Keywords: Basalt fiber reinforced polymer, pre-reinforcement, T-section reinforced concrete beam, ultimate flexural capacity.

Transcription

1 Send Orders or Reprints to The Open Construction and Building Technology Journal, 215, 9, Open Access Experimental Research on the Flexural Capacity o Reinorced Concrete Beams Reinorced with BFRP Cheng Haigen 1,*, Tian Qin 2, Shang Jingmiao 1 and Lu Dinkun 1 1 School o Civil Engineering, East China Jiaotong University, Nanchang Jiangxi, 3313, P.R. China; 2 School o Civil Engineering, Nanchang University, Nanchang Jiangxi, 3313, P.R. China Abstract: In order to study the ultimate lexural capacity o reinorced concrete beams with BFRP (Basalt iber reinorced polymer), the test is designed and poured our T-section reinorced concrete beams. At irst, monotonous static loading is carried on two o the beams until the chinks appeared. Aterward, all beams are strengthened by BFRP sheets. The contrast experiment studied and analyzed the dierent cracking load, ultimate load, delection, reinorcement strain, concrete strain, iber cloth strain, crack development o pre-reinorced beams and damaged beams strengthened by BFRP sheets. At the same time, the theoretical analysis and inite element simulation are perormed to veriy the result o experiment. The results show that the ultimate lexural capacity o reinorced concrete beams with BFRP has signiicantly increased. The circular bead treatment raises woke eect and reduces stress concentration o BFRP sheets. Keywords: Basalt iber reinorced polymer, pre-reinorcement, T-section reinorced concrete beam, ultimate lexural capacity. 1. INTRODUCTION Basalt iber reinorced polymer (BFRP) is made rom natural basalt ore, while the price o BFRP is 1/3 the price o domestic carbon iber material and 1/1 the price o imported products respectively [1]. The advantage o BFRP is that its melting process does not produce alkali oxides and toxic and harmul gases. In addition, because the residual waste o underground landill treatment or BFRP does not have eect on the soil pollution and water pollution, BFRP has a very good prospect. Although the research on BFRP is started relatively late in China, people recently ocus on the BFRP research which has been considered as a key national plan [2]. Many researchers studied on the shear behavior and lexure behavior, but the contrast experiment is lacking [3-7]. Based on the previous study, this paper ocuses on the ultimate lexural capacity o reinorced concrete beam with BFRP. The research methods are experiments combined with the theoretical analysis and inite element simulation. 2. EXPERIMENTAL DESIGN 2.1. Manuacture and Material Properties o Test Beam Unlike the actual T-section reinorced concrete beam with the length o 16 m, the test reinorced concrete beams are manuactured by size reduction. The section o prototype beam is composed o seven T-section reinorced concrete beams. Based on the stress similitude, the dimension o test beam is shown in Fig. (1) and Fig. (2). Similarity ratios o the test beams are 1:13.3 and 1:2.5 or longitudinal and transverse directions respectively. *Address correspondence to this author at the School o Civil Engineering, East China Jiaotong University, Nanchang, Jiangxi, 3313, P.R. China; Tel: ; bridge47@126.com There are our test beams in this study, which are divided into two groups. The test beams in one group are prereinorced beam, while the test beams in the other group can be used to simulate actual reinorcement beam. The number o beam, reinorcement ratio and lange height are shown in Table 1. In this paper, concrete design strength grade is C4, while hot rolled ribbed bars (HRB335Φ12 and HRB335Φ1) are used as main steel bars. Ten hot rolled plain round bars (HPB235Φ6) equipped as stirrups and hot rolled plain round bars (HPB235Φ1) are adopted as supports. The measured mechanical property parameters o steel bars are presented in Table 2. Basalt iber reinorced polymer applied in this test is BUF9-3 produced in GBF Company. The material property parameters are illustrated in Table Cracking Test Beore Reinorcement In order to compare with the mechanical property parameters o pre-reinorcement concrete beam, loading tests or two test beams are carried out ater 28 days maintenance. Fiber reinorced polymer sheets do not reinorce these two test beams. The compression orce o the hoisting jack is 3 kg/cm 3, while the maximum output load is 3 t. The oil pump used in this test is manual pump made in De Zhou hydraulic equipment Company and each manual operation can generate 8 KN o output load. Test results: For the beam o DB-1, two cracks appear in the region supported on two bearing supports when loading value is 168 KN. The angle o the crack is 45 degree, while the crack extends slowly. Near the region o bearing supports, the maximum crack width is mm, which is larger than the limit o crack width. Since the phenomena o concrete-lake-o appear in the region o bearing supports, the region is repaired by the / Bentham Open

2 278 The Open Construction and Building Technology Journal, 215, Volume 9 Haigen et al. Fig. (1). Dimensions and reinorcements o test beams (unit:mm). Fig. (2). Cross-section shape o test beams (unit:mm). Table 1. Parameters o test beams. Numbering Reinorced Case Depth o the Designed Flange mm Depth o the Actual Flange mm DB DB-2 Tensile reinorcement is divided into two layers. First layer includes two Φ12 bars o HRB335. Second layer includes two 1 18 YJG-1 Φ1 bars o HRB335.Stirrup spacing is 125mm. Stirrup is Φ bar o HPB235. YJG Table 2. Steel mechanical property. Model Diameter /mm Yield Strength /MPa Tensile Strength /Mpa Elongation /% HPB HRB

3 Experimental Research on the Flexural Capacity The Open Construction and Building Technology Journal, 215, Volume Table 3. Parameters o basalt iber cloth material. Product Model Unit Weight (g/m 2 ) Design Thickness /mm Tensile Strength /Mpa Young's Modulus /Gpa Extension Rate /% BUF Fig. (3). Loading mode. Table 4. Non-reinorcement beam characteristics. Number Whether Existing Cracks Whether Corners are Rounded Suraces DB-1 yes no DB-2 yes yes YJG-1 no no YJG-2 no yes concrete mixed reinorcement adhesives. For the beam o DB-2, three cracks appear between bearing support and beam centroid, when loading value is 22 KN. The maximum crack width is.64 mm, which is also larger than the limit o crack width. Loading mode is shown in Fig. (3) Reinorcement Scheme When carbon iber sheet pastes on the concrete member, the curvature radius should be larger than 2 mm at the surace o the concrete member corner. However, because it is very diicult to deal with the complicated corner, the angle is 9 degree at the corner in actual engineering. The eect o circular bead treatment on the experiment results is considered in this test. In the our T-section beams, DB-1 and DB-2 are loaded until cracks beore the test, while YJG-1 and YJG-2 keep intact. For DB-1 and YJG-1, the angle at the web bottom corner is 9 degree. For DB-2 and YJG-2, the radius is 2 mm at the web bottom corner. The properties o the our T- section beams are shown in Table 4. When basalt iber reinorced polymer is used to reinorce the positive bending moment area o T- section beam, the basalt iber reinorced polymer length should extend to the bearing supports edge. The truncation place o the carbon iber sheet is determined by the ull use o section [8, 9]. The extent length o carbon iber sheet is 58 mm (43+15), while the width o carbon iber sheet is 72 mm. The measured deviation is ±2 mm. Two layers o carbon iber sheets are applied at the beam bottom, while the actual thickness is.218 mm (2.19). Two sides o the web or T-section beam are anchored by carbon iber sheet U-shaped hoop, while the paste height is 348mm. Two sides o the web are equipped with three U- shaped hoops, the width and clear spacing are 2 mm and 75 mm respectively. Diagonal section o test beam is reinorced by U-shaped hoop which is ixed to the attached iber cloth above it. The iber cloth is one layer o 9mmx9mm abric, which is close to the lange at the bottom [1]. The paste order o carbon iber sheet is shown as ollows: carbon iber sheet at the beam bottom U-shaped hoop carbon iber sheet at two sides o web cover U-shaped hoop with carbon iber sheet. Paste position and size are shown in Fig. (4).

4 28 The Open Construction and Building Technology Journal, 215, Volume 9 Haigen et al. In order to make sure the objectivity o the test results, more strain gauges are pasted on the beam. Four strain gauges are symmetrically pasted on the main steel bar. Two pieces o strain gauges are symmetrically pasted on lange o mid-span along the longitudinal direction. The distance rom one o the strain gauges to cross-sectional symmetry axis is 16mm. Two pieces o strain gauges are symmetrically pasted on the tensile abric cloth o bottom surace o the midspan tension zone. Four pieces o strain gauges are pasted on U-shaped hoop o web, its margin increases rom bottom to top. Four pieces o strain gauges are symmetrically pasted on oblique section. Strain gauge glued location and spacing are shown in Fig. (5) Fig. (5). Strain gauge glued location (unit: mm). Fig. (4). Positioning map o BFRP sheets (unit:mm) Strain Gauge Arrangement The strain gauges are pasted on the main steel bars o T- section beam at mid-span beore pouring the concrete. Ater the carbon iber sheet is pasted on the beam bottom, the strain gauges are pasted on the web U-shaped hoop and oblique section at mid span. Strain gauge speciication is shown in Table Test Process In order to check the working perormance o the test equipment, preloading o the reinorced beam is carried out beore the test. The maximum preloading value is 7% o the maximum cracking load. During the test, cracks do not appear in the reinorced beam. Loading test method is step loading, and each step loading is 2 KN. The limit loading time is 6 s, while the time under sustained loading is 12 s. Because the deormation is stable, the strain, crack width and reading data o the dial indicator can be easily recorded. 3. THEORETICAL ANALYSIS AND FINITE ELE- MENT SIMULATION 3.1. Theoretical Analysis Bearing Capacity o Normal Section Based on the previous study, the strengthened section equation o reinorced concrete beam is illustrated in related literature [11]. According to the ormula ( ) α bx+ b b h = A + A 1 c y s py p x=66.46 mm h =6. mm (1) Table 5. Speciications o strain gauges on dierent sticking positions. Sticking Position Model Resistance /Ω Gate Length Gate Width /mm Sensitivity Coeicient Steel bar Concrete Fiber cloth BX12-2AA BX12-8AA BX12-5AA ± ± ±2.

5 Experimental Research on the Flexural Capacity The Open Construction and Building Technology Journal, 215, Volume The test beam is second class T-section beam, according to the ollowing ormula x b M α 1 cbx h + α1 (2) c 2 ( ) b b h h 2 The maximum design bending moment M=52.57kN m. Loading location is at mid span in the test, while the maximum load capacity is N=175.24kN. The carbon iber sheet size can be substituted into the ormula [12]: k m n E t = 1.16 (3) 38 Solution: k m = So k m is.9 the eective cross section area o the carbon iber sheet is calculated as per the ollowing ormula. A e = A k m = 72!.19! 2! mm 2 (4) ψ = (.8 εcuh/ x) εcu ε ε / =.1 =.98 < 1. According to the ormula α + (5) 1 cbx = s As ψ A e (6) Solution results x=14.753mm ( ) y s Solution results: the maximum design bending moment ater reinorcement, M=66.91KN m, the increase value is 27.28%. The ultimate bearing capacity is KN in the case o the design loading at mid span Load Capacity o Oblique Section 1.75 = =.7 λ + 1 x h M α1cbx h + α1c b b h h 2 2 A h h a λ = = 1.2 h λ = 1.5 ( ) σ x (9) Asv Vcs = αcv tbh + yv h s = = KN (7) (8) (1) The design value o the shear capacity Vcs=177.87KN h / b= > 6 w Based on the ormula V!.2! c c bh, the design maximum value o the shear capacity o oblique section is KN V cs The design width and clear spacing o U-shaped hoop can be substituted into the ormula: V =ψ A h / s b vb.58 (.56 21) = 275 = 13.73KN (11) V! V b + V b = kn (12) Solution results: The design value o the shear capacity ater reinorcement, V=238.5 KN 3.2. Finite Element Model Finite element analysis is carried out by the sotware o ANSYS. The elements o Solid 65 and Link 8 can be used to simulate concrete and steel bar respectively. The mesh generation and the loading are shown in Fig. (6). The ultimate bearing capacity o reinorcement beam model is KN, while the displacement at mid-span is14.7 mm. The steel strain and stress are 1671 µε and MPa respectively. The carbon iber sheet strain in the tension area is 1694 µε. 4. THE TEST RESULTS AND ANALYSIS 4.1. Loading Test and Damage Condition Loading Test Damage or DB-1 Beam When loading value is 6 KN, origin crack decreases rom mm to 1.32 mm because o bearing restraining. When loading value is 14 KN, the crack width gradually increases and the delection at mid-span is.49 mm. When loading value is 22 KN, the crack width is mm and the delection at mid-span is.78 mm. The steel stress and strain are MPa and µε respectively. The sound o U-shaped hoop and cover strip generates, while the crack width near the U-shaped hoop is.84 mm. When loading is continuous, the concrete near the bearing is damaged, while steel strain and the delection at mid-span increase. When loading is 265 KN, the size o two cracks sharply increases. The concrete near the bearing begins to all o, while the shear break o carbon iber sheet occurs near the bearing. The displacement at mid-span transiently decreases. Both sides o the cover strip and U-shaped hoop appear peeling phenomenon at crack area. Because the beam o DB-1 is damaged, the reading o loading sensor decreases. The delection at mid-span is 1.6 mm, while steel bar strain and stress are 57.8 µε and11.56 MPa respectively. When the loading is applied on the beam o DB-1, both the width o the crack and the damage degree o the beam are large. The ultimate load can be greatly promoted ater reinorcement, but the damaged concrete has eect on the ultimate load to a certain degree. The beam o DB-1 quickly presents brittle ailure pattern when carbon iber sheet and concrete are separated, as shown in Fig. (7).

6 282 The Open Construction and Building Technology Journal, 215, Volume 9 Haigen et al. Fig. (6). Element division and loading o test beams. Fig. (7). The ailure mode o Team DB Loading Test Damage or DB-2 Beam When loading value is 12 KN, the width o crack is.98 mm. Ater that the width o crack obviously increases. As the loading value is 32 KN, the extension o crack is obvious and the cracks extend to the lange bottom o the mid-span. Many new ine cracks appear in the area near the origin cracks, while the width o new cracks is less than.5 mm. The delection at mid-span is 2.56 mm, and steel tension strain is µε. The steel compression strain at midspan is µε. When loading reaches 38 KN, the sound o U-shaped hoop comes out. The width o new cracks becomes large. When loading value is 42 KN, some part o U- shaped hoop appears racture. Cover strip separates rom concrete ace, while the delection at mid-span increases. The steel strain and steel stress are µε and MPa respectively. The steel strain in compression area is µε. The recorded maximum loading is 446 KN. The peeling phenomenon between U-shaped hoop and cover strip obviously appears. The delection at mid-span sharply increases, and the carbon iber sheet is cut at bearing support. The width o crack extends to mm. The width o the crack at lange bottom is 3.42 mm. At the same time, the concrete all o at bearing support. Based on the above statements, the beam o DB-2 is completely destroyed, as shown in Fig. (8) Loading Test Damage or YJG-1 Beam When loading value reaches 16 KN, the extension sound o carbon iber sheet is obvious. The delection at mid-span is.95 mm, while steel strain and carbon iber sheet strain are µε and 31.7 µε respectively. The concrete strain at compression area is µε. When loading is 24 KN, the sound o U-shaped hoop is obvious. The extension orce o carbon iber sheet increases. When loading is 28 KN, many cracks o oblique section symmetrically appear. The width o crack extends to.42 mm. The angle between the crack and the horizontal line is 36.2 ~43.7. At the same time, the delection at mid-span is 4.27 mm, while the strain o carbon iber sheet in extension area is

7 Experimental Research on the Flexural Capacity The Open Construction and Building Technology Journal, 215, Volume Fig. (8). The ailure mode o Team DB-2. Fig. (9). The ailure mode o Team YJG-1. µε. Steel strain and steel stress are µε and MPa respectively. The concrete strain in compression area is µε. When loading is 328 KN, the width o crack extends to16.82 mm at the bending shear region. The concrete at bearing support all o and the peeling between U-shaped hoop and cover strip appears. The delection at mid-span reaches the maximum value, while the beam o YJG-1 is damaged, as shown in Fig. (9) Loading Test Damage or YJG-2 Beam When loading value reaches 24 KN, the extension sound o carbon iber sheet is obvious. The delection at mid-span is 2.34 mm, while steel strain and carbon iber sheet strain are µε and µε respectively. The concrete strain at compression area is µε. When loading value is 34 KN, the width o crack on the bearing sup- port is less than.2 mm. The delection at mid-span is 2.93 mm, while steel strain and carbon iber sheet strain are µε and 147 µε respectively. The concrete strain at compression area is µε. The width o crack gradually increases with the increase o loading. New vertical cracks appear, while the cover concrete begins to all o. When loading value is 4 KN, the width o crack is 1.56 mm. Carbon iber sheet generates sound during loading process. Cover strip and concrete separates, while U-shaped hoop and concrete also separates. The separating area gradually increases and cracks o some carbon iber sheets extend to the bottom o U-shaped hoop. The variation rate o delection at mid-span obviously increases, while increasing rate o carbon iber sheet strain deceases and the steel strain continues increasing. When loading value is 426 KN, lexural and tensile carbon iber sheets at bearing support are neatly

8 284 The Open Construction and Building Technology Journal, 215, Volume 9 Haigen et al. Fig. (1). The ailure mode o Team YJG-2. Table 6. Ultimate bearing capacity o iber reinorced concrete beam. Number Ultimate Bearing Capacity o Test Values KN Improved Ratio % Failure Modes DB DB YJG YJG Extended tensile abric parts are broken o, u-shaped clamps and cover are stripped o, supports concrete are broken o. Tensile abric parts are torn to disconnect, u-shaped clamps and cover are stripped o, partial concrete are broken o, cracks o lange bottom are noticeable. Tensile abric o supports are cut o, u-shaped clamps and cover are stripped o, partial concrete o supports are broken o. Tensile abric o supports are cut o, u-shaped clamps and cover are stripped o, cracks about lexure-shear zone o concrete are noticeable. cut. Both the U-shaped hoop and the cover strip are separated rom concrete. The maximum delection at mid-span is mm, while steel strain and steel stress are µε and MPa respectively. The maximum strain o carbon iber sheet is µε. The concrete strain in compression area is µε. The reading o loading suddenly changes, while the beam o YJG-2 is completely damaged, as shown in Fig. (1) Analysis o Test Results The ultimate bearing capacity o the pre-reinorcement concrete beam and reinorcement concrete damaged beam is shown in Table 6. The main tensile steel bars in reinorced concrete beam are Φ12HRB335 and Φ1HRB335. Concrete cover thickness is 3 mm. Load-strains curves are shown in Fig. (11) and Fig. (12). According to Fig. (11) and Fig. (12) because there is no slip between steel and concrete beore the loading value is 3 KN, the stress o the steel bar in pre-reinorcement beam obviously changes. The deormation o beam can be eectively reduced. However, when loading value is over 3 KN, the cracks appear in the concrete and the capacity o the steel bar decreases to a certain degree. It is that carbon iber sheet aords bending moment. Strain gauges on carbon iber sheet are glued on both sides o U-shaped hoop at mid-span. Strain curves are shown in Fig. (13). According to Fig. (13), carbon iber sheet o prereinorcement beam can work together with steel bar earlier. Carbon iber sheet strain o pre-reinorcement beam is larger than that o comparison beam. Because concrete cover is damaged, carbon iber sheet aords most o the tensile stress. When the loading is 4 KN, the strain o carbon iber sheet sharply increases.

9 Experimental Research on the Flexural Capacity The Open Construction and Building Technology Journal, 215, Volume strain 5 DB-1 DB-2 YJG-2 YJG-1 Fig. (11). Load-strains curves o Φ12 steel Applied load(kn) strain 5 DB-1 DB-2 YJG-2 YJG Applied load(kn) Fig. (12). Load-strains curves o Φ 1 steel Strain 1 5 DB-1 DB-2 YJG-2 YJG Applied load (kn) Fig. (13). Load-strains curves o tension iber cloth.

10 286 The Open Construction and Building Technology Journal, 215, Volume 9 Haigen et al. CONCLUSION According to the results o test on our reinorcement beams, the ollowing conclusions can be made. (1) Both cracking load and yield load o the reinorcement beams can be obviously improved. Cracking rate o concrete is reduced because o carbon iber sheets extension orce eects. When the loading reaches the ultimate load, carbon iber sheet aords tensile stress o the beam. The strain o carbon iber sheet approaches or exceeds the strain o steel bar. (2) Comparing with reinorcement damaged beam, carbon iber sheet o pre-reinorcement beam can aord external orce together with steel bar. The strain o carbon iber sheet has similar value with the strain o steel bar. In addition, the stiness o pre-reinorcement beam is larger than the one o reinorcement damaged beam. The delection o pre-reinorcement beam at mid-span is less than the one o reinorcement damaged beam at late phase o loading. The stiness can be signiicantly improved or the prereinorcement beam. (3) The protective eect is better or lexure and shear zone o the concrete in the case o pre-reinorcement beam. The ailure pattern o pre-reinorcement beam includes peeling or shear break o carbon iber sheet. In addition, there are many cracks in the concrete o pre-reinorcement beam. However, the phenomena o concrete-lake-o occur beore the peeling o carbon iber sheet or reinorcement damaged beam. (4) Flexural behavior is better than shear behavior or the test beam due to the eects o carbon iber sheet layers and U-shaped hoop anchoring type. Thereore, the ailure patterns are concrete crush damage and carbon iber sheet bond ailure, but the tension ailure o carbon iber sheet does not occur. In order to overcome the above damage types, wooden ormwork can be used to compact the carbon iber sheet. Thereore, the high strength o carbon iber sheet can be made ull use o. (5) The circular bead treatment o the test beam could improve the unction o carbon iber sheet and U-shaped hoop. The stress concentration at the corner o beam can be obviously reduced, while the ultimate load can also be signiicantly improved. (6) According to Code or design o concrete structures and Code or design o strengthening concrete structure, theoretical derivation o the design ultimate bearing capacity o normal section and the design ultimate bearing capacity o oblique section can be obtained respectively. Comparing with the test results, the numerical solution o ANSYS is more saety. CONFLICT OF INTEREST The authors conirm that this article content has no conlict o interest. ACKNOWLEDGEMENTS The authors wish to acknowledge the support and motivation provided by the National Natural Science Foundation o China (Grant No ). REFERENCES [1] C. Zhou, Production status o domestic carbon iber material, Lu Tian Hua Ke Ji, vol. 3, pp , 211. [2] J. Ni, Research o Reinorced Concrete T-Beams Strengthened with BFRP, M.S. thesis, Chongqing University, Chongqing, P.R. China, 213. [3] O. Yu, Y. Zhang, and X. Li, The research on she-ar capacity o RC beams strengthened with BFRP sheets, Industrial Construction, vol. 39-1, pp , 29. [4] Y. Sun, Y. Liu, and H. Hu, Experimental study on reinorced concrete beams strengthened with BFRP, Journal o Qingdao Technological University, vol. 31-1, pp , 21. [5] L. Wan, and Z. Chen, Experiment research on reinorced concrete slabs strengthened by three kinds o FRPS, Structural Engineers, vol. 23-1, pp , 27. [6] Y. Yang, X. Chen, J. Xing, J. Wang, and L. Hu, Study on atigue perormance o reinorced concrete beams strengthened with BFRP sheet, Journal o Huaqiao University, vol. 31, no. 3, pp , 21. [7] L. Ouyang, B. Ding, and Z. Lu, BFRP and its application review in structural strengthening, FRP /CM, vol. 3, pp , 21. [8] China association or engineering construction standardization, CECS 25:9 Technical Speciication or Strengthening Concrete Structures, P.R. China, Beijing, 199, pp [9] China association or engineering construction standardization, CECS 146: 23 Technical Speciication or Strengthening Concrete Structures with Carbon Fiber Reinorced Polymer Laminate, P.R. China: Beijing, 23, pp [1] L. Tan, GB Design Code or Strengthening Concrete Structure, Beijing, P.R. China 26, pp [11] S. Zhao, Design Principles o Reinorced Concrete Structure, Shanghai, P. R. China 24, pp [12] L. Bu, L. Song, and C. Shi, Experimental and theoretical study on lexural behavior o RC beams strengthened with carbon iber plates, Journal o Building Structures, vol. 2, pp , 27. Received: May 26, 215 Revised: July 14, 215 Accepted: August 1, 215 Haigen et al.; Licensee Bentham Open. This is an open access article licensed under the terms o the ( which permits unrestricted, noncommercial use, distribution and reproduction in any medium, provided the work is properly cited.