Search results
1 – 10 of 478Ala Taleb Obaidat, Yasmeen Taleb Obaidat and Ahmed Ashteyat
In this experimental investigation, the behavior of strengthened/repaired heat-damaged one-way self-compacted concrete (SCC) slabs with opening utilizing…
Abstract
Purpose
In this experimental investigation, the behavior of strengthened/repaired heat-damaged one-way self-compacted concrete (SCC) slabs with opening utilizing near-surface-mounted-carbon fiber reinforced polymers (NSM-CFRP) strips was explored.
Design/methodology/approach
CFRP strip configurations, number of strips and inclination were all investigated in this study. For three hours, slabs were exposed to temperatures of 23°C and 500°C. Four-point load was applied to control slabs, enhanced slabs and repaired slabs.
Findings
The results indicate that exposing the slabs to high temperatures reduces their load capability. The number of strips and angle of inclination around the slab opening have a considerable impact on the performance of the strengthened and/or repaired slabs, according to the experimental results. The load capacity, toughness and ductility index of a strengthened and/or repaired slab with opening increase as the number of CFRP strips increases by 143.8–150.5%, 137.3–149.9% and 122.3–124.5%, respectively. The use of NSM strips around the opening with zero inclination showed higher load compared to the NSM strips around the opening with other angles.
Originality/value
It is frequently important to construct openings in the slabs for ventilation, electrical supply, and other purposes. Making openings in slabs might affect the structure’s performance since the concrete and reinforcing would be cut off. SCC is a new type of concrete mixture that can fill in all the voids in the formwork with its own weight without the help of external vibration. As a result, it is necessary to reinforce the slab under flexure and increase the flexural strength of the SCC slab. Therefore, this work investigates the effect of using NSM-CFRP strip on the behavior of one way SCC slabs that have been heat-damaged.
Details
Keywords
Ahmed Ashteyat, Ala Taleb Obaidat, Yasmeen Taleb Obeidat and Ahmad Bani Awwad
The paper aims to introduces an experimental work to investigate the torsional behavior of reinforced concrete (RC) beams strengthened by near-surface mounted (NSM) carbon…
Abstract
Purpose
The paper aims to introduces an experimental work to investigate the torsional behavior of reinforced concrete (RC) beams strengthened by near-surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) ropes.
Design/methodology/approach
In this research, nine rectangular RC beams of 250 mm × 300 mm cross-section and 1,600 mm in length were constructed and tested considering the studied parameters. These parameters include the length of the CFRP rope, the orientation of the CFRP rope, the arrangement of longitudinal and the scheme of NSM-CFRP ropes.
Findings
In comparison to control specimens, the results demonstrate a considerable improvement in the torsional response of RC beams strengthened with the CFRP rope. Additionally, specimens strengthened with 90° vertical ropes increase torsional moment capacity more efficiently than specimens strengthened with 45° inclined ropes since the stress concentration leads to premature debonding of the CFRP rope. Whereas RC beams' ability to withstand torsional moments is reduced as the distance between reinforcing CFRP ropes is increased. According to test results, adding CFRP ropes to RC beams' bottoms had a slightly positive impact on torsional response.
Originality/value
This paper fulfills an identified need to study how the using of the CFRP rope is effective in strengthening RC beam subjected to torsion moment.
Details
Keywords
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
Details
Keywords
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/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.
Details
Keywords
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…
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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%.
Originality/value
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.
Details
Keywords
Kristina Bliznakova, Zacharias Kamarianakis, Aris Dermitzakis, Zhivko Bliznakov, Ivan Buliev and Nicolas Pallikarakis
The purpose of this paper is to develop a realistic computational model of carbon fibre reinforced polymer (CFRP) structures dedicated for in-silico investigations of the use of…
Abstract
Purpose
The purpose of this paper is to develop a realistic computational model of carbon fibre reinforced polymer (CFRP) structures dedicated for in-silico investigations of the use of X-ray-based imaging techniques as non-destructive testing (NDT) of CFRP parts.
Design/methodology/approach
CFRPs contain layers of carbon-fibres bundles within resin. Bundles’ orientation in the different layers is arranged with respect to each other at a well-defined primary direction. In the model, the bundle was simulated as a circular cylinder. The resulted model is a stack of layers of unidirectional bundles having orientation of 0°/90°/45°/−45°. Two CFRP structures were modelled: a flat CFRP part and a real shaped CFRP clip. A porous layer and non-carbon fibres were inserted within each model, respectively. X-ray projection images were generated with a dedicated simulation programme. Three setups were investigated: radiography, tomosynthesis and cone-beam CT (CBCT).
Findings
Results showed that porosity and non-carbon fibres were visible with all X-ray-based techniques. Tomosynthesis and CBCT, however, provide higher quality image of defects.
Practical implications
The CFRP computational model is a valuable tool in design, testing and optimization phase of X-ray-based imaging techniques for use in NDT of composite materials. Simulated images are generated within a short time; thus results from virtual optimization and testing are obtained very fast and at low cost.
Originality/value
An innovative computational model of CFRP structures, dedicated for X-ray imaging simulations, has been developed. The model is characterized by simplicity in its creation and realistic visual appearance of the produced X-ray images.
Details
Keywords
Saeed Bakhtiyari, Arsalan Kalali, Leila Taghi Akbari and Farhang Farahbod
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.
Abstract
Purpose
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.
Design/methodology/approach
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.
Findings
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.
Originality/value
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.
Details
Keywords
To make full use of the tensile strength of near surface mounting (NSM) pasted carbon fiber reinforced plastics (CFRP) strips and further increase the flexural bearing capacity…
Abstract
Purpose
To make full use of the tensile strength of near surface mounting (NSM) pasted carbon fiber reinforced plastics (CFRP) strips and further increase the flexural bearing capacity and flexibility of reinforced concrete (RC) beams, a new composite reinforcement method using ultra-high performance concrete (UHPC) layer in the compression zone of RC beams is submitted based on embedding CFRP strips in the tension zone of RC beams. This paper aims to discuss the aforementioned points.
Design/methodology/approach
The experimental beam was simulated by ABAQUS, and compared with the experimental results, the validity of the finite element model was verified. On this basis, the reinforced RC beam is used as the control beam, and parameters such as the CFRP strip number, UHPC layer thickness, steel bar ratio and concrete strength are studied through the verified model. In addition, the numerical calculation results of yield strength, ultimate strength, failure deflection and flexibility are also given.
Findings
The flexural bearing capacity of RC beams supported by the new method is 132.3% higher than that of unreinforced beams, and 7.8% higher than that of RC beams supported only with CFRP strips. The deflection flexibility coefficient of the new reinforced RC beam is 8.06, which is higher than that of the unreinforced beam and the reinforced concrete beam with only CFRP strips embedded in the tension zone.
Originality/value
In this paper, a new reinforcement method is submitted, and the effects of various parameters on the ultimate bearing capacity and flexibility of reinforced RC beams are analyzed by the finite element numerical simulation. Finally, the effectiveness of the new method is verified by the analytical formula.
Details
Keywords
Jiawei Wang, Yanmin Jia, Guanhua Zhang, Jigang Han and Jinliang Liu
Most existing studies are confined to model beam tests, which cannot reflect the actual strengthening effects provided by prestressed carbon-fiber-reinforced polymer (CFRP) plates…
Abstract
Purpose
Most existing studies are confined to model beam tests, which cannot reflect the actual strengthening effects provided by prestressed carbon-fiber-reinforced polymer (CFRP) plates to existing bridges. Hence, the actual capacity for strengthening existing bridges with prestressed CFRP plates is becoming an important concern for researchers. The paper aims to discuss these issues.
Design/methodology/approach
Static load tests of in-service prestressed concrete hollow slabs before and after strengthening are conducted. Based on the results of the tests, the failure characteristics, failure mechanism and bending performance of the slabs are compared and analyzed. Nonlinear finite element method is also used to calculate the flexural strength of the strengthened beams prestressed with CFRP plates.
Findings
Test results show that prestressed CFRP plate strengthening technology changes the failure mode of hollow slabs, delays the development of deflection and cracks, raises cracking and ultimate load-carrying capacity and remarkably improves mechanical behavior of the slab. In addition, the nonlinear finite element analyses are in good agreement with the test results.
Originality/value
Strengthening with prestressed CFRP plates has greater advantages compared to traditional CFRP plate strengthening technology and improves active material utilization. The presented finite element method can be applied in the flexural response calculations of strengthened beams prestressed with CFRP plates. The research results provide technical basis for maintenance and reinforcement design of existing bridges.
Details
Keywords
Kexin Zhang, Dachao Li, Xinyuan Shen, Wenyu Hou, Yanfeng Li and Xingwei Xue
This paper aims to describe carbon fiber reinforced plastics (CFRP) bars as a way to strengthen a 40-year-old stone arch bridge. To investigate effectiveness of the strengthening…
Abstract
Purpose
This paper aims to describe carbon fiber reinforced plastics (CFRP) bars as a way to strengthen a 40-year-old stone arch bridge. To investigate effectiveness of the strengthening method, fielding-load tests were carried out before and after strengthening.
Design/methodology/approach
High-strength CFRP bars with minor radius, high tensile strain and good corrosion resistance were used in this reinforcement. The construction process for strengthening with CFRP bars – including CFRP bars cutting, crack grouting, original structural surface treatment, implant drilling, CFRP bars installation and pouring mortar – was described. Ultimate bearing capacity of the bridge after strengthening was discussed.
Findings
The results of concrete stress and deflection show that the strength and stiffness of the strengthened bridge are improved. The strengthened way with CFRP bars is feasible and effective.
Originality/value
This paper describes CFRP bars as a way to strengthen a 40-year-old stone arch bridge.
Details