Prestressed CFRP Plates Research Articles

Evaluation of the Strengthening Effects on Prestressed Carbon-Fiber-Reinforced-Polymer-Strengthened Steel Beam Bridges Using Macro-Strain Influence Lines

Effectively evaluating the effectiveness of bridge strengthening is a necessary means to ensure the normal operation of existing strengthened bridges, especially when evaluating the effectiveness of bridge strengthening without interrupting normal traffic. Based on a distributed long-gauge Fiber Bragg Grating (FBG) sensor, this paper derived the macro-strain influence line (MSIL) formula for a simply supported beam bridge under a moving vehicle load, studied the changes in the MSIL at the bottom of the beam under the vehicle load before and after the prestressed CFRP plate strengthening, and proposed a rapid evaluation method for the strengthening effect based on the amplitude of the MSIL as the evaluation index for the strengthening effect. Finally, the prestressed CFRP-strengthened steel beam was tested under the moving vehicle load. The theoretical analysis and the experimental results confirm that under the load of moving vehicles, the macro-strain–time history amplitude of the strengthened steel beams under different prestressed tensioning conditions is different. The amplitude of the macro-strain time history of the strengthened bridge is reduced compared to before strengthening, and the local strengthening effect of the bridge can be monitored by the amplitude change in a single sensor. The change in global stiffness can be evaluated by monitoring the MSIL obtained from multiple long-gauge strain sensors.

Research on seismic performance of reinforced concrete structures reinforced with CFRP plates

In the modern construction industry, natural disasters such as earthquakes pose an increasingly prominent threat to reinforced concrete structures, which often lead to serious damage to the structures. Therefore, how to enhance the seismic performance of reinforced concrete structures has become an urgent problem to be solved in the field of construction. This study delves into the seismic performance of CFRP plates in strengthening reinforced concrete structures. Firstly, the material characteristics of CFRP panels were analyzed, including the mechanical and adhesive performance indicators of carbon fiber panels, and corresponding specimens were made. Subsequently, through specimen loading experiments, the performance of reinforced specimens and unreinforced specimens under load was compared. The experimental results show that prestressed CFRP plates can significantly increase the cracking load and enhance the seismic resistance of reinforced concrete structures. In addition, simulation tests were conducted using a finite element model. Through simulation testing, the load deflection curve of the specimen was obtained, revealing the influence of CFRP plates on beam stiffness. Especially in the critical stages of concrete cracking and yielding of tensile steel bars, carbon fiber board has a particularly significant effect on improving the stiffness of beams.

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates with High Ductility

Finite Element Analysis of Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates with High Ductility

Experimental study on large-scale compression members strengthened with circumferential prestressed CFRP plate

There have been many research reports on the reinforcement of small-sized square columns with a cross-section of 200mm–300mm using prestressed carbon fiber-reinforced polymer (CFRP) materials, while there are few studies on piers in bridge and tower columns in cable-stayed bridges with a cross-section of several meters or even tens of meters. The horizontal prestressed steel tendons in the anchorage zone of tower columns in cable-stayed bridge replaced by prestressed CFRP sheets can not only facilitate construction and maintenance, but also have good fatigue resistance. The prestressed CFRP plate is used to reinforce the large-sized tower columns by using a specific device to tension the CFRP plate wrapped around the surface of the members. The tensioning device and test pedestal based on WSGG (wave-shaped-gear-grip) anchor clamping of CFRP plate have been developed in this paper, and the CFRP plate circumferential tensioning tests on the pedestal have been conducted. The test results are as follows: (1) the developed device can achieve circumferential tensioning of single-layer CFRP plate to 0.5ftk of the material, reaching a tensile force of 60kN, and generate effective restraint pressure on a 2-m long composite compression component; (2)The calculation formula for the constraint pressure generated by the circumferential prestressed CFRP sheet on the component has been derived and verified, and the maximum error between the calculated value and the experimental value is within 5%; (3) When iron sheet serves as the interface medium between CFRP plate and compression components, the prestress loss of the CFRP plate tensioned at one end is about 84% and 58%–60% when tensioned at both ends. It can be seen that the effective prestress of the CFRP plate with iron sheet as the interface medium is relatively small. Meanwhile, based on the distribution of compressive stress in the components and the effective pre tension value of CFRP plate, it can be seen that two end tensioning is better than one end tensioning; (4) The tensile stress of CFRP plate along the member is a cubic function when the tension force is 60kN, so it is deduced that the constrained compressive stress generated by CFRP plate on the member is a quadratic function distribution.

A review on flexural behavior of reinforced concrete beams strengthened with prestressed carbon fiber reinforced polymer plates

In recent years, with the rapid development of China’s economy, reinforced concrete structure as an economical and good mechanical properties material, is widely used in buildings. In bridge engineering, Carbon Fiber Reinforced Polymer materials is mostly used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. However, this method makes the strength of CFRP plates cannot be fully utilized, while the prestressed technology can significantly improve the efficiency of CFRP materials and the flexural strength of the RC beams. This paper compares different methods of prestressed CFRP plates strengthening RC beams and discuss the development of the technology. The results shows that RC beams strengthened with prestressed CFRP plates have better flexural performance. The cracking, yield and ultimate loads increase significantly compared with ordinary beams or non-prestressed strengthened beams. The effectiveness of strengthening process are related to many factors ranging from anchorage methods, prestress levels, ratio of corrosion to bond length. Future research suggestions are also given. At present, most of the experiments are operated in ordinary environment, which is different from the project in real life. More testing environment like chlorine corrosion must be considered. The trials about prestress loss during strengthening process are not enough. There also need more comparative trials in prestressed CFRP plates strengthening concerning prestress loss and non-prestressed CFRP plates.

Cracking behavior of prestressed CFRP strengthened RC beams subjected to wetting/drying cycling under flexural load

The cracking pattern and spacing are essential for the structural durability of RC structures strengthened by prestressed CFRP plates. In this study, the effects of prestressing levels and wetting/drying cycling (WDC) on the cracking behavior of RC beams strengthened by prestressed CFRP plates were investigated. A modified model for calculating the average crack spacing was developed by incorporating the interfacial stress between adjacent cracks, the prestressing levels, and the WDCs. The effects of interfacial properties and prestressing levels on the average crack spacing were analytically studied. Besides, four-point bending tests were conducted on seventeen strengthened beams subjected to WDC. The results show that cracking propagation was restrained by prestressing forces but facilitated by WDCs. Moreover, WDC and prestressing force lead to an increase in the average cracking spacing of the strengthened beams. The average cracking spacings calculated by different equations were compared to the experimental results, and it can be found that the modified modelprovides the closer prediction of the average crack spacing for CFRP-strengthened beams under WDC and prestressing.

Strain driven mode-switching analytical framework for estimating flexural strength of RC box girders strengthened by prestressed CFRP plates with experimental validation

This paper presents a pioneering study that developed the first analytical model to analyse and design reinforced concrete (RC) box girders strengthened by prestressed CFRP plates. The proposed analytical model considered and addressed prestress loss, shear lag effect and failure modes under different design configurations at elastic, elastoplastic and plastic stages. An experimental study was also conducted to validate the proposed analytical model. The study was motivated by the increasing demand for the structural strengthening of aged and over-used hollow RC box girders in transport and other infrastructure systems, as well as the lack of previous attempts to incorporate prestressed CFRP plate strengthening for hollow RC beams. It is very common in many developing countries, the traffic flow increased dramatically due to the economic growth. The original design underestimated the traffic loads. When demolition and re-building may not always be the best option, thus, strengthening and enhanced maintenance have become promising alternatives. But the lack of existing analytical models that can guide the engineers to analyse and design this type of structures effective, has become an urgent need from the industry. In the experimental study, eight box girders with different types, cross-section sizes, and prestress levels were prepared and tested. Two samples were preloaded to create damaged beams before strengthening to simulate the aged or over-used members. The experimental results are in good agreement with the analytical prediction. The proposed analytical framework provides a comprehensive yet practical method for designing the prestressed CFRP strengthened RC box girders in bending and laid the foundation for further studies on shear and torsion behaviours.

Experiments on the flexural behavior of full-scale PC box girders with service damage strengthened by prestressed CFRP plates

Two full-scale PC box girders with typical damage were derived from an in-situ bridge that was in service about 20 years, to understand the strengthening effects of prestressed CFRP plates for the entire bottom slab, casting of a RC layer in composite action with the entire top slab and steel plates anchored on the webs of the shear span. The flexural tests were conducted on the two full-scale PC box girders with and without strengthening measures, and comparative analysis was conducted regarding flexural capacity, failure mechanism, rigidity, ductility and overall structural behavior. The test results showed that the strengthening measures improved the girder rigidity by 40 % before reaching cracking state and increased the yielding and ultimate capacity by 39 % and 28% respectively. The theoretical analysis was conducted to discuss failure modes for PC box girder strengthened by prestressed CFRP plates. Theoretical equations are derived to calculate the flexural capacity of strengthened PC box girder according to typical failure modes. Good agreement with tested results was obtained. The strengthening design of the prestressing CFRP plate was verified by application in a PC box girder bridge.

Static and Fatigue Properties of RC Beams Strengthened with Prestressed CFRP Plates

Static and Fatigue Properties of RC Beams Strengthened with Prestressed CFRP Plates

Experimental Study on Steel‒Concrete Composite Beams Strengthened by Externally Prestressed CFRP Strips

PDF HTML XML Export Cite reminder Experimental Study on Steel‒Concrete Composite Beams Strengthened by Externally Prestressed CFRP Strips DOI: 10.59238/j.pt.2023.01.004 Author: Affiliation: (Department of Construction Engineering, School of Civil Engineering, Tongji University, shanghai 200092, China) Clc Number: Fund Project: Article | Figures | Metrics | Reference | Related | Cited by | Materials | Comments Abstract:This paper mainly studies the mechanical properties of simply supported bridges of steel?concrete composite structures strengthened with externally prestressed CFRP plates. The introduction of the prestress of the CFRP plate from the support rods can not only apply prestress to the main beam but also provide an upward lifting force at the bottom end of the main beam to reduce the deflection of the original structure. Therefore, the CFRP board is prestressed by the support rods, which can improve the speed and efficiency of rein-forcement construction. The effects of the CFRP amount, prestress size, support rods amount and other parameters on the stiffness and bearing capacity of composite beams were studied by a static test of the scaled model. In the flexural test of the tensioned combination beam, by increasing the prestressing level and the number of CFRP plates, the flexural moment of inertia of the combination beam section was effectively improved, the reinforcement effect on the yield bearing capacity and ultimate flexural bearing capacity of the combination beam was obvious, and the reinforced specimens still had good ductility. For the third com-bination beam, a CFRP plate with a 15% prestressing level and 3 mm thickness was used for reinforcement. The ultimate load carrying capacity of the combined beam was increased by 47.9%; the yield load of the lower flange was increased by 39.8%; and the stiffness in the elastic phase was increased by 21.66%. Reference Related Cited by

Mechanical performance evolution and life prediction of prestressed CFRP plate exposed to hygrothermal and freeze-thaw environments

The long-term prestressed loss of anchorage system and mechanical property evolution play the significant role for the steel/concrete structures strengthened with prestressed CFRP plates. In the present study, a wedge-extrusion bond anchorage system was applied to provide the reliable anchorage load-bearing capacity for CFRP plate. A new prestressed tension device was put forward to realize the coupling exposure of elevated temperature (20 °C, 60 °C and −20 to 30 °C), distilled water and sustained loading (20%, 40% and 60%). The mechanical and thermal properties of CFRP plate were conducted to obtain the long-term evolution exposed to the above environments. The mechanical analysis and tensile tests of anchorage system showed the tensile failure modes under the static and cyclic loads were the CFRP burst, and there was no debonding occurring in the anchor. The higher anchorage capacity was attributed to the uniform stress distribution of CFRP plate parallel to the greatest dimension of cross section in the anchor. The new prestressed tension device can realize the maximum prestressed level (∼70%) with an allowable prestressed loss (∼300 με). Meanwhile, the prestressed loss of CFRP plate exposed at the maximum temperature (60 °C) and longest time (90 days) was found to be ∼300 με. Immersed at higher temperature and prestressed level brought about an additional degradation rate of tensile strength (5%∼10%). The minimum strength retention of CFRP plate was found at the freeze-thaw exposure for 90 days. The long-term life prediction showed the residual tensile strength retentions of CFRP plates were more than 50% for the maximum prestressed level (60%) for the service life of 30 years in civil engineering structures.

Comparative analysis of flexural performance of old full-scale hollow slab beams reinforced with fiber composites

To address the problems of inadequate load carrying capacity, deformation and deflection of the main beams of in-service reinforced concrete (RC) bridges, the flexural performance of old full-scale hollow slab beams was investigated based on four-point bending tests in the field, and a qualitative and quantitative comparison was made between innovative solutions (TRC, TRECC) and conventional solutions (prestressed CFRP plates). The results show that the three fibre composite reinforcements increase the load carrying capacity of the hollow slab beams by 9.09% to 21.2% and the stiffiness by 0.4% to 46%, and that the deflection is effectively controlled and limits the development of cracks, while the ductility is reduced. The prestressed CFRP plates are more beneficial in delaying the stiffness degradation under service loads, and the deflection values of their reinforced beams are smaller; while TRECC shows better performance in controlling the crack width. On this basis, the effect of the axial stiffness of the reinforcement on the overall performance and local stress distribution of the beam was evaluated by load calculation and numerical simulations, and showed good agreement between the experimental and theoretical results. The effect of external reinforcement on the beam depends more on the axial stiffness than on the nature of the reinforcement material, and the effect of external reinforcement on the tensile side of the beam is mainly concentrated on the plastic phase.

RC beams strengthened by prestressed CFRP plate subjected to sustained loading and continuous wetting condition: Flexural behaviour

Time-dependent prestress loss of RC beams strengthened by a prestressed CFRP plate subjected to sustained loading and continuous wetting condition was investigated in a previous study, which showed obvious deflection and crack development after long-term service. Thus, the degradation of flexural behaviour is investigated in this paper for the concern of safety. Eleven RC beams were prepared with different prestressing levels (0, 20% fu and 40% fu), environmental conditions (dried and wet), and sustained loading levels (0, 94 kN and 120 kN). After a year of exposure, four-point bending tests were conducted. The results showed that the cracking load of the strengthened beams was decreased by up to 23.9% after suffering the sustained loading, while the reductions for both the yield load and the ultimate load were insignificant. In addition, moisture exposure can improve the cracking load and stiffness by 6.8% and 26.1% respectively, but the effect on the yield load and ultimate load was not obvious. Moreover, the ultimate utilization ratio of CFRP plate in the 20% prestressed specimens can be decreased by approximately 8.5% due to moisture exposure, whereas there was no change in the higher prestressed specimens. Consequently, the test results reveal that strengthening RC structures by using prestressed CFRP plate could be a reliable method in a moist environment. Finally, a model to predict the bearing capacity was proposed based on the test results and a satisfactory agreement was reached.

RC beams strengthened by prestressed CFRP plate subjected to sustained loading and continuous wetting condition: Time-dependent prestress loss

Prestress loss of CFRP during prestressing and service stage is one of the critical technical issues in concrete structures rehabilitation. In this work, the prestress loss of reinforced concrete (RC) beams strengthened by a prestressed CFRP plate subjected to sustained loading and continuous wetting condition were experimentally studied. Eight RC beams strengthened by prestressed CFRP plate were prepared with different prestress levels of 20% and 40% respectively. The initial prestress loss was monitored up to 28 days and the loss ratios of all specimens were around 5%, which was dominated by slippage of the end anchorage system. Then, the specimens were sustainedly loaded at two levels under wet or dried environments for 170 days. The average prestress loss ratios during this period were all less than 2%, which indicates that the CFRP plate end anchorage system had good long-term performance. Moreover, the adhesive bonding was weakened by the moisture penetration, and the specimens with lower prestress levels were more susceptible to the wet condition. Nevertheless, regardless of the environmental exposure, the maximum crack widths of 40% prestressed specimens remained less than 0.2 mm even subjected to high sustained load level, which is within the limitation of the prestressed concrete structures.

Flexural strengthening of RC slabs with nonprestressed and prestressed CFRP strips using EBROG method

This paper proposes a fully nonmetallic system for strengthening RC one-way slabs with prestressed CFRP composites. The flexural behaviors of RC slabs strengthened with nonprestressed and prestressed CFRP strips were compared through four-point bending tests. The externally bonded reinforcement on grooves (EBROG) method was utilized to delay premature debonding of the CFRP composites and was compared with conventional externally bonded reinforcement (EBR). The experimental results indicated a significant enhancement in slabs flexural performance of slabs that were strengthened via the EBROG method and the novel anchorage system. The nonprestressed and prestressed CFRP plates attached using the EBROG method increased the bending capacity by 34% and 77%, respectively, compared with the nonprestressed EBR CFRP plate. Furthermore, the maximum CFRP strain reached 8.9‰ for the nonprestressed EBROG CFRP strip, whereas that for the nonprestressed EBR CFRP strip was only 5.9‰. Thus, the EBROG method delayed CFRP debonding and increased the strain in the reinforcement by 50% compared with the EBR method. In the prestressed CFRP strip, the strain reached 12.4‰ prior to the debonding, confirming the high efficiency of the proposed strengthening system.

Short-term bond behavior and debonding capacity of prestressed CFRP composites to steel substrate

In this study, the short-term bonding behaviors of prestressed CFRP plates to steel substrates and their debonding capacities have been investigated. For this purpose, single lap-shear and prestress release tests were performed on adhesively bonded CFRP-to-steel joints. The feasibility of accelerated curing (AC) of the adhesive by heating was also investigated based on the conducted tests. Moreover, bond tests with partial prestress release and subsequent lap-shear loading were conducted to examine the feasibility of prestressed strengthening of steel members using AC. A three-dimensional (3D) digital image correlation (DIC) technique was utilized to monitor the bond behavior of CFRP-to-steel joints. Experimental results demonstrated that a mixed-mode I/II (tensile/shear) fracture governs the debonding failure of CFRP-to-steel joints during the prestress release. However, given that the steel substrate cannot undergo tensile failure, a relatively high prestressing force can be transferred to the steel substrate prior to debonding. The experimental results also revealed that the AC of the epoxy adhesive can be an advantageous alternative to the conventional room temperature curing (RTC) for strengthening steel members with prestressed bonded CFRP plates.

Behavior of prestressed CFRP plates bonded to steel substrate: Numerical modeling and experimental validation

In recent years, retrofitting of steel structures has emerged as a major issue in structural engineering and construction management. As the adhesive bond is often the critical aspect controlling the actual performance of steel profiles externally strengthened by composite plates, this paper investigates the bond behavior of fiber reinforced polymer (FRP) composites glued to steel substrate; the effect of prestress, being relevant in practical applications, is also covered herein. A simplified mechanical model, based on assuming mode II fracture for FRP-to-steel debonding is formulated at first, and then, a numerical solution is implemented. The proposed solution is validated by experimental tests. Finally, a parametric study highlights the role of several relevant parameters on the response of carbon FRP plates under prestress-release tests; it paves the way for further developments of the present study aimed to predict the prestress force release and lap-shear behavior of FRP-to-steel bonded joints based on the mechanical properties of the materials and the bond-slip relationship assumed for the adhesive interface.

Experimental study of flexural fatigue performance of reinforced concrete beams strengthened with prestressed CFRP plates

Fiber reinforced polymers (FRPs) have commonly been used for the retrofitting and strengthening of bridges, especially in the strengthening flexural members. Considerable research has been conducted to investigate the static behavior of reinforced concrete (RC) beams strengthened with externally bonded FRP laminates, initially using non-prestressed FRPs and more recently using prestressed FRPs. However, the research examining the flexural fatigue behavior of beams with either non-prestressed or prestressed FRPs is not adequate. In this paper, seven RC beams (two regular and five beams strengthened with externally bonded non-prestressed and prestressed CFRP plates) were studied to examine the effects of the different strengthening methods on the flexural fatigue performance of the beams. Furthermore, the effect of debonding on the fatigue behavior of the strengthened beams was investigated. It is evident from the experimental results that strengthening with prestressed CFRP plates significantly enhanced the monotonic and fatigue performances of reinforced concrete beams. The prestressed CFRP plates significantly reduced the deflection and reinforcing bar stress of the beams. The test results also indicated that under similar loads, the strain range and maximum strain of the reinforcing bars of beams with prestressed CFRP plates were significantly less than those of beams with non-prestressed CFRP plates. Moreover, the debonding, observed between the CFRP plate and the concrete during the fatigue test resulted in stress redistributions between the CFRP plate and the reinforcing bars.

Finite Element Analysis of Reinforce RC Beams Considering Loading History with Pre-Stressed CFRP Sheets

Reinforcement of beams and plates in high-pile wharf is important measures to ensure the safe operation of the old pier. Performance of prestressed CFRP plate reinforced concrete beam was carried out finite element calculation and analyzed in secondary load conditions use of the cell death technology and load multi-step control, various parameters impact analysis was performed. The results were showed that the bearing capacity of RC beams reinforced and stiffness were improved greatly; Ultimate bearing capacity of RC beams were strengthened by unstressed condition, compared with decline in the secondary load conditions and stiffness did not change significantly; CFRP plate reinforcement should give full play to the role of being the initial cracking reinforcement in the beam in the same reinforced conditions.

Prestressed CFRP Fabrics for Flexural Strengthening of Concrete Beams with an Easy Prestressing Technique

It is proposed to use prestressed CFRP plates for strengthening in order to prevent their debonding and thus to increase their strengthening efficiency. For this purpose, and easy-to-use piece of equipment was created. To determine the effectiveness of this method, an experimental program was carried out, and the effect of prestressed CFRP on the behavior and ultimate strength of reinforced concrete beams was examined in threepoint bending tests. A remarkable increase in their strength with debonding was seen for every specimen to which a prestressed CFRP plate had been applied.