Microsoft Word - ETASR_V12_N4_pp8884-8890 Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8884 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … Flexural Strengthening of Prestressed Girders with Partially Damaged Strands Using Enhancement of Carbon Fiber Laminates by End Sheet Anchorages Hayder Qays Abbas Department of Civil Engineering University of Baghdad Baghdad Iraq haider_q@yahoo.ocm Alaa Hussein Al‐Zuhairi Department of Civil Engineering University of Baghdad Baghdad Iraq alaalwn@coeng.uobaghdad.edu.iq Received: 23 April 2022 | Revised: 13 May 2022 | Accepted: 21 May 2022 Abstract-This paper examines the impact of flexural strengthening on the percentage of damaged strands in internally unbonded tendons in partially prestressed concrete beams (0, 14.28%, and 28.57%) and the recovering conditions using CFRP composite longitudinal laminates at the soffit, and end anchorage U-wrap sheets to restore the original flexural capacity and mitigate the delamination of the soffit of longitudinal Carbon Fiber Reinforced Polymer (CFRP) laminates. The composition of the laminates and anchors affected the stress of the CFRP, the failure mode, and thus the behavior of the beam. The experimental results revealed that the usage of CFRP laminates has a considerable impact on strand strain, particularly when anchors are employed. The EB-CFRP laminates increased the flexural capacity by approximately 13%, which corresponds to strand damage of 14.28%, while flexural capacity increased by 9.3%, strand damage increased by 28.57% for members strengthened with laminates only, and around 21.58% and 16.85% for members reinforced with laminates and end anchorings. Quasi-experimental equations have been proposed to estimate the actual stress of untethered tendons considering the effect of CFRP laminates and final fixation winding. Keywords-CFRP laminates; debonding; post-tensioned girder; strand damage; unbonded strand I. INTRODUCTION Recent destructive failures of pre-stressed (PS) concrete bridges have prompted a reassessment of the condition of several PS members [1], giving rise to new postings and, in some cases, emergency closure. Some of these failures are the result of terrorist attacks involving explosives [2], which damage PS bridge members or tendons [3]. The losing strands on the concrete member have a great effect on the design PS force which reflects a reduction of the nominal capacity and lack of serviceability [4]. One of the strengthening findings that will be investigated in this paper is the evaluation of the use of CFRP laminates with and without end anchorages for strengthening enhancement. CFRPs are increasingly being used to strengthen and repair Reinforced Concrete (RC) structures. The advantages of using Fiber-Reinforced Polymer (FRP) include the application's ease to use, the high ultimate strength, and corrosion resistance. The experimental results show that due to premature CFRP debonding from the concrete substrate, the maximum capacity of PS externally reinforced beams with CFRP sheets is not always completely realized. External FRP composites have emerged as a viable alternative to strengthening methods. FRP composites have been used for PS girder structures. It is not easy to determine strain and stress in unbonded tendons at ultimate flexural capacity due to the tendons' slip relatively to the surrounding concrete [5]. In practice, it is preferable to prevent the brittle failure mode by either eliminating it or shifting it to a more ductile mode. Anchoring the laminates to the concrete substrate with metallic or CFRP anchors may be a practical way to accomplish this [4]. CFRP U-wrapped anchors or other mechanical anchor systems have demonstrated high effectiveness in delaying the delamination process and increasing the strengthening efficiency. This study, along with [15], is a part of the ongoing investigating research regarding the efficiency of strengthening techniques that are conducted at Baghdad University (Civil Engineering Lab). The current paper focuses on the strengthening techniques using Externally Bonded CFRPs. II. MATERIAL PROPERTIES AND METHODOLOGY A. Design of the Tested Member All tests were conducted in the laboratory of the College Faculty of Baghdad University under 4 points of loading as shown in Figures 1 and 4. Seven girders, as illustrated in Table II, have been used in this paper, spanning 3000mm and resting on simply supported ends of 2800mm apart. The specimens were reinforced with 2φ16mm at the bottom and 2φ10mm at the top whereas φ10mm bars were used for stirrups. Two unbonded strands were used inside the 22.5mm PVC duct with end grips, and the strand extended by 0.45m from each side. CFRP laminates (bf=50mm and tf=1.2mm) were attached to the soffit to strengthen the specimen in addition to two CFRP sheets at the end for anchorage purposes with tf =0.167mm, set up on U wrapping shape as shown in Figure 2. Corresponding author: Hayder Q. Abbas Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8885 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … Fig. 1. Specimen and strand damage details. Fig. 2. Strengthening types considered in this study. B. Properties of the Tested Beams The design of the concrete mixture consisted of: Portland cement C45 with densities of 412kg/m 3 for cement, 1030kg/m 3 for aggregates, 548kg/m 3 for coarse sand, and 245kg/m 3 for fine sand (f’c=44.60N/mm 2 and ft=5.80N/mm 2 ), while 5.46lt/m 3 of superplasticizer were used. The yield, ultimate, strain, and area of steel bars are 518.20N/mm 2 , 658.970N/mm 2 , 12.20%, and 77.21mm 2 respectively for D10 bars and 577.30N/mm 2 , 710.74N/mm 2 , 13.40%, and 199.10mm 2 for D16 bars (Es=200000MN/m 2 ). Nominal area, ultimate strength, yield strength, and ultimate strain were 98.7mm 2 , 1860.00MN/m 2 , 1725.00MN/m 2 , and 5.00% respectively for the 7 wires of Grade 270 unbonded tendons (Es=197.5GPa). The manufacturer provided the carbon fiber fabrics' mechanical properties in addition to the resin, in which the nominal thickness, tensile strength, and ultimate elongation were 1.2mm, 3100MN/m 2 , and 0.02 respectively for laminates (Ef=170GPa), and 0.167mm, 3500MN/m 2 , 1.59% for unidirectional sheets (Ef=220GPa). The first letter B in the specimens' designation in Table II stands for beam, and the numbers 1 and 2 after the second letter designate the 14.25% and 28.57% strands damage groups, respectively. The letter R corresponds to individual group references, S to CFRP laminate strengthening, and W to laminate and end anchorage wrapping strengthening. TABLE I. PROPERTIES AND LOCATIONS OF STRAIN GAUGES Usage Type Ω Adhesive type QTY, location Steel FLAB–6–11 118.5±0.5 CN 2 @ tension bars Strand YEFLAB-2-3 119.5±0.5 CN 3 Concrete PL-60-11 120±0.5 CN-E 2 @ 5cm below the top CFRP BFLAB-5-3 119.5±0.5 CN 2 C. Recording Gauges and Setup All members were tested using a unidirectional electrical resistance strain gauge attached at the middle span to measure strain in the strand, FRP, concrete, and steel (Table I). D. Experimental Testing The steel cages were instrumented with strain gages of electric type before being placed in wood forms for concrete casting, using ready-mixed concrete. In addition to the dial gauge for measuring camber, the strain gauge wires were linked to a data logger to capture the strain of the strands during the pre-stressing process, as shown in Figure 3. Fig. 3. Post-tensioning process. Fig. 4. Test setup. TABLE II. TESTED GIRDER DETAILS Group Girder ID D (%) Aps (mm 2 ) Laminate (Lf) Sheets (Sf) ρρρρp ρρρρs tLf bLf LLf tsf bsf Lsf (mm) (%) Ref. B0 0 197.40 - - - - - - 0.490 0.810 B1 B1R 14.28 169.20 - - - - - - 0.385 B1S 1.2 50 2.7 - - - B1SW 1.2 50 2.7 0.167 250 76 B2 B2R 28.57 141.00 - - - - - - 0.320 B2S 1.2 50 2.7 - - - B2SW 1.2 50 2.7 0.167 250 76 Two 1cm thick end steel plates were used at the ends of each specimen with the incision at one of the endplates to protect and guide the strain gauge’s wires during the pre- stressing process. Τhe 2 endplates were punched with 2.2cm diameter PS ducting. For anchorage at the unbonded strands, 2 pieces of split-wedge anchor grips (barrel-type) were used. The grips were attached to the ends of the strands, which were then marked using a permanent marker to determine the pre-strain level that was applied in each strand. (∆L=15.5cm as per the member design required). The first strand was pulled out to the requisite pre-stressing value in two stages: initial for starching the strand and final to the preferred pre-stressing value. Then the piston was released. The procedure was then repeated with the second strand, with pressure gauge readings from the hydraulic jack used in the post-tensioning procedure [6]. Two Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8886 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … dial gauges were attached to each end of the strand to find out the slipping of the strand slip during the loading process. Four LVDTs were used to measure the deflection of the 2 specimens near the support, one under the point load, and the other under the quarter point. All LVDTs were set up to zero strain at the start of testing as shown in Figure 4. To progressively raise the load, a 50-ton hydraulic jack was installed to a load cell with a maximum capacity of 50ton. Increments of 15kN were added until the cracking load was reached. The load was then applied in 30kN increments until failure occurred. Each beam took approximately 2 to 3 hours to complete the test. The load cell was used to monitor the applied load from the frame of the test and to collect the reading data. The applied cracks were signified for each load step after the appearance of the first crack. The fracture pattern on the 2 sides of the cross-section was captured on camera after the test. The modes and ultimate loads of failure were reported. During testing, the first crack and crack propagation were monitored as well as the load deflection. III. RESULTS The test girders' performance was measured in terms of maximum load-bearing capability. All the reference girders failed in the compression zone due to flexure tensile steel reinforcing yielding, whereas the strengthened beams failed by laminate debonding followed by sudden compression and tension of concrete and steel bars (Figure 6). The first flexural crack appeared in the midspan of sub-reference girders PC1R, and PC2R, with respective cracking loads approximately 94%, and 85% of the reference girder’s cracking load. The cracking propagation is typically shown in Figure 5 at the end of the test members in the various test series. Fig. 5. Representative beam crack patterns. When the specimens were subjected to the externally applied load, the cracking patterns were quite similar and typical of flexural members. During the initial cyclic loading between Pmin and Pmax, the first flexural cracks appeared within the constant moment zone. Table IIII shows the cracking loads Pcr for the various members before FRP application. As the applied load increased, the number of cracks increased as they began to form within the shear zone. The cracks tended to separate as the load increased and additional flexural cracks were formed. Table III contains a summary of the members' modes of failure. Unbonded PC specimens failed due to concrete crushing, CFRP ultimate strain (rupture), CFRP debonding, or combinations of these modes. The propagation of interface cracks in the concrete near the CFRP in a horizontal direction along with the embedded tension reinforcement until connecting with the vertical flexural cracks caused peeling off of the concrete cover, indicating FRP debonding failure. The control girder failed in a more brittle mode than the strengthened girders, which was evidenced by faster crack propagation and fewer cracks but with wider widths, whereas the control girder showed a more brittle mode [7]. That is explained by the propagation of fewer and faster cracks in wide widths. A large number of cracks with smaller widths occurred for girders strengthen by carbon fibers. Fig. 6. Representative beam failure modes. A. Flexural Capacity and Load Deflection The tested members were investigated at 3 different load levels: cracking loads, post cracking elastic stage, and peak loads as shown in Figure 7. The CFRP laminates and tendons had almost no influence on the member behavior when the applied load did not reach the cracking load. The findings demonstrate that Group 1 and 2 exhibited more strength than the undamaged member. However, the strengthened members with laminates exhibited an increase in flexural capacity of 13- 9% for groups 1 and 2 and 21-16% for laminates with anchors when compared to the undamaged girders of the same group as illustrated in Figure 7, indicating the effect of the end anchorage on strength and ductility. The stiffness of the reference girders decreases slightly and the strengthened girders did not significantly differ from the damaged reference girders of the same group. When the applied load exceeded the cracking load, the damaged members exhibited a relatively high rate of stiffness deterioration [8] due to the absence of a portion of the pre-stressing force, which increases the development rate of crack and displacement. Likewise, the flexural-strengthening CFRP EB of the laminates exhibited their ability to postpone the fracture formation and deterioration of the stiffness of the strengthened girders [9], and the girders strengthened with laminates and anchors were observed to be superior to the girders strengthened with laminates only. The deflection is at the same value as the applied load which is equal to 0.79 of the ultimate load. The serviceability limitation for deflection (span over 250) is considered and the corresponding value is used in this paper, as B B1SW Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8887 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … per the result of control, the deflection at the serviceability limit is 1.12cm and this value is referred to as the permissible load which is about 79% of the ultimate load. The displacement of the strengthened girders was slightly reduced by 9–18% for B1S and B2S whereas almost the same amount (11-19%) of reduction occurred for B1SW and B2SW. It should be noted that in each case, the member with the end anchorage had a smaller drop in the value of the load, higher strength, and much more stiffness [10]. The CFRP girders strengthened with CFRP laminates and U-wrapping of CFRP sheets demonstrated increased deflection at the maximum load due to the absence of a relatively gradually load drop after the initiation of partial debonding. The ability of the members with an anchor to preserve their ductile response was exhibited. The ultimate displacement increased significantly when the specimen strengthened with laminates only and laminates with end anchorage, and the increment reached 18.16% and 11.39% respectively for B1SW and B2SW in comparison with B1S and B2S. TABLE III. SUMMARY OF SPECIMEN TESTING AND RESULTS Girder ID Cracking load (kN) Cracking load concerning control (%) Ultimate load (kN) Mid-span deflection at ultimate load (mm) Pcr/Pult (%) Change in flexural strength (%) Failure mode B0-control 55.03 - 166.240 26.9 33.10 - SF, CC B1R 52.05 94.5 157.250 25.5 33.10 5.410 R SF, CC B1S 62.79 14.06 187.990 24.1 33.40 13.080 I SF, CC-DL B1SW 66.78 25.9 202.120 28.5 33.00 21.580 I SF, CC-CD B2R 47.00 85.38 148.710 29.9 31.60 10.540 R SF, CC B2S 58.37 6.09 182.420 23.8 32.00 9.730 I SF, CC-DL B2SW 62.16 21.21 194.250 26.5 32.00 16.850 I SF, CC-CD SF, steel failure at tension zone, CC crushing of concrete, DL, delamination of CFRP laminate. CD covers delamination, a Negative sign is for reduction, and a positive sign is for increasing. R is for reduction, and I is for increase Fig. 7. Load deflection curves. B. Applied Load and Strain for the CFRP Laminates The cracks in CFRP laminates before the cracking load are minimal and nearly equal (Figure 6). After the load reaches the cracking load, the strain clearly increases, and after the bonded steel reinforcement yields, the strain increment rate increases significantly. The increased rates of strain in the CFRP laminates, with and without the end anchors, were almost similar but the maximum strain of the strain increases in CFRP laminates end by anchors was much higher. At the serviceability load limit, the rise in a strain of strengthened members B1S and B2S was 0.265% and 0.346%, in comparison with the 13.25% and 17.3% of the ultimate strain of laminate capacity (εffu =2%) with no significant change to the strengthened specimens with laminates and anchorage sheets, B1SW and B2SW. The strain increase at the ultimate load was 0.830% and 0.90% corresponding to 41.5% and 45.1% of the ultimate strain of the fiber capacity of B1S and B2S. The B1SW and B2SW specimens achieved more strain at the ultimate load, which is about 1.0235% and 1.033% corresponding to the 51% of the laminate strain capacity. Furthermore, the use of FRP laminates with end U-wrapping anchorage sheets had a significant impact on the compressive concrete strain. The CFRP laminates, as previously mentioned, were able to stop the development of cracks in their path. C. Applied Load and Effect on the Strands Strain Because of the minor strain increases, the strand did not contribute to flexural strength before the first crack. The increase in the strand strain was calculated by subtracting the post-tensioning initial strain from the actual strain (Figure 8). During this loading stage, the strand exhibited the same behavior in all the tested members. The strain increases in the strand for the references groups 1 and 2 were greater than the control girder's, whereas the strand strain increases in the members strengthened with laminates was less than in the same group members without strengthening. At the serviceability load limits, the increase in the strand strain for B1R and B2R was 7500με and 89501με, representing an increase of 8.5% and 29.5% from the control member. Similarly, the strain increases in the strands of the strengthened girders B1S and B2S were 6750με and 7620με, with a reduction of 14.670% and 14.860%. The references' strand strain increments were much smaller in the loading stage after the load in the serviceability manner in the strengthened members B1S and B2S at the same loading level. The lessening of the tendon strain increases in the member strengthened with end anchors was 14.67% and 17.88% for B1SW and B2SW girders. The above results prove that the CFRP strengthened with laminates, including the end U-wrapped anchors, have a great influence on the behavior of the strands. As previously mentioned, the CFRP laminates were able to delay the cracks, prevent their development, and slow down the degradation of the member stiffness. Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8888 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … Fig. 8. CFRP and strands load-strain. IV. EVALUATING THE NOMINAL MOMENT CAPACITY OF THE MEMBER A. The Increased Strain in the Strands Determining the increase in a strain of unbonded strands is a critical case in estimating the flexural strength of unbonded post-tension members strengthened with CFRP laminates. Regrettably, the design guidelines, such as [11] have only suggested one approach to evaluate the increase in the strain of bonded post-tendons and pre-tension members strengthened with EB-CFRP sheets, whereas the correlating approaches for unbonded strands in members strengthened with CFRP laminates were not included. Additionally, the result of the experimental work exhibited that CFRP laminates significantly influence the unbonded tendons' behavior [5]. The increase in the strain of the strand of the unbonded post-tension member strengthened with CFRP was evaluated using the equations for unbonded tendons in normal reinforced concrete members, as below [12]: For members without end CFRP U-wrapped sheet anchors: ∆���,��� �� ���� �� � � �1 � 100 �� �� ��� �� ���� ! ".$% (1) For members with end CFRP U-wrapped sheet anchors: ∆���,��� �� ���� �� � � �1 � 100 �& �& �&' �� �� �&((� ).*$ (2) The overall strain of the unbonded strands ∆���,��� is calculated as: ���,��� ��+ � ∆���,��� (3) where εfe is the initial strain of a strand not including strain losses = Fp/ (Ep Ap), Fp (N) is the actual tensile force in a strand, Ap (mm 2 ) and Ep (MPa) are the cross-sectional area and elasticity modulus of a strand respectively, ∆���,��� is the increase in a strain of strands, ψ is "the length of the plastic zone divided by the height of the compressive concrete zone": ψ = 10.50 [13] for un-cracked, simply supported unbonded post-tensioned members, reinforced with CFRP laminates, and ψ = 9.80 [14] for pre-cracked unbonded post-tensioned members reinforced by EB-CFRP, � is the maximum strain at the concrete compression fiber [11], dp, (mm) is the distance between the compressive concrete fiber's furthest point and the centroid of the strands' cross-sectional area, c (mm) represents the compression zone height [6], L0 (mm) represents the effective span of the member, and εfe represents the actual strain in CFRP laminates at the ultimate applied load. B. Evaluation of the Proposed Formula The suggested equations (2)–(4) were applied for the estimation of flexural strength of the 23 unbonded post tensioned members reinforced with CFRP laminates including the 7 simply supported members reinforced with EB-CFRP laminates investigated in this manuscript and the 16 slabs and beams of [7]. The theoretical (predicted) flexural strength, Mu,pred, was calculated as per [11] considering 1.0 as the factor of strength reduction, as below: • Step # 1: Estimation of the compression concrete zone depth. The depth of the neutral axis, c (mm), is initially assumed as depth/10 [11]. • Step # 2: Evaluate the strain in CFRP laminates, concrete, and strands. The CFRP laminate strain, �,+ , for failure detected by concrete crushing is: �,+ � - ���� � . �/0 1 �,� (4) where df is the effective CFRP laminate depth, εcu is the concrete’s ultimate compressive strength which is equal to 0.003, and �/0 represents the initial strain in the substrate: ε34 ����� �� �1 � + 56 78 � � 9:;56 <��� (5) where Fp is the initial prestressing force (N) after excluding the losses, e (mm) represents the prestressing force's eccentricity Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8889 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … concerning the concrete cross-centroid section, yb (mm) represents the distance from the gross-centroidal section (ignoring steel rebars) to the farthest bottom fiber, r (mm) represents the radius gyration of the member section = (Ic/Ac) 0.5 , Ic (mm 4 ) represents the moment of inertia of concrete cross concerning the neutral axis, MDL (N.mm) is the applied dead load’s moment, and εfd is the strain’s debonding, defined by: �,� 0.41 ∗ ? ,� @ A��B� 1 0.9�,,- (6) where fc′ is the concrete strength, εffu, tf, and Ef are the ultimate strain, thickness, and elasticity modulus of CFRP respectively, and n represents the CFRP layer’s numbers. The strain in CFRP laminate, εfe, for failure detected by the rupture of prestressing strands is: �,+ D��- . ��0 E ���� � . �/0 1 �,� (7) where εpu is the strand rupture strain which is equal to 0.05 and εpi is the strand initial strain, which can be estimated as: ��0 ���� �� � �� �� �� �1 � + 8 78 � (8) • Step # 3: Estimation of the steel rebars strain, εs: �� D�,+ � ��0 E � �� ��� ! (9) • Step # 4: The depth of c must be recalculated, using the summation of forces equal to zero. F ��,�GH�G,GH��,��IJ,�@KJ/ (10) where ffe (MPa) is the CFRP laminate stress = Ef × εfe, fps (MPa) is the strand’s stress = Ep × εps,CFRP ≤ fpy, and fs (MPa) is the tensile rebars’ stress = Es × εs ≤ fy. • Step # 5: Checking the c for the depth of the compressive concrete zone. Now, when the assumed value of c (cassumed) and the calculated through the above equations (ccalculated) meet the presented criterion of convergence in (11), the appropriate value of c is obtained. If not, another cassumed value is calculated, and the process is iterated starting at the second step until convergence is achieved. criterion of convergence | WGG � �WX| WGG 1 0.1% (11) • Step # 6: Evaluating the flexural strength of EB-CFRP strengthened member. The flexural strength of the EB-CFRP strengthened unbonded prestressed concrete member, Mu,pred can be calculated as: Z-,�7+� [�\�� �]� . KJ ^ � � [, \,+ �], . KJ ^ � � [� \� �] . KJ ^ � � [�_ \�_ � KJ ^ . ]_� (12) Fig. 9. Flexural capacity predictions and experimental results comparison. TABLE IV. THEORETICAL AND PREDICTED VALUE COMPARISON Members from [7] Members from this study Member Mu-P Mu-E Mu-P/Mu-E Member Mu-P Mu-E Mu-P/Mu-E UB1_H_F1 41.778 41.800 0.999 B0 90.706 91.43 0.99 UB1_H_F2 51.381 54.300 0.946 B1R 85.734 86.49 0.99 UB1_P_F1 34.749 41.400 0.839 B1S 103.774 103.39 1.00 UB1_P_F2 51.678 55.600 0.929 B1SW 104.61 111.17 0.94 UB2_H_F1 54.846 50.500 1.086 B2R 80.498 81.80 0.984 UB2_H_F2 63.855 65.500 0.975 B2S 100.0175 100.33 1.00 UB2_P_F1 50.787 58.500 0.868 B2SW 100.7985 106.84 0.94 UB2_P_F2 58.905 63.300 0.931 Average M 0.979 US1_H_F1 22.374 21.400 1.046 Standard deviation SD 0.026 US1_H_F2 27.324 26.900 1.016 COV 2.63% US1_P_F1 19.701 21.600 0.912 US1/P/F2 28.314 30.100 0.941 US2_H_F1 25.443 26.600 0.957 US2_H_F2 30.690 35.800 0.857 Totals US2_P_F1 27.423 29.800 0.920 M 0.953 US2_P_F2 31.680 37.400 0.847 SD 0.063 Average M 0.942 COV 6.56% SD 0.071 Mu-P is the theoretical (predicted) and Mu-E is the experimental value COV 7.5% Engineering, Technology & Applied Science Research Vol. 12, No. 4, 2022, 8884-8890 8890 www.etasr.com Abbas & Al‐Zuhairi: Flexural Strengthening of Prestressed Girders with Partially Damaged Strands … The predicted-to-experimental flexural strength ratios are illustrated in Table IV and Figure 9. The mean value of 0.953 and the Coefficient of Variation (COV) of 6.56%, describe the precision of the theoretical flexural strength values and their applicability for predicting the flexural strength of the EB- CFRP reinforced unbonded prestressed concrete members with and without wrapped sheet anchorages. V. CONCLUSION • Beams outfitted with the proposed U-anchor had an about 15% higher debonding load, as well as companion beams with the anchor have a higher maximum load and corresponding deflection. Anchors experienced greater CFRP strain than their counterpart members without anchorages, and the maximum strain is much more than the theoretical strain-based [11] The anchorage was discovered to be effective in restricting the extent of debonding of the laminate, thus indirectly contributing to member flexural stiffness by restricting the crack width. • For the same loading level, the flexural capacity of post- tensioned girders decreases as the strand damage ratio increases, whereas the displacement of girders increases the damaged strands ratio. 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