FRP Sheets Research Articles

Discussion of “Dynamic Bond Stress-Slip Relationship between Basalt FRP Sheet and Concrete under Initial Static Loading” by Dejian Shen, Yong Ji, Fenfang Yin, and Jinyang Zhang

Discussion of “Dynamic Bond Stress-Slip Relationship between Basalt FRP Sheet and Concrete under Initial Static Loading” by Dejian Shen, Yong Ji, Fenfang Yin, and Jinyang Zhang

One-Way Slab of Structural Insulated Panel Strengthened with FRP

In order to promote the usage of structural insulated panels (SIP) as floor and roof for residential buildings, the bending capacity of SIP should be improved. In this paper, fiber reinforced polymer sheets were used as strengthening materials. The new variation of SIPs, which is called Fiber Reinforced Structural Insulated Panel (FSIP), was tested in this paper. Five one-way slabs were subjected to uniformly distributed loads till failure. It is observed that the flexural bearing capacity and stiffness of the slabs were affected by the thickness of foam core and the strength of FRP sheet. By strengthened with FRP sheets, the one-way slab of structural insulated panel can be used for floor and roof in residential and light commercial buildings.

Retrofitting of RC girders using pre-stressed CFRP sheets

Pre-stressing of existing structures using steel cables, FRP cables or FRP laminates has been successfully tried in the past. Retrofitting of beams using pre-stressed laminates does not utilize the full strength of the FRP due to de-bonding of the laminates before the fibre fracture. In the present study attempt has been made to overcome this problem by replacing the FRP laminates by the FRP sheets. In the present paper the effect of initial damage level and pre-stress level on strength, stiffness, cracking behaviour and failure mode of girders retrofitted using pre-stressed CFRP sheets has been studied. The results indicate that rehabilitation of initially damaged girders by bonding pre-stressed CFRP sheets improves the flexural behaviour of beams appreciably. However, it has been observed that with increase in pre-stressing force the load carrying capacity of the girders increases up to a particular level up to which the mode of failure is fibre fracture. Thereafter, the mode of failure shifts from fibre fracture to debonding and there is no appreciable increase in load carrying capacity with further increase in pre-stressing force.

친수성 에폭시를 사용하여 FRP 시트로 보강된 슬래브의 휨거동 평가

In this study, the hydrophilic chemical grout using silanol (HCGS) was introduced to overcome the limitations of conventional epoxy resin which have been used for strengthening reinforced concrete (RC) structures. Then, flexural tests on the RC slabs strengthened by FRP sheets were conducted. Three slab specimens were tested in this study; a control specimen with no strengthening, and two specimens strengthened by a typical epoxy resin or HCGS, respectively, as a binder between the slabs and the FRP sheets. In addition, an analytical model was developed to evaluate the flexural behavior of strengthened slab members, considering the horizontal shear force at the interface between concrete slabs and FRP sheets. The analysis results obtained from the proposed model indicated that the strengthened specimens showed fully composite behavior before their flexural failure. Especially, the specimen strengthened by HCGS, which can overcome the limitations of conventional epoxy resin, showed a similar flexural performance with that strengthened by a conventional epoxy resin.

T-section RC beams shear-strengthened with anchored CFRP U-strips

This paper presents the experimental results of a total of 11 full-scale T-section beams which can be divided into two series of specimens with and without steel stirrups. Each series of the beams consisted of one control beam without any strengthening and one beam strengthened with CFRP U-strips only which was used for comparison purpose, with the rest specimens being strengthened with CFRP U-strips anchored with different types of anchoring devices. The discrete FRP U-strips instead of continuous FRP sheets were used in this study, allowing a better observation on the failure process/failure mode of the strengthened beams. A newly patented anchor was used and shown to have excellent performance in improving the shear strengthening effect of FRP. Both fiber anchors and mechanical anchors (including the new anchor) were studied and their performance was compared in terms of failure mode, shear enhancement effect, load-displacement response, and the strain levels in FRP U-strips. A salient feature of the present study is that all the strengthened beams were fully instrumented to measure the strains development in the CFRP U-strips, allowing an accurately quantitative assessment on the shear interaction among different components (i.e. concrete, steel stirrups and FRP) of the shear-strengthened RC beams.

Seismic Retrofit of a Historical Building in Tehran University Museum Using FRP Technology and Steel Jacketing

In this paper evaluation of seismic capacity of a historical building is carried out. It had been used as a national library about 40 years ago. Also, before that, it had been constructed as a part of a Royal complex. This building has been constructed by traditional methods using bricks and mortars. The ceilings system of the structure consists of jack arches. Also, the roof of the building has been constructed with wood trusses. The building does not have any designed lateral bearing system. Lateral resistant of the building is due to masonry walls and due to the brittle and non-ductile performance of it. In secondary cycles of earthquake vibration, it will loose its stiffness and strengthening radically. Also, the building does not have any reliable about integrity. Load bearing systems are not reliable too. In this paper, the evaluation of the resistant capacity of the building is established, and the weak points of the system are distinguished. For some masonry columns some traditional method of steel jacketing is designed, and for increasing the reliability of the columns, FRP sheets are applied. In order to retrofits the walls, FRP sheets are installed on its surfaces; the externally bonded FRP sheets are strengthening the wall against in-plane and out of plane applied horizontal forces. The combination of the steel jacketing and externally bonded FRP sheets is prescribed to achieve an integrated system of the elements.

Improving the Punching Shear Strength of RC Slabs by FRP and Steel Sheets

This paper deals with the modeling of punching shear failure in reinforced concrete slabs using nonlinear finite element analysis. The 3D finite element analyses (FEA) were performed with the appropriate modeling of element size and mesh, and the constitutive modeling of concrete. The FE numerical models are validated by comparing with the experimental results obtained from tested specimens and previous research. One slab served as a control without any modification while three slabs were strengthened. The ultimate behavior of FRP strengthened RC flat slabs under a centrally applied load. Each method of repair or strengthening is reviewed with emphasis on its performance with respect to the application details. The punching shear capacity, stiffness, ductility were investigated. In addition, the analytical results were compared with the predictions using the provision of ACI 318-08. The results showed that for control slab and strengthened specimens an increase varied from 4% to 105% in punching shear capacity is determined.

Fiber-Element Modeling for Seismic Performance of Square RC Bridge Columns Retrofitted with NSM BFRP Bars and/or BFRP Sheet Confinement

This paper presents an analysis of the seismic performance of square RC bridge columns retrofitted with near-surface-mounted (NSM) basalt fiber-reinforced polymer (BFRP) bars and/or BFRP sheet confinement based on fiber element modeling. An axial stress versus loaded-end displacement model of NSM FRP bars, including both elastic elongation and bond-slip effects, is proposed to account for the significant slippage of FRP bars in the plastic hinge region of strengthened columns. The simplified FRP bar model is then converted into the equivalent stress-strain relationship for easy implementation in fiber-based analysis. Moment-curvature analysis is performed based on the proposed FRP bar model, and the analytical moment versus fixed-end rotation relationship of a strengthened column is calculated and assigned to the rotational spring in the fiber element model. The proposed method avoids the nested iterations in sectional analysis that require force equilibrium and deformation compatibility. Comparisons between the numerical simulations and experimental results indicate that the proposed method is appropriate for predicting pushover curves and the hysteretic response of strengthened columns. Furthermore, the mechanism of the hybrid effect of combining NSM FRP bars with externally bonded FRP sheets can be interpreted after the analytical study; that is, confining the column with FRP sheets improves the bond conditions for NSM FRP bars, while the bond-slip effect mitigates the premature fracturing of the FRP bars, leading to more effective utilization of the NSM reinforcement and a more ductile column behavior.

Experimental Study on Fracture Behaviors of Concrete Beams Strengthened with FRP Sheet of Different Width

A total of six beams have been tested to investigate the influence of FRP sheet on the mechanical behavior of concrete beam with different FRP sheet width. In addition, the failure mode of the concrete beam and FRP reinforced concrete beams were also studied by numerical simulation method named Realistic Failure Process Analysis (RFPA). The results indicate that, the loading capacity is increased and maximum deflection of the concrete beam is also increased with the increasing of the FRP sheet width. Moreover, the interfacial debonding easily propagates along the interfacial concrete layer at a load that is below the estimated maximum strength of the FRP-strengthened structure. The maximum strength of the FRP sheet in the experiment was not achieved due to the adhesive layer between the concrete and FRP sheet was not strong enough compared with the numerical simulation result. It showed that the FRP sheet width was considered to be an important factor influence the failure mode and load capacity. So does the interface between the concrete and FRP plate.

Steel Fibres: Effective Way to Prevent Failure of the Concrete Bonded with FRP Sheets

Although the efficiency of steel fibres for improving mechanical properties (cracking resistance and failure toughness) of the concrete has been broadly discussed in the literature, the number of studies dedicated to the fibre effect on structural behaviour of the externally bonded elements is limited. This experimental study investigates the influence of steel fibres on the failure character of concrete elements strengthened with external carbon fibre reinforced polymer sheets. The elements were subjected to different loading conditions. The test data of four ties and eight beams are presented. Different materials were used for the internal bar reinforcement: in addition to the conventional steel, high-grade steel and glass fibre reinforced polymer bars were also considered. The experimental results indicated that the fibres, by significantly increasing the cracking resistance, alter the failure character from splitting of the concrete to the bond loss of the external sheets and thus noticeably increase the load bearing capacity of the elements.

Flexural load-carrying capacity of H-shaped steel beams strengthened with FRP sheet

Flexural load-carrying capacity of H-shaped steel beams strengthened with FRP sheet

Experimental Study on Failure Mode of Concrete Beams Strengthened with FRP Sheet

The failure mode of the FRP reinforced concrete beam with different sheet length was investigated by experiments. The results indicate that, more cracks distributed on the bottom of the beam in the failure process of the FRP reinforced concrete structure. The effect of the FRP sheet length is considered to be an important factor not only to significantly influence the loading capacity but also to control the maximum deflection of the concrete beam. In addition, the loading capacity is increased and maximum deflection of the concrete beam is also increased with the increasing of the FRP sheet length. It showed that FRP strengthened beams failed prematurely in a brittle and sudden manner due to debonding between FRP and concrete substrate and therefore the full strength of the FRP sheet cannot be sufficiently utilized.

A study on prediction method of fatigue life of RC highway bridge slabs strengthened with FRP sheets

A study on prediction method of fatigue life of RC highway bridge slabs strengthened with FRP sheets

Numerical analysis of reinforced concrete beams containing bending and shear opening and strengthened with FRP sheet

Article history: Received 6 September, 2015 Accepted 18 January 2016 Available online 18 January 2016 Various methods are available to reinforce concrete members and structures. Wrapping the concrete beams with composite sheets is one of the suggested methods for increasing the load bearing capacity of concrete beams and specially those containing opening. In this paper, the influence of using two composite sheets reinforced with carbon (CFRP) and glass (GFRP) is studied on increasing the strength of concrete beams having opening. A number of concrete beams with and without openings were modeled in ANSYS and using the nonlinear analyses, the initial cracking load, ultimate failure load, cracking pattern and deflection were determined numerically for each beam. Different wrapping schemes were examined for increasing the load bearing capacity of the opening section and it was concluded that wrapping from both inside and exterior of opening with the mentioned composite patches provide the most enhancement in the opening zone. Also the CFRP patch showed better performance in comparison with the GFRP wrapping. © 2016 Growing Science Ltd. All rights reserved.

RC connections strengthened with FRP sheets using grooves on the surface

In this paper, an experimental study has been conducted on strengthening of reinforced concrete (RC) connections by FRP sheets. The innovation of this research is using narrow grooves on critical regions of connection to increase the adherence of FRP sheets and prevent their early debonding. Therefore, four RC connections were made and tested under a constant axial load on the column and an increasing cyclic load on the beam. The first specimen, as the standard reference specimen, had close tie spacing in ductile regions of beam, column and panel zone based on seismic design provisions, and the second specimen, as the weak reference specimen did not have these conditions in all regions. Two other weak specimens were strengthened using two different strengthening patterns with FRP sheets; one by ordinary surface preparation and the other with surface grooving method for installing FRP sheets on the connection. The results showed that ultimate load and ductility of the weak specimen compared to standard specimen decreased 25% and 17%, respectively. The shear failure and concrete crushing were prevented in the ductile regions of the beam and panel zone in both strengthened specimens. Also, it was observed that early debonding of FRP sheets was prevented in the strengthened connection with grooving pattern and so had desirable ductility and bearing capacity similar to the standard specimen.

Uniaxial Tensile Stress-Strain Relationships of RC Elements Strengthened with FRP Sheets

The shear behavior of fiber-reinforced-polymer–strengthened reinforced concrete (FRP-strengthened RC) members is not fully developed and accurately predicted because of the lack of accurate constitutive laws for the components of the composite members. This paper presents experimental and analytical investigations of tensile stress-strain relationships of concrete and steel in FRP-strengthened RC members. These stress-strain relationships are required in formulations of softened truss models to predict the shear behavior of the FRP-strengthened RC element. Thirteen full-scale FRP-strengthened RC prismatic specimens with different FRP reinforcement ratios, steel reinforcement ratios, and FRP wrapping schemes were tested under uniaxial tension loading. The results show that the tensile behavior of the concrete and steel is altered because of the externally bonded FRP sheets. Modified constitutive laws are proposed and incorporated in the softened membrane model (SMM) to demonstrate through two tests the behavior of FRP-strengthened RC element subjected to pure shear. Moreover, crack spacing and crack width were studied and compared with existing code provisions.

Comparison and Evaluation of Retrofitting Different Modes of Concrete Structures by FRP

Abstract. After recent earthquakes in the majority of seismic areas around the world including our country Iran and considering the irretrievable casualties and economic lost due to these earthquakes, natural catastrophic mitigation committees, research and scientific centers that are responsible for providing structural and seismic codes presented the concept of performance design, study of lifelines and retrofit and rehabilitation of existing and vital structures and the majority of researches in the field of earthquake engineering and structural engineering is focused on retrofit of structures considering economic and feasibility problems. Considering the increasing use of concrete structures in Iran and their substituting for steel structures ( due to weaknesses, constructional problems and defects) and considering the internal defects and failure modes, these structures should be retrofitted against earthquakes or preparations should be provided to decrease and minimize failure modes. concrete frames that consist of beam, column and connection is a essential part of concrete structures. Internal defect of concrete frame results in failure modes such as debonding and delamination in beams, buckling and torsion in column, local crashing in connection. Considering the several benefits of FRP sheets and their increasing use during years, these composites can be used for compressive-tensile, shear, bending, torsional retrofitting as well as for ductility increasing. In this study different types of failure modes of concrete frames and internal defects of them that lead to collapse are investigated. In addition different cases of retrofitting by FRP sheets to prevent failure modes and exciting defect are presented and these cases are compared.

Experimental Study of Circular RC Columns Strengthened with Longitudinal CFRP Composites under Eccentric Loading: Comparative Evaluation of EBR and EBROG Methods

AbstractApplication of carbon fiber-reinforced polymer (CFRP) composites has been promoted successfully for strengthening or repairing concrete structural members. However, if a column member is strengthened with longitudinal FRP sheets in which fibers are laid parallel to the column axis, the FRP composite will soon buckle under compression to ultimately debond off the concrete surface. It is the objective of the current research to investigate the effect of the recently developed grooving method (GM) on cylindrical specimens strengthened with FRP sheets under compressive loading, and to determine whether GM postpones the buckling of FRP sheets and their debonding off the concrete substrate. For the purposes of this study, 35 cylindrical reinforced concrete specimens, 150 mm in diameter and 500 mm in height, were tested under compressive loading with eccentricities of zero, 30, 60, and 90 mm. The specimens were additionally subjected to the four-point flexural bending test to represent infinity eccentric...

Mixed-mode fracture and load misalignment on the assessment of FRP-concrete bond connections

A comprehensive literature review shows considerable dispersion in experimental data concerning the material properties of FRP-concrete bond connections. In pure shear models, the direction of FRP loading is usually assumed to be parallel to the axis of the concrete specimen. However, in practice, it is very difficult to prevent a load misalignment. This fact can have important consequences on the derivation of material properties from experimental data. This is why a parametric study is herein undertaken to thoroughly identify the role of the load misalignment in the behaviour of the connection. It is concluded that the load capacity of the connection significantly decreases in the case of a misaligned load pointing outwards the reinforced surface. It is also found that this effect is less relevant for thick laminates when compared to thin FRP sheets.

Mechanical behavior of FRP sheets reinforced 3D elements printed with cementitious materials

A method to improve the mechanical behavior of 3D-printed elements is presented. 3D-printed elements are orthotropic and weak in their interlayers; thus, FRPs, which are easy-formed, light-weighted and high-strength, are ideal materials to enhance 3D-printed elements. To investigate the reinforcement effect, uniaxial compression tests were conducted on circular column specimens, and four-point flexural tests were conducted on beam specimens. The results indicated that wrapping 3D-printed columns with FRPs changed their failure modes from brittle to ductile, increased the peak loads that they could endure by 1427.2–1792.0% and increased the largest deformations they could achieve by 833.9–1171.3% using different numbers of layers and types of reinforcement. For the 3D-printed beams reinforced with FRPs, the bearing capacities were increased by 179.6–604.5%, and their flexure deflections at their mid-spans were increased by 40.8–225.8%. The failure modes of the 3D-printed beams were affected by numbers of layers and types of reinforcement. Additionally, finite element analyses were conducted to simulate the failure modes of the 3D-printed elements based on the maximum stress criterion. The results showed that the predicted failure locations corresponded with the experimental failure locations observed. According to this study, 3D-printed elements reinforced with FRP sheets showed potential for future development and applications in construction.