Abstract BRIDGE DESCRIPTION

Transcription

1 Taylor Bridge - A Bridge For the 21 st Century WORLD WISE'99- Winnipeg, Manitoba Taylor Bridge - A Bridge For the 21 st Century Emile ShehataI, Rick Haldane-Wilsone 1, Doug Stewart!, Gamil Tadros 2 and Sami Rizkalla 2 Abstract Wardrop Engineering Inc. was commissioned by the Province of Manitoba to design and build the Taylor "smart" Bridge utilizing fibre reinforced polymer (FRP) reinforcing materials as the primary reinforcement for precast concrete bridge girders, concrete bridge deck, and traffic barrier. An experimental program which included testing large scale model bridge girders prestressed and reinforced for shear using carbon FRP and a full-scale bridge deck slab was undertaken by the Canadian Network of Centres of Excellence on Intelligent Sensing for Innovative Structures (ISIS Canada) at the University of Manitoba. The test results were used to develop guidelines for the design of prestressed concrete girders, the bridge deck and the barrier wall using FRP reinforcement. The Taylor Bridge, located in Headingley, Manitoba, is considered to be the world's longest highway bridge with girders prestressed with FRP reinforcements and FRP as shear shear reinforcement. To provide an additional level of confidence to the Province of Manitoba, Wardrop Engineering Inc. and ISIS Canada, the bridge was instrumented with a series of fibre optic sensors (FOS) to monitor the performance of the new construction materials relative to the conventionally reinforced portions of the bridge. The bridge is remotely monitored to evaluate the effects of temperature, traffic loads and the long-term behaviour, as well as durability of the FRP materials relative to conventional steel reinforcements. Design philosophies and construction techniques used for the bridge to handle these new materials are presented. The paper also discusses the expert system used to reduce the data collected from the bridge into engineering information which can be used to assess the performance of the FRP material and the behaviour of the bridge. BRIDGE DESCRIPTION Taylor Bridge is located on Provincial Road No. 334 over the Assiniboine River in the Parish of Headingley, Manitoba, and was opened to traffic in October The 165m-long bridge consists of 40 prestressed concrete AASTO type girders, as shown in Figure 1. Four girders of the Taylor Bridge were prestressed by two different types of carbon fibre reinforced polymer (CFRP) material using straight and draped tendons, as shown in Figure 2. The girders were also reinforced by CFRP stirrups protruded from the AASHTO type girders to act in composite action with the bridge deck. A portion of the deck slab is reinforced by CFRP reinforcement. Glass fibre reinforced polymer (GFRP) was also used to reinforce the barrier wall. The barrier wall is connected to the deck slab with double-headed stainless steel bars. To obtain continuous 1 Wardrop Engineering Inc., Winnipeg, Manitoba R3C 4M8 2 ISIS Canada, University of Manitoba, Winnipeg, Manitoba R3T 2N2 1

2 Taylor Bridge - A Bridge For the 21 st Century information on the behaviour of the bridge and the performance of FRP as reinforcement and prestessing tendons, the bridge is monitored to provide data to evaluate the long-term behaviour and durability of the FRP materials used. SECTION A A C0 7 I FRP (Leadline) no. of sensors FRP (CFCC) A PLAN VIEW 5 33 m Figure 1. Bridge Layout Figure 2. Girder Reinforcement 2

3 Taylor Bridge - A Bridge For the 21" Century FRP Materials Two different types of CFRP reinforcements were used. Carbon fibre composite cables (CFCC), produced by Tokyo Rope in Japan, were used to pretension two girders while the other two girders were pretensioned using Leadline bars, produced by Mitsubishi Chemical Corporation in Japan. Two of the four girders were reinforced for shear using CFRP stirrups, while the other two beams were reinforced for shear using epoxy-coated steel stirrups. The stirrups were projected out of the top surface of the girder to act as shear connectors and to provide the composite action between the girder and the deck slab. A portion of the deck slab was reinforced by CFRP Leadline bars similar to the reinforcement used for prestressing. C-BAR (GFRP) reinforcement, produced by Marshall Industries Composites Inc., in the United States, was used to reinforce a portion of the Jersey-type barrier wall. Double-headed stainless steel tension bars were used for the connection between the barrier wall and the deck slab. DESIGN PHILOSOPHY Due to a lack of codes and standards on the use of FRP as reinforcement and prestressing materials for concrete bridges, an extensive experimental program was conducted over the last five years. The program included testing of a large scale model of a bridge girder totally reinforced and prestressed with carbon FRP (Fam et ai., 1997) and a full scale portion of the bridge deck slab reinforced with CFRP under simulated traffic loads up to failure (Charleson et ai., 1997, and Louka 1999). Straight and draped CFRP reinforcements were also tested under axial tension. Performance of CFRP as shear reinforcement (Shehata et ai., 1999), including effect of bend and orientation of the crack on the tensile strength, was investigated. Transfer and development lengths of the CFRP reinforcement were also evaluated and a theoretical model was introduced by Mahmoud et al. (1999). In addition, a research project (Maheu and Bakht, 1994) was conducted by the Ministry of Transportation of Ontario (MTO) to examine the barrier wall and the deck slab for steel-free bridge decks. The results were used to design the Taylor Bridge. Bridge girders prestressed and reinforced by CFRP were designed to behave similar to other girders of the bridge reinforced and prestressed with steel strands under service loading conditions. The prestressing force and the eccentricity of the reinforcement were kept the same for all girders. The initial prestressing level was 60 percent of the guaranteed ultimate tensile strength for CFRP prestressing bars compared to 75 percent for steel strands. The flexural design of girders prestressed by CFRP reinforcement was based on strain compatibility and the material characteristics of CFCC, Leadline and concrete. The predicted flexural behavior of girders prestressed by CFRP was identical to that of girders with steel before cracking as shown in Figure 3. The design capacity of girders with CFRP, based on the ultimate strength of the reinforcement, was 50 percent higher than that of the girder with steel. It should be noted that the ultimate tensile strength of CFRP reinforcement is higher than the guaranteed value reported by the manufacturer. Based on AASHTO Code 1989, the girders reinforced by CFRP were designed for a stress level in the stirrups of 250 MPa (36.25 ksi) at factored applied load, compared to 200 MPa (29.00 ksi) stress level used for the steel stirrups. The reduced stress in the CFRP stirrups is lower than 40 percent of its ultimate capacity. 3

4 WORLD WISE '99 - Winnipeg. Manitoba Taylor Bridge -A Bridge For the 21'1 Century 25~ T ' Girder with CFCC moment capacity based on ~ guaranteed strength Girder with ~--- Leadline... Girder * with... steel....',..1 5 moment due to service load o ~ Failure Mechanism -L ~ ~~ 1000 kn-m = 749 kip-ft ~ ~ -5 o Curvature ( m) Figure 3. Flexural Capacity of Bridge Girders Dr. Gamil Tadros has introduced the concept of providing an alternative load path in the design of the bridge in order to avoid progressive collapse in case of failure of one of its components. The alternative load path mechanism is illustrated in Figure 4. The cross diaphragms were designed to support the dead load of the bridge in case of the unlikely event of failure of the two girders prestressed by CFRP. In addition, non-prestressed reinforcements were provided in the girders prestressed by CFRP to develop catenary action in case of breakage of the stressed reinforcement. cross diaphragms Figure 4. Alternative Load Path Mechanism 4

5 Taylor Bridge - A Bridge For the 2]" Century MONITORING SYSTEM A total of 63 fibre-bragg grating (FBG) sensors and two multi-bragg sensors were glued to the reinforcing CFRP bars of the structural members of Taylor Bridge. The number of sensors installed on each member is given in Figure 1. The FBG sensors were installed at different locations along the girders. FBG sensors located at the midspan were designed to monitor the maximum strain in the reinforcement due to applied loads, while FBG sensors located at the girder ends were designed to evaluate the transfer length of prestressing tendons. Due to the relatively high initial prestressing strain (-8800 microstrain) and the limited full range of the FBG sensors, most of the sensors were installed after tensioning the prestressing tendons. Some of the FBG sensors were installed before prestressing to measure the initial prestressing strains of the CFRP and steel tendons. FBG sensors were installed according to the installation manual prepared by the University of Toronto Institute for Aerospace Studies (UTIAS) for ISIS Canada (Tennyson, 1998). Twenty-two AD590 electric-based temperature sensors, produced by E-TEK Electrophotonics Solutions, were installed for the purpose of compensation for thermal apparent strain. Temperature sensors provide representative temperature measurements among different girders and at various locations along and through the depth of the girder and the deck slab. The reading of a FBG sensor, 8sensor, was used to estimate the temperature-compensated strain, 8comp, as follows: 8 = 8sensor +_1 [p (a -a )+rlat comp P P & s F ~.JLl & & where L1T(=T;- To) is the temperature variation, Ti is the temeperature reading as recorded by the temperature sensor co-located with the FBG sensor under consideration, To is the reference temepature (=23.5 C), as and af are the coefficients of thermal expansion of the structural material and fibre; respectively, S is the thermal-optic coefficient, and P & is the strain-optic coefficient. A total of 26 electric strain gauges were also used at locations as close as possible to some of the FBG sensors. The electric strain gauges were installed on the CFRP tendons prior to pretensioning to monitor the prestressing strain. Even though the strain gauges were properly sealed, more than 60 percent of the electric strain gauges malfunctioned due to the excessive moisture resulting from steam curing of the concrete girders. None of the FBG sensors were found to be affected by the moisture content. The strains were recorded using a fibre grating strain indicator (FLS3500R TM), a 32-channel multiplexing unit for quasi-static strain measurements and a 24-channel multiplexing unit for temperature measurements, as schematically shown in Figure 5, The FLS3500 is a stand-alone unit with programmability and strain measurement from either the front panel display or the back panel analog/digital output ports. The FLS3500 handles input from AD590 temperature sensors and FBG optical sensors, with digital output through an RS232 digital port. The FLS3500R TM strain indicator is connected to a resident computer which can be accessed by modem for data logging and downloading. Correction for thermal apparent strain may be performed either in real time within the FLS3500R TM device, or by post-processing after the data has been logged. The monitoring devices and the computer are housed in a heated enclosure mounted in the 5

6 Taylor Bridge - A Bridge For the 21" Century abutment of the bridge, as shown in Figure 6. A camera was recently installed at the bridge site to provide video infonnation synchronized with the optic sensors' signals. The bridge is also being monitored by 26 conventional electrical strain gauges mounted on the reinforcement used to verify the readings of the optic sensors. The multiplexing unit and the data logging system were installed in a heated enclosure, located in the cross diaphragm under the bridge deck slab. Steel Steel Steel Steel ""f.:stee~el,. l"~' Bridge site ~ FLS3500R Fibre Optic Grating Strain Indicator 32-channel Fibre optic multiplexing unit ' ~ , ;l Engineers' office ~. e --I Figure 5. Schematic of Optical Sensing Technology Figure 6. Data Acquisition System of Taylor Bridge 6

7 Taylor Bridge - A Bridge For the 21'1 Century Sensors' Expert System Program A full-featured software package "ESP AN" has been developed by the researchers of ISIS Canada for analyzing FBG sensors' data downloaded from the Taylor Bridge computer (Maalej et ai., 1998). The main features of the "ESP AN" software are: a- Interactive visualization of measurements b- Strain profiles c- Moment profiles d- Estimation of the coefficient of thermal expansion of sensor substrate materials e- Image viewing of diagrams or photographs of the structure f- Estimation of vehicle velocities g- Graphical user interface driven interaction The "ESP AN" software is portable in the sense that it can run on any major platform (operating system) including Windows'98 and Unix. In addition to the Taylor Bridge, the software was successfully used to process the sensors' data of the Salmon River Bridge in Nova Scotia (Maalej et ai., 1998). A detailed description of the features of "ESP AN", along with hardware and software requirements, manuals and other instructions, are provided by Maalej et al. (1998). MONITORING RESULTS Monitoring results recorded address the following stages: a- Construction stage b- Load testing of the bridge c- Long-term behavior due to the temperature effect Construction Stage Most of the available research on bond behavior of CFRP reinforcement was obtained by testing specimens reinforced with single CFRP bars or strands; therefore, it is important to assess the behavior in case of multiple CFRP tendons used for the bridge girder. FBG sensors were installed on the CFRP tendons at the end of the bridge girders to measure the effective stress level in the tendons after release of the prestressing force. Figure 7 shows the effective-to-initial prestressing ratio along five meters at the end of the bridge girders prestressed by two differ~nt types of CFRP tendons. It can be seen that the transfer lengths, L t, are 600 mm (60 db) and 340 mm (22.3 db) for CFRP tendons type 1 and type 2, respectively, where db is the bar diameter. Based on an independent research program conducted to investigate the bond characteristics of CFRP tendons (Mahmoud et ai., 1999), transfer lengths in the bridge girders were recommended as 66 db and 22.5 db for the same CFRP tendons type 1 and type 2, respectively. The observed values for transfer lengths showed good agreement with the values determined based on the equations proposed in (Mahmoud et ai., 1999). The strain in the CFRP prestressing tendons was monitored during transportation of the girders to the bridge site. The strain signal of a selective sensor at the midspan of the girder was recorded at 14 intermediate stations along the trip from the pre-casting plant to the bridge site. 7

8 Taylor Bridge - A Bridge For the 21 st Century Figure 8 shows the variation in the CFRP strain relative to the effective prestressing strain at different stations during the trip. _ ~-~~-~-~-~~~~-c:.~~~j. :~ Ii fpe '-'.'.... fp; i! L, I i /=34Omm 0.4! _..._----- ~~_~_~J!:~~!!l..c:_~~l ~.~;-----!~ I! L, i i~6oomm 0.4 P.2f ~ 0.2 ~1~i _4 0.2 i! fpe = the effective prestressing stress J, = the effective prestressing stress /Pi = the initial prestressing stress 1; = the initial prestressing stress 0+-~-4_~~4_---4_~--~~--~ 0+---~+---~ _ ~ o o distance from girder end (mm) distance from girder end (mm) Figure 7. Transfer Length, L" ofcfrp Tendons 1.1, ~ A _ A A A A A A A 0.95 t:p = the recorded strain t:pe = the effective prestressing strain Station ill ~ 'r;; o.gf c CQ Figure 8. Girder Transportation Data Load Testing The output signal of a FBG sensor installed on a CFRP prestressing tendon at midspan was recorded every 0.24 second during a test loading conducted using a slow moving truck and trailer, as shown in Figure 9. The 36-ton truck made several passes over the girder span, forward and backward. The FBG sensor was able to record the strain change experienced by the CFRP tendon as shown in Figure 9. The figure clearly identifies both the truck and the trailer loading as two distinct peaks in the response curve even though the magnitude of the strains are quite small. The direction of travel can also be detected by the relative magnitudes of the peaks since 8

9 Taylor Bridge - A Bridge For the 21 st Century the truck load is larger than the trailer load. Hence, the first event in Figure 9 represents a backward pass and the subsequent one is a forward pass over the span til :t '-' C.~... en 10 5 o -5 o time (seconds) Figure 9. Test Loading Using a Slow Moving Truck and Trailer Temperature Effect The strains in CFRP reinforcement are being continuously monitored to detect any loss in the prestressing forces. Since the long-term monitoring initially commenced, no significant loss in the pres stressing force has been observed. Sample data is given in Figure 10 showing the variation in the strain and the temperature of a CFRP prestessing tendon over a period of seven days. The signals from the FBG sensors and the temperature sensors were recorded every five minutes. The strain variation is attributed to the difference in the coefficient of thennal expansion of CFRP reinforcement (acfrp-o) and the concrete (aconcrete=12xlo-6fc). The strains 9

10 Taylor Bridge - A Bridge For the 21" Century in the FRP and steel reinforcement are continuously monitored to investigate the temperature and creep effects on the structural performance of the bridge structure ~ Cf) to.) ::t c 0 '(6 L () ~ ::l..- C1l 5 L- a> c.. 0 E a> -5 I Time (days) Figure 10. Strain and temperature data - February 1998 CONLCUSIONS A sophisticated monitoring system has been successfully deployed in the Taylor Bridge, Headingley, Manitoba. The optical sensing system is used to remotely monitor the bridge structure, giving the bridge engineer a warning signal if abnormal conditions should occur. This project provides an example for the practical issues of the design and implementation of such a system for long-term structural monitoring. The FBG sensors' data are processed using an interactive software package, specially implemented for this purpose. Preliminary data collected from the bridge shows that such a monitoring system can prove to be a very effective tool for the bridge engineer. Monitoring of the Taylor Bridge provides essential data related to the shortterm and long-term performance of FRP material used to reinforce the bridge members. In summary, the monitoring system can provide a profile of the bridge with detailed information on 10

11 Taylor Bridge - A Bridge For the 21" Century its structural behaviour, as well as the applied loads and environmental effects. Wardrop Engineering Inc. and ISIS CANADA currently undertake further development of the monitoring system utilizing a video camera at the bridge site. ACKNOWLEDGEMENT The authors wish to acknowledge the support of the Network of Centres of Excellence on Intelligent Sensing for Innovative Structures (ISIS Canada) and Industrial Research Assistance Program (IRAP) of the National Research Council (NRC). The writers gratefully acknowledge support provided by E-TEK Electrophotonics Solutions, Toronto, Ontario, Canada, for providing the materials used in the Taylor Bridge. Financial support provided by ISIS Canada and Manitoba Highways and Transportation, Winnipeg, Manitoba, Canada, made it possible to conduct this project. Special thanks are extended to Mr. M. McVey for his assistance during construction of the bridge. REFERENCES Charles on, K., A. Abdelrahman, S. Rizkalla, and W. Saltzberg "Behavior of a Model Concrete Bridge Deck Reinforced by CFRP", Proceedings of FRPRCS-3 International Conference, Sapporo, Japan, Vol. II: Fam, A., S. Rizkalla, and G. Tadros "Behavior of CFRP for Prestressing and Shear Reinforcements of Concrete Highway Bridges", ACI Structural Journal, 94(1): Louka, H "Behavior of a Hybrid reinforced Concrete Bridge Deck", M.Sc. Thesis, Department of Civil Engineering, University of Manitoba, 140p. Maalej, M., S.J. Pantazopoulou, A. Karasaridis, and D. Hatzinakos "Intelligent Monitoring of Instrumented Infrastructure Facilities", Proceedings of the 30th SAMPE Conference, "Materials - The Star at Center Stage", San Antonio, Texas. Maheu, J., and B. Bakht "A New Connection Between Concrete Barrier Walls and Bridge Decks", Proceedings of the 22nd CSCE Annual Conference, Winnipeg, Manitoba, Canada, Vol. II: Mahmoud, Z., S. Rizkalla, and E.-E. Zaghloul "Transfer and Development Lengths of Carbon Fibre Reinforced Polymers Prestressing Reinforcement", ACI Structural Journal, 96(4): Shehata, E., R. Morphy, and S. Rizkalla "Fibre Reinforced Polymer Reinforcement for Concrete Structures", ACI Special Publication SP-188, Editors: C. Dolan, S. Rizkalla, and A. Nanni: Tennyson R "Installation, Use and Repair of Fibre Optic Sensors", Technical Manual submitted to ISIS Canada NCE, Institute for Aerospace Studies, University of Toronto, Ontario, Canada, 74p. 11

12 Taylor Bridge - A Bridge For the 21 st Century Speaker Biography Emile Shehata, is a Structural Engineer with over ten years of academic and engineering experience. He received his B.Sc. in 1989 from Ain-Shams University, Egypt, M.Sc. in 1994 from Cairo University, Egypt, and Ph.D. in 1999 from the University of Manitoba, Canada. He is currently working in the Product Development Department at Wardrop Engineering Inc. Dr. Shehata is currently holding the NSERC Industrial Research Fellowship (lrf). He is an associate member of the ACI Committee 440 on FRP Reinforcement. He has published over than 20 journal and conference papers in the area of composites and remote monitoring. 12