土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究.docx

1、土木毕业设计外文翻译近表面埋置加固的钢筋混凝土梁抗弯性能实验研究中文2630字AN EXPERIMENTAL STUDY ON FLEXURAL BEHAVIOR OF RC BEAMSSTRENGTHENED WITH NSM REINFORCEMENTWoo-Tai JUNG1, Young-Hwan PARK2, Jong-SupABSTRACT: This study presents the results of experiments performed on RC (Reinforced Concrete) beams strengthened with NSM(Near Sur

2、face Mounted) reinforcement. A total of 6 specimens have been tested. The specimens can be classified into EBR(Externally Bonded Reinforcement) specimen and NSM reinforcements specimens. Two NSM specimens with space variables were strengthened with 2 CFRP(Carbon Fiber Reinforced Polymer) strips. Exp

3、erimental results revealed that NSMspecimens used CFRP reinforcements moreefficiently than the EBR specimens. Even if CFRP crosssection areas of NSM specimens have 30%,50% of EBR Specimen, the strengthening effect of NSMspecimens is superior to EBR specimen. NSM specimens with space variables showed

4、 that thstrengthening effect of the specimen with narrow space is slightly increased as compared to thespecimen with wide spaceuKEYWORDS: carbon fiber reinforced polymer, externally bonded CFRP reinforcements, nearsurface mounted CFRP reinforcements, strengthening1. INTRODUCTIONAmong the various str

5、engthening techniques that have been developed and applied to strengthendeteriorated RC structures, a number of applications using FRP reinforcements have significantly increased recently. FRP reinforcements are bonded to concrete surfaces by adhesives but frequently experience debonding failure at

6、the interface between FRP reinforcements and concrete. Most research, to date, has focused on investigating the strengthening effects and failure modes of EBR systemThe problem of premature failure of EBR system may be solved by increasing the interface between FRP and concrete. Using this principle

7、, the NSM system has been introduced recently. The NSM system for concrete structure using steel reinforcement already began in 1940s. However, the corrosion of the steel reinforcement and the poor bonding performance of the grouting material largely impaired its application. The development of impr

8、oved epoxy and the adoption of FRP reinforcement offered the opportunity to implement NSM system (Hassan and Rizkalla 2003; Tljsten and Carolin 2001). Because of their light weight, ease of installation, minimal labor costs and site constraints, high strength-to-weight ratios, and durability, FRP re

9、pair systems can provide an economically viable alternative to traditional repair systems and materials(Mirmiran et al. 2004). Rizkalla and Hassan (2002) have compared EBR and NSM system in terms of cost, including costs of materials and labor,and strengthening effect. They concluded that the NSM sy

10、stem was more cost-effective than the EBR system using CFRP strips.This experimental study investigates the applicability and strengthening performances of NSM using CFRP strips. For comparison, flexural tests on RC beams strengthened by EBR and by NSM have been performed. In addition, specimens wit

11、h space variables have been tested to compare the strengthening performance by cross section with wide and narrow space.2. EXPERIMENTAL PROGRAM2.1 MANUFACTURE OF SPECIMENSA total of 6 specimens of simply supported RC beams with span of 3m have been cast. The details andcross-section of the specimens

12、 are illustrated in Figure 1. A concrete with compressive strength of31.3 MPa at 28 days has been used. Steel reinforcements D10(9.53mm) of SD40 have been arrangedwith steel ratio of 0.0041 and a layer of three D13(12.7mm) has been arranged as compressionreinforcements. Shear reinforcements of D10 h

13、ave been located every 10 cm in the shear zone to avoidshear failure. Table 1 summarizes the material properties used for the test beams.2.2 EXPERIMENTAL PARAMETERSTable 2 lists the experimental parameters. The control specimen, an unstrengthened specimen, has been cast to compare the strengthening

14、performances of the various systems. CPL-50-BOND, EBR specimen, has been strengthened with CFRP strip. The remaining 4 specimens were strengthened with NSM CFRP strips. Among the specimens strengthened with NSM reinforcements, an embedding64 depth of NSM-PL-15 and NSM-PL-25 is 15mm and 25mm, respect

15、ively. A space between grooves of NSM-PL-25*2 and NSM-PL-2S is 60mm and 120mm, respectively. The strengthened length of all thespecimens has been fixed to 2,700 mm2.3 INSTALLATION OF THE FRP REINFORCEMENTSFigure 2 shows the details of cross-sections of the specimens. The strengthening process of EBR

16、 specimen (CPL-50-BOND) was proceeded by the surface treatment using a grinder, followed by the bonding of the CFRP strip. The strengthened beams were cured at ambient temperature for 7 days for the curing of epoxy adhesive. The process for NSM strengthening progressed by cutting the grooves at the

17、bottom of the beams using a grinder, cleaning the debris, and embedding the CFRP strip after application of the adhesive. The strengthened beams were cured for 3 days so that the epoxy adhesive achieves its design strength.2.4 LOADING AND MEASUREMENT METHODSAll specimens were subjected to 4-point be

18、nding tests to failure by means of UTM (Universal Testing Machine) with capacity of 980 kN. The loading was applied under displacement control at a speed of 0.02 mm/sec until the first 15 mm and 0.05 mm/sec from 15 mm until failure. The measurement of alltest data was recorded by a static data logge

19、r and a computer at intervals of 1 second. Electrical resistance strain gauges were fixed at mid-span and L/4 to measure the strain of steel reinforcements.Strain gauges to measure the strain of concrete were located at the top, 5 cm and 10 cm away from the top on one side at mid-span. Strain gauges

20、 were also placed on the FRP reinforcement located at the bottom of the mid-span and loaded points to measure the strain according to the loading process.3. EXPERIMENTAL RESULTS3.1 FAILURE MODESBefore cracking, all the strengthened specimens exhibited bending behavior similar to theunstrengthened sp

21、ecimen. This shows that the CFRP reinforcement is unable to contribute to the increase of the stiffness and strength in the elastic domain. However, after cracking, the bending stiffness and strength of the strengthened specimens were seen to increase significantly until failure compared to the unst

22、rengthened specimens.Examining the final failure, the unstrengthened control specimen presented typical bending failure mode which proceeds by the yielding of steel reinforcement followed by compression failure of concrete. The failure of CPL-50-BOND, EBR specimen, began with the separation of CFRP

23、reinforcement and concrete at mid-span to exhibit finally brittle debonding failure (Figure 3). Failure of NSM-PL-15, NSM specimen, occurred with the rupture of the FRP reinforcement. Failure of the remaining NSM specimens(NSM-PL-25, NSM-PL25*2, and NSM-PL-2S) occurred through the simultaneous separ

24、ation of the CFRP reinforcement and epoxy from concrete (Figure 4, 5, and 6).Table 3 summarizes the failure modes.3.2 STRENGTHENING EFFECTFigure 7 ploted the load-deflection curves of EBR and NSM specimens. The specimens with EBR,CPL-50-BOND, presented ultimate load increased by 30% compared to the

25、unstrengthened specimen, while NSM specimens (NSM-PL-15, NSM-PL-25) increased the ultimate load by 40 to 53%.Observation of Figure 7 reveals that even if CPL-50-BOND with relatively large cross-sectional areaof CFRP reinforcement developed larger initial stiffness, premature debonding failure occurr

26、ed because its bonding area is much smaller than NSM-PL-15, NSM-PL-25. EBR specimen behaved similarly to the unstrengthened control specimen after debonding failure. In Figure 7, the stiffness of NSM specimens before yielding of steel reinforcement was smaller than the stiffness developed by EBR spe

27、cimen because NSM specimens have the smaller cross-sectional area of CFRP reinforcement than EBR specimen. The ultimate load and yield load are seen to increasewith the cross-sectional area of NSM reinforcement.Examining the ultimate strain of FRP summarized in Table 3, the maximum strain for EBR sp

28、ecimenappears to attain 30% of the ultimate strain, and 80 to 100% for NSM specimens. This proves that the NSM system is utilizing CFRP reinforcement efficiently（2S with the same cross-sectional area as CPL-50-Bond resented ultimate load increased by 95%, 90% compared to the unstrengthened specimen,

29、respectively. Considering the same cross-sectional area, the strengthening effect of NSM specimens issuperior to the EBR specimen. In Figure 8,NSM-PL-25*2 and NSM-PL-2S, NSM specimens with space variables,showed that the strengthening effect of the specimen with narrow spaceis slightly increased by

30、2.5%as compared to the specimen with wide space.4. CONCLUSIONSPerformance tests have been carried out on RC beams strengthened with NSM systems. The followingconclusions were derived from the experimental results.It has been seen that NSM specimens utilized the CFRP reinforcement more efficiently th

31、an the EBR specimen. According to the static loading test results, the strengthening performances were improvedin NSM specimens compared with EBR specimen. However, the specimens NSM-PL-25, NSM-PL-25*2 and NSM-PL-2S failed by the separation of the CFRP reinforcements and epoxy adhesive from the conc

32、rete. Consequently, it is necessary to take somecountermeasures to prevent debonding failure for NSM specimens.Considering the same cross-sectional area, the strengthening effect of NSM specimens is superior to EBR specimen. NSM-PL-25*2 and NSM-PL-2S, NSM specimens with space variables, showed that

33、the strengthening effect of the specimen with narrow space is slightly increased as compared to the specimen with wide space.5. REFERENCES1. Hassan, T. and Rizkalla, S. (2003), Investigation of Bond in Concrete Structures Strengthenedwith Near Surface Mounted Carbon Fiber Reinforced Polymer Strips”, Journal of Composite