FRP FOR THE 21st CENTURY

Transcription

1 ';.1... FRP FOR THE 21st CENTURY by Sami H. Rizkalla(l) and Amr A Abdelrahman(2) Abstract Population growth followed by the dramatic increase and demand for new services created an urgent and overwhelming need for infrastructures of civil engineering structures. However, the current infrastructure work using various techniques and conventional materials for construction will not solve the traditional and continuous deterioration of concrete structures due to corrosion of steel. One of the most promising avenues, which has been recently explored is to use fibre reinforced plastic, (FRP), for civil engineering applications. FRP could be extremely effective in rehabilitation and repair of deteriorated structures as well as new construction. This paper briefly describes some selected projects to demonstrate the wide range of the current and future use of FRP for civil engineering applications. The paper also summarizes the Canadian experience in the construction of the first smart concrete highway bridge built in Calgary, Alberta. Design and construction details of the second bridge to be built in Canada using FRP shear and prestressing reinforcement is also presented. (1) Professor and Program leader of the Canadian Network of Centre of Excellence on Intelligent Sensing for Innovative Structures, FAG. FCSCE, FASCE. FEIC. (2) Ph.D. Candidate, Civil and Geological Engineering Department, University of Manitoba. Winnipeg. Manitoba. Canada, R3T 5V6.

2 Introduction There has been a rapid growth in the use of fibre reinforced plastic, (FRP), materials in the civil engineering applications during the last few years. However, the full potential use of FRP has not been fully realized for civil and structural engineering applications. FRP is currently produced in the fonn of laminates, structural sections, reinforcing bars, grids and prestressing tendons. FRP materials should not be treated as direct substitution for conventional materials, however, it should be utilized according to its own fundamental characteristics. The advantages of FRP should provide the designers the opportunity to design structural systems that could not be built using conventional materials. One of the major problems that readily reduces the life of concrete structures is the corrosion of steel reinforcement. This problem is more serious in cold climate countries, where de-icing salts accelerate the deterioration. Since FRP are nonmetallic materials, they have major advantage to steel. Use of these materials could significantly increase the life time of structures, minimizing the maintenance requirements and consequently offset the current high cost of FRP products. FRP have high strength-to-weight ratios, approximately fifty times higher than reinforcing bars and eight times higher than prestressing steel strands. The light weight of the FRP makes the handling and installation generally much easier and consequently reduces the cost of assembly. These characteristics also introduce FRP as an attractive material for rehabilitation projects. The other important properties of FRP are the electro-magnetic neutrality and relatively favourable fatigue behaviour which are sometimes control the design for special types of structures. Applications of FRP FRP have been used in many civil engineering applications, such as bridges, buildings, off shore structures and retaining walls in Japan, Europe, USA and Canada. The following describes briefly some selected completed, in progress and future applications to highlight the potential use of these materials for the 21st century. Short Span Bridges Many pedestrian bridges have been constructed using FRP. E.T. Techtonics, Philadelphia, designed and constructed several pedestrian bridges using Kevlar 49 cables to prestress glass FRP king-post. queen-post truss bridges, as shown in Figure 1. The spans of the bridges vary from 7 to 10 meters. The same company constructed recently a 24 meter span pedestrian bridge along a popular hiking trail in Olympic National Park, W A, USA. Fibre reinforced plastic tendons have been also used as reinforcement and to prestress concrete bridges to enhance the durability for severe environmental

3 '- conditions. In addition to the high strength and good fatigue properties, the low young's modulus of FRP tendons could also be an advantage to reduce the prestressing losses. These characteristics greatly enhance the use of FRP as prestressing tendons for short span bridges. Several pedestrian and highway bridges in different countries have been built using FRP as structural sections and as prestressing reinforcement for concrete girders and slabs (Minosaku 1992). Table 1 shows different types of concrete bridges prestressed by FRP tendons. Figure 1. E. T. Techtonics pedestrian bridge with Kevlar 49 cables and glass FRP Long Span Bridges As a result of the superior advantage of high strength-to weight ratio of FRP compared to conventional materials, FRP provide unique alternative to steel and concrete materials to construct long span bridges, which can not be built by conventional materials currently used in construction. FRP structural sections can be utilized effectively in producing unique bridge girder configuration in combination with FRP cables to build very long span bridges. Prof. Meier presented a comparative study to examine the feasibility of constructing bridges using steel, glass fibre reinforced plastics (GFRP) and carbon fibre reinforced (CFRP) plastics, for cable-stayed and classical suspension types. The study concluded that the most feasible design would be a cable-stayed bridge using CFRP, as shown in Figure 2. The specific design loads versus the centre spans for the classical form of suspension bridges made of steel are compared with those made of GFRP or CFRP in Figure 2. The comparison shows that the use of advanced composites would allow doubling or tripling of the limiting span in comparison to steel structures. Based on this study, Prof. Meier challenged the international engineering community to construct a bridge across the strait of Gibraltar at its narrowest site, as shown in Figure 3, (Meier 1988).

4 Table 1 Examples of concrete bridges prestressed by FRP reinforcements Material Bridge description Diameter of Dimensions of PlP u ' reinforcements the bridge BASF post-tensioned pre- Four cables, 11.2 m wide x 80 m 50 % under stressed concrete highway each is made of long, four 20 m design load bridge, Gennany, x7 cp12.5 spans, 2 straight and 2 curved Nagatsugawa pretensioned Cables of lx7 2.5 m wide x 8.0 m 60, 55 and 50 %, simple slab pedestrian cp 12.5 mm C long jacking, initial and bridge, Japan at design load F Kitakyusyu prestressed 8 multi~ables 35.8 m long, 55 % under R concrete highway bridge, bundled with 8 pretensioned girder design load p Japan, 1989 CFRP rods of 8 (18.2 m span) and mm diameter post-tensioned girder (17.5 m span) Shinmiya pretensioned eight lx7cpl m span and 7 60, 55 and 45 %, concrete slab highway m wide jacking. initial and bridge, Japan, 1988 at design load Demonstration bridges for 3cp m span for the 75, 70, and 60 %, Technora. pre tensioned pretensioned pre tensioned bridge jacking, initial and composite slab and post- strands. 19cp6 and 24.1 m span for at design load tensioned box girder, lapan. post-tensioned the post-tensioned A 1990 and 1991 cables and 7cp6 girder external cables F Mito city post-tensioned 16 cables. each 2.1 m wide and % under R concrete pedestrian is made of 8 m long design load p suspended slab bridge bands 4.86 x 19.5 mm Nasu pretensioned Braided AFRP 3 spans m 50 % under prestressed concrete highway 14 mm diameter each design load bridge, Japan The Marienfelde pedestrian Cables of lx19 5 m wide and two nja t externally prestressed bridge, cp 7.5 spans of 17.6 and 23 G Gennany, 1989 m long F The U1enbergstrasse post- 59 cables of two spans of % under R tensioned prestressed lxi9 cp 7.5 and 25.6 m long design load highway bridge. Gennany, p 1986 LiiDe~'sche Gasse siogle 100 rods of In span nja t span slab bridge. Gennany. mm diameter 1980 * PIP u is the ratio of the prestressing force to the ultimate strength of the cables t not available

5 4~----~------~------~ ~ ~~ ~ Sleel GRP ( ) CFRP ( ) ~ - no N/mml r 1800 Icglm J ~ N/mml r Icg/m J N/mm l r Icglm J.... 2~----~ ~------~ GO GO.. ~. <.; e...:j O :[4~~rn o I Span iii Figure 2. Specific design load vs. main span length for classical suspension bridges Repair of Structures I m I. 8400m m.1 Figure 3. Proposed bridge across the strait of Gibraltar A number of chimneys, columns, slabs and girders have been repaired and strengthened with CFRP products due to earthquake damage andlor structural needs to increase their capacity. Many products are currently available for this type of retrofitting. The products are often unidirectional and produced in the form of fibre tapes, fibre winding strands and fabrics. The materials are effective for both flexural and shear strengthening of structures. 1 A retrofit process of a structure, such as a chimney, begins with preparation of the concrete surface, trowelling the surface with mortar or epoxy, followed by placement of the auto-adhesive tapes in the longitudinal direction and contining of the outer surface in the circumferential direction by winding small diameter carbon cables. To facilitate the cable winding operation, an automatic winding machine is currently available, as shown in Fig.4. To satisfy the fire resistance requirements, the surface is normally covered by a fire-resistant material, such as cement mortar.

6 " Figure 4. Repair of chimneys Repair of Bridges Many highway bridges, which were built 40 years ago, have been deteriorated due to the continuous increase of the truck capacity legally permitted on highways. In addition, the corrosion problem, caused by de-icing salts, has made the deterioration even more severe. Strengthening deteriorated steel and concrete structures by bonding carbon fibre reinforced epoxy laminates to the exterior of the structure, has been studied in Switzerland and Germany (Meier and Kaiser 1991). The study has shown that the use of CFRP laminates in place of steel plates for such applications could reduce the total cost of the project by about 20 percent Although the FRP materials are currently more expensive than steel, the lighter weight and better corrosion-resistant properties could result in significant reductions in the overall long term costs. " The repair of a prestressed concrete bridge located in the county of Lucerne, Switzerland, is shown in Figure 5. The damage was caused accidentally by cutting several prestressing wires during the installation of a highway sign. Dr. Meier's study indicated that using carbon fibre reinforced epoxy laminates instead of steel plates for repair caused considerable reduction of construction time. Despite the fact that the cost of the carbon FRP is fifty times more expensive, per kilogram, than the

7 " steel, the use of 6.2 kg of carbon FRP instead of 175 kg of steel made the high prices no longer seem to be outrageous. Furthermore. all the work was carried out from a mobile platform, thus eliminating the need for expensive scaffolding.,,.,., '" -'- Figure 5. Repair of prestressed concrete bridge using carbon FRP laminates Bridge Enclosures The concept of "bridge enclosure" involves hanging a t100r from the girders of a steel bridge, at the level of the bottom flanges of the girders. The bridge enclosure protects the steel girders from the severe environment effect which cause corrosion and consequently the need for frequent maintenance. The enclosure also provides access for inspection and maintenance. Corrosion rates of steel within such enclosures have been found to drop to negligible levels. The first system of this type in the world was installed on the A19 Tees Viaduct in Middlesbrough. England in 1989, and the material used was GRP (Maunsell International Consulting Engineers 1989). The structural Hoor of the enclosure, as shown in Figure 6, is composed of pultruded glass re.inforced plastic (GRP) panels which is characterised by light weight and high durability. The modular GRP panels were selected on the basis of a cost/benefit analysis. which took into account total costs of inspection and maintenance of the steel plate girders. Other cost saving attributes to the system were the minimum weight. reliable life to tust maintenance (30 years). good fire resistance and good long term appearance.

8 " '.~:.....t-l,. -,;...,"... ~ I.. -. '. ~ ~_"._(_ 1... ' :Tt... ~.. ~1"'......,~.. _, '.. ~;..fi ~---.. ~.' ,,.,. t... _:tl.. Figure 6, Bridge enclosure of the A19 Tees Viaduct in Middlesbrough, England Tunnel Lining FRP grids could be extremely effective as reinforcement for tunnel lining using shotcrete technique to form the skin surface. It has advantages over the steel due to its high corrosion-resistance and flexibility which is convenient for curved surfaces, as shown in Figure 7, in addition to their excellent alkali, acid and chemical resisting properties. The material is very light weight, having approximately one fourth the specific gravity of steel, and may be cut easily with a hack-saw, FRP grids have been used in many tunnel lining projects (NEFMAC, 1987) such as "Kakkonda hydroelectric power plant", where glass FRP was used to reinforce the arch, side wall and invert of water-conveyance tunnel for crack prevention for a total area of 430 m 2, Figure 7. Tunnel lining by FRP grids /

9 Marine Structures Glass FRP has been used over the last 45 years in several marine applications. Fibreglass boats present roughly 95 percent of all the constructed boats in USA. Durability and performance of fibre glass in salt water has thus been proven with time. Sen, Issa and Iyer (1992) reported a feasibility study for fibre glass pretensioned piles in a marine environment. Another application of the composite material in marine structures is the hardcore marine fender manufactured by Hardcore Composite Ltd., New Castle, shown in Figure 8 (Hardcore Dupont Composites). The fender system is designed to replace the traditional wood and steel fender pile clusters. The hardcore marine fender is composed of three primary parts, the composite truss panel, MY elements, which are heavy-duty wear-resistant rubber, and ultra high molecular weightpolyethylene face, which is thermoplastically bonded to the truss panel to resist abrasion. Special Applications Figure 8 Hardcore marine fender using composite material The non magnetic neutrality of FRP makes it an attractive material to be used in some special applications. For example, fibre glass cables were used in the rehabilitation of the Mairie d'ivry subway station in Paris, where the non-magnetic nature of the cables played an important role in the selection of this type of cables instead of high stress steel cables. As a result of one sided excavation directly adjacent to the subway station, considerable cracking had occurred in the 70 year old concrete vault over a length of about 110m. Thirty six glass FRP tendons were used

10 ',' to strengthen the vault. as shown in Figure 9. A computer research centre was also constructed using glass fibre pultruded sections, as shown in Figure 10. The use of glass fibre material in this structure was mainly due to its superior non-magnetic and invisible characteristics to radio waves. glass fiber ties I S.2om L f m ,1 1 1m Figure 9. Cross section of Marie d'ivry subway station Figure 10. House for communications equipments built with composite material

11 .... The First Highwav Bridge Built in Canada The flrst prestressed concrete highway bridge in canada using fibre reinforced plastic tendons for prestressing and optical fibre sensors for monitoring the behaviour has been completed in November 1993 (Rizkalla and Tadros 1994). Two different types of carbon fibre-based tendons were used to prestress six precast concrete girders of a two continuous span skew highway bridge in Calgary, Alberta. Canada. The girders were bulb-tee sections of 1100 mm in depth, with spans of and meters. The girders were pre tensioned to carry their own weight and the weight of the deck slab. The girders were post-tensioned by conventional prestressing steel tendons to provide continuity over the middle pier for live loads. Two girders were pre tensioned by 8 mm diameter Leadline tendons produced by Mitsubishi Kasei. The other four girders were pre tensioned using 15.2 mm diameter carbon fibre composite cables (CFCC) produced by Tokyo Rope. The completed bridge is shown in Figure 11. A.multichannel fibre optic sensing system, including a number of sensors to monitor the change of light and consequently the strain, was used to monitor the behaviour of the bridge over the lifetime serviceability of the bridge. The optical fibres were installed and monitored by the research group of the University of Toronto Institute for Aerospace Studies Figure II. The first smart highway bridge built in Canada

12 The HeadingJey Bridge in Manitoba The province of Manitoba accepted the Challenge to construct the world largest span concrete highway bridge prestressed and reinforced for shear using carbon FRP reinforcement. The bridge consists of five spans, 32.5 meters each, covering a total length of meters. The bridge is prestressed by straight as well as draped tendons. The two types of CFRP reinforcements will be used for prestressing and stirrups are the Leadline and CFCC produced by Mitsubishi Kasei and Tokyo Rope, respectively. Portion of the concrete deck slab will be also reinforced exclusively by FRP reinforcements. All the bridge girders are precast pretensioned and simply supported. The bridge girders have an I-section AASHTO type, transversely spaced at 1.8 meter and supporting 187 mm thickness deck slab. A typical pretensioned concrete girder is shown in Figure 12. (Fam, Abdelrahman, Rizkalla and Saltzberg 1995).,t b t-i a.. ~.... I I...! c.l. I ~::::::::::: 1800 c.g.s. of 40 strands ~ 660 Sec.(a-a) I.\-a -... I I 16 strands :.: I I. I I I I 24 strands,'. ' Sec.(b-b) Fig.12 Pre tensioned concrete girder of Headingley bridge, Manitoba ISIS Canada Network Centres of Excellence A new network centres of excellence on Intelligent Sensing for Innovative Structures, (ISIS), has been recently established in Canada. ISIS - Canada will develop innovative systems that combine advanced composite materials, new optical sensors and microchip technology for the use in the design, reinforcement and repair of civil engineering structures. These structures will be classified as smart by virtue of their integrated fibre optic structural sensing system and innovative through the use of advanced composite materials to make them light, yet strong and non-corrosive. The data generated from each structure, such as bridges, will be intelligently processed and transmitted through phone or satellite links to a central monitoring

13 " station where it will be interpreted and the status of the structure evaluated. ISIS concept is illustrated in Figure 13. Conclusions Figure 13. ISIS - Canada network centres of excellence FRP will certainly playa major role in the construction, rehabilitation and repair of civil engineering structures in the 21st century. The high-strength-to-weight ratio and non-corrosive characteristics of these materials could be utilized to build innovative structures that can not be built using the current conventional materials. FRP could be used to build light, yet more durable and economical structures. Designers should be encouraged to utilize these materials based on its own unique characteristics rather than a replacement for the current conventional materials.

14 References 1- Fam A.Z., Abdelrahman A.A., Rizkalla S.H. and Saltzberg W., 1995 "FRP Flexural and Shear Reinforcements for Highway Bridges in Manitoba. Canada", Proceeding of the Second International RlLEM Symposium (FRPRCS-2), Non Metallic (FRP) Reinforcement for Concrete Structures, Ghent, Belgium, August, pp Hardcore Dupont Composites, 42 Lukens Drive, New Castle, Delware Maunsell, International Consulting Engineers, 1989 "A 19 Tees Viaduct. Middlesbrough Bridge Enclosure", Technical Report, London. 4- Meier, U., 1988 "Proposal For Carbon Fibre Reinforced Composite Bridge Across The Strait of Gibraltar at Its Narrowest Site", Les Materiaux Nouveaux pour la Precontrainte et la Renforcement d'ouvrages d'art, Paris. 5- Meier, U., and Kaiser, H., 1991 "Strengthening of Suuctures with CFRP Laminates", Advanced Composite Materials in Civil Engineering Structures, Proceeding of The Specialty Conference, Las-Vegas, Nevada, Jan 31-Peb 1, ASCE, pp l. 6- Minosaku, K., 1992 "Using FRP Materials in Prestressed Concrete Structures", ACI Concrete International, Vo1.14, No.8, pp NEFMAC, 1987, "Technical Leaflet 2", New Fibre Composite Material For Reinforcing Shotcrete, Technical Report, NEFCOM Corporation, Japan. 8- Rizkalla, S.H., and Tadros, G., 1994 "First Smart Bridge in Canada," to be published by ACI Concrete International, June, pp Sen, R., Issa, M., and Iyer, S., 1992 "Feasibility of Fibreglass Pretensioned Piles in a Marine Environment", Final Draft Report, University of South Florida, Tampa, January, 300 p.