土木工程專業(yè)外文翻譯---使用加固纖維聚合物增強混凝土梁的延性（英文）

1、692 ACI Structural Journal/September-October 2002ACI Structural Journal, V. 99, No. 5, September-October 2002. MS No. 01-349 received October 23, 2001, and reviewed under Institute publication policies. Copyright ©

2、2002, American Concrete Institute. All rights reserved, includ- ing the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion will be published in the July-August 2003 ACI St

3、ructural Journal if received by March 1, 2003.ACI STRUCTURAL JOURNAL TECHNICAL PAPERAn innovative, uniaxial ductile fiber-reinforced polymer (FRP) fabric has been researched, developed, and manufactured (in the Structura

4、l Testing Center at Lawrence Technological University) for strengthening structures. The fabric is a hybrid of two types of carbon fibers and one type of glass fiber, and has been designed to provide a pseudo-ductile beh

5、avior with a low yield-equivalent strain value in tension. The effectiveness and ductility of the developed fabric has been investigated by strengthening and testing eight concrete beams under flexural load. Similar beam

6、s strengthened with currently available uniaxial carbon fiber sheets, fabrics, and plates were also tested to compare their behavior with those strengthened with the developed fabric. The fabric has been designed so that

7、 it has the potential to yield simultaneously with the steel reinforcement of strengthened beams and hence, a ductile plateau similar to that for the nonstrengthened beams can be achieved. The beams strengthened with the

8、 developed fabric exhibited higher yield loads and achieved higher ductility indexes than those strengthened with the currently available carbon fiber strengthening systems. The developed fabric shows a more effective co

9、ntribution to the strengthening mechanism.Keywords: concrete; ductility; fiber reinforcement; flexure.INTRODUCTION The use of externally bonded fiber-reinforced polymer (FRP) sheets and strips has recently been establish

10、ed as an effective tool for rehabilitating and strengthening reinforced concrete structures. Several experimental investigations have been reported on the behavior of concrete beams strengthened for flexure using externa

11、lly bonded FRP plates, sheets, or fabrics. Saadatmanesh and Ehsani (1991) examined the behavior of concrete beams strengthened for flexure using glass fiber-reinforced polymer (GFRP) plates. Ritchie et al. (1991) tested

12、reinforced concrete beams strengthened for flexure using GFRP, carbon fiber-reinforced polymer (CFRP), and G/CFRP plates. Grace et al. (1999) and Trian- tafillou (1992) studied the behavior of reinforced concrete beams s

13、trengthened for flexure using CFRP sheets. Norris, Saa- datmanesh, and Ehsani (1997) investigated the behavior of concrete beams strengthened using CFRP unidirectional sheets and CFRP woven fabrics. In all of these inves

14、tigations, the strengthened beams showed higher ultimate loads com- pared to the nonstrengthened ones. One of the drawbacks experienced by most of these strengthened beams was a con- siderable loss in beam ductility. An

15、examination of the load- deflection behavior of the beams, however, showed that the majority of the gained increase in load was experienced af- ter the yield of the steel reinforcement. In other words, a significant incr

16、ease in ultimate load was experienced without much increase in yield load. Hence, a significant increase in service level loads could hardly be gained. Apart from the condition of the concrete element before strengtheni

17、ng, the steel reinforcement contributes significantlyto the flexural response of the strengthened beam. Unfortunately, available FRP strengthening materials have a behavior that is different from steel. Although FRP mate

18、rials have high strengths, most of them stretch to relatively high strain values before providing their full strength. Because steel has a relatively low yield strain value when compared with the ultimate strains of most

19、 of the FRP materials, the contri- bution of both the steel and the strengthening FRP materials differ with the deformation of the strengthened element. As a result, steel reinforcement may yield before the strengthened

20、element gains any measurable load increase. Some designers place a greater FRP cross section, which generally increases the cost of the strengthening, to provide a measurable contri- bution, even when deformations are li

21、mited (before the yield of steel). Debonding of the strengthening material from the surface of the concrete, however, is more likely to happen in these cases due to higher stress concentrations. Debonding is one of the n

22、ondesired brittle failures involved with this technique of strengthening. Although using some special low-strain fibers such as ultra-high-modulus carbon fibers may appear to be a solution, it would result in brittle fai

23、lures due to the failure of fibers. The objective of this paper is to introduce a new pseudo-ductile FRP fabric that has a low strain at yield so that it has the potential to yield simultaneously with the steel reinforce

24、ment, yet provide the desired strengthening level.RESEARCH SIGNIFICANCE FRPs have been increasingly used as materials for rehabil- itating and strengthening reinforced concrete structures. Currently available FRP materia

25、ls, however, lack the ductility and have dissimilar behaviors to steel reinforcement. As a result, the strengthened beams may exhibit a reduced ductility, lack the desired strengthening level, or both. This study present

26、s an innovative pseudo-ductile FRP strengthening fabric. The fabric provides measurably higher yield loads for the strengthened beams and helps to avoid the loss of ductility that is common with the use of currently avai

27、lable FRP.DEVELOPMENT OF HYBRID FABRIC To overcome the drawbacks mentioned previously, a ductile FRP material with low yield strain value is needed.Title no. 99-S71Strengthening of Concrete Beams Using Innovative Ductile

28、 Fiber-Reinforced Polymer Fabricby Nabil F. Grace, George Abdel-Sayed, and Wael F. Ragheb694 ACI Structural Journal/September-October 2002(1 in.) and were tested in tension according to ASTM D 3039 specifications. The av

29、erage load-strain curve for four tested samples is shown in Fig. 3 together with the theoretical prediction. It should be noted that the behavior is linear up to a strain of 0.35%, when the LE fibers started to fail. At

30、this point, the strain increased at a faster rate than the load. When the strain reached 0.90%, the ME fibers started to fail, resulting in an additional increase in strain without a significant increase in load, up to t

31、he total failure of the coupon by failure of theHE fibers. A yield-equivalent load (the first point on the load-strain curve where the behavior becomes nonlinear) of 0.46 kN/mm width (2.6 kips/in.) and an ultimate load o

32、f 0.78 kN/mm (4.4 kips/in.) are observed.BEAM TESTS Beam details Thirteen reinforced concrete beams with cross-sectional dimensions of 152 x 254 mm (6 x 10 in.) and lengths of 2744 mm (108 in.) were cast. The flexure rei

33、nforcement of the beams consisted of two No. 5 (16 mm) tension bars near the bottom, and two No. 3 (9.5 mm) compression bars near the top. To avoid shear failure, the beams were over- reinforced for shear with No. 3 (9.5

34、 mm) closed stirrups spaced at 102 mm (4.0 in.). Five beams were formed with rounded corners of 25 mm (1 in.) radius to facilitate the installation of the strengthening material on their sides and bottom faces without st

35、ress concentrations. Figure 4 shows the beam dimensions, reinforcement details, support locations, and location of loading points. The steel used was Grade 60 with a yield strength of 415 MPa (60,000 psi), while the conc

36、rete compressive strength at the time of testing the beams was 55.2 MPa (8000 psi).Strengthening materials The developed hybrid fabric was used to strengthen eight beams. Two different thicknesses of fabric were used. Th

37、e first (H-system, t = 1.0 mm) had a thickness of 1.0 mm (0.04 in.), and the second (H-system, t = 1.5 mm) had a thickness of 1.5 mm (0.06 in.). Four other beams were strengthened with three currently available carbon fi

38、ber strengthening materials: 1) a uniaxial carbon fiber sheet with an ultimate load of 0.34 kN/mm (1.95 kips/in.); 2) two layers of a uniaxial carbon fiber fabric with an ultimate load of 1.31 kN/mm (7.5 kips/in.) for th

39、e two layers combined; and 3) a pultruded carbon fiber plate with an ultimate load of 2.8 kN/mm (16 kips/in.). The tested load-strain diagrams forFig. 4—Details of test beams.Fig. 5—Comparison between carbon fiber plate,