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The effects of failure mode and strain conditions of CFRP, concrete and stirrups on the shear capacity of reinforced beams bonded by geopolymer and epoxy are studied. In addition, a prediction model of the ultimate bearing capacity of CFRP-shear-strengthened beams is proposed, which considers adhesive performance parameters adhesive performance parameter ßE and FRP width parameter ßw.

This paper presents an experimental study on ultimate bearing capacity of CFRP-shear-strengthened pre-cracked beams with geopolymer and epoxy resin, which considers parameters such as impregnated adhesives types and CFRP-strengthened scheme.

The failure modes of CFRP-strengthened beams bonded by geopolymer are the combination of the CFRP-concrete interface substrate failure and fracture failure of CFRP, and that of epoxy is the local substrate failures with small area. The ultimate load of CFRP-strengthened beams is directly affected by the failure modes. The ultimate bearing capacity of CFRP-strengthened beams with geopolymer is 91.4% of that of epoxy resin. Compared with ultimate bearing capacity of CFRP-strengthened beams with U-shaped, that of complete-wrapping increases by 2.5%. Moreover, the stirrup peak strain is reduced by more than 30% in CFRP-strengthened beams bonded with geopolymer and epoxy resin in comparison with the unstrengthened beam. The existing prediction model cannot accurately predict the CFRP shear capacity contribution of strengthened beams with different CFRP-strengthened schemes and adhesive properties. The estimated results are much lower than the test data, and the deviation is much larger than 20%.

Geopolymer alternative to epoxy as an adhesive is feasible and effective for CFRP reinforcement. Furthermore, the accuracy is improved by introducing parameters about adhesive properties based on the existing prediction model. The estimated results are in excellent agreement with the test data, and the deviation is controlled within −12.80%, and the model is suitable for predicting the shear capacity of FRP-strengthened beams with ßf = 90° in shear capacity database.

In this paper, to obtain shear and bending performance of carbon fiber-reinforced polymer (CFRP)-strengthened beams bonded by geopolymers, the effects of impregnated adhesive types, strengthened scheme, CFRP layer and pre-cracked width are investigated, and the performance of CFRP-strengthened beams is validated by the establishment of Finite Element Models (FEMs).

In this paper, static loading test and finite element analysis of epoxy-CFRP-strengthened (ECS) and geopolymer-CFRP-strengthened (GCS) were carried out, and the bearing capacity and stiffness were compared, the results show that GCS reinforced concrete (RC) beam is feasible and effective.

The bearing capacity, crack distribution and development, load–deflection curves of GCS RC beams with different pre-crack widths were investigated. The reinforcement effect of geopolymer achieves the same as epoxy, effectively improving the ultimate bearing capacity of the beam, with a maximum increase rate of 28.9%. The failure mode of CFRP is broken in the yield failure stage of GCS RC beam with reasonable strengthening form, and the utilization rate of CFRP is improved. CFRP-strengthened layers, pre-cracked widths significantly affect the mechanical properties, and deformation properties of the strengthened beams.

Compared with ECS RC beams, the bearing capacity and stiffness of GCS RC beams are similar to or even better, indicating that GCS RC beam is feasible and effective. It is a new method for CFRP-strengthened beams, which not only conforms to the concept of national ecological civilization construction, but also provides an economical, environmentally friendly and excellent performance solution for structural reinforcement.

The effects of carbon fiber reinforced polymer (CFRP) reinforcement form, adhesive type and pre-crack width on failure mode, shear capacity, deflection response, CFRP strain response and crack patterns of strengthened specimens were investigated.

This paper presents a geopolymer adhesive that matches the performance requirements of CFRP adhesive, which is applied to pre-cracked beams reinforced with CFRP strips.

For specimens with varying structural properties, two failure modes, the CFRP-concrete interface substrate failure and the fracture failure of CFRP, are observed. Moreover, the shear capacity, ultimate deflection and bending stiffness of the U-shaped CFRP-strengthened beams are enhanced in comparison to the complete-wrapping CFRP-strengthened beams. With an increase in pre-crack width, the increase in shear capacity of RC beams shear-strengthened with CFRP strips is less than that of non-cracked beams, resulting in a limited influence on the stiffness of CFRP-strengthened beams. The comparison of experimental results showed that the proposed finite element model (FEM) effectively evaluated the mechanical characteristics of CFRP-strengthened RC beams.

Taking into consideration the reinforcement effect and the concept of environmental protection, the geopolymer adhesive reinforcement scheme is preferable to applying epoxy resin to the CFRP-strengthened RC beams.

This paper aims to evaluate fire resistance of carbon fiber-reinforced polymer (CFRP)-strengthened concrete slabs in two forms of unprotected and protected against fire.

To achieve the objective, an unstrengthened and two CFRP-strengthened concrete slabs were first subjected to increasing gravity loading until failure. Subsequently, the unstrengthened concrete slab was placed on a furnace and was subjected to a constant service gravity load and then, the temperature of the furnace was increased according to a standard temperature–time curve until the failure of the slab occurred. This slab was strengthened by CFRP with two different amounts and then, in two cases of unprotected and protected against fire, was tested in accordance with the aforementioned method.

The gravity test results revealed that CFRP strips bonded to concrete slabs increased the load-bearing capacity considerably. So, this method can be suitable for flexural strengthening of concrete slabs. The fire test results showed that because of more load-bearing capacity and subsequently increase in service gravity load, the strengthened concrete slab failed in a short time due to the lack of CFRP resistance against fire. By contrast, the protected specimens resisted the fire in a considerable time. In addition, it was revealed that details of fire protective coating had an important effect on fire resistance duration.

It is notable that in the literature, there is a lack of data on the fire endurance of fiber-reinforced polymer-strengthened concrete slabs alone without any fire protection system. Furthermore, the applicability and effectiveness of a new kind of spray mineral fire protective coatings was evaluated.

This paper presents an experimental investigation on the effect of indirect fire on axially loaded CFRP retrofitted columns. Tests were performed on 28 half scale CFRP retrofitted columns, coated with proposed heat insulating covers (two specimens were cast for each type). Twelve materials - known for their low coefficients of thermal conductivities- were used in the mixes of these protective covers on CFRP. Commercially available fire protective material was subjected to the same tests also. All protected columns were exposed to elevated temperature tests following ASTM (E119-95a) fire test curve 900°C for half an hour, while an axial load is applied to simulate working load conditions.

Thermal distribution results along columns cross sections- for different insulating covers- at different stages of the fire test- were compared to evaluate the efficiency of the proposed heat protecting mixes.

Post fire tests, all columns were loaded up to failure. Hence, the reduction in their load capacity due to fire exposure is calculated.

Throughout these comparisons, it is concluded that the most of the suggested insulating mixes acted efficiently to protect CFRP strengthened sections during fire. Temperature was significantly reduced at CFRP level -below the protective covers. It ranged between 100-120°C, for most of the mixes. Thus, enhancing significantly the fire resistance for CFRP retrofitted columns. Reduction in failure load capacity -due to fire exposure- was limited to 10-20% for most of the protected specimens. Even for the insulating mixes that resulted in lowest - post fire- residual strength, CFRP layer was highly damaged, but the reinforced concrete section was slightly affected, which still makes the damage repairable.

The use of recycled coarse aggregate in concrete structures promotes environmental sustainability; however, performance of these structures might be negatively impacted when it is used as a replacement to traditional aggregate. This paper aims to simulate recycled concrete beams strengthened with carbon fiber-reinforced polymer (CFRP), to advance the modeling and use of recycled concrete structures.

To investigate the performance of beams with recycled coarse aggregate concrete (RCAC), finite element models (FEMs) were developed to simulate 12 preloaded RCAC beams, strengthened with two CFRP strengthening schemes. Details of the modeling are provided including the material models, boundary conditions, applied loads, analysis solver, mesh analysis and computational efficiency.

Using FEM, a parametric study was carried out to assess the influence of CFRP thickness on the strengthening efficiency. The FEM provided results in good agreement with those from the experiments with differences and standard deviation not exceeding 11.1% and 3.1%, respectively. It was found that increasing the CFRP laminate thickness improved the load-carrying capacity of the strengthened beams.

The developed models simulate the preloading and loading up to failure with/without CFRP strengthening for the investigated beams. Moreover, the models were validated against the experimental results of 12 beams in terms of crack pattern as well as load, deflection and strain.

In this paper, the effects of geopolymer adhesive, the number of CFRP layers and the width of pre-crack on the flexural performance of reinforced concrete beams strengthened with CFRP were studied, and the flexural capacity of strengthened beams was calculated theoretically.

Reinforced concrete beams were strengthened with CFRP by geopolymer adhesive, and flexural load tests were conducted to observe the reinforcement effect. Based on the method of calculating the flexural capacity of reinforced concrete beams, a theoretical calculation model on the flexural capacity of reinforced concrete beams strengthened with geopolymer adhesive bonded CFRP was established.

The test data shown the flexural capacity of epoxy resin adhesive CFRP strengthened reinforced concrete beams is 7.76% higher than that geopolymer adhesive is used. The flexural capacity of reinforced concrete beams strengthened with three layers of CFRP is 1.86% higher than that two layers are adopted. The mean ratio of the test data and the calculation results of the flexural capacity is 0.973, and the mean square error is 0.008. It can be seen that the test data are in good agreement with the theoretical value.

This paper provides data support for the popularization and application of the new environment-friendly reinforcement technology, contributes to the cause of environmental protection, and provides a new method for strengthening reinforced concrete beams.

The main aim of this study is to examine the behavior of reinforced concrete short columns strengthened using longitudinal near surface mounted (NSM)-carbon fiber reinforced polymer (CFRP) strips.

A full 3D-finite element (FE) model was developed using ABAQUS in order to conduct the analysis. The model is first validated based on experimental data available in the literature, and then the effect of concrete compressive strength, number of CFRP strips that are used and the spacing between them were taken in consideration for both concentric and eccentric loading cases. The parametric study specimens were divided into three groups. The first group consisted of unstrengthened columns and served as control specimens. The second group consisted of columns strengthened by longitudinal CFRP strips at two opposite column faces.

The results of this study are used to develop interaction diagrams for CFRP-strengthened short columns and to develop best-fit equations to estimate the nominal axial load and moment capacities for these strengthened columns. The results showed that the specimens that were strengthened using more longitudinal CFRP strips showed a significant increase in axial load capacity and a significant improvement in the interaction diagram, especially at large load eccentricity values. This result can be justified by the fact that longitudinal strips effectively resist the bending moment that is generated due to eccentric loading. Generally, the process of strengthening using longitudinal strips only has a reasonable effect and it can be typically considered an excellent choice considering the economic aspect when the budget of strengthening is limited.

This research aims at studying the performance of strengthened rectangular reinforced concrete short columns with CFRP strips using FE method, developing interaction diagrams of strengthened columns in order to investigate the effect of different parameters such as compressive strength (20, 30 and 40 MPa), number of CFRP strips (1, 2, 3 and 4) and the spacing between CFRP strips in terms of the ratio of CFRP center point distance to column outside dimension ratio (0.60, 0.70 and 0.80) on the behavior of strengthened RC columns and improving empirical formulas to predict the nominal axial load and moment capacities of strengthened RC columns. These parameters that directly affect short column load carrying capacity are presented in ACI-318 (2014).

This paper aims to develop a non-linear finite element model predicting the response of externally strengthened beams under a three-point flexure test.

The ANSYS software is used for modeling. SOILD65, LINK180, SHELL181 and SOLID185 elements are used, respectively, to model concrete, steel reinforcement, polymer and steel plate support. A parametric study was carried out. The effects of compressive strength, Young’s modulus, layers number and carbon fiber-reinforced polymer thickness on beam behavior are analyzed. A comparative study between the non-linear finite element and analytical models, including the ACI 440.2 R-08 model, and experimental data is also carried out.

A comparative study of the non-linear finite element results with analytical models, including the ACI 440.2 R-08 model and experimental data for different parameters, shows that the strengthened beams possessed better resistance to cracks. In general, the finite element model’s results are in good agreement with the experimental test data.

This model will predict the strengthened beams behavior and can describe the beams physical conditions, yielding the results that can be interpreted in the structural study context without using a laboratory testing.

On the basis of the results, a good match is found between the model results and experimental data at all stages of loading the tested samples. Crack models obtained in the non-linear finite element model in the beams are also presented. The submitted finite element model can be used to predict the behavior of the reinforced concrete beam. Also, the comparative study between an analytical model proposed by of current code of ACI 440.2 R-08 and finite element analysis is investigated.

This paper aims to present performance comparison of fiber sheet-strengthened reinforced concrete (RC) beams bonded with geopolymer and epoxy resin under ambient and fire conditions.

This study presents experimental results of bending tests at ambient temperature and fire resistance tests on two control beams and eight fiber sheet-strengthened RC beams. The test variables include fiber sheet type (carbon fiber [CF] and basalt fiber [BF] sheet), number of layers of fiber sheet (one and two layers) and adhesive agent type (geopolymers and epoxy resin). Data generated from these tests were used to evaluate and compare the strengthening effectiveness of CF-reinforced polymer (CFRP) and CF-reinforced geopolymer (CFRG) at ambient temperature and under fire exposure conditions.

Test results clearly show that the CFRG system can provide good strengthening effectiveness on RC beams at ambient temperature, as the CFRP system, owing to excellent bond properties of geopolymers. Although geopolymers possess better bonding properties at high temperature than organic matrix, the strengthened beams bonded with geopolymer do not exhibit better fire resistance than that those bonded with epoxy resin, owing to early falling-off of fire insulation. Thus, in CFRG-strengthened beams, relevant measures are to be taken to minimize falling-off of fire insulation to achieve good fire resistance.

The presented results are from unique fire tests and provide valuable insight (and information) on the performance of fiber sheet-strengthened RC beams bonded with geopolymer and epoxy resin under ambient and fire conditions.