UNIAXIAL COMPRESSION TEST OF STEEL PLATE BONDED VARIOUS FRP SHEETS

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1 UNIAXIAL COMRESSION TEST OF STEEL LATE BONDED VARIOUS FR SHEETS Takeshi MIYASHITA Specially appointed associate professor Nagaoka University of Technology 1631 Kamitomioka, Nagaoka, Niigata, Japan Yusuke OKUYAMA h.d. Student Nagaoka University of Technology Dai WAKABAYASHI Nippon Expressway Research Institute Company Ltd. Norio KOIDE Kawasaki Heavy Industries, Ltd. Yuya HIDEKUMA, Akira KOBAYASHI Nippon Steel Composite Company, Ltd. Wataru HORIMOTO Kurabo Industries, Ltd. Masatsugu NAAI rofessor Nagaoka University of Technology Abstract This paper is a fundamental study on rational repair and reinforcement of webs in corroded steel girder bridges using Fiber Reinforced lastic (FR). Uniaxial compression test of steel plates bonded various FR sheets is carried out. The objective of this test is to select FR sheets that have reinforcing effect following large deformation induced by buckling. Furthermore, a layer of polyurea putty is inserted between the steel plate and the FR sheet and its effect is investigated. Lastly, the method that predicts elastic buckling load of the steel plate with FR is developed. Keywords: Fiber Reinforced lastic, steel plate, uniaxial compression test, buckling 1. Introduction Most of the deterioration for steel bridges is the corrosion. During their period of service, progress of corrosion is inevitable due to the influence from surrounding circumstance. The conventional methods repairing and reinforcing the damage are the replacement of corroded members or the attachment of steel plate on them. However, these methods are regulated in service because of requiring heavy machineries. Therefore, efficient and rational method repairing and reinforcing the damage is strongly needed. In this situation, Fiber Reinforced lastics (FR) has been paid to attentions due to light weight and high stiffness, and many studies have been reported so far [1], []. revious studies mainly focus on the applications to members subjected to normal stress; flanges in a steel girder bridge or chord members in a steel truss bridge. However, corrosions in the steel age 1 of

2 bridges mostly occur at webs near the ends of supports where shear force with large deformation at the ultimate state is dominant. Herein, although debonding of FR under large deformation becomes a problem, this type of investigation has been few reported. Therefore, the objective of this research is to carry out a fundamental study on rational repair and reinforcement of webs in corroded steel girder bridges using FR. Uniaxial compression test of steel plates bonded various FR sheets is carried out. This test aims to select FR sheets that have reinforcing effect following large deformation induced by buckling. Furthermore, a layer of polyurea putty is inserted between the steel plate and the FR sheet and its effect is investigated. Lastly, the method that predicts elastic buckling load of the steel plate with FR is developed.. Outline of experiment.1 Materials The property used in this research is shown in Table 1. In this study, six kinds of FR sheets are selected ; high elastic carbon fiber (), high strength carbon fiber (CU), carbon fiber strand sheet (), glass fiber (), high strength polyethylene () and hybrid fiber (H, C:=1:1). Table shows the dimensions and the material characteristic of a steel plate used in this study. Table 3 shows the material properties of the polyurea putty and resin. Table 1. roperties of FR sheets. Fiber sheet FR Design value Sign Type M easured value Thickness Young's modulus Ecm t FR EFR Thickness Young's modulus Young's modulus t cd Ecd High elastic carbon fiber E+5 7.E E+4 CU High strength carbon fiber.11.4e+5.79e E+4 Carbon fiber strand sheet.6 6.4E E E+5 glass fiber E+4 1.5E E+4 High strength polyethylen.1.e+4 9.3E E+4 H Hybrid fiber E+5 5.1E E+4 Table. roperties of steel plate. Length SM 49YB Cross section Young's modulus Yield stress / 69.E+5 4 Table 3. roperties of putty and resin. olyurea putty FUZ FRE5 Density g/cm Amount of coating g/m 1 1 thickness Young's modulus FBE7S for s Figure 1 shows the cross section of specimens. FR sheets were bonded to both sides of the steel plate. The parameters in this experiment are shown in Table 4. The types of the specimen are classified into two cases according to the number of laminated FR sheets. In Case 1, the number of FR layers bonded to both sides of the steel plate is one. In Case, the number of FR layers is two. age of

3 Fiber sheet olyurea putty rimer Steel Steel Fiber sheet rimer Figure 1. Cross section of. Table 4. Experimental parameter (Unit: ). Case 11.3 s FR FR Sheet length Sign 1st layer nd layer 1st layer / nd layer N Steel length olyurea putty 1 U 13 CUN CU 14 CUU CU 15 N 16 U 17 N 1 U 19 N 11 U 111 HN H 11 HU H 113 N U 3 1 N 45/ U 45/ 3 N 45/ 4 U 45/ N 45/ 6 U 45/ 7 U 45/ U 75/7 Experimental method In this experiment, horizontal displacements and strains on both sides of the specimen were measured. Figure shows the measurement positions of strain gauges and displacement sensors. In order to realize simple supported boundary conditions, both ends of the steel plate were sharply cut. As a preliminary experiment, uniaxial compression test for a steel plate revealed its maximum load as Since theoretical value () of the plate is 9.6, it can be said that expected boundary condition is realized. age 3 of

4 (b) Case 1 (Steel:, FR: 3) 9 9 (a) Case 1 (Steel:, FR: ) (c) Case (Steel:, FR: 45) 17 (d) Case (Steel:, FR: 75) Figure. Details of specimen. 3. Results and discussions 3.1 Reinforcing effect Table 5 shows the results of experiment. In the table, E and max mean and the maximum load in experiment respectively. The reinforcing effect is defined as the following equation. Reinforcing effect (%) = max E 1 E (1) Figure 3 shows the reinforcing effect in Case1 and Case. Table 5. Result of experiment. N1 N N3 U1 U U3 CUN1 CUN CUN3 CUU1 CUU CUU N1 N N3 U1 U U3 N1 N N3 U1 U U N1 N N3 U1 U U3 HN1 HN HN3 HU1 HU HU N1 N N3 U1 U U3 U N1 N N3 U1 U U3 N1 N N3 U1 U N1 N N3 U1 U U3 U1 U U3 U1 U U age 4 of

5 1 Average N U CUN CUU N U N U N U HN (max E) / E 1 (%) (max E) / E 1 (%) 1 Average HU N U () () N U (a) Case 1 N U N U U U (b) Case Figure 3. Reinforcing effect. 3. Deformation In Table 5, central horizontal displacement at the ultimate states of FR is also shown. Herein, the ultimate state, which were debonding or breaking, was determined from measurements by the strain gauges. It was confirmed from the result of Case 1 that low modulus fiber sheets such as and showed better performance on deformation. 3.3 Loaddisplacement curve Representative examples of loaddisplacement curve in and are shown in Figure 4. In the figures, U and N mean the cases with and without putty. In the case of N, the load dropped suddenly when the central displacement reached beyond 5 due to the fracture of FR sheets. On the other hand, the load in U did not show sudden drop by the effect of putty. Similarly, in the case of N, the load dropped suddenly when the central displacement reached beyond 4. On the other hand, the load in U did not show sudden drop. Therefore, it is found that the polyurea putty used in this study can prevent the debonding or breaking of FR, and improve the flexibility. 1 U1 16 N1 U1 16 N1 14 Load [] Load [] Displacement [] Displacement [] (a) (Case1 FR: ) (b) (Case FR: 45) Figure 4. Loaddisplacement curve. 3.4 Failure modes Case1 The most of failure mode in this case was debonding or breaking at the center of the specimens in tensile side. However, the case using only shown other failure mode that was debonding at the end of the specimens in Figure 5. This is the reason why the change of cross section at the end of the specimen is larger since is thicker than other FR sheets. In the case of N, FR sheets were delaminated at the end of the specimen in small deformation. On the other hand, in the case of U, the polyurea putty suppressed the age 5 of

6 progress of delamination although FR sheets were delaminated at the end of the specimen. (a) N (b) U Figure 5. (Case1 FR:) Case In this case, the combination of FR sheets lead to different failure modes. In the case of, which is the case using two layers, failure mode was the delamination at the end of the specimen in spite of the existence of the polyurea putty. In the case using low elastic FR sheets such as or, the most of failure mode was the breaking at the center of FR sheet although there was a little difference by the existence of the polyurea putty. In the case of that and were used in the first and second layer, failure modes were the delamination at the end of the all specimen. However, U shown different failure mode comparing to other two specimen as shown in Figure 6. The specimen bent at the end of FR sheet. On the other hand, in the case of U, the specimen bent at its center in spite of using sheet as shown in Figure 7. Thus, when the length of FR sheet having high stiffness such as is short on the steel plate, it is necessary to consider the effect of reinforcing length. Figure 6. U(Case FR:). Figure 7. U(Case FR:75). age 6 of

7 4. rediction of elastic buckling load 4.1 Formulation In the case not considering FR bonding length, for composite section of the steel and FR is the following. V EI V L () where (EI)V is a flexural rigidity of composite cross section, L is a length of the steel plate. In this method, it is assumed that the bonding length of FR sheet is equal to the length of the steel plate. Next, in the case considering FR bonding length, the method predicting elastic buckling load is needed to develop. At first, as shown in Figure, differential equations of wi, which are displacements in beam i (i = 1 ~ N), are expressed as follows. d 4 wi d wi i dx 4 dx (3) i EI i (4) where N is the total number of beam segments, Li is a length of each beam, (EI)i is a composite flexural rigidity, is an applied axial load. eneral solutions of equation (3) are given as the followings. wi C1i sin i x Ci cos i x C3i x C4i (5) where Cji (j = 1,, 3, 4) are unknown coefficients determined from boundary, continuity and syetrical conditions. Then, equations determining unknown coefficients can be suarized as follows. B C (6) where C is a vector consisting of unknown coefficients. Condition having nontrivial solution in equation (6) is det B (7) The minimum value of ( ) satisfying equation (7) affords the elastic buckling load in Figure. The calculation of equation (7) is carried out numerically since it is difficult to calculate analytically as the number N increases. Figure. Analytical model for formulation. age 7 of

8 4. Result Figures 9 and 1 show predicted result from equations () and (7) in Case1 and Case respectively. Here, vertical axes in the figures are evaluated by the following equation. max V 1 V (1) where, max means the maximum load in experiment and V means the predicted loads from equations () and (7). It is found from Figures 9 and 1 that the accuracy of prediction becomes better in equation (7) than in equation () since the exact FR bonding length is considered in equation (7). 3 3 Average Avarage (max ) / (%) (max V) / V (%) N U CUN CUU N U N U N U HN HU N U () () N U CUN CUU N U N (a) eq. () U N U HN HU N U () () (b) eq. (7) Figure 9. rediction of elastic buckling load (Case1). 3 3 Avarage Average (max ) / (%) (max V) / V (%) N U N U N U U 3 U (a) eq. () N U N U N U U U (b) eq. (7) Figure 1. rediction of elastic buckling load (Case). 5. Conclusions In this research, a fundamental study on rational repair and reinforcement of webs in corroded steel girder bridges using Fiber Reinforced lastic (FR) was carried out. Uniaxial compression test of steel plates bonded various FR sheets was conducted in order to select FR sheets that have reinforcing effect following large deformation induced by buckling. Lastly, the method that predicts elastic buckling load of the steel plate with FR was developed. References [1] Okura I., Fukuui T., Nakamura K. and Matsugami T., Decrease in Stress in Steel lates by Carbon Fiber Sheets and Debonding Shearing Stress, Journal of Structure Mechanics and Earthquake Engineering, No.69, pp.3949, 1 (in Japanese). [] Kishi N., Mikami H. and Zhang, Numerical Analysis of Debonding Behavior of FR Sheet for Flexural Strengthening RC Beams, Journal of Materials, Concrete Structures and avements, No.7, pp.57, 3 (in Japanese). age of