Lateral Confinement of Concrete Using FRP Reinforcement

SP 138-13

Lateral Confinement of Concrete Using FRP Reinforcement by A. Nanni, M.S. Norris,

and N .M. Bradford

Synopsis: Lateral confinement of concrete members by means of spirally wrapping fiber-reinforced-plastic (FRP) composites onto the concrete surface may increase compressive strength and ultimate strain (pseudo-ductility). It may also provide a mechanism for shear resistance, and inhibit longitudinal steel reinforcement buckling. Lateral confinement of concrete members as a strengthening/repair technology is expected to have an impact in the rehabilitation/renovation of buildings and infrastructure. Structures that have been damaged, or need to comply with new code requirements, or are subjected to more severe usage are the primary targets. In this project, an experimental and analytical study of concrete strengthened with FRP lateral confinement is conducted using compression cylinders (300 and 600 mm in length) and 1/4 scale column-type specimens. The latter specimens have a circular cross section and given longitudinal/transverse steel reinforcement characteristics. Column-type specimens are subjected to cyclic flexure with and without axial compression. When an aramid FRP tape is used as the lateral reinforcement, the variables are tape area and spiral pitch. In the case of filament winding with glass fiber, the thickness of the FRP shell is varied. The limited experimental results obtained at this stage of the research program indicate that lateral confinement significantly increases compressive strength and pseudo-ductility under uniaxial compression.

Keywords: Bend tests; compression tests; concretes; fiber reinforced plastics: fibers; glass fibers; lateral confinement; loading tests; reinforcing materials; repairs; strengthening; wrapping

193

194

Nanni, Norris, and Bradford

ACI member Antonio Nanni is an associate professor in the Department of Architectural Engineering at the Pennsylvania State University. His research interests are in concrete materials and structures. He is Chairman of ACI Committee 440, FRP Reinforcement. ACI member Michael S. Norris is a graduate research assistant in the Department of Architectural Engineering at the Pennsylvania State University. He received his BArch from the University of Idaho in 1991. His research interests are in new structural materials. Nick M. Bradford is a graduate research assistant in the Department of Architectural Engineering at the Pennsylvania State University where he received his BAE in 1992. His research interests are in structural retrofitting using new construction materials.

INTRODUCTION Strengthening/Repair by Lateral Confinement

The aging of the U.S. infrastructure and buildings inventory, the better understanding of natural phenomena (e.g., earthquakes) with the consequent upgrading of building code requirements, and the need for improved structural performance (due to more sophisticated uses or heavier loads) are among the major reasons challenging the construction industry for the development of new strengthening/repair technologies. Traditionally, the U.S. approach has given preference to the demolition/reconstruction option. In a more immediate past, due to both economical and cultural reasons, there has been a shift in attitude, with greater attention being devoted to the strengthening/repair option. The events following the 1989 Lorna Prieta earthquake have epitomized this tendency. It is therefore necessary for researchers, practitioners, and contractors to devote attention to this technical area and to develop economically sound and safe technologies. When considering strengthening/repair type of work, the following should be considered: a) predominance of labor and shut-down costs as opposed to material costs; b) time and site constraints; c) durability; and d) difficulty in selection, design and effectiveness evaluation. Research and development efforts in new technologies should address the issues of automation and formulation of design/prediction algorithms. Lateral confinement of concrete members by means of spirally wrapping an FRP tape or a resin-impregnated strand (filament winding) onto the concrete surface is a potential strengthening/repair technique. Lateral confinement may increase compressive strength and ultimate strain (pseudo-ductility), provide a mechanism for shear resistance, and inhibit longitudinal steel reinforcement buckling. For lateral confinement, the advantages of FRP composites over steel reinforcement or jacketing are: larger contact area and low profile, no corrosion, flexibility, possibility of pretensioning (even with prismatic cross sections), and

FRP Reinforcement

195

ease of automatic installation. In this project, an experimental and analytical study of this strengthening/repair technology is conducted using conventional compression cylinders, double-length compression cylinders, and l/4 scale column-type reinforced concrete (RC) specimens with different longitudinal/transverse steel reinforcement characteristics. The latter specimens are subjected to cyclic flexure with and without axial compression. The lateral FRP reinforcement consists of a continuous flattened tube made of braided aramid fiber in one case, and, in the other, of a continuous glass strand placed by a filament winding machine. The effects of different areas and spiral pitches for the tape, and thickness of the FRP shell for filament winding are investigated. Previous Experiences Japan-- In the mid eighties, Ohbayashi Co. and Mitsubishi Kasei Co. developed the concept of strengthening and retrofitting existing RC structures using carbon fiber strands and mats (CFRP). Three types of structures were targeted: building columns (Katsumata et al. 1987; Katsumata et al. 1988), bridge columns (Kobatake et al. 1990), and chimneys (Katsumata and Kimura 1990). According to their method, CFRP strands impregnated with resins are spirally wound onto the surface of an existing RC member. In the case of bridge columns and chimneys, CFRP mats may be adhered first to the concrete surface in the longitudinal direction of the structural member so that flexural strength is also enhanced. The primary function of the spirally wound strand is to improve shear capacity and ductility of the member. Experimental work to evaluate the potential of this method and the development of the first winding machine has been undertaken at the Technical Research Institute of Ohbayashi Co. This research shows that the benefits of the strengthening/repair method are remarkable. Improvements in strength of 1.5 times and maximum deformation ability up to four times greater than that of the original member were recorded using zero-pretension winding (Katsumata et al. 1987). Both circular and prismatic cross section elements without conventional steel hoop or spiral reinforcement were investigated. Specimens were not subjected to axial compression, only shear and bending moment were applied. Tests have shown that the low strain capacity of carbon fiber and its brittleness (even when epoxy impregnated) are a limiting factor. For prismatic elements, corners needed to be beveled prior to fiber winding (Kobatake et al., 1989). U.S.A. -- In the area of structural rehabilitation, the firm of Fyfe Associates is proposing to retrofit bridge columns with glass/epoxy FRP jackets (Fyfe Jan. 1992). The initial work was supported by the California Department of Transportation with the objective of developing a method to enhance flexural and shear performance in the critical regions of bridge columns (Priestley et al. Dec. 1991 ). Experimental results on columns subjected to combined axial compression and lateral loads, have demonstrated that jackets made of glass FRP are effective in inhibiting shear failure and forcing the development of ductile flexural modes of inelastic deformation.

196


EXPERIMENTAL PROGRAM

Materials The following is a description and a characterization of the materials being used in this research project. Concrete and Steel -- All specimens were made with ready-mix concrete having the characteristics shown in Table 1. The longitudinal steel reinforcement for column-type specimens was deformed wire, size D8 (8.1 mm in diameter), and 516 MPa yield point. Welded wire mesh (2 mm wire diameter and 25 by 25 mm wire spacing) was used in lieu of transverse ties for some column-type specimens. Braided Aramid FRP Tapes -- Tapes consisting of a collapsed tubular section (made of braided aramid fiber and impregnated with epoxy resin) were used for the first type of lateral reinforcement. The aramid fiber was Kevlar 49 (grade 6000 denier). The epoxy resin was Dow Chemical DER 330 combined with the hardener Ancamide 506 by Pacific Anchor Chemical (mixing ratio 100 to 55 parts). Three tape sizes were used and were identified as: K24, K48, and K64. The corresponding fiber-only areas were: 10.8, 21.7 and 28.9 mm2. The nominal cross section areas after impregnation and flattening were: 19, 39, and 52 mm2. The nominal transverse side of each tape after flattening was: 10, 13, and 18 mm. The amount of pretension in the tape during wrapping has a significant effect on the mechanical properties of the braided tape itself. This is because braided strands run at an angle with respect to the longitudinal axis of the tape, and the presence of pretension during resin hardening increases the overall stiffness of the tape. In order to evaluate the effect of pretensioning, an epoxy-impregnated tape (size K64) was wound around a rectangular hollow steel pipe. The pipe was longitudinally split into two halves, so that jacks inside the pipe could be activated to apply the desired level of tension to the tape after it was wound. The jack pressure was maintained until the tape had completely cured. After resin hardening, two types of tape samples were obtained by cutting the rectangular-shaped spiral: straight samples (A type) and comer samples (B type, corner diameter= 62 mm). For the straight samples (A type), conventional uniaxial tensile testing was conducted after fabricating molded anchors at the ends of the specimen. For the corner samples (B type), one leg of the specimen was fully embedded into concrete (to provide anchorage) while the other leg was pulled to failure by a jack. The area bonded in concrete extended to past the end of the corner so that no bending was applied to the tape during the test. The results of 30 tests for the straight section and 15 tests for the corner section are given in Table 2. The specimens were subdivided into three groups depending on the tensioning force in the tape during resin hardening (i.e., 0.0, 0.2 and 1.0 kN). From an analysis of the results given in the table, it appears that pretensioning affects the ultimate capacity and stiffness of the tape. However, a low level of pretension (0.2 kN) provides adequate efficiency. Considering that the average strength of the mechanically manufactured rod of the same geometry is 68.87 kN, the efficiency of the tape pretensioned at 0.2 kN is 87 percent. Corner sections, as expected, are relatively weaker. It was concluded that for

FRP Reinforcement

197

lateral reinforcement, a pretensioning force of 0.2 kN was easily attainable and, at the same time, was sufficient to ensure acceptable strength and stiffness of the tape. The nominal load capacity of the three tape sizes pretensioned at 0.2 kN (straight sample) was 21, 42, and 56 kN. Glass Filament Winding -- Twelve concrete samples 600-mm in length were shipped to a fabricator for the application of lateral confinement by filament winding. In this case, the FRP shell was made of E-Glass strands impregnated with a polyester resin. The strand were helically wound around the specimen (mounted on a rotating mandrel). The winding angle was 65 degrees. The thickness of the FRP shell was 0.6, 1.2, 2.4 and 3.6 mm, respectively. Two specimen per each shell type were fabricated using a bonding agent at the concrete-FRP interface. For the 14-mm shell, two additional cases were considered: alternative bonding agent, and no bonding. Prior to compression testing, the 600-mm cylinders were saw-cut in halves.

Specimen Fabrication Specimen Type -- Three groups of concrete specimens, all with same diameter (150-mm), were used: Group A -conventional compression cylinders (300 mm long); Group B - double-length compression cylinders (600 mm long); and Group C- column-type specimens (1525 mm long). Groups A and B were used exclusively for uniaxial compression tests. The longer length of Group B was needed for two reasons: first, to facilitate filament winding (a 25-mm diameter pipe was inserted along the axis of the cylinder to allow placement in the rotating mandrel of the winding machine); and, second, to allow for the placement of longitudinal steel reinforcement as for the specimens of Group C (see Figure I). Specimens of Group C simulate a 1/4 scale circular column and were intended for cyclic flexural test with and without axial compression. All specimens in this group were reinforced with six D8-size longitudinal rods (see Figure 1). Some specimens also had transverse reinforcement in the form of a welded wire mesh cage. Specimens were cast with a sleeve along the central axis to receive a postensioning rod for the application of the axial compression. The sleeve diameter was 19 or 32 mm, depending on the rod size. Tape Wrapping-- In the first wrapping technique, the braided aramid FRP tape was applied to the specimen in the university laboratory. The aramid tape was dipped into the epoxy resin bath for approximately one minute and rumpled by hand to remove air trapped in the interstices of the tape. The impregnated tape was passed through a die made of silicone rubber to remove excess resin, and wound around a steel pipe. This intermediate step allowed the operator to maintain the desired pretension of 0.2 kN in the tape during winding onto the concrete cylinder. Prewinding also allowed a better control on the tape pitch. Three pitches of 0, 25, and 50 mm were used for the three tape sizes. After wrapping, the FRP was allowed to cure for at least seven days at room temperature. Filament Winding-- Filament winding was executed at the industrial plant of an FRP manufacturer specializing in pressure pipe and tank production.

198


Experimental Results

Uniaxial Compression-- As of now, 20 specimens of Group A have been tested in uniaxial compression. The results of these tests are summarized in the stress-strain diagrams of Figures 2, 3, and 4. Each figure corresponds to a specific tape size and each curve is the average response of two specimens (the curve relative to plain concrete is the average of six specimens). Figure 2 shows that the presence of the K24 tape has no effect when wrapped at a 50-mm pitch (K24-2). The photograph in Figure 5 shows that the typical failure mode for one specimen of sub-group K24-2 is still of the shear type. At 25 mm pitch (K24-1 ), the pseudo-ductility of the specimen is increased without increasing ultimate strength. At 0 mm pitch (K24-0), the maximum capacity of the machine (1.3 MN) was reached without taking the specimen to failure. The increase in both strength and stiffness occurring in this case is evident. The photograph in Figure 6 shows the condition of one of the two K24-0 specimens after the conclusion of the test. No sign of FRP deterioration is visible. The diagram of Figure 3, relative to the K48 tape, shows that at 50 mm pitch (K48-2) there is no significant contribution from the lateral confinement. For the case of 25 mm pitch (K48-l ), again the maximum capacity of the testing machine was reached prior to failure. A photograph of one specimen of this series is shown in Figure 7. Extensive cracking and bulging of the fractured concrete can be seen between the tape spirals. The K48-0 specimens are to be tested with a different machine having a capacity of 4.4 MN. The case of K64 tape is presented in Figure 4. This time the 50 mm pitch (K64-2) shows a considerable increase in pseudo-ductility with no strength improvement (a photograph of a failed specimen is given in Figure 8). The specimens with 25 mm pitch (K64-I) could not be failed. The K64-0 specimens were not tested. Considering the stress-strain curves of all the sub-t:,rroups tested, the slope of the second branch of the curve, when it exists, is clearly proportional to the area of lateral reinforcement as suggested by other researchers (Katsumata eta!. 1988) Specimens which were not failed will be re-tested with the higher capacity machine together with those of sub-groups K48-0, k64-0, and those of Group B. Flexure-- As of now, four specimens have been tested in flexure without axial compression. All four specimens were wrapped with aramid FRP tape at 25-mm pitch. The first sample used K24 tape (C04). Two samples, one with steel shear reinforcement and one without, used K48 tape (C07 and ClO). The fourth sample used K64 tape (COl). The testing set-up is shown in the sketch of Figure 9. The specimen was simply supported over a span of 1372 mm and loaded at mid-span. Full load cycles (push and pull) were applied below the cracking strength (half-cycles 1 to 4), in the elastic-cracked region (half-cycles 5 to 10), and in the plastic-cracked region (half-cycles 11 to 16). The following load cycles (half-cycles 17 and higher) attempted to be at peak-load and post-peak load levels. The analytical interaction diagram for the RC cross section without considering the lateral confinement is presented in Figure 10. The diagram shows that the nominal moment capacity at zero axial force is 8.81 kNm, which corresponds to a load of 28.9 kN.

FRP Reinforcement

199

The experimental load-deflection diagrams for the four specimens as tested are shown in Figures I 1, 12, 13, and 14, following the order assigned by the specimen code (i.e., CO I, C04, C07, and C 10). Since only a selection of hysteresis loops is reported in the diagrams, the number shown in the proximity of each curve indicates the half-cycle number (odd value for the "push" direction and even value for the "pull" direction). The peak loads were +34.4 and -34.3 kN for specimen C-Ol, +38.7 and -31.6 for specimen C-04, +34.8 and -30.1 for specimen C-07, and +31.2 and -31.1 for specimen C-10. The experimental strength of all specimens is higher than the predicted value. Apart from specimen C-04 that failed immediately after peaking, the hysteresis loops are very similar among specimens. This indicates that the contribution of the lateral confinement is not significant. This was expected because failure is tension-controlled. The crack pattern was very similar in all specimens. All cracks, including those in proximity of the supports, were vertical (flexural type). After starting from the tensile zone of the specimen during one half-cycle, almost every crack propagated through the entire cross section at the inversion of the load. DISCUSSION Effect of Confinement In uncracked and microcracked concrete under compression, axial strain due to loading can be converted to transverse strain using the Poisson's ratio. The effect of confinement on concrete is directly related to its ability to restrain this transverse strain. As the transverse strain increases, the amount of pressure exerted by the confinement increases. The resulting biaxial state of stress is beneficial to the cracking capacity and strength of concrete (Kupfer eta!. 1969, Newman and Newman 1972). Since the confining stress is dependant upon the transverse strain, the confinement is said to be passive in nature (Ahmad and Shah 1982). The benefits of the biaxial state of stress can be observed, for example, in the stress-strain curve relative to sub-group k24-0 (Figure 2), as it departs from the plain concrete curve in the range 25 to 45 MPa. Independent of the amount of lateral confinement, all specimens so far tested show a bend-over point at approximately the strain level which corresponds to the maximum capacity of the plain concrete. After this point, concrete undergoes extensive cracking and the relationship between axial and transverse strain cannot be accurately determined using the Poisson's ratio. The confinement carries an increasingly greater portion of the load (as an analogy, the lateral confinement has become a pressure pipe holding liquified material). During this stage, the specimen shows a flat or a rising curve depending on the amount of lateral confinement. The slope of the curve also depends on the stress-strain curve of the confining material. If steel tubing is used and reaches its yielding point, then a gradual loss of load capacity in the post-cracking zone is experienced (Chai eta!. I 991, Mander eta!. 1988). With a sufficient amount of FRP as the confining material (linear-elastic behavior till failure), the specimen experiences a slow increase in load capacity which may continue until the FRP wrapping has achieved its ultimate strength. Experimental results obtained by Bazant eta!. (1986) on concrete cylinders encased in a pressure

200


vessel with 150-mm walls show that specimens with this confinement could carry loads in excess of 2,000 MPa. With reference to the interaction diagram of Figure I 0, it is hoped to demonstrate that lateral confinement alters the behavior of a column-type specimen, when concrete crushing controls the failure mode. The next set of experiments, conducted under cyclic flexure with an axial compression of 200 kN, should demonstrate this point. Analytical Model

Prior to the development of design procedures for concrete members with lateral FRP confinement, an analytical model must be established to predict the performance of the confined concrete. The model must account for different material types (concrete and FRP), volume and distribution of confinement, and wrapping techniques. The model could be used in both the areas of uniaxial compression and compression-controlled flexure. Concrete failure has been modeled following the Mohr-Coulomb theory (failure occurs along the critical shear plane of the specimen). In the case of laterally confined concrete, it appears possible to consider a combination of this approach (to predict the first part of the curve) and the pressure-pipe analogy (to predict the second part of the curve). Work is being conducted in this area and will be reported at a later date. CONCLUSIONS

Only preliminary conclusions can be drawn at this stage of the research project. Lateral confinement in the form of braided, "field-produced" aramid FRP tape has been used. The loss of efficiency with respect to the "factory-produced" tape form is relatively modest, provided that some pretension is present in the tape at the time of winding. There is experimental evidence to demonstrate that the compressive strength and pseudo-ductility of concrete is increased by the presence of lateral FRP confinement. Experimental work will continue in order to establish the upper values of this enhancement, and to evaluate a second type of FRP confinement produced according to the method of filament winding. On the analytical side, a model based on a combination of the Mohr-Coulomb theory and the pressure pipe-analogy is being developed. Testing on column-type specimen will continue with the more interesting case of specimen subjected to axial compression and flexure. For specimens subjected to flexure and with tension-controlled failure, the effect of lateral confinement is not significant. ACKNOWLEDGMENTS

The support of the National Science Foundation under Grant No. MSS-91 08598 is gratefully acknowledged. Mitsui Construction Co., Tokyo, Japan, has provided materials and financial support. Dow Chemical and Pacific Anchor Chemical have provided materials.

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REFERENCES Ahmad, S.H and S.P. Shah (1982). "Stress-Strain Curves of Concrete Confined by Spiral Reinforcement," ACI Journal, Vol.79, No.6, pp 484-490. Bazant, Z.P., Bishop, F.C. and Chang, T.P. (1986). "Confined Compression Tests of Cement Paste and Concrete up to 300 ksi," ACI Journal, Vol.83, No.4, pp. 553-560. Chai, Y.H, Priestley, M.J.N. and Seible, F. (1991). "Seismic Retrofit of Circular Bridge Columns For Enhanced Flexural Performance," ACI Structural Journal, Vol. 88, No.5, pp. 572-584. Fyfe, E. (Jan. 1992). "Strengthening Bridge Columns with Composites," Transportation Research Board, 71 Annual Meeting, Washington, D.C. Katsumata H., Kimura K. (May 1990). "Applications of Retrofit Method with Carbon Fiber for Existing Reinforced Concrete Structures," The 22nd Joint UJNR Panel Meeting, U.S.- Japan Workshop, Gaithersburg, MD, pp. 1-28. Katsumata H., Kobatake Y., and Takeda, T. (1987). "A Study on The Strengthening with Carbon Fiber for Earthquake-Resistance Capacity of Existing Reinforced Concrete Columns," Proceedings of the Seminar on Repair and Retrofit of Structures, Workshop on Repair and Retrofit of Existing Structures, U.S.-Japan Panel on Wind an Seismic Effects, UJNR, pp. 18-1 to 18-23. Katsumata, H., Kobatake, Y., and Takeda, T. (1988). "A Study on Strengthening with Carbon Fiber for Earthquake-Resistant Capacity of Existing Reinforced Concrete Columns," Proceedings of 9WCEE, VII, pp. 517-522. Kobatake, Y., Katsumata. H., and Okajima, T. (1990). "Retrofitting with Carbon Fiber for Seismic Capacity of Existing Reinforced Concrete Bridge Columns," Proceedings of the 45th Annual Conference of the Japan Society of (in Japanese) Kupfer, H., Hilsdorf, H.K. and Rusch, H. (1969). "Behavior of Concrete Under Biaxial Stresses," ACI Journal, Vol. 66, pp. 656-66. Mander, J.B, Priestley, M.J.N. and Park, R. (1988). "Theoretical Stress-Strain Model For Confined Concrete," J. Struct. Engrg., ASCE, Vol. 114, No.8, pp. 1805-1826. Newman, K. and Newman, J .B. ( 1972). "Failure Theories and Design Criteria for Plain Concrete," Part 2, Solid Mechanics and Engineering Design. Wiley-Interscience, New York, pp. 83/1-83/33. Priestley, M.J.N., Fyfe, E., and Seible F. (Dec. 1991). "Retrofitting Bridge Columns with Fiberglass/Epoxy Composite Jackets," Proceedings, Caltrans Research Seminar, Sacramento, CA, 8 pp.

202


TABLE 1 -MATRIX PROPORTIONS AND PROPERTIES Portland Cement Type I (kg/m3) Fly-ash Class F (kg/m3) Water (kg/m3) Coarse Aggregate (9 mm MAS)* (kg/m3) Fine Aggregate* (kg/m3) Water Reducer (1/100 kg of cement) Slump Unit Weight Air Content

I I

*

0. 8

(mm) 100 (kg/m3) 2268 (%)

28-day Compressive Strength Standard Deviation (6 samples) Note:

327 53 168 950 823

= Saturated

(MPa) (MPa)

1. 3

35.6 2. 5

Surface Dry

TABLE 2 -RESULTS OF TENSILE TESTS FOR BRAIDED ARAMID FRP TAPE (K64)

I I I I I I

Specimen Type

I lA

0.0

I I I

type!straight

avg. (C.V.)

typelcorner

avg. (C.V.)

I IB

Pu (kN)

I I 54.3 I (12. 8> I I 38.5 I (4. 8)

Pretension Force (kN) 0.2

Elastic Modulus (GPa)

Pu (kN)

60.4 (24. 6)

59.8 (7. 7)

N/A

46.2 (7. 5)

1.0


(kN)


62.2 (10. 0)

61.9 (9. 9)

60.6 (6.8)

48.3 (3. 6)

N/A

N/A

Pu

FRP Reinforcement

--'

'

,-----·

203

---

·---

Longitudinal~·- •• ,

DB Reinforcement (Group C)

''

\ \

'\

'

:Steel Pipe

.

C)~--~------r,', ',\ 19 or 32mm ~ 8 151.7mm ·- · - - - --------- --f----- ----~--- -~~ -~:~e_r_ - - · - - \ ........ ___ .:.::~---- -/ ::' (Groups B &

'

'

I I

\

I

\

\

I I J

I

I

Welded Wire M e s h / ' Transverse Reinforcement

''

...... __

_...... -

Fig. 1-Typical cross-section for specimens of Groups Band C

80 70 60 ~50

e"" 40 rJl

~

30 20 10 0 0

--- Plain Concrete

0.005 STRAIN (mm!mm) -ir-

K24- 2

-+- K24-1

0.01

O.ot5

...... K24-0

Fig. 2-Uniaxial compression stress-strain diagram (Group A, K24 tape)

204

Nanni, Norris, and Bradford ~r-------------,-------------r-----------~ Not Failed

~50 r-------~~----r---------------~------~t---~

6

~

: t--------#---+-----+----+---------l

0.005

0.01

0.015

SIRAIN (mm/mm)

-----Plain Concrete

-il-

K48- 2

--+-- K48-1

Fig. 3--Uniaxial compression stress-strain diagram (Group A, K48 tape)

~

Not Faile

70 60

';' 50

=-

1: 20 10

0.005

0.01

0.015

SIRAIN(mm)

----- Plain Concrete

-il-

K64- 2

--+-- K64-1

Fig. 4-Uniaxial compression stress-strain diagram (Group A, K64 tape)

FRP Reinforcement

205

Fig. 5-Typical failure of specimen type K24-2

Fig. 6-Specimen type K24-0 after loading to 1.3 MN (machine capacity)

206


Fig. 7-Specimen type K48-1 after loading to 1.3 MN (machine capacity)

Fig. 8-Typical failure of specimen type K64-2

FRP Reinforcement

207

Fig. 9-Flexural test set-up for Group C (no axial force)

,c- . .... ... 4·

...

'

~,

\\ \

I

'Z'Z-

0

---

,., .....

/

-* , -----

,., .....

---

/

..........

,_8,., .....

.....

,/'

t?J.r.. Mt>MEoH

Fig. 10-Interaction diagram for reinforced concrete section (Group C)

208


40 30 20

z

10

~

Ci