Bonded Glass Fiber-reinforced Polymer Research Articles

Fracture research of adhesive-bonded joints for GFRP laminates under mixed-mode loading condition

Abstract The mixed-mode fracture characterization of adhesively bonded glass fiber-reinforced polymer (GFRP) plate joints is studied based on theoretical and experimental techniques. An improved beam model is used to estimate the compliance and the mixed-mode energy release rate (ERR) for GFRP four-point mixed-mode bending specimens. In this model, the deformation of the upper and lower GFRP plates is mutually independent, and the deformable adhesive is considered to satisfy the displacement compatibility conditions on the bonding interface. The explicit theoretical solutions of the compliance and ERR using the compliance method are reduced. The present theoretical solutions fit well with the finite element solutions by comparison with the rigid joint model. From the critical loads in experiment, the variation in fracture toughness on mixed-mode I/II has been determined by modifying the stiffness of the composite GFRP/GFRP substrate.

Experimental and numerical investigation of short GFRP- reinforced steel tubular short columns

Abstract This study presents the experimental and analytical modelling of externally bonded glass fibre-reinforced polymer (GFRP) sheets for strengthening circular steel tubular short columns. The GFRP sheets are easy to handle due to the lightweight property and the high-strength can provide a degree of restraint to delay buckling of the thin steel wall. Four short columns of cold-formed steel circular hollow section (CHS) were experimentally tested. One column is conventional (without GFRP wrap) and other 3 columns are externally bonded unidirectional (hoop) GFRP sheets which are varying with numbers of layers (1, 2 and 3 layers). In addition to the experimental studies, finite element analysis was also carried out using ABAQUS software. The experimental result shows that the steel tube is strengthened by GFRP sheets and enhances the axial section capacity. The load carrying capacity of externally bonded GFRP column increases about 17%−49% on comparison with the column without confinement. The study also concluded that the column externally warped with 3 layers of GFRP sheet is found to be optimum and it attains maximum load caring capacity. The prediction of analytical results has been found to be in good correlation with the experimented results.

Experimental investigation of fatigue behavior for adhesively-bonded GFRP/steel joints

The fatigue behavior of an adhesively bonded glass fiber-reinforced polymer (GFRP)/steel double-lap joint (DLJ) under cyclic tensile loading with load ratio R = 0.1 was experimentally studied. Results in terms of failure mode, F-N curve, stiffness degradation law, crack initiation and propagation laws were obtained. Linear and nonlinear models of stiffness degradation and a mathematical model of the crack growth rate were developed for the adhesive GFRP/steel DLJ under fatigue loading. The fatigue performance of adhesive GFRP/steel DLJ was compared with that of adhesive GFRP/GFRP DLJ to identify the differences between these behaviors. The results demonstrated that the stiffness degradation law of the adhesive GFRP/steel DLJ can be objectively and accurately characterized by the nonlinear stiffness degradation model in terms of the equivalent shear stiffness. The crack initiation life and the ratio between the crack initiation life and fatigue life increased with the deceasing maximum applied load. The fatigue life of the GFRP/steel DLJ was more sensitive to the variation in the maximum applied load compared with that of the GFRP/GFRP DLJ. Moreover, the decaying rate of stiffness and the interfacial crack propagation rate for the GFRP/steel DLJ under fatigue loading were larger than those for the GFRP/GFRP DLJ.

Shear Strengthening of RC Deep Beam Using Externally Bonded GFRP Fabrics

This work presents the experimental investigation of RC deep beams wrapped with externally bonded Glass Fibre Reinforced Polymer (GFRP) fabrics in order to study the Load versus deflection behavior, cracking pattern, failure modes and ultimate shear strength. A total number of five deep beams have been casted, which is designed with conventional steel reinforcement as per IS: 456 (Indian standard plain and reinforced concrete—code for practice, Bureau of Indian Standards, New Delhi, 2000). The spans to depth ratio for all RC deep beams have been kept less than 2 as per the above specification. Out of five RC deep beams, one without retrofitting serves as a reference beam and the rest four have been wrapped with GFRP fabrics in multiple layers and tested with two point loading condition. The first cracking load, ultimate load and the shear contribution of GFRP to the deep beams have been observed. A critical discussion is made with respect to the enhancement of the strength, behaviour and performance of retrofitted deep beams in comparison to the deep beam without GFRP in order to explore the potential use of GFRP for strengthening the RC deep beams. Test results have demonstrated that the deep beams retrofitted with GFRP shows a slower development of the diagonal cracks and improves shear carrying capacity of the RC deep beam. A comparative study of the experimental results with the theoretical ones predicted by various researchers available in the literatures has also been presented. It is observed that the ultimate load of the beams retrofitted with GFRP fabrics increases with increase of number of GFRP layers up to a specific number of layers, i.e. 3 layers, beyond which it decreases.

Structural behaviour of HFRC beams retrofitted for shear using GFRP laminates

This paper summarizes the experimental study of the shear behaviour of Hybrid Fibre Reinforced Concrete (HFRC) beams retrofitted by using externally bonded Glass Fibre Reinforced Polymer (GFRP) laminates. To attain the set-out objectives of the present investigation, steel fibre of 1% and polypropylene fibre of 0.30% was used for hybrid steel-polypropylene fibre reinforced concrete: whereas for hybrid glass-polypropylene fibre reinforced concrete, glass fibre by 0.03% and polypropylene fibre of 0.03% by volume of concrete was used. In this study, 9 numbers of beams were cast and tested into three groups (Group I, II & III). Each group containing 3 numbers of beams, out of which one serve as a control beam or a hybrid steel-polypropylene fibre reinforced concrete beam or a hybrid glass - polypropylene fibre reinforced concrete beam and the remaining two beams were preloaded until shear cracks appeared up to 75% of ultimate load and then preloaded beams (damaged beams) were retrofitted with GFRP laminates at shear zone in the form of strips, as one beam in vertical position and another beam in inclined position to restrict the shear cracks. Finally, the retrofitted beams were loaded until failure and test results were compared. The experimental tests have been conducted to investigate various parameters of structural performance, such as load carrying capacity, crack pattern and failure modes, load-deflection responses and ductility relations. The test results revealed that beams retrofitted using GFRP laminates considerably increased the load carrying capacity. In addition, it was found that beams retrofitted with inclined strip offers superior performance than vertical one. Comparing the test results, it was observed that hybrid steel-polypropylene fibre reinforced concrete beam retrofitted with GFRP laminates showed enhanced behaviour as compared to other tested beams.

Experimental and Theoretical Study of Sandwich Panels with Steel Facesheets and GFRP Core

This study presented a new form of composite sandwich panels, with steel plates as facesheets and bonded glass fiber-reinforced polymer (GFRP) pultruded hollow square tubes as core. In this novel panel, GFRP and steel were optimally combined to obtain high bending stiffness, strength, and good ductility. Four-point bending test was implemented to analyze the distribution of the stress, strain, mid-span deflection, and the ultimate failure mode. A section transformation method was used to evaluate the stress and the mid-span deflection of the sandwich panels. The theoretical values, experimental results, and FEM simulation values are compared and appeared to be in good agreement. The influence of thickness of steel facesheet on mid-span deflection and stress was simulated. The results showed that the mid-span deflection and stress decreased and the decent speed was getting smaller as the thickness of steel facesheet increases. A most effective thickness of steel facesheet was advised.

On the flexural behaviour of GFRP beams obtained by bonding simple panels: An experimental investigation

This paper presents some experimental results dealing with the mechanical performance of composite beams obtained by bonding Glass Fibre Reinforced Polymer (GFRP) rectangular pultruded panels by means of an epoxy structural adhesive. The flexural response of these bonded beams was compared with those obtained by the pultrusion process with the same geometrical and material properties. As a matter of fact, no significant loss of performance emerged in terms of failure load; moreover, an increase of pre-failure stiffness was observed. This result may allow us to consider bonded GFRP beams as a viable simplification within the field of composite structures.

Earthquake Performance of Two Vintage URM Buildings Retrofitted Using Surface Bonded GFRP: Case Study

AbstractAs part of a seismic retrofit scheme, surface bonded glass fiber-reinforced polymer (GFRP) fabric was applied to two unreinforced masonry (URM) buildings located in Christchurch, New Zealand. The unreinforced stone masonry of Christchurch Girls’ High School (GHS) and the unreinforced clay brick masonry Shirley Community Centre were retrofitted using surface bonded GFRP in 2007 and 2009, respectively. Much of the knowledge on the seismic performance of GFRP retrofitted URM was previously assimilated from laboratory-based experimental studies with controlled environments and loading schemes. The 2010/2011 Canterbury earthquake sequence provided a rare opportunity to evaluate the GFRP retrofit applied to two vintage URM buildings and to document its performance when subjected to actual design-level earthquake-induced shaking. Both GFRP retrofits were found to be successful in preserving architectural features within the buildings as well as maintaining the structural integrity of the URM walls. Succe...

Experimental and numerical study of adhesively bonded glass fibre-reinforced polymer – to-steel double-shear lap splices

This study investigates, experimentally and using finite element analysis, the adhesive bond between glass fibre-reinforced polymer (GFRP) and steel. Seventeen double-shear lap-splice were fabricated and tested in tension. The results show that the methacrylate adhesive used had higher bond strengths than the epoxy adhesive. A finite element model for selected test specimens was developed to analyze the stress within the adhesive. The model was verified by comparison with strain data from the shear lap-splice tests. The model was used to determine the maximum principal stress in the epoxy adhesive and the maximum shear strain in the methacrylate adhesive at failure, and thus quantify the characteristic strength of these adhesives. It was shown that the ductility of the methacrylate adhesive allowed it to yield at locations of stress concentrations, providing higher splice capacity, despite having a lower nominal shear strength as compared with the epoxy adhesive.

Shear strengthening of polystyrene aggregate concrete beams with near surface mounted GFRP bars

The application of near surface mounted (NSM) fibre reinforced polymer (FRP) bars is emerging as an innovative and promising technology for increasing flexural and shear strength of deficient reinforced concrete members. In order for this technique to perform effectively, a series of experimental works have been carried out to characterise the flexural and shear behaviour of reinforced concrete members strengthened with NSM FRP bars. The latter is the focus of this paper, and some of the preliminary results are included. A total of eight beams were loaded under a two-point symmetrical bending test. The parameters examined were the type and inclination of NSM bars and the type of adhesives employed. Characterisation of the tested beams, including mode of failure and load–deflection response, is presented and discussed in this paper. The results of this investigation showed that the NSM bonded glass FRP bars can be used to significantly increase both shear and flexural stiffness and the ultimate moment capacity of the beams, with an efficiency that varies depending on the tested variables.

Effects of Variation of Axial Load and Bidirectional Loading on Seismic Performance of GFRP Retrofitted Reinforced Concrete Exterior Beam-Column Joints

Most of the experimental studies available in literature on the seismic assessment and retrofit of existing, poorly detailed, reinforced concrete (RC) beam-column joints, typical of pre-1970s construction practice, have concentrated on the two-dimensional (2D) response, using unidirectional cyclic loading testing protocol and constant axial load. Even more limited information is available on the performance of exterior (corner) three-dimensional (3D) RC beam-column joints with substandard detailing subjected to bidirectional loading regime. In this study, the results of a comprehensive experimental program is presented, aiming to show the effects of varying axial and bidirectional loading on the seismic performance of deficient exterior RC beam-column joints before and after retrofit. Ten exterior beam-column joint subassemblies are tested, including four as-built specimens and six retrofitted specimens using externally bonded glass fiber-reinforced polymer (GFRP) sheets. Test results are herein presented...

Fracture Evaluation of GFRP—Concrete Interfaces for Freeze—Thaw and Wet-Dry Cycling

Externally bonded glass fiber-reinforced polymer (GFRP) fabrics are being increasingly used for seismic retrofit and rehabilitation of concrete structures due to their high strength to weight ratio and low cost in comparison to carbon and aramid fibers. However, previous studies have shown that glass fibers are vulnerable to attack caused by harsh environmental weathering agents such as freezing—thawing, wetting—drying, and exposure to alkaline and acidic environments. Concerned with durability, this study is based on a fracture mechanics approach to evaluate the interface durability of GFRP bonded to normal concrete (NC) and high-performance concrete (HPC), subjected to two types of weathering protocols: (1) freeze—thaw cycling under calcium chloride, which is used to simulate the deleterious effect of the de-icing agents used on highways in wintry weather; and (2) alternate wetting and drying in a sodium-hydroxide solution, which is used to simulate the naturally occurring alkalinity due to the presence of concrete pore water, that can cause degradation due to a combination of mechanisms such as leaching and pitting of the glass fibers, and cracking and spalling of the resin matrix. Durability of the GFRP—concrete interface is characterized based on the critical strain energy release rate, under Mode-I loading, and weight and strain measurements. Unconditioned companion specimens are fractured alongside their aged counterparts to provide baseline-feedback and also enable comparative analysis of the fracture surfaces. Considerable degradation of the interface bond integrity is found to have resulted with increasing cycling period.

RETROFIT OF EXISTING BUILDINGS FOR EARTHQUAKE RESISTANCE

Buildings sited on soft soils are sometimes subjected to tremors due to earthquakes occurring some 400 to 700 kilometers away as a result of the amplifying effect of soft soils on low-frequency, long-distance waves. This study focuses on the seismic vulnerability of existing reinforced concrete (RC) buildings in Singapore that are designed primarily for gravity loads, and examines the use of externally bonded glass fiber-reinforced polymer (FRP) systems in retrofitting these buildings to resist lateral forces due to seismic action. Two case studies were considered: (1) a four-story frame building, representing typical low-rise buildings; and (2) a 25-story shear wall-frame building, representing typical high-rise buildings. Pushover tests were carried out correspondingly on 1/2-scale sub-frames and 1/5-scale shear walls. The one-and-a-half bay, two-storey frame specimens represent the critical part of the low-rise building while the I-shaped wall specimens represent the lower critical 2.6 stories of the high-rise building. Test results revealed a strong column–weak beam failure mechanism for both the un-retrofitted and retrofitted frames. The retrofitted frame was 30 percent higher in ultimate strength but 12 percent lesser in ultimate drift ratio compared to the un-retrofitted frame. For the wall specimens, sudden failure of the un-retrofitted shear wall was observed at the base of the side walls due to shear. Failure of the retrofitted wall was however more ductile with FRP debonding, followed by concrete crushing and FRP rupture at the compressive base of the side wall. The ultimate load capacity and lateral displacement of the retrofitted wall increased respectively by 45 and 66 percent.