No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Externally post-tensioned carbon FRP bar system for deflection control
Abstract
Externally post-tensioned steel tendons have long been an attractive option for increasing the design loads or correcting strength and serviceability problems in bridge and building structures. More recently, alternative solutions have been developed and implemented that use straight post-tensioned carbon fiber reinforced polymer (CFRP) tendons, ideally enlisting their high-strength to failure, small relaxation, corrosion resistance, and light weight. In this paper, a novel CFRP system for external post-tensioning is presented. The solution consists of unbonded CFRP bars connected to dead- and live-end steel anchors by means of couplers that allow the bar to develop the full tensile strength. Intermediate deviators can be extended vertically to impart additional post-tensioning (PT) force and achieve a profiled bar configuration. The required uplift forces for deflection control of a flexural member are provided by modifying the number, position and extended height of the deviators, similarly to commercially available systems that use steel wire strands. The structural efficiency of such approach in controlling deflection is analyzed and discussed for single-span one-way members on the basis of a parametric study that considers the influence of member geometry, flexural stiffness, boundary conditions, and PT system layout. A design example is also provided.
... The major problem encountered by using FRP tendons for prestressing is how to provide a proper, reliable anchorage. 30,37 Susceptibility of composite tendons to transversal point loads and the possibility of interlaminar shear cause that the design of an anchorage system which can sustain the full static and fatigue strength is challenging. Furthermore, galvanic corrosion which occurs on the interface between carbon fibres and steel elements is problematic as well. ...
... An example of external prestressing of concrete beams with composite tendons is described by Matta et al. 37 as a better solution than strengthening with FRP strips in terms of deflection control. In a trial installation, CFRP tendons were anchored on the soffit of a reinforced concrete slab with one dead-end and one live-end anchorage using stainless steel swage couplers. ...
... Authors provided an efficiency analysis based on parametric study (where the influence of geometry, stiffness, boundary conditions, and posttensioning layout were considered) and a description of a design approach for such type of strengthening. 37 ...
... Traditionally, high-tensile steel bars and steel strands are often utilized in the field of external prestressing with many antirust technologies to keep away their corruption from outside condition. Whereas in this paper, CFRP (Carbon Fibre Reinforced Plastic) tendons were selected due to their being lighter in weight, more resistant to corrosion [1] and higher in tensile capacity than steel bars [2]. However, the challenge in the use of CFRP lies in its performance differently from traditional prestressed tendons in transverse mechanical properties which typically behave two orders of magnitude smaller than that in the longitudinal direction of the tendons [1].To overcome the shortcoming, this paper proposed a developed external prestressing technique with convenient implementation in construction sites. ...
... Whereas in this paper, CFRP (Carbon Fibre Reinforced Plastic) tendons were selected due to their being lighter in weight, more resistant to corrosion [1] and higher in tensile capacity than steel bars [2]. However, the challenge in the use of CFRP lies in its performance differently from traditional prestressed tendons in transverse mechanical properties which typically behave two orders of magnitude smaller than that in the longitudinal direction of the tendons [1].To overcome the shortcoming, this paper proposed a developed external prestressing technique with convenient implementation in construction sites. This technique is also able to avoid mounting the external tendons with anchorages too close to the two ends of the beam which is the conventional tenique [1,3,4,5]. ...
... However, the challenge in the use of CFRP lies in its performance differently from traditional prestressed tendons in transverse mechanical properties which typically behave two orders of magnitude smaller than that in the longitudinal direction of the tendons [1].To overcome the shortcoming, this paper proposed a developed external prestressing technique with convenient implementation in construction sites. This technique is also able to avoid mounting the external tendons with anchorages too close to the two ends of the beam which is the conventional tenique [1,3,4,5]. ...
With the rapid development of heavy-load railway system, it has become a key facility in the freight transportation. The structural elements in this system, in particular for bridge beams, experienced vibration and damage when subjected to long-term moving load during service. The external prestressing technique is widely used in railway system due to its significant improvement in bearing capacity of damaged bridge beams. This paper adopted an innovative external prestressing method to study the flexural behavior of externally prestressed CFRP (Carbon Fibre Reinforced Plastic) tendons strengthened T-shaped section RC (reinforced concrete) beams under static loads. The influences of concrete strength, reinforcement ratio of non-prestressed tensile steel bars and tension control stress of CFRP tendons on the flexural behaviour in terms of bearing capacity and ductility were examined. The test results revealed that, compared with un-strengthened RC beams, the specimens externally strengthened with prestressed CFRP tendons showed a better performance in the flexural capacity, as well as overall stiffness and ductility. For the above mentioned factors, the flexural bearing capacity appears to be further improved as the reinforcement ratio of non-prestressed tensile bars and the tension control stress of CFRP tendons increase. However, a worse ductility on the strengthened RC beams is observed with the increase in the concrete strength, the reinforcement ratio of non-prestressed tensile bars and the tension control stress of CFRP tendons. Finally, the calculation formula for flexural capacity of externally prestressed CFRP tendons strengthened T-beams was established, which can provide a reference for practical engineering design.
... ，并将 研究成果成功应用于实际工程 [8][9][10][11] 。 体外预应力加固混凝土梁设计中，需要合理计 算其在使用荷载下的挠度，以满足正常使用极限状 态的要求。但从既有研究成果来看，对体外预应力 混凝土梁在使用荷载下的挠度计算研究较少 [9] ，且 主要集中在数值分析方面 [10,12] ，而 CFRP 筋体外预 应力加固混凝土梁的挠度计算方法尚未见诸报道。 目前，体内无粘结预应力混凝土梁的短期挠度计算 方法主要有两种 [13] ：双直线法和有效惯性矩法。我 国现行《无粘结预应力混凝土结构技术规程》(JGJ 92-2004) [14] 中的短期刚度计算公式以双直线法为基 础，通过不同参数下的数学变换来考虑不同因素对 无粘结预应力混凝土结构短期挠度的影响。与双直 线法相比，有效刚度法概念明确、表达式简单， ACI440.4R-04 [15] 数 Ω 的值为 0.6。 ...
... ，并将 研究成果成功应用于实际工程 [8][9][10][11] 。 体外预应力加固混凝土梁设计中，需要合理计 算其在使用荷载下的挠度，以满足正常使用极限状 态的要求。但从既有研究成果来看，对体外预应力 混凝土梁在使用荷载下的挠度计算研究较少 [9] ，且 主要集中在数值分析方面 [10,12] ，而 CFRP 筋体外预 应力加固混凝土梁的挠度计算方法尚未见诸报道。 目前，体内无粘结预应力混凝土梁的短期挠度计算 方法主要有两种 [13] ：双直线法和有效惯性矩法。我 国现行《无粘结预应力混凝土结构技术规程》(JGJ 92-2004) [14] 中的短期刚度计算公式以双直线法为基 础，通过不同参数下的数学变换来考虑不同因素对 无粘结预应力混凝土结构短期挠度的影响。与双直 线法相比，有效刚度法概念明确、表达式简单， ACI440.4R-04 [15] 数 Ω 的值为 0.6。 ...
A static test and theoretical analysis were conducted to investigate the service performance of concrete T-shaped beams strengthened with externally CFRP tendons under short-term loading, and the calculation method of short-term deflection was explored. The test results indicate that the load-midspan deflection curves of strengthened beams can be simplified as a tri-segmentsegment line. The average strains of concrete and CFRP tendon of strengthened beams basically vary linearly over the depth of the beams at the midspan section before cracking. The average strain of CFRP tendon is obviously less than the strain of bottom concrete after cracking. Based on the test results, the reduction coefficient of cracking stiffness and the bonding characteristic coefficient of CFRP tendons were calculated, and the calculation formula for the short-term deflection on beams strengthened with externally prestressed CFRP tendons was proposed in term of an effective inertia moment method considering the influence of second order effects, and it can provide a reference for practical engineering design.
... Matta et al. [94] presented a novel external post-tensioning system for CFRP tendons. The basic arrangement of this EPT system contains a set of two pultruded CFRP bar assemblies, each with a live and dead end. ...
... Prestressing systems for externally post-tensioning CFRP & Steel (Rods)[94]. ...
Compared to prestressed steel, prestressed FRPs exhibited good structural properties. CFRPs are suitable prestress materials, it covers all the advantages of other FRPs. The NSM technique offers a shield to the prestressed material against the environment. The 40% prestressing in NSM CFRP rod can give maximum flexural strength of the beam. Among different CFRP shapes, CFRP rods are the most effective type under prestressing. Keywords: Strengthening Composite RC beam Flexure Anchorage Fiber reinforced polymer Prestressing Near surface mounted a b s t r a c t The use of steel and fiber reinforced polymers (FRPs) for strengthening RC beams can significantly improve the flexural strength, fatigue life and the serviceability of the beams compared to un-strengthened beams. Prestressing materials enable the material to become more efficient since a greater portion of its tensile capacity is employed. Investigations have shown that prestressed FRPs are effective materials for strengthening deteriorated structures. This paper presents a comprehensive review on the flexural behavior of strengthened RC beams using prestressed FRPs. The review covers the near surface mounted (NSM), externally bonded reinforcement (EBR) and externally post-tensioned techniques (EPT) and the corresponding advantages and disadvantages are highlighted. Anchorage systems and the effect of pre-stressing levels on the ductility, deformability and bond behavior of prestressed FRPs are also addressed. Recommendations for the future research are also presented.
... Matta et al. [94] presented a novel external post-tensioning system for CFRP tendons. The basic arrangement of this EPT system contains a set of two pultruded CFRP bar assemblies, each with a live and dead end. ...
... Prestressing systems for externally post-tensioning CFRP & Steel (Rods)[94]. ...
The use of steel and fiber reinforced polymers (FRPs) for strengthening RC beams can significantly improve the flexural strength, fatigue life and the serviceability of the beams compared to un-strengthened beams. Prestressing materials enable the material to become more efficient since a greater portion of its tensile capacity is employed. Investigations have shown that prestressed FRPs are effective materials for strengthening deteriorated structures. This paper presents a comprehensive review on the flexural behavior of strengthened RC beams using prestressed FRPs. The review covers the near surface mounted (NSM), externally bonded reinforcement (EBR) and externally post-tensioned techniques (EPT) and the corresponding advantages and disadvantages are highlighted. Anchorage systems and the effect of prestressing levels on the ductility, deformability and bond behavior of prestressed FRPs are also addressed. Recommendations for the future research are also presented.
... A schematic of the proposed method is shown in Fig. 1b. The method is classified as an external unbonded posttensioned prestressing technique, which usually employs FRP bars or tendons as prestressing materials [37][38][39]. In the proposed method, both ends of the CFRP plate are fixed on the soffit of the beam, and the tensile stress in the CFRP plate is applied by driving the deviator away from the beam. ...
This paper proposes a novel strengthening method for reinforced concrete (RC) beams using prestressed carbon fibre-reinforced polymer (CFRP) plates. In the proposed method, the CFRP plate is stressed by adjusting the position of the mid-span deviators. The strengthening process is fast and easy to apply because there is no need for hydraulic jacks or adhesives. To investigate the behaviour of the strengthened RC beams, a series of tests were conducted on both intact and damaged beams with different strengthening configurations, and the full range behaviours of the beams are reported in detail. According to the test results, the maximum stress of the CFRP plate reached 1500 MPa, and the beam strength was enhanced up to 43%. Some of the strengthening schemes achieved good ductility. As a result, the proposed strengthening method is found to be effective and can be further developed into a pseudoplastic CFRP strengthening system.
... Since no permanent anchorage is installed at the bar end that found in the post-tensioned structures [13][14][15], the anchoring of pretensioned bar is thereby achieved by the bond at bar-concrete interface. The bond stress activated by releasing the bar diminishes from the maximum value at the extreme end of PPC member to zero over a finite distance, which is termed as the "transfer length" [16]. ...
This study presents an experimental investigation on the fatigue performance of CFRP reinforced pretensioned prestressed beams. A total of 10 specimens were designed and tested under monotonic or fatigue conditions. The investigated variables included the prestressing level, fatigue load range, and the absence or presence of novel additional aluminum alloy ribs (ARs) anchorage. Specimens using a high prestressing level or subjected to a low fatigue load range would have a reduced deflection and crack width development compared to those in their counterparts. In addition, the fatigue loading was found to cause cumulative bond damage of pretensioned FRP bar to concrete and finally led to an uncontrollable slippage failure of the beam. Such bond issue was demonstrated to have been avoided by using the ARs anchorage at beam ends. The applicability of three theoretical models proposed for steel reinforced beams to predicting the deflection of CFRP reinforced pretensioned prestressed beams under fatigue loading were evaluated, and CEB-FIP model was found to be the most suitable one to describe the deflection development of the tested specimens.
... However, the desired effect was not achieved, owing to the anchorage. Matta et al. [133] controlled the vertical deflection of a bridge with a reinforcement of external posttensioned CFRP tendons (the CFRP bar with a diameter of 12.7 mm was arranged under the beam). Macdougall et al. [134] successfully replaced corroded posttensioned unbonded prestressed steel tendons with CFRP tendons via the posttensioned method in a parking garage in Toronto. ...
In recent years, fiber-reinforced polymer (FRP) composites have been widely used as a new type of high-performance material in concrete structures. FRP composites have the advantages of high strength, light weight, and corrosion resistance. Based on existing studies in the literature, this paper reviews the development and applications of FRP materials for the strengthening and rehabilitation of bridge structures. The types and properties of FRP composites are summarized, and the applications and development of FRP sheets, FRP bars, FRP grids, and prestressed FRP tendons for bridge structures are discussed. Different types of FRP composites result in different failure characteristics and bearing capacities. Moreover, this paper covers the FRP strengthening methods and the response properties of the flexural performance, bonding performance, and ductility. Significant conclusions regarding the strengthening/repair of bridge structures with FRP composites are presented. The review details the current state of knowledge and research on strengthening bridge structures with FRP composites and is helpful for better understanding and establishing design criteria.
... Also, pre-stressing can be more effectively applied in the NSM system than in the EB system. Research is being performed on external bond systems so that the material properties of FRPs can be applied to building structures [4][5][6]. However, external bond systems exhibit disadvantage with respect to bond failure, vehicle accident, and fire resistance. ...
... Verankerungen, die durch Aufpressen funktionieren, sind Matta [173] und Mönig [191]. ...
... Miere, (1987) [6], and Fabio M. Et al.(2006) [3] developed and highlighted the advantages of using the FRP for strengthening the existing structures. He showed that, retrofitting by Carbon Fiber reinforced plastics (CFRP) strips is less expensive than the technique of external steel plate bonding especially if ease of handling is a dominant cost factor. ...
This study presents an experimental and analytical investigation and comparison of the structural behavior of externally bonded different method of strengthening R.C. beams (steel plates, steel angels , steel Channels and Carbon fiber Sheets (CFRP) .) For the experimental investigation, five R.C. beams were tested, one of them was tested without strengthening to act as the control beam. The second beam was strengthened using steel plate externally bonded to the bottom surface of the beam. The third beam was strengthened using two steel angels. The forth beam was strengthened using steel Channel, while the last beam was strengthened using CFRP laminate. The test results show that, the beam strengthened with CFRP laminate recorded a slightly higher failure load compared to the beam strengthened with steel plate. While the beam strengthened with steel plate recorded a higher cracking load and less deflections, reinforcement bar strains, concrete strains and crack widths compared to the CFRP laminate strengthened beam. Results also showed that the beam strengthened with CFRP laminate failed by premature concrete cover separation failure. The theoretical study using the Finite Element Method (FEM) package (ANSYS11) shows a good agreement with the experimental study with the modeling KEYWORDS Flexure behavior , Strengthened beams, Externally Bonded, CFRP .
... Moreover, because of their low weight, they are easy to use in the field in a broad range of applications. Research is being performed on external bond systems so that the material properties of FRPs can be applied to building structures [4][5][6][7]. However, external bond systems exhibit weaknesses with respect to fire resistance, vehicle collision and bond failure. ...
... Accepted Article redistribution and ductility performance were highlighted in the works by Bonaldo (2008) and Glaucia and Joaquim (2013). Dalfré (Matta, et al., 2009;Fang, et al., 2008). However, it was established that without a special treatment, the CFRP bars in the anchor could be easily crushed and that the rupture of the CFRP bars often happened on the turning point (Fang, 2014;Mahroug et al., 2014). ...
An experimental programme was proposed and carried out to assess the effectiveness of the mineral‐based composite (MBC) technique for the flexural strengthening of negative moment regions in continuous reinforced concrete slabs. In addition to the testing of the two reference specimens, the experimental programme included the testing of nine continuous RC slab specimens with different strengthening techniques, namely, using ordinary steel bars and MBC material. This experimental programme was conducted to study the failure modes, the load‐deflection behaviour and the failure loads.
Furthermore, we present and describe a comparative study between the two strengthening techniques, namely, steel reinforcing bars with MBC or steel bars with epoxy mortar. Based on the experimental results presented, both strengthening techniques for continuous slabs are evidently efficient. In this study the measured results for the average crack spacing were compared with the limits stipulated in CEB‐FIP code 1990 and the failure load calculations were extended with an analytical approach based on the ultimate theory for the failure load calculation. In conclusion, the results obtained from the analytical model are in agreement with the experimental results.
... (2) -Temperatura ambiente entre os -20ºC e os +40ºC (Matta, Nanni, et al. 2007), (Matta, Aquino, et al. 2008) ...
This work presents the various systems of external post tensioning applicable to reinforcement of
structures and describes all the components that comprise them. Some nationally and internationally
structures are presented, where external post tensioning was applied. A practical work was carried out
also, which involves the strengthening of a flat slab with external post tensioning. The application of
external post tensioning served to recover part of the deformation on the slab and therefore stabilizing
it.
The slab was analyzed by the limit state of deformation, in order to determine the best layout of the
external post- tensioning. It was also verified the security against the ultimate limit states. These
analyzes were performed using a commercial finite element program.
Some components of external post tensioning were designed, such as passive anchors, the deviation
saddles and anchor bolts. The application of external post tensioning was accompanied on site, and
described the various stages of the construction process and outcome of reinforcement.
... Naser, (2012) studied the application of external prestressing tendons for strengthening of existing bridges which has been used in many countries since the 1950s and has been found to provide an efficient and economical solution in a wide range of the bridge types and conditions.Shear strengthening, flexural strengtheningand torsional strengthening of reinforcement concrete beams using composite materials were studied by several researchers and investigators at several institutions. Especially, studying the strengthening of structural elements using EPT was studied by Atta, (2012), El-Shafiey and Atta, (2012), Jeyasehar, (2008), Matta and et al, (2009) and Algorafi and et al, (2010). The reasons for the lack of research in this area include the specialized nature of the problem and the difficulties in conducting realistic tests and representative analyses. ...
This paper investigate the behavior of reinforced concrete box beam under pure torsion. The box beam was strengthened experimentally with external prestressing technique (EPT) using two different directions horizontally and vertically. Ten strengthened box beams, with and without web opening, were tested. The study emphasizes prestressing direction and transverse opening dimensions. The failure modes, torsional capacities, rotation, stress in external tendon and strain in internal reinforcements were studied in details. The experimental results indicated that the contribution of EPT strengthening using the horizontal and vertical directions to torsional capacity of box beam, with and without opening, is significant with ratios ranged between31% to 58% respectively. The contribution was enhanced using the vertical direction. It was found that the presence of transverse openings decrease the torsional capacity. While EPT strengthening at the opening increased torsional capacity compared to beams without opening. A computing procedure is presented to predict the torsional capacities of RC beams under torsion. The calculated results fit well with the experimental one.
... While external FRP tendon members are expected to be more and more popular, the behaviour of this new-type system has yet to be fully understood, as few studies in this area have been available so far [9][10][11]. In this study, a numerical work is conducted to examine the short-term behaviour of external FRP tendon beams (time-dependent effects such as prestress losses and concrete creep are not considered). ...
... Miere, (1987) [6], and Fabio M. Et al.(2006) [3] developed and highlighted the advantages of using the FRP for strengthening the existing structures. He showed that, retrofitting by Carbon Fiber reinforced plastics (CFRP) strips is less expensive than the technique of external steel plate bonding especially if ease of handling is a dominant cost factor. ...
This study presents an experimental and analytical investigation and comparison of the structural behavior of externally bonded different method of strengthening R.C. beams (steel plates, steel angels , steel Channels and Carbon fiber Sheets (CFRP) .) For the experimental investigation, five R.C. beams were tested, one of them was tested without strengthening to act as the control beam. The second beam was strengthened using steel plate externally bonded to the bottom surface of the beam . The third beam was strengthened using two steel angels. The forth beam was strengthened using steel Channel, while the last beam was strengthened using CFRP laminate. The test results show that, the beam strengthened with CFRP laminate recorded a slightly higher failure load compared to the beam strengthened with steel plate. While the beam strengthened with steel plate recorded a higher cracking load and less deflections, reinforcement bar strains, concrete strains and crack widths compared to the CFRP laminate strengthened beam. Results also showed that the beam strengthened with CFRP laminate failed by premature concrete cover separation failure. The theoretical study using the Finite Element Method (FEM) package ( ANSYS11 ) shows a good agreement with the experimental study with the modeling
... In addition, The Near-Surface Mounted (NSM-CFRP) strengthening technique has been used in the recent years in order to increase the flexural strength [8,9]. Recently, several attempts have deployed CFRP bar as external post-tensioning tendons in order to strengthen structures [10,11]. However, without special treatment, the CFRP bar in the anchor will be crushed effortlessly and also, the rupture of the CFRP bar often happens on the turning point [11]. ...
Pre-cast and cured Engineered Cementitious Composites (ECC) strips were placed in the tension cover zone of one-way reinforced concrete (RC) slabs beside the main steel reinforcement. Using pre-cast and cured ECC mitigates issues associated with volumetric changes associated with the ECC material. In order to assess the structural performance enhancement of the new hybrid system, four point bending tests were performed on two different sizes of RC slabs. The tested slabs were geometrically similar in thickness but and differed in their width and span. Small, 300 mm wide × 900 mm long, slabs were strengthened using one 150 × 500 × 20 mm ECC strip. Larger, 300 × 2000 mm slabs were strengthened with two 150 × 1600 × 20 mm ECC strips. A small amount of conventional reinforcing steel was provided inside the ECC strips in order to enhance the strain hardening behavior of the ECC strengthening strip, and thereby increase its efficiency. The structural evaluation of the slabs considered crack width and spacing, deflection at the service load level, and ultimate capacity and ductility. Test results showed that the ECC strips enhanced the structural performance of the slabs at both service and ultimate limit states. Providing additional internal reinforcement by a reinforcing ratio of 1.88% exhibited outstanding performance in terms of decreased crack width, better crack distribution, and improved capacity and ductility compared to control slabs without internal ECC strips.
This list contains the journal articles related to FRP-strengthened metallic structures, in seven categories:
A. Bond
B. Flexural Strengthening
C. Compression Strengthening and Stability
D. Dynamic and Cyclic Loading
E. Durability
F. Applications and Design Guides
G. Structural Health Monitoring.
The list is currently updated to 2021, and it will be renewed annually.
To download the PDF file, please click "More" on the upper-right corner.
The flexural properties of concrete beams strengthened by external prestressing carbon fibre-reinforced plastic (CFRP) tendons are studied through static loading tests. The loading processes, failure modes, right-sectional strain features, and ductility of the strengthened concrete beams are analysed, permitting comparisons of the influences of the bending angle of the external CFRP tendons, the strength grade of the concrete, the reinforcement ratio of the internal non-prestressing steel, and the loading strengthening level of the external prestressing CFRP tendons on the flexural properties of the beams. Test results show that the external prestressing CFRP tendons can improve the anti-cracking properties, stiffness, and flexural properties of concrete beams. The bending angle of the external CFRP tendons should not exceed 10°, while the reinforcement ratio and loading strength have obvious effects on the flexural properties of the beams they reinforce; conversely, the strength grade of the concrete has relatively little influence on the flexural properties. Based on the results, a bending bearing capacity formula for concrete beams strengthened with external prestressing CFRP tendons is determined according to the design theory of externally prestressed concrete structures; this formula provides the accuracy required for construction and therefore it can be used as a reference for practical engineering.
Strengthening as well as correcting unsightly deflections of reinforced concrete (RC) beam may be accomplished by retrofitting. An innovative way to do this retrofitting that is proposed in this study utilizes turnbuckle to apply external post-tensioning. This Turnbuckle External Post-Tensioning (T-EPT) was experimentally proven to improve the serviceability and load carrying capacity of reinforced concrete beams. The T-EPT system comprises a braced steel frame and a turnbuckle mechanism to provide the prestressing force. To further develop the T-EPT, this research aims to develop a numerical scheme to analyze the structural performance of reinforced concrete beams with this kind of retrofitting. The fiber method analysis was used as the numerical scheme. The fiber method is a simplified finite element method that is used in this study to predict the elastic and inelastic behavior of a reinforced concrete beam. With this, parametric study was conducted so that the effective setup of doing the T-EPT retrofitting may be determined. Different T-EPT configurations were investigated and their effectiveness evaluated. Overall, the T-EPT was effective in improving the serviceability condition and load carrying capacity of reinforced concrete beam.
In this study, a static experiment on RC T-beams strengthened with externally prestressed CFRP tendons was carried out. The flexural behaviors of strengthened beams, including loading process, failure mode, ductility and stress increment of CFRP tendon, were studied. The influences of tension control stress, the reinforcement ratio of non-prestressed rebar, and concrete strength grade on their flexural behaviors were analyzed. The test results show that flexural bearing capacity, overall stiffness and ultimate deformability of strengthened beams may be improved more significantly than unstrengthened beams, and the development of cracks can be restrained by external prestressing CFRP tendons. It was observed that the tension control stress and the reinforcement ratio of non-prestressed rebar have remarkable influences on the flexural bearing capacity of strengthened beams, but the influence due to concrete strength grade is much less. Based on test results and existing theory of externally prestressed concrete structure, the calculation formula for flexural bearing capacity of concrete T-beams strengthened by external prestressing CFRP tendons was established, which may provide a reference for practical engineering design.
A full-scale experimental study was undertaken to observe and assess the behavior of continuous concrete beams with external prestressed bars. Three beams - a control beam and two comparable beams strengthened using external prestressed bars - were tested in two-point loading of the interior span of three continuous spans. The diameters of the external prestressed bars were 18 and 22 mm (0.71 and 0.87 in.), respectively. For the strengthened beams, V-shaped profiles were used with a deviator located at the middle bottom of the interior span, and the effective prestress was 45% of the yield strength of the external steel bars. Test results indicate that the external prestressing increased the load-carrying capacity by about 25% and the flexural stiffness by about 15%. An analytical model developed by the authors was applied that uses the beam collapse mechanism, plastic hinge length, and deformation of external bars depending on the beam deformation at the deviator point. Predictions of the nominal strength and the corresponding external bar stress compared closely to the test results.
This paper shows the test results of continuous reinforced concrete beams with external post-tensioning rods. Six three-span beams were prepared and tested to fail. Three beams were designed to have flexure-dominating behavior and the others to have shear-critical behavior. In each group, one beam without external post-tensioning rods was designated as a control beam and two beams had the external post-tensioning rods of 18 mm or 22 mm diameter. External post-tensioning rods were installed within an interior span of 6000 mm. They show V-shaped configuration because two anchorages were located at the top of interior supports and a saddle pin at mid-span was installed at the bottom of the beam. Test results show that the load and shear capacities of strengthened beams were increased when compared with the control beam. Additionally, the measured shear strength was compared with the strength predicted by ACI 318-11 code equations. The detailed ACI 318-11 equation predicted the measured shear strength and failure location of the continuous beam reasonably well.
An efficient frame finite element (FE) is developed and applied for nonlinear analysis of reinforced concrete beams flexurally strengthened with externally bonded fibre reinforced polymer (FRP) strips/plates. The developed nonlinear model is able to capture different failure modes associated with concrete crushing and cracking, yielding of steel, FRP rupture and intermediate crack-induced debonding of FRP sheets/plates. The element is formulated using force interpolation concept and a simple approach based on application of discrete springs and linear interpolation of bond forces along the element axis is adopted to take account of shear-slip. The developed formulation and analytical tool are employed to predict the loading capacity and the load-deflection response of reinforced concrete beams strengthened with FRP and the numerically simulated responses agree well with the corresponding experimental results. The major features of this frame element are its simplicity and efficiency compared with more complex FEs which makes it a suitable tool for practical use in design-oriented parametric studies.
Due to inductive impedance caused by steel meshes in traditional reinforced ballastless track slabs, the electric properties, primarily rail resistance and inductance, of the track circuit are affected by electromagnetic induction between the slabs and the electric current in the rail. This problem results in poor transmission performance through the track circuit. Insulating heat-shrinkable sleeves between the steel meshes have been used to improve the insulation capability of steel meshes in slabs; however, they reduce the bonding performance between the steel bars and concrete. Because of the highly insulating properties of fiber reinforced polymer (FRP) and steel-fiber reinforced polymer composite bar (SFCB), these composite materials have shown promise to overcome the insulation problem. In the study reported in this paper, single and double layer meshes and ballastless track slabs were manufactured and tested for the first time. In the research reported herein, basalt fiber reinforced polymer (BFRP) and SFCB were used in meshes and slabs, respectively. The electric properties of the rail affected by these meshes and slabs were investigated and compared with steel meshes and ordinary reinforced ballastless track slabs (RC). As the test results demonstrated, the signal frequency and distance between the slabs or meshes and the rail had a significant impact on the electric properties of the rail. Furthermore, the variation in rail resistance induced by the slabs or meshes increased drastically, while the change in rail inductance increment varied slowly. BFRP and SFCB used as transverse reinforcement of slabs or meshes reduced the variation in the electric properties of the rail. BFRP reinforced ballastless track slabs had the highest insulating performance, while those with SFCB demonstrated the second highest performance.
High tensile strength, good resistance to degradation and creep, low weight and, to some extent, the ability to change the modulus of elasticity are some of the advantages of using prestressed, unidirectional FRP (Fibre Reinforced Polymer) tendon systems. Bonded and non-bonded versions of these systems have been investigated over the last three decades with results showing that prestressing systems can be very efficient when the FRP properties are properly exploited. However, there are often concerns as to how to exploit those properties to the full and how to achieve reliable anchorage with such systems. This is especially important in external post-tensioned tendon systems, where the anchorage points are exposed to the full load throughout the life span of the structure. Consequently, there are large requirements related to the long-term capacity and fatigue resistance of such systems. Several anchorage systems for use with Aramid, Glass and Carbon FRP tendons have been proposed over the last two decades. Each system is usually tailored to a particular type of tendon. This paper presents a brief overview of bonded anchorage applications while the primary literature review discusses three methods of mechanical anchorage: spike, wedge and clamping. Some proposals for future research are suggested. In general, the systems investigated showed inconsistent results with a small difference between achieving either a successful or an unsuccessful anchorage. These inconsistencies seem to be due to the brittleness of the tendons, low strength perpendicular to the fibre direction and insufficient stress transfer in the anchorage/tendon interface. As a result, anchorage failure modes tend to be excessive principal stresses, local crushing and interfacial slippage (abrasive wear), all of which are difficult to predict.
The deterioration attributable to corrosion of concrete structures reinforced with unbonded, posttensioned tendons is a costly problem. Recent research has shown composite materials such as fiber-reinforced polymers (FRP) to be suitable alternatives to steel because they provide similar strength without susceptibility to electrochemical corrosion. Carbon-FRP (CFRP) in particular has great promise for prestressed applications because it shows resistance to corrosion in environments that might be encountered in concrete and experiences less relaxation than steel. This paper outlines the testing and implementation of a posttensioned system that uses CFRP tendons to replace corroded, unbonded posttensioned steel tendons. This system was then implemented in a parking garage in downtown Toronto. To the writers' knowledge, this is the first example of an unbonded, posttensioned tendon replacement using FRP tendons. The system used split-wedge anchors designed specifically for CFRP tendons. The dead end was anchored by directly bonding the tendon to the concrete slab. The CFRP tendon was successfully inserted in the opening created by the removal of the corroded tendon and stressed. Although the system was shown to be feasible, the current anchorage configuration results in load losses of up to 60% during the transfer. Changing the orientation of the anchor was found to reduce the load loss to an acceptable range of 1-9%. DOI: 10.1061/(ASCE)CF.1943-5509.0000146. (C) 2011 American Society of Civil Engineers.
Carbon fiber reinforced polymer (CFRP) bars were prestressed for the structural strengthening of 8 T-shaped reinforced concrete
(RC) beams of a 21-year-old bridge in China. The ultimate bearing capacity of the existing bridge after retrofit was discussed
on the basis of concrete structures theory. The flexural strengths of RC beams strengthened with CFRP bars were controlled
by the failure of concrete in compression and a prestressing method was applied in the retrofit. The field construction processes
of strengthening with CFRP bars—including grouting cracks, cutting groove, grouting epoxy and embedding CFRP bars, surface
treating, banding with the U-type CFRP sheets, releasing external prestressed steel tendons—were introduced in detail. In
order to evaluate the effectiveness of this strengthening method, field tests using vehicles as live load were applied before
and after the retrofit. The test results of deflection and concrete strain of the T-shaped beams with and without strengthening
show that the capacity of the repaired bridge, including the bending strength and stiffness, is enhanced. The measurements
of crack width also indicate that this strengthening method can enhance the durability of bridges. Therefore, the proposed
strengthening technology is feasible and effective.
This study deals with the use of carbon fiber reinforced polymer (CFRP) cables as external prestressing for strengthening of concrete flexural members. The study examines experimentally the effectiveness of externally prestressed CFRP cables in increasing the capacity and improving the serviceability of pre-cracked reinforced and partially prestressed concrete beams. The CFRP cables used were 7-wire “Carbon Fiber Composite Cables,” (CFCC) manufactured by Tokyo Rope, Japan. The objective was to investigate the effects of the span-to-depth ratio and the partial prestressing ratio or the reinforcing index on the performance of reinforced and prestressed concrete beams after being strengthened with external CFCC. The experiments showed an enhancement of the overall performance of the beams and an increase up to 83 percent in their ultimate resistance after strengthening. Reference is made to an analytical investigation that leads to an equation suggested for estimation of the change in stress in the external CFCC at any load level and at ultimate.
The use of fiber-reinforced polymers (FRPs) for the strengthening and repair of existing concrete structures is a field with tremendous potential. The materials are very durable and, hence, ideally suited for use as external reinforcement. Although extensive work has been carried out investigating the use of FRPs for flexural strengthening, a fairly recent development is the use of these materials for the shear strength enhancement of concrete. The current system investigates the use of posttensioned, nonlaminated, carbon fiber-reinforced polymer (CFRP) straps as external shear reinforcement for concrete. Experiments were carried out on an unstrengthened control beam and beams strengthened with external CFRP straps. It was found that the ultimate load capacity of the. strengthened beams was significantly higher than that of the control specimen. Existing design codes and analysis methods were found to underestimate the ultimate resistance of the control specimen and the strengthened beams. Nevertheless, the modified compression field theory provided insight into possible failure mechanisms and the influence of the strap prestress level on the structural behavior. It is concluded that the use of these novel stressed elements could represent a viable and durable means of strengthening existing concrete infrastructure.
This paper documents two projects funded through the Federal Highway Administration's Innovative Bridge Research and Construction (IBRC) program. The IBRC program was developed to assist bridge owners in applying emerging technologies in bridge engineering. In these projects, the Iowa Department of Transportation employed techniques for strengthening steel girder bridges using carbon fiber reinforced polymers (CFRP). Two bridges were strengthened using CFRP composite materials in an effort to improve the live load carrying capacity of the bridges. In one case, a bridge was strengthened using CFRP post-tensioning rods in the positive moment regions. In the other case, a bridge was strengthened by installing CFRP plates to the bottom flange of girders in the positive moment regions. of the author(s), who are responsible for the facts and accuracy of the information presented herein.
In accordance with the ASCE's 2005 Report Card, 27.1% (160,570) of nation's 590,750 bridges are rated structurally deficient or functionally obsolete. It will cost nearly $9.4 billion a year for the next 20 years to eliminate all bridge infrastructure related deficiencies. The Federal Highway Administration's (FHWA's) strategic plan mandates that this number should decrease to less than 25% by 2008. Advanced composite materials are considered to be an innovative solution for repair, strengthening, or replacement of substandard bridges. The application of advanced carbon fiber reinforced polymer (CFRP) composite prestressing laminates, utilized to rehabilitate the severely deteriorated sidewalk beams of a 6-span precast-prestressed concrete box beam bridge will be presented here. In this innovative application, the first of its kind in the United States, the CFRP laminates are post-tensioned and bonded to the bottom surface of deteriorated sidewalk beams. Capitalizing on CFRPs inherent light-weight and handling qualities, all work was accomplished expediently from scaffolding that was suspended from the bridge without using any special tools. The project, one of two bridges repaired utilizing this approach, was sponsored by the Federal Highway Administration (FHWA) through the Innovative Bridge Research and Construction (IBRC) Program. The design methodology along with construction issues identified in the design phase and their resolution during construction will be discussed herein.
This paper briefly reviews the results of NCHRP Project 12-28(4), Methods of Strengthening Existing Highway Bridges. The initial task was a thorough review of international literature to determine strengthening procedures currently being used and to investigate innovative ideas now being considered. The types of structures that show the most need for cost-effective strengthening were identified. A procedure for determining equivalent uniform annual costs was developed to assist the engineer in determining whether to strengthen or replace a given bridge. The culmination of the study was the development of a strengthening manual for practicing engineers. The eight sections of that manual, which contain different strengthening procedures, are briefly summarized.
The use of carbon fiber reinforced polymer (CFRP) strands for prestressed concrete bridges has been rapidly increasing over the past few years. This is primarily attributed to several advantages including excellent corrosion resistance, good fatigue and damping response, and low relaxation losses. However, CFRPs may lead to poor ductility in improperly designed structural components due to their inability to absorb inelastic energy. Researchers at the Lawrence Technological University in Southfield, MI, have conducted studies to determine the ductility of entire prestressed concrete bridge superstructures, with both rectangular and skew geometries. These studies aim to develop a design approach that exhibits a reasonable increase in absorbed energy.
Successful use of carbon fiber reinforced polymer (CFRP) tendons in prestressed concrete bridges can be achieved by combining bonded internal tendons with unbonded externally draped tendons. To examine this theory, four bridge models were tested under static, repeated (7 million cycles), and ultimate loads. Also, the combined effects of factors such as: (a) draping angle; (b) deviator diameter; (c) number of attached die-casts used to anchor the tendons; (d) presence of cushioning material between the deviator and the tendon; and (e) twist angle on the strength of the tendons were examined. It was concluded that the use of externally draped CFRP tendons in bridge construction improves ductility and forces the concrete to undergo inelastic deformation resulting in compression failure. It is also noted that increasing the deviator diameter and using cushioning material at the deviators minimize the reduction in the breaking force of the draped tendon.
External bonding of fiber-reinforced polymer (FRP) composite laminates to the tension soffit of reinforced concrete beams has become a popular method for flexural strengthening. However, the long-term performance of FRP-bonded beams under service loads is still a concern. This study was therefore aimed at investigating, both analytically and experimentally, the long-term deflection characteristics of FRP-bonded beams under sustained loads. Nine reinforced concrete beams, six of which were externally bonded with glass FRP composite laminates, were subjected to sustained loads for 2 years. The test parameters were the FRP ratio and sustained load level. The long-term deflections of the beams were reduced 23 and 33% with a FRP ratio of 0.64 and 1.92%, respectively. The total beam deflections were accurately predicted by the adjusted effective modulus method, and overestimated by about 20% by the effective modulus method.
The need to upgrade a large number of under-strength bridges in the United States has been well documented in the literature. Through several Iowa Department of Transportation projects, the concept of strengthening simple-span steel-beam composite concrete-deck bridges by post-tensioning has been developed. The purpose of this paper is to describe how this strengthening procedure has been extended for use on continuous-span steel-beam composite concrete-deck bridges. The feasibility of using this strengthening procedure was demonstrated on a laboratory 1/3-scale-model three-span bridge. The laboratory model was subjected to various post-tensioning systems in which the positive-moment regions, negative-moment regions and combinations thereof were post-tensioned. Post-tension strengthening systems were then implemented and tested on two existing three-span bridges; both bridges (Bridges 1 and 2) were 150 ft (45.72 m) in length with a roadway width of 24 ft (7.27 m). From analysis, it was determined that both bridges, when subjected to legal live loads, were overstressed in both the positive- and negative-moment regions. The bridges, instrumented so that strains and deflections could be measured, were loaded with trucks prior to and after strengthening to determine the effectiveness of the strengthening systems. To alleviate the flexural overstress in Bridge 1, a post-tensioning scheme was designed in which the positive-moment region of all beams were post-tensioned. In Bridge 2, superimposed trusses were employed over the piers on the exterior beams in addition to the post-tensioning of the positive-moment regions of all beams. In both bridges, considerable end-restraint was measured; also it was determined that the guardrails on both bridges were making a structural contribution. In this paper, the effectiveness of both strengthening systems is presented as well as numerous behavioral characteristics noted in the field. This paper summarizes transverse and longitudinal distributions, behavioral changes noted and the effectiveness of the strengthening systems. A design methodology for use by practicing engineers for designing strengthening systems for continuous-span bridges is also briefly described.
The concept of prestressing has been used as an effective technique to strengthen composite steelconcrete girders in bridges and buildings. Although several researchers have investigated the behavior of this structural system under static loading, no one has addressed the fatigue behavior. This paper analyzes and summarizes the fatigue test data for the main constituent components of prestressed composite steel-concrete girders—strands, shear studs, and cover plates. The data are also compared with the American Association of State Highway and Transportation Officials (AASHTO) requirements. It appears that end-anchored strands for nonbonded, prestressed structures can be designed for fatigue to the AASHTO allowable stress range for category C. AASHTO’s approach to designing shear studs and cover plates seems reasonable for prestressed composite girders. A companion paper presents the fatigue behavior of these elements within a prestressed composite girder.
Thanks to intensive research and development projects at the Swiss Federal Laboratories for Material Testing and Research (EMPA) in Dübendorf, Switzerland and Sika a composite strengthening system with externally bonded CarboDur CFRP plates were developed and successfully applied to strengthen the Ibach bridge in 1991 in Switzerland. This paper presents a new technique to strengthen reinforced concrete structures with pre-stressed bonded and/or non-bonded CarboDur CFRP plate systems with world-wide applications especially for bridge strengthening.
Keywords: strengthening, carbon fiber, structures, rehabilitation, composites, steel. Thesis (Ph.D.)--North Carolina State University. Includes bibliographical references. Includes vita.
Acceptance criteria for adhesive anchors in concrete and masonry elements – AC58
- Icc Evaluation
- Service
ICC Evaluation Service Inc. Acceptance criteria for adhesive anchors in concrete and masonry elements – AC58. Whittier, CA: ICC-ES; 2005. F. Matta et al. / Construction and Building Materials 23 (2009) 1628–1639 1639
Switzerland: Fédé Internationale du Bé
- Lausanne
Lausanne, Switzerland: Fédé Internationale du Bé; 2001. p. 75–88.
ACI) Committee 440. Prestressing concrete structures with FRP tendons – ACI 440.4R-04
- American Concrete
American Concrete Institute (ACI) Committee 440. Prestressing concrete structures with FRP tendons – ACI 440.4R-04. Farmington Hills, MI: ACI; 2004.
Externally post-tensioned CFRP system for deflection control of reinforced concrete slabs - volume I: design and analysis
- A Nanni
- F Matta
- N Galati
Nanni A, Matta F, Galati N. Externally post-tensioned CFRP system for deflection control of reinforced concrete slabs – volume I: design and analysis. Report CAE 06-01. Miami, FL: Department of Civil, Architectural and Environmental Engineering, University of Miami; 2006. 92pp.
External prestressing in bridges – ACI SP-120
- Naaman Ae
- Breen
Naaman AE, Breen JE, editors. External prestressing in bridges – ACI SP-120. Farmington Hills, MI: ACI; 1990. 458pp.
Behavior of RC beams strengthened with externally post-tensioning CFRP strips Fiber reinforced composite reinforcement for concrete structures – FRPRCS-7. ACI SP-230
- Choi Ks
- You
- Yc
- Park
- Yh
- Park
- Js
- Kim
- Shield Ck
- J Busel
- S Walkup
Choi KS, You YC, Park YH, Park JS, Kim KH. Behavior of RC beams strengthened with externally post-tensioning CFRP strips. In: Shield CK, Busel J, Walkup S, Gremel D, editors. Fiber reinforced composite reinforcement for concrete structures – FRPRCS-7. ACI SP-230. Farmington Hills, MI: American Concrete Institute; 2006. p. 515–27.
Strengthening of steel girder bridges using FRP. In: Proceedings of the 2003 mid-continent transportation research symposium
- Phares Bm Wipf Tj
- A Klaiber Fw
- Y-S Lee
Phares BM, Wipf TJ, Klaiber FW, Abu-Hawash A, Lee Y-S. Strengthening of steel girder bridges using FRP. In: Proceedings of the 2003 mid-continent transportation research symposium; 2003. 12pp.
Reinforcement technology by prestressed carbon fiber reinforced plastics (CFRP)
- S Shang
- Y Jin
- H Peng
- M Wang
- Q Leng
Shang S, Jin Y, Peng H, Wang M, Leng Q. Reinforcement technology by prestressed carbon fiber reinforced plastics (CFRP). In: Mirmiran A, Nanni A, editors. Proceedings of the third international conference on composites in civil engineering (CICE 2006); 2006. p. 479–82.
Development of a post-tensioning system using unbonded CFRP tendons
- T Berset
Berset T. Development of a post-tensioning system using unbonded CFRP tendons. In: Proceedings of the fourth PhD symposium in civil engineering; 2002. 6pp.
Present situation of durability of post-tensioned PC bridges in Japan. Durability of post-tensioning tendons - fib Bulletin 15
- H Mutsuyoshi
Mutsuyoshi H. Present situation of durability of post-tensioned PC bridges in Japan. Durability of post-tensioning tendons – fib Bulletin
Continuous CFRP prestressed concrete bridges
- Grace
- Nf
- Sayed
Grace NF, Abdel-Sayed G. Continuous CFRP prestressed concrete bridges. Concr Int 1999;21(10):42–7.
Instandsetzung von brücken mit einer neuen generation von spanngliedern auf basis von CFK-bändern (Rehabilitation of bridges by a new generation of tendons based on CFRP)
- Andrä
Andrä HP, Maier M. Instandsetzung von brü cken mit einer neuen generation von spanngliedern auf basis von CFK-bä (Rehabil-itation of bridges by a new generation of tendons based on CFRP). Bauingenieur 2005;80:7–16.
Innovation in structural engineering: strengthening with composites and in-situ load testing
- A Nanni
Nanni A. Innovation in structural engineering: strengthening with
composites and in-situ load testing. In: Proceedings of the second fib
congress; 2006. 12pp.
Strengthening box-girder bridges using external post-tensioning
- K Ahmadi-Kashani
Continuous CFRP prestressed concrete bridges
- Grace
Externally post-tensioned CFRP system for deflection control of reinforced concrete slabs - volume II: installation guide
- D Gremel
- R Koch
- A Nanni
- F Matta