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1、A C 1 SP-338 73 0bb2747 O530034 654 ?ber-Reinforced-Plastic Reinforcement for Concrete Structures - International Symposium - Antonio Nanni Charles W. Dolan Editors I a B SP-138 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI Internat
2、ional (American Concrete Institute) Licensed by Information Handling Services A C 1 SP-138 73 m Ob62747 0530035 570 i Fiber-Reinforced-Plastic Reinforcement for Concrete Structures - International Symposium - Antonio Nanni Charles W. Dolan Editors COPYRIGHT ACI International (American Concrete Insti
3、tute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services A C 1 SP-138 93 0bb2947 O530036 427 DISCUSSION of individual papers in this symposium may be submitted in accordance with general requirements of the AC
4、1 Publication Policy to AC1 headquarters at the address given below. Closing date for submission of discussion is April 1, 1994. All discussion approved by the Technical Activities Committee along with closing remarks by the authors will be published in the JanuaryFebruary 1994 issue of either AC1 S
5、tructural Journal or AC1 Materiais Journal depending on the subject emphasis of the individual paper. The Institute is not responsible for the statements or opinions expressed in its publications. Institute publications are not able to, nor intended to, supplant individual training, responsibility,
6、or judgment of the user, or the supplier, of the information presented. The papers in this volume have been reviewed under Institute publication procedures by individuals expert in the subject areas of the papers. Copyright O 1993 AMERICAN CONCRETE INSTITUTE P.O. Box 19150, Redford Station Detroit,
7、Michigan 48219 All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by any electronic or mechanical device, printed or written or oral, or recording for sound or visual reproduction or for use in any knowled
8、ge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. Printed in the United States of America Editorial production Victoria Wieczorek Library of Congress catalog card number 93-71893 I COPYRIGHT ACI International (American Concrete Institute) Lice
9、nsed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services A C 1 SP-138 93 0662947 0530037 363 = PREFACE The American Concrete Institute sponsored an unprecedented six technical sessions on FRP reinforcement for concrete
10、at the Vancouver Conference on March 28-31,1993. Speakers and attendees were present from Europe, Japan, Canada and the United States. The papers in this Special Publication are organized in the same subject areas as the conference. The subject topic areas and symposium sections are: 1. FRP Material
11、 Properties and Testing Methods 2. FRP Reinforcement for Reinforced Concrete 3. FRP Reinforcement for Prestressed Concrete 4. Analysis And Design 5. The Japanese National Project for FRP Development 6. Applications of FRP Reinforcement The 55 technical papers in this report represent the most compre
12、- hensive compilation to date of FRP research, design, and application infor- mation. A comparison of the papers provides an insight to the approach to the use and development of FRP reinforcement within the research commun- ities of Europe, Japan and North America. The two symposium volumes are als
13、o significant because substantial portions of the extensive Japanese national research project have been translated into English. The Japanese papers provide an insight to both the magnitude of the technical work being conducted in Japan and the organization of the Japanese research program. The tec
14、hnical sessions generated substantial discussion, technical concerns were articulated, and differences of philosophy emerged. The following is a synopsis of the most important discussion points raised at the symposium. I i MATERIAL PROPERTIES FRP reinforcement may be constructed from a variety of fi
15、bers and resins. Comparison of test data and development of design recommendations is dependent upon knowing the composition of the FRP reinforcement. As a minimum, this includes the fiber type, fiber characteristics, fiber volume and the resin used to bind the fibers. FRP manufacturers further may
16、add fillers or release agents to assist in the manufacture of the FRP product. I . 111 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services A C 1 SP-138
17、93 = 0662747 0510038 2 T T Researchers were encouraged to provide as complete identification of the FRP reinforcement as possible when reporting project results. Closer col- laboration with FRP specialists is needed in order to develop systems, resins in particular, which complement the fiber proper
18、ties and have the desired properties for concrete reinforcement. It is possible to capitalize on the knowledge acquired by composite industry in the last 30 years through such a collaborative effort. CREEP-RUPTURE Creep-rupture, the tendency of a material subjected to a sustained load to fail at a l
19、oad much lower than its static strength, was identified as one of the principal differences between FRP and steel reinforcement. The time to failure of an FRP tendon is a function of the sustained stress level. Consequently, the selection of a sustained stress level is equivalent to selecting a true
20、 service life for the structure. Available test data are insufficient to fully define the creep-rupture performance of FRP materials currently being used. Some statistical testing to define the time dependent behavior of FRP reinforcement is in progress and accelerated testing prom- ises to provide
21、additional insight to the creep-rupture performance. During the discussion there was general agreement among the researchers that sus- tained loads in the range of 50-60 percent of the static tensile strength of FRP reinforcement are sufficiently low that a 100 year structure life is likely. DUCTILI
22、TY There was a general lack of agreement on the definition of ductility as it applies to FRP reinforced structures. Since the reinforcement remains elastic to failure, energy absorption remains mainly in the elastic range and plastic dissipation of energy is limited. It was agreed that FRP reinforce
23、d structures can be designed to undergo substantial deformation prior to fail- ure, and that these structures give ample warning of overload. At the same time, plastic energy absorption is achieved primarily by fracturing the con- crete. Methods to incorporate additional ductility, such as hybrid te
24、ndons, controlled bond failure, partial prestressing or staggered reinforcement stress levels need to be incorporated into design and testing programs. DURABILITY FRP reinforcement is extolled as superior to steel because of its super- ior corrosion resistance. Accelerated aging tests on aramid, car
25、bon and glass fiber based reinforcement were reported. These accelerated aging tests exam- ined FRP response when exposed to concentrated chloride and alkali solu- tions. Aramid and carbon based products indicated excellent resistance to these environments. Several researchers reported serious loss
26、of strength and fiber cross section for glass FRP reinforcement. The alkali corrosion of glass iv 1 COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services
27、A C 1 SP-33 73 0662747 0530039 136 led researchers to a heated discussion of the extraordinary methods which may be necessary to protect glass FRP reinforcement. Long term durability of FRP reinforcement is the single most important factor needed for the successful application of composites as reinf
28、orcement to concrete. It is imperative that questions and doubts related to specific systems be addressed before field implementation of FRP materials is initiated. REINFORCEMENT FORM FRP systems consisting of 1-D, 2-D, and 3-D shapes were discussed. The 2-D and 3-D shapes are a significant innovati
29、on with respect to conven- tional steel reinforcement. Manufacturing techniques for composites allow for the development of multi-dimensional systems that hold out exceptional promise for considerable installation and labor savings. FIRE RESISTANCE A widespread belief that FRP reinforcement could no
30、t meet fire resis- tance requirements was challenged by some Japanese research. FRP pre- stressed concrete members were subjected to standard fire tests. While no firm conclusions were provided, some data would suggest that FRP prestressed members came close to meeting a 2 hour fire rating. Addition
31、al research on FRP at elevated temperature indicated that below 250 degrees centigrade, FRP reinforcement regains it full tensile strength upon cooling. JAPANESE NATIONAL PROJECT The format and organization of the Japanese National Project for the development of FRP reinforcement was presented. The
32、five year project in- volved funding from the government and private industry. The private indus- try contribution includes contractors, FRP manufacturers and fiber suppliers and firms normally associated with distributing the final product. Research is conducted by government laboratories, universi
33、ties and construction com- pany R the Elasto Plastic approach, the Concrete Deformation approach and the Fracture Energy approach. The Elasto Plastic model has been checked using a discrete element model including tensile softening of concrete. The presented formula are confirmed by a few tests on A
34、rapree pretensioned prims. Kevwords: Fiber reinforced plastics; lightweight concrete; pretensioning; splitting stresses; stress transfer COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licen
35、sed by Information Handling Services A C 1 SP-138 93 Obb29Y9 05L0050 8T7 2 de Sitter and Vonk W. Reinold de Sitter Hollandsche Beton Groep nv director R release of pretension causes radial expan- sion of the prestress material due to its Poisson coefficient. This leads to radial compressive stresses
36、 resulting in increa- sed bond in the anchorage zone. 2. Transfer of bond stresses along a prestress bar or strand i n the anchorage zone introduces tensile stresses in the tangenti- al direction in the concrete. The Hoyer effect is restrained by the concrete leading to radial stresses p, normal to
37、the interface of the bar/strand with the concrete. A high level op p, increases the bond stres- ses and the angle 4. Therefore both causes of splitting forces are interrelated. In section 3 it will be shown that even in the case of smooth surface texture and very low bond the Hoyer effect may lead t
38、o splitting. At the extreme end of the ancho- rage zone the shear stress 7, must be zero because 7, is zero at the free concrete surface. In this area the Hoyer effect will dominate the splitting forces. The material properties make FRPR sensitive to the Hoyer effect. The coefficient of radial therm
39、al expansion ar of FRPR is governed by the (more or less) linear thermal expansion of the bonding resin. In many types of FRPR the value of ar i s 5 to 8 times the value for concrete. An increase in temperature then will lead to tangential splitting stresses in the concrete. The combination of therm
40、al stresses with stresses caused by the Hoyer effect and prestress force transfer did lead t o severe longitudinal cracking in thin pretensioned elements (f ig.2). Acknowledgement This research program is supported by the European Community through the Brite-Eurniii prograiii. COPYRIGHT ACI Internat
41、ional (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services A C 1 SP-138 93 Ob62949 05L0051 733 FRP Reinforcement 3 THE HOYER EFFECT COMBINED WITH TEMPERATURE EXPANSION The E-modulus
42、 E, in the longitudinal direction of FRPR is governed by the E-modulus E, of the fibers. The E-moduli vary from 80 O00 to 140 O00 MPA for aramid fibers and 4000 to 6000 MPa for resins. If the contribution of the resin is neglected: E, = A, E, /A, The longitudinal strain E, and the radial contraction
43、 E, in prestensioned state: El0 = 01f0 E, = 010 1 E, Er0 = “r The radial contraction is governed by the poisson coefficient u, of the resin if we neglect the influence of the radial contraction of the fibers. After release of pretension the expansion of the resin in the longitudinal direction is res
44、trained by the concrete and by the fibers. Transfer zone: and After the transfer zone radial expansion due to release of pretension does not play a role but longitudinal deformation of the resin is restrained bv the fibers as well as the surroun- ding concrete. Hence, the pparent modulus varies betw
45、een After the transfer zone: er es/-,) and Eres/(-,-2*,) they can only be approximated from the moduli of the constituent materi- als. COPYRIGHT ACI International (American Concrete Institute) Licensed by Information Handling Services COPYRIGHT ACI International (American Concrete Institute) License
46、d by Information Handling Services A C 1 SP-138 93 O662949 0530052 67T 4 de Sitter and Vonk Comparing expression (2) and (4) it follows that, depending on the relative relation between the Hoyer stress and the tempera- ture induced stresses craking will start either in the anchora- ge zone or at som
47、e distance from the free end. PULL-OUT AND PUSH-IN BOND STRENGTH In pretensioned concrete bond in the transfer zone is identical with bond as observed in a push-in test. However in the ultima- te load situation bond in the anchorage zone is more analogous with a pull-out condition. The influence of
48、transverse expansion and contraction on bond has been investigated by comparison of bond in pull-out and push-in tests (fig.3) i . These tests were too few to permit firm quantative conclusions but they indicate significant differences in bond. In the push-in tests arapree bars (nomi- nal: 8 mm) wit
49、h embedded sand were tensioned t o values varying between 23.64 and 26.46 kN. The circular samples o f lightweight concrete were cast around these bars with cover 21 to 35 mm. After 3 days wet curing the tensile splitting strength f , , was 1.6 to 2.5 MPa. Then the force FI in the upper part o f the bar was gradually released. The reaction forces were measured as a check on (F2-F1) as well as the slip of the bar with respect to the 1.w. concrete. In the pull-out tests the bars were stressed to a force 2.4 - 6.6 kN. Then the force F, in the lower half of the