-strain characteristics and durability. Given that a full replacement and/or demolition option is economically inefficient for fire-damaged structures, a better alternative for lengthening their service life involves repair or strengthening the damaged members. The current testing program primarily investigated the influence of strengthening by glass fiber reinforced polymer (GFRP) sheets on the behavior of heat-damaged plain and fiber-reinforced normal and high strength concretes. Strengthening was considered for concrete cylinders after being exposed to 400 °C and 600 °C temperature and left to cool by air cooling or water quenching. Fiber-reinforced concrete (FRC) mixes were cast with steel, polypropylene, or a hybrid of steel and polypropylene fibers. For plain and various fiber-reinforced normal strength concretes exposed to 400 °C and cooled by ambient air cooling or water quenching, the compressive strength of GFRP confined concrete increased by 39% to 48% and 42% to 56%, respectively (in comparison to the unheated specimens). However, this enhancement was observed to be higher for concretes heated at 600 °C.

Effect of utilizing glass fiber-reinforced polymer on flexural strengthening of RC arches

An experimental study on the flexural behavior of reinforced concrete (RC) arches strengthened with glass fiber-reinforced polymer (GFRP) layers is performed. Totally, 36 specimens including 3 un-strengthened (control) and 33 strengthened RC arches were tested under centrally concentrated point load. The variables of this study were the steel reinforcement ratios, number of GFRP layers, and location and arrangement of GFRP layers. The failure mode, load-displacement response of specimens, crack propagation patterns, and GFRP debonding were examined. The extrados strengthening method was more effective than intrados strengthening approach in improving the failure load and rigidity of the arches. However, applying excessive GFRP layers at extrados can change the failure mode of arches from flexural to shear failure. The dominant failure mode of specimens was flexural and ductile failure due to the formation of five-hinge mechanism. Generally, GFRP strengthening could augment the ultimate load carrying capacity, secant stiffness, and energy absorption capacity of arch specimens by up to about 154, 300, and 93 percent, respectively. Statistical analyses were performed to assess the level of influence of each considered parameters on the behavior of RC arches. Finally, Analytical approach predicts the experimental data on arches with five-hinge failure mechanism satisfactorily.

Shear deformable super-convergent finite element for steel beams strengthened with glass-fiber reinforced polymer (GFRP) plate

The present study investigates the flexural behaviour of steel beams strengthened by adhesively bonding a glass-fiber reinforced polymer (GFRP) plate to one of the flanges. The model captures shear deformation effects and partial interaction between the steel and GFRP owing to the relative flexibility of the adhesive. A general closed form solution is first developed for the governing coupled system of differential equations. The solution is then used to formulate mechanics-based shape functions and develop a finite element with superior convergence characteristics. The model is used to investigate the response of multi-span continuous beams, determine the strength gained by GFRP strengthening, and quantify shear deformation effects on the response of strengthened beams. A technique capturing partial interaction effects is devised to characterize the flexural strength of Class 3 strengthened beams. A classification limit for strengthened Class 3 sections is also proposed within the framework of the Canadian Standard CAN-CSA S16 (2014).

Strengthening of Axially Loaded Reinforced Concrete Rectangular Columns with GFRP Strips

Abstract The present study focuses on studying the load carrying capacity of short reinforced concrete rectangular axially loaded columns with rounded edges strengthened using Glass Fiber Reinforced Polymer (GFRP) bi-directional fabric strips glued with epoxy resin. Columns are wrapped with GFRP in the form of strips of different sizes. The area/material of GFRP wrapped in all patterns for each aspect ratio is the same. The number of FRP layers is varied. Different column sizes with the same cross sectional area and length are considered with aspect ratios 0.5, 0.6, 0.72, 0.84 and 1. Experimental results indicate a significant increase in load carrying capacity of RC rectangular column when strengthened by wrapping GFRP fabric with epoxy resin as glue. Wrapping with 83.3mm strips gave good results than 50mm strips. As number of layers increases load carrying capacity increases up to two layers only, sticking of three layers showed decrease in load carrying capacity. The GFRP strengthening is more effective when the aspect ratio is less.

Lateral torsional buckling of STEEL beams strengthened with GFRP plate

The present study investigates the lateral-torsional buckling of wide flange steel members strengthened by a Glass Fiber Reinforced Polymer (GFRP) plate bonded to one of the flanges through an adhesive layer. A variational formulation and two finite elements are developed for the problem. The formulation captures global and local warping effects, shear deformation due to bending and twist, and partial interaction between the steel and GFRP provided by the flexible layer of adhesive. The destabilizing effects due to strong axis bending, axial force and load height effect are incorporated into the formulation. The first element involves two nodes and 16 buckling degrees of freedom (DOFs) while the second element involves three nodes and 14 DOFs. Comparisons of present model results against those based on 3D finite element analysis based on solid elements demonstrate the ability of the present models to accurately predict the buckling loads and mode shapes at a fraction of the modelling and computational efforts. Practical examples quantify the gain in elastic buckling strength achieved by GFRP strengthening, and characterize the moment gradient factors and load height effects. Elastic buckling interaction diagrams are developed for beam-columns and comparisons are provided to interaction diagrams of un-strengthened beams.

Elastic Analysis of Steel Beams Strengthened with GFRP Plates Including Preexisting Loading Effects

The present study develops a theory for the elastic analysis of a preloaded wide flange steel beam, strengthened with two glass fiber-reinforced polymer (GFRP) plates bonded to both flanges, then subjected to additional loads. Starting with the principle of stationary potential energy, the governing equilibrium equations and corresponding boundary conditions are formulated prior to and after GFRP strengthening. The resulting theory involves four coupled equilibrium equations and 10 boundary conditions. A general closed form solution is then provided for general loading and boundary conditions. Detailed comparisons with three-dimensional finite-element solutions show that the theory provides reliable predictions for the displacements and stresses. A parametric study is then developed to quantify the effects of strengthening, GFRP plate thicknesses, and preexisting loads on the capacity of the strengthened beam.

Experimental and Analytical Modeling of GFRP Strengthened Grouted Mortarless Masonry Prisms

The compressive performance of grouted mortarless masonry prisms strengthened with glass fiber-reinforced polymer (GFRP) composites was investigated in this study. A total of 18 grouted mortarless masonry specimens, i.e., nine strengthened with GFRP (called G-GMM) and nine without GFRP (called GMM), were tested under uniaxial compression. The effect of grout strength on the compressive strength of the prisms was discussed. Moreover, the effect of GFRP on the cracking load, modulus of elasticity, ultimate bearing capacity, failure modes, compressive stress–strain behavior, and deformation behavior of the specimens was analyzed. The test results indicated that GFRP strengthening increased the ratio of initial cracking load and ultimate load bearing capacity of mortarless masonry to a great extent, i.e., the ratio is 50–80% for G-GMM and 40–65% for GMM. In addition, GFRP clearly improved the deformation capability of the GMM. The tested experimental data were in good agreement with the predicted values using classic expressions.

EFFECT OF WET-DRY CYCLING ON BOND BEHAVIOR OF GFRP STRENGTHENED HISTORIC MASONRY STRUCTURES

The objective of this research work is to determine the effect of wet-dry cycling on bond behavior of historic masonry structures strengthened by Glass Fiber Reinforced Polymer (GFRP). Shear bond testing was carried out through total 36 specimens exposed to dry, full moisture or wet-dry cycling conditions. The selected samples were then tested at 0, 30, 60 and 90 days. Post-ageing test was also preceded on total sixty masonry prisms exposed to dry, full moisture or wet-dry cycling conditions. The compressive strengths of selected samples were then tested at 0, 40, 70 and 100 days. The test results showed an obvious decrease of the bond strength between GFRP sheets and bricks in the wet-dry cycling condition. For masonry prisms with or without GFRP strengthening, in the first 40 days, the compressive strength of GFRP bonded prism decreased quickly to the value near that of prism without GFRP. After 40 days the rate of decrease became slow, which means that, sheets retrofitted outside the masonry prisms helped to improve their durability by reducing water permeation.

Behaviour of soft brick masonry small assemblies with and without strengthening under compression loading

A large percentage of the building stock in India and around the world comprises of non-engineered unreinforced masonry (URM) structures. The performance of these buildings in the past has shown that they are highly vulnerable to failure under seismic loads. Very few studies in the past have focused on behaviour of URM structures made of bricks with low strength and stiffness. Hence, the main objective of this study is to improve the understanding of brick masonry made of low strength and low stiffness bricks and assess the effectiveness of various strengthening schemes namely glass fiber reinforced polymer (GFRP) composites and textile reinforced mortar (TRM) systems. The scope of the study includes the following: (i) experimentally characterising the mechanical properties including stress strain curves for bricks, mortar and prisms cast with various mortar composition under pure compression and (ii) to experimentally assess the performance of masonry assemblies such as prisms and triplets strengthened with GFRP and TRM composites. TRM strengthening involves external application of poly-propylene (PP) grid as reinforcement using cement mortar layers as a matrix. GFRP strengthening is found to increase the strength, stiffness and deformational capacity of masonry prisms made with all grades of mortar. TRM strengthening using PP grid increased the strength, stiffness and deformational capacity of prisms made of low strength mortar but resulted in premature failure in prisms made of high mortar strength. In case of shear triplets, both the GFRP and TRM strengthening increased the strength and stiffness.

Axially Loaded Reinforced Concrete Columns with a Square Section Partially Confined by Light GFRP Straps

The study presents the experimental behavior of reinforced concrete columns strengthened externally by transverse glass fiber-reinforced polymer (GFRP) sheets. The columns had a square section and very low concrete strength. The internal steel reinforcement comprised sparse stirrups and longitudinal bars with two different qualities, S220 or B500C. The specimens were lightly confined by full wraps or partial GFRP straps. The straps were placed in between the existing steel stirrups. Three different widths of GFRP straps were examined. A series of plain concrete columns with identical GFRP strengthening was designed in order to assess the partial wrapping effects and compare them with reinforced concrete columns. The columns were subjected to axial compressive monotonic load up to failure. The achieved strength and ductility levels of the strengthened columns suggest that partial wrapping can efficiently upgrade the mechanical behavior of columns with a square section. Fully or partially GFRP wrapped columns with S220 slender bars require relatively higher GFRP strengthening than their counterparts with B500C columns to achieve similar ultimate strains.

Mechanical behavior of concrete filled glass fiber reinforced polymer-steel tube under cyclic loading

The mechanical behavior of concrete-filled glass fiber reinforced polymer (GFRP)-steel tube structures under combined seismic loading is investigated in this study. Four same-sized specimens with different GFRP layout modes were tested by a quasi-static test system. Finite element analysis (FEA) was also undertaken and the results were presented. Results of the numerical simulation compared well with those from experimental tests. Parametric analysis was conducted by using the FE models to evaluate the effects of GFRP thickness, axial compression rate, and cross sectional steel ratio. The experimental and numerical results show that the technique of GFRP strengthening is effective in improving the seismic performance of traditional concrete-filled steel tubes, with variations related to different GFRP layout modes.

GFRP Strengthening and Applications of Unreinforced Masonry wall (UMW)

Abstract Glass Fiber-Reinforced Polymer (GFRP) composites are more and more used in the building trade for the set up of reinforcing and strengthening applications devices. As known, GFRP composites offer higher strength and Young modulus than traditional steel devices. The majority of these buildings were built before any provisions for earthquake loadings were established. The failures and damages reported in recent earthquakes attest to the need for efficient strengthening procedures. The effectiveness of increasing the shear strength of brick masonry coating with epoxy-bonding by Glass Fiber-Reinforced Polymer (GFRP) overlays to the exterior surfaces was evaluated. Out-of-plane failures are common in unreinforced masonry wall (UMW) constructed in seismic regions. This paper deals with the experimental characterization of the mechanical tensile and shear bond behavior of Glass Fiber-Reinforced Polymer (GFRP) sheets externally glued on masonry wall, in terms of load capacity and stress distribution along the bonded length. A combined experimental program was conducted to study the out-of-plane shear behavior of (i) Burned Clay Brick Masonry Walls and (ii) Strengthened with Glass Fiber Reinforced Polymer (GFRP) over the Burned Clay Brick Masonry Walls surface.

Glass Fiber Reinforced Polymer Strengthening and Evaluation of Railroad Bridge Members

In this work, damaged timber railroad bridge stringers and piles were rehabilitated with glass fiber reinforced polymer (GFRP) composites, and tested. Four timber stringers (152 × 203 × 3560 mm) removed from the field were rehabilitated with GFRP spray lay-up and GFRP wrap vacuum bagging methods. GFRP strengthening increased the shear moduli of the two stringers by 41 and 267%. Rehabilitation and load testing were also performed on an open-deck-timber railroad bridge built during the early 1900s on the South Branch Valley Railroad (SBVR) owned by the West Virginia Department of Transportation (WVDOT) in Moorefield, WV, USA. Specifically, field rehabilitation involved repairing piles using GFRP composite wraps and phenolic formaldehyde adhesives. Static and dynamic tests using a 80 ton locomotive showed that the rehabilitated piles and pile cap showed a 43 and 46% strain reduction, respectively. Dynamic load amplification factor was noted to be almost close to a speed of 24 km/h.

Behaviors of Historic Masonry Walls Retrofitted with GFRP under Axial Load

The purpose of this research is to determine the mechanical properties of historic masonry walls retrofitted with Glass Fiber Reinforced Polymer (GFRP) under axial load through experimental method. Four ancient masonry wall specimens were tested under axial load acted at the top surface. Two wall specimens were served as reference without retrofitting. The third wall was retrofitted with GFRP on full surface before loading. The forth wall was strengthened with three GFRP strips before loading. The behaviors of historic masonry walls in Thailand were particular because of their special bond manner and dimension. The tested results demonstrated that the bearing capacity of historic masonry walls was distinctly improved after GFRP strengthening.

Light Vaults With Frescoes or Stuccoes Strengthened by Glass Fiber-Reinforced Polymer (GFRP) — the Role of the Reinforcement on Intrados Strains: First Experimental Data

In many historical buildings built between the 16th and 19th centuries, light vaults are present made by wooden structures and mats of reeds and plaster carrying frescoes or stuccoes of architectural and historical value on the lower surface. Some of these structures today are in a precarious state of conservation, and a wide program of rehabilitation has started, especially with the use of glass fiber-reinforced polymer (GFRP) bandages on the upper surface. This article experimentally evaluates the effect that GFRP extrados bandages may have on the mechanical behavior of this system. In particular, the main issue is to evaluate how GFRP extrados reinforcement affects the intrados surface strains of the fresco or stucco plaster. Results show that GFRP reinforcement changes the mechanical behavior of the original system. In particular, under a particular load condition, intrados plaster surface — and thus frescoes or stuccoes — may deform more in the reinforced case than in the original case. Thus, looking forward to have more experimental results, GFRP strengthening should be carefully applied to this historic system to avoid frescoes and stuccoes on the intrados surface that could more easily crack for loads that were carried with no fissures before GFRP strengthening.

Shear Strengthening Masonry Panels with Sheet Glass-Fiber Reinforced Polymer

This paper investigates strengthening masonry walls using glass-fiber reinforced polymer (GFRP) sheets. An experimental research program was undertaken. Both clay and concrete brick specimens were tested, with and without GFRP strengthening. Single-sided strengthening was considered, as it is often not practicable to apply the reinforcement to both sides of a wall. Static tests were carried out on six masonry panels, under a combination of vertical preload, and in-plane horizontal shear loading. The mechanisms by which load was carried were observed, varying from the initial, uncracked state, to the final, fully cracked state. The results demonstrate that a significant increase of the in-plane shear capacity of masonry can be achieved by bonding GFRP sheets to the surface of masonry walls. The experimental data were used to assess the effectiveness of the GFRP strengthening, and suggestions are made to allow the test results to be used in the design of sheet GFRP strengthening for masonry structures.