Advanced Materials for the New Millennium

Transcription

1 Advanced Materials for the New Millennium Sami Rizkalla, P.Eng. ISIS Canada University of Manitoba 227 Engineering Building Winnipeg, Manitoba, R3T 5V6 Telephone: Facsimile: Abstract: 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 offrps to reinforce the deck slabs and the barrier walls for the same bridge and other bridges across the country is discussed. Current research progress on hybrid FRP/concrete structural systems is also reviewed. 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 and structures 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, as well as new material being developed for the rehabilitation of wood bridges. 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 offrps 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 of ISIS 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. 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 offrp 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( I). 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 ofthe steel-free deck(2). 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 1 and 2.

3 g; mm steel strands ; ;./ CFCC mm 4-1Omm Leadline Leadline l00mm mm CFCCcables rf,*~~ 4 stirrups T II ,-----\' w i 178mm ->l'llif- ~660mnL-l Girder Prestressed by Steel strands Girder Prestressed by CFCCCables section at mid-span section at end block Girder prestressed by Leadline bars Figure 1: Layout of the Taylor Bridge. FRP X~'( L "di ; ",1 'NNh FRP I ICFCC\' '\ i i ~ \. i i i i! K m 33.0 ~ m m Plan ~ i [d e 18m Sectio n X -X Figure 2: Cross-section of the girders at the mid-span and end block.

4 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 ofthe four girders were reinforced for shear using 15.2 mm diameter 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 of 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 ofthe Jersey-type barrier wall. Double-headed 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 I.

5 Figure 4: Bridge deck of the Taylor Bridge reinforced by CFRP. type of shape dimensions area guaranteed strength elastic modulus reinforcement mm mm' MPa GPa CFCC 7 wire Leadline circular Leadline rectangular 10 x C-BAR circular Table 1: Material properties of FRP reinforcement. 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 10 mm 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.

6 A typical bridge girder was pretensioned using 12.7 rnm steel strands with a cross sectional area of99.0 mm 2. The ultimate tensile strength and modulus of the steel were 1860 MPa and 190 GPa, respectively. Epoxy-coated 15 rnm 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: 1. the girders reinforced by CFRP; 2. selective girders reinforced by steel; 3. deck slab portion reinforced by CFRP; and 4. barrier wall portion reinforced by GFRP. In addition, 20 thermocouples were used at different location of the bridge to permit compensation 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. optical sensors multiplixing unit (I-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.

7 Steel Steel Steel Bridge site Fibre Optic Grating Strain Indi 3~~elFibre optic muliplexing unit Engineers' office Figure 6: Optical sensing technology. 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 adj acent 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.

8 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.

9 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. 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). Carbon FRP NEFMAC grids were used to reinforce the deck slabs. The NEFMAC was produced by Autocon Composites lnc. 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.

10 Figure 10: A portion of the deck slab of the Joffre Bridge reinforced by carbon NEFMAC. HYBRlD FRP/CONCRETE STRUCTURAL SYSTEM Currently, the research at ISIS Manitoba includes the use oftubular, rectangular and round FRP structural members with different cross-sectional areas and placing one member inside the other. The gap between the two shells is filled with concrete or grout. The structural system provides advantages of saving the cost of form work and, at the same time, the outer and inner FRP shell acts as a reinforcement as shown in Figure 11. The system also provides confmement on the concrete and, therefore, increases the ultimate compression strength leading to an overall increased ductility of the member. The experimental program includes testing small and medium-sized winded FRP tubular members to provide optimum use of fibres to resist both flexural and shear resistance. The various parameters considered in the program include thickness of the shell, directions of the fibres, and the type of fibres. The research findings anticipate development of an innovative construction system for bridges and structures which is more economical and will increase their service life.

11 thin layer of concrete outer FRP skin _ inner FRP skin --- fibers at 45 degrees void layer of uniaxial fibers degrees Figure 11: Hybrid FRPlconcrete member. 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 ofthe 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 siguificantly 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. 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

12 (SEH51 /TYFO S), from Composite Retrofit International Inc. were used, see Figure 11. FRP was needed in this case to increase the confinement of the concrete, as well as providing a protective surface to the crumbled and cracked concrete surface(4). Figure 12: Strengthening of the pier of the Champlain Bridge. Maryland Bridge Carbon FRP is planned to be used to strengthen the shear capacity of the I shaped concrete AASHTO girders ofthe 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 of CFRP 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(5).

13 Figure 13: Proposed configuration of CFRP sheets for Maryland Bridge. Webster Parking Garage Carbon and glass fibre sheets were used for rehabilitation of the Webster parking garage built in 1959 in Sherbrooke, Quebec, Canada(6)l. The rehabilitation included strengthening the main beams for flexure and shear, as well as the columns which had lost their carrying capacity due to severe corrosion of the steel reinforcements. High-performance self-leveling concrete was used to replace the severely damaged and cracked concrete for some of the beams and columns before applying the external FRP sheets as shown in Figure 13. Wrapping of the columns provided a confinement effect and was used to increase both strength ofthe concrete and ductility of the columns. Sheets used for the main beams increased the flexural capacity by IS percent and the shear capacity by 20 percent. Depending on the degree of deterioration, some of the beams needed strengthening for the negative moment region, especially in the rigid frame system and other needed strengthening in the positive moment regions.

14 Figure 14: Webster parking garage. REHABILITATION OF WOOD BRIDGES In cooperation with the Swiss Federal Laboratories for Materials Testing and Research (EMP A), ISIS Canada is undertaking a new research program to develop an innovative technique to strengthen highway timber bridges to carry the new design requirements specified by most Departments of Highways and Transportation. The research focuses on the use offrp materials due to its non-corrosive characteristics, easy handling and high strength. More specifically, the research uses non-laminated FRP materials currently under development by EMP A(7) to prestress the wood stringers as shown in Figure 15. The specific objective ofthe research is to optimize the post-tensioning technique and to determine details of the most convenient and economical connections which could be used to prestress these types of bridges. The study consists of an experimental program using old timber bridge stringers of an abandoned and dismantled timber bridge. Manitoba Highways and Transportation has provided ten beams, 10.4 meters long with 200 x 600 mm cross section; six beams, 6.7 meters long with 500 x 150 mm cross section; and two beams, 2.75 meters long with 300 x 300 mm cross section for the experimental program. The project is currently in its preliminary stages and one beam was tested in November 1998.

15 Figure 15: Non-laminated strips for the rehabilitation of wood bridges. 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.

16 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 proj ects 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. 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, JanuaryfFebruary 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 l'utilisation de l'arnatyre en materiaux composites pour les structures en beton: Cas du pont Joffre", Seminaire annuel1997 sur Les Progres dans Ie domaine du beton - Section du Quebec et de l'est de l'est l'ontario de I'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. (6) Neale, K.W. and Labossiere, P. (1997), "State-of-the-Art Report on Retrofitting and Strengthening by Continuous Fibre in Canada", Proceedings of the Third International Symposium on Non-metallic (FRP) Reinforcement for Concrete Structures, Vol. 1, October 1997, pp (7) Winistoerfer, A. and Moltrarn, T. (1997), "The Failure of Pin-Loaded Straps in Civil Engineering Applications", Recent Advances in Bridge Engineering, US-Canada-Europe Workshop Proceedings edited by Urs Meier and Raimondo Betti, Dubendorf and Zurich, July 1997, pp