ADVANCED COMPOSITE MATERIALS FOR BRIDGES

Transcription

1 ADVANCED COMPOSITE MATERIALS FOR BRIDGES Sami RIZKALLA ISIS Canada Network of Centres of Excellence Room 227, Engineering Building, University of Manitoba Winnipeg Manitoba, Canada, R3T 5V6 1. SUMMARY New bridges are being built with materials that have significantly higher strength in comparison to steel, are lighter, and are more durable for longer service life. The use of fibre reinforced polymer (FRP) bars and tendons is considered to be one of the most promising solutions to overcome the deterioration problems associated with concrete bridges due to the corrosion of steel reinforcements. This paper presents the Canadian experience in the design and construction of highway bridges built with these new materials. The paper reviews the design and construction of the Taylor Bridge in Headingley, Manitoba, where FRPs were used to prestress four of the main girders, as well as stirrups for the shear reinforcements. The use of FRPs to reinforce the deck slabs and the barrier walls for the same bridge and other bridges across the country is also discussed. The high strength and light weight of these materials and the fact that they are now available in the form of very thin sheets, provide an attractive and economical solution for strengthening existing concrete bridges to increase their ductility, flexure and shear capacity in response to the increasing demand to use heavier truck loads. This paper reviews some of the Canadian projects which have been completed using these materials. The paper presents a new technology for remote monitoring of bridges to minimize the need for frequent site inspections. Monitoring is based on using a new generation of fibre optic sensors which have already been implemented in the construction of new bridges in Canada, as well as in the strengthening of existing ones. 2. INTRODUCTION The Canadian Network of Centres of Excellence on Intelligent Sensing for Innovative Structures (ISIS Canada) was established in 1995 to conduct research and development on the innovative use of FRPs for bridges as a solution for deterioration of concrete due to corrosion of steel reinforcements, as well as the development of structurally-integrated fibre optic sensing technologies that will allow engineers to monitor the bridge from a remote location. One of the other main thrusts ofisis Canada is to use FRPs for the repair and strengthening of bridges in response to increased demand for heavier truck loads and to increase ductility of existing bridges for earthquake resistance. This paper reviews some of the new bridges built in Canada reinforced and/or prestressed with FRP, as well as the use of FRPs for strengthening existing bridges. In both cases, the experience gained from using a new generation of fibre optic sensors, remote monitoring and intelligent processing of the collected data are discussed.

2 3. FRP FOR NEW HIGHWAY BRIDGES Due to severe environmental conditions and the use of salt for de-icing roads in Canada, the use offrps for bridge girders, deck slabs and barrier walls has been used for several new bridges. These projects were completed through networking and collaboration between ISIS Canada and various provincial and municipal highway departments across the country. Due to a lack of codes and standards for the use of FRP for bridges and structures, ISIS Canada has undertaken the challenge of launching a comprehensive research program for each field application using a new design approach to examine the various aspects of the strength requirements, severiceability performance and the durability of these materials. In the case of the Taylor Bridge in Headingley, Manitoba, the research included an experimental program conducted at the University of Manitoba using full-scale models to examine behaviour and provide design guidelines for the construction details used in the bridge[l]. The following section reviews the design and construction of three bridges in Manitoba, Quebec and Alberta which have been completed using a variety of FRPs in terms of the type of fibre and reinforcement and which, in some cases, have been combined with the new design concept of the steel-free deck12]. 3.1 Taylor Bridge The Taylor Bridge is located on Provincial Road No. 334 over the Assiniboine River in the parish of Headingley, Manitoba. The total length of the bridge is metres (540 feet), divided into five equal spans. Each span consists of eight I-shaped precast prestressed concrete girders as shown in Figures land 2. FRP FRP,~(Lead"ne) ;1'"'.. \ \... \ 33.0Sm ~ S m (~ ~n I Figure 1: Layout of the bridge., ~, 1R,\ 1m Plan./FRP I 8 18m I Section X-X 7 + ~660~ Girder Prestressed by Steel strands Girder Prestressed by CFCC Cables section at mid span section at end block Girder prestressed by Lcadline bars Figure 2: Cross-section of the girders at the mid-span and end block.

3 Two different types of carbon FRP reinforcements were used. Carbon fibre composite cables (CFCC) of 15.2 mm diameter, produced by Tokyo Rope Mfg. Co., Ltd. of Japan, were used to pretension two girders while the other two girders were pretensioned using 10 mm diameter indented Leadline bars, produced by Mitsubishi Chemical Corporation of Japan, as shown in Figure 3. Two of the four girders were reinforced for shear using 15.2 mmdiameter CFCC stirrups and lox 5 mm Leadline bars of rectangular cross section. The other two beams were reinforced for shear using 15 mm diameter epoxy coated steel rebars. Figure 3: Details or reinforcement of girder prestressed by CFCC. A two-lane width of the deck slab was reinforced by 10 mm diameter indented Leadline bars similar to the reinforcement used for prestressing, as shown in Figure 4. C-BAR (GFRP) reinforcement of 15 mm diameter, produced by Marshall Industries Composites Inc. of the United States, was used to reinforce a portion of the Jersey-type barrier wall. Doubleheaded stainless steel tension bars of 19 mm diameter were used for the connection between the barrier wall and the deck slab. Material properties of FRP reinforcement used in the bridge are shown in Table 1. type of reinforcement shape dimensions area guaranteed strength elastic modulus mm mm 2 MPa GPa CFCC 7 wire Leadline circular Leadline rectangular lox C-BAR circular Table 1,' Material properties of FRP reinforcement.

4 Figure 4: Bridge deck of the Taylor Bridge reinforced by CFRP. The anchorage system used for CFCC was the die cast wedge type, where a 300 mm steel tube is attached to the cable by a low point braze alloy. Steel wedges were used to clamp individual cables to an anchorage head, similar to the conventional method for prestressing cables. The 10mm Leadline bars were anchored using 150 mm long steel wedges and a steel anchor head. Aluminum tubes were placed between the Leadline bars and the steel anchorage to reduce the transverse stresses in the bars. Both anchorage systems were supplied by the manufacturers of the reinforcement. A typical bridge girder was pretensioned using 12.7 mm steel strands with a cross sectional area of 99.0 mm 2 The ultimate tensile strength and modulus of the steel were 1860 MPa and 190 GPa, respectively. Epoxy-coated 15 mm steel rebars with a yield stress of 400 MPa were used as stirrups for the other girders. The specified concrete strength for the bridge girders was 30 MPa at release and 40 MPa after 28 days. The specified concrete strength of the deck slab and the barrier wall is 30 MPa Monitoring System A total of 63 single and two multiplexed fibre optic sensors were installed on the carbon FRP, GFRP and steel reinforcement to monitor the bridge from a central monitoring station remote from the bridge. The 65 sensors were installed on the following bridge components: i) the girders reinforced by CFRP; ii) selective girders reinforced by steel; iii) deck slab portion reinforced by CFRP; and iv) barrier wall portion reinforced by GFRP. In addition, 20 thermocouples were used at different location of the bridge to compensate for the temperature change. A 32-channel fibre optic grating strain indicator (FLS 3500R), shown in Figure 5, is used for strain measurements. The system is connected to a computer to download the strain readings using a telephone line. A general description for the fibre optic sensing technique used for Taylor Bridge is given in Figure 6.

5 optical sensors multiplixing unit (l-to-32) temperature sensors multiplixing unit (l-to-24) Fibre optic grating strain indicator (FLS 3500R) Computer with built-in modem Figure 5.' Fibre optic multiplexing and recording units. optic mulipjexing unit Figure 6: Optical sensing technology. 3.2 Crowchild Bridge The Crowchild Bridge is located in Calgary, Alberta. The bridge's superstructure and the prestressed concrete box girders were demolished in May 1997 and replaced by a new superstructure system using steel girders, a steel-free concrete deck for the intermediate deck spans and glass FRP for the cantilever sidewalks. C-Bar (GFRP) reinforcements of 15 mm diameter, produced by Marshall Industries Composites Inc. of the United States, was used to reinforce the two cantilever sidewalks including the top reinforcements of the adjacent slabs as shown in Figure 7. The composite action between the steel-free deck and the steel girder was achieved by using Nelson studs welded to the top flange of the steel girder and the steel straps required for the arch action mechanism in the steel-free deck as shown in Figure 8. The bridge was instrumented with 81 strain gauges, 19 embedded gauges, five thermisters, three smart glass rebars and two fibre optic gauges.

6 A wireless data acquisition system which consists of a 24-bit data acquisition chip, a radio transmitter and trigger is currently being developed to remotely monitor the bridge from the office of an engineer. A static truck load test and an ambient vibration test have been performed on the bridge and the preliminary results show extremely encouraging results. Figure 7: Use of C-Bars in combination with the steel-free deck system in Crowchild Bridge. Figure 8: Steel straps for the arch action mechanism of the steel-free deck. 3.3 Joffre Bridge The Joffre Bridge, located over the Saint-Francois River in Sherbrooke, consists of five spans (26 to 35 meters). The superstructure is supported by steel girders spaced 3.7 meters in a composite action of the deck slab. Construction started in August 1997 and the bridge opened to traffic on December 6, 1997[3].

7 Carbon FRP NEFMAC grids were used to reinforce the deck slabs. The NEFMAC was produced by Autocon Composites Inc. of North York, Ontario. Some of the CFRP NEFMAC grid was instrumented using structurally-integrated fibre optic sensors during the manufacturing process, as shown in Figure 9. The grids were used to reinforce a portion of the deck slab of the bridge side-by-side with conventional steel reinforcements to examine the effectiveness of this material in increasing the service life of the bridge, as shown in Figure 10. The bridge is extensively instrumented using fibre optic sensors, vibrating wire strain sensors and electric resistance strain. All sensors are connected to telephone lines for continuous monitoring of the bridge from remote locations. Figure 9: Structurally-integratedfibre optic sensors in the NEFMAC. Figure 10: A portion of the deck slab of the Joffre Bridge reinforced by carbon NEFMAC.

8 4. STRENGTHENING WITH FRP More than 40 percent of the bridges operating in Canada were built over 30 years ago and most are in urgent need of replacement or rehabilitation. Many of the structural deficiencies are due to deterioration of the concrete as a result of corrosion of the steel. Other bridges have become functionally obsolete due to an increase in service loads and traffic volumes which exceed those for which they were designed. FRPs provide an excellent solution to repairing and/or strengthening bridges. For bridge piers, wrapping can significantly improve the strength and ductility. FRPs are also used for strengthening the superstructure of the bridge by strengthening the flexure and shear capacity of the girders and slab. The following are selected demonstration projects illustrating the use offrp for strengthening bridges. 4.1 Champlain Bridge In October 1996, the Jacques Cartier and Champlain Bridges Inc. proceeded with the rehabilitation of a concrete pier of the Champlain Bridge located in Montreal. The pier is 1.37 meters in diameter and was repaired over a 4 meter length measured from the base. The rehabilitation began with restoration of the column surface using shotcrete. After curing, the surface was prepared using a sand blast technique followed with a resin application. Nine layers of glass fibre, type E (SEH51ITYFO S), from Composite Retrofit International Inc. were used, see Figure 11. FRP was needed in this case to increase the confmement of the concrete, as well as providing a protective surface to the crumbled and cracked concrete surface[41. Figure II: Strengthening of the pier of the Champlain Bridge. 4.2 Maryland Bridge Carbon FRP is planned to be used to strengthen the shear capacity of the I-shaped concrete AASHTO girders of the Maryland Bridge in Winnipeg, Manitoba. The bridge was built 27 years ago. Analysis of the precast prestressed concrete girders indicates a deficiency in the shear capacity using the current AASHTO code. A 1 :35 scale model of the bridge girder was tested using three different types ofcfrp and six configuration schemes, as shown in Figure 12. The diagonal configuration for the carbon FRP was found to be the most effective configuration in reducing the tensile force in the stirrups[sl.

9 Figure 12: Proposed configuration ofcfrp sheets for Maryland Bridge. 5. CONCLUSION In spite of the lack of codes and standards, several bridges have been built around the world using carbon FRPs for prestressing and/or reinforcing of the concrete structural girders, deck slab and barrier wall. The design is based on a rational approach of the material characteristics which was relatively simple due to the linear behaviour of the FRPs to failure. FRPs were also used to strengthen existing bridges due to the increased demand for heavier truck loads. The strengthening was in the form of wrapping columns to increase the strength and ductility as well as to increase flexure and shear capacity of the girders. Most of the field applications have been instrumented for continuous monitoring to provide data related to the material's long-term behaviour and to ensure safety of the bridge by monitoring their performance under service loading conditions. 6. ACKNOWLEDGEMENTS The author would like to acknowledge Dr. Brahim Benmokrane of the Universite de Sherbrooke, Dr. Kenneth Neale of the Universite de Sherbrooke and Dr. Roger Cheng of the University of Alberta for allowing citing of some of ISIS Canada's projects whereby they had provided the leadership for design and construction. Thanks also to the provincial and municipal agencies across Canada for their cash and in-kind contributions to ISIS Canada. A special thank you to Autocon Composites Inc, Marshall Industries Composites Inc., Mitsubishi Chemical Corporation, Tokyo Rope Mfg. Co., Ltd.., RocTest Ltd. and Electrophotonics Corporation for donating the materials required for these projects. 7. REFERENCES [1] Fam, A., Rizkalla, S.H. and Tadros, G. (1997), "Behaviour ofcfrp for Prestressing and Shear Reinforcements of Concrete Highway Bridges", ACI Structural Journal, January/February 1997, Vol. 94, No.1, pp [2] Newhook, J.P. and Mufti, A.A. (1996), "A Reinforcing Steel-free Concrete Deck Slab for the Salmon River Bridge", Concrete International, June 1996, Vol. 18, No.6, pp [3] Benmokrane, B., Chekired, M., Rahman, H. and Tadros, G. (1997), "Progres recents dans I 'utilisation de I' arnatyre en materiaux composites pour les structures en b6ton: Cas du pont Joffre", Seminaire annuel1997 sur Les Progres dans Ie domaine du beton - Section du Quebec et de l'est de I'Est l'ontario de l' ACI, Montreal, December 2 to 3, 1997,9 p. [4] Neale, K.W. and Labossiere, P. (1998), "Applications of Structural Rehabilitation with Fibre Composite Sheets in Cold Climates", Concrete International, June issue. [5] Hutchinson, R., Abdelrahman, A. and Rizkalla, S.H. (1998), "Shear Strengthening Using FRP Sheets for a Concrete Highway Bridge in Manitoba, Canada", Second International Conference on Composites in Infrastructure (ICCI '98), January 5 to 7, 1998, Tucson, Arizona.