Road Bridges: Finding a better way to build
This question is important considering the deteriorating state of infrastructure everywhere. In the United States there are more than 200,000 deficient bridges, and approximately 30,000 in Canada. Bet...
This question is important considering the deteriorating state of infrastructure everywhere. In the United States there are more than 200,000 deficient bridges, and approximately 30,000 in Canada. Between 150 to 200 bridge spans collapse every year in North America, sometimes with tragic consequences. Often these failed bridges are concrete structures with steel reinforcements, and were built
Lloyd McGinnis, P.Eng. & Jennifer Redston, ISIS Canada With the newest global positioning technology your car can be identified anytime, anywhere in the world, via satellite. You can start your vehicle remotely and it can be monitored for any mechanical failures or for having emissions that exceed global allowances. Electronic faults can even be corrected via satellite. However, all this smart technology, purchased for your own “peace of mind,” won’t help when the bridge you’re crossing is in the process of catastrophic failure. If society is at the point where vehicles can be outfitted with miniaturized remote monitoring systems, doesn’t it make sense that we should all benefit from “smart” infrastructure?
decades ago. They are crumbling under the attack of corrosion due to the use of de-icing and marine salts. They also suffer from environmental pollutants and from the long-term effects of traffic loads that weigh substantially more than the bridge’s original designed structural capacity. Many have simply come to the end of their service life cycle.
There is a remedy: fibre-reinforced polymers (FRPs). Glass and carbon fibre-reinforced polymer composites are used extensively in the automotive, aerospace and defence industries, and for sporting equipment and microwave cookware. Over four million pounds of the material were used for cables in making the Eurotunnel.
Although the use of fibre-reinfored polymers for civil engineering is relatively new, the idea is rapidly gaining acceptance. A Canadian research and development initiative led by ISIS, working with owners, manufacturers and consulting engineers, is at the forefront in applying the technology to civil engineering structures and in gathering data for establishing codes and guidelines.
ISIS Canada (Intelligent Sensing for Innovative Structures) is part of the federal Networks of Centres of Excellence program and is a collaborative effort of 11 universities. The organization works with filament wound and pultruded fibre-reinforced polymer composites in new and rehabilitation projects. ISIS also brings a new spin to the technology. Its field applications are outfitted with the newest generation of fibre optic sensing for remote monitoring.
The ability to monitor the behaviour of concrete structures reinforced with carbon or glass fibre-reinforced polymer will give industry confidence in the material and hasten its widespread acceptance. Given FRP’s well known advantages, the data gathered and analyzed by the fibre optic sensors could catalyze a revolution in the design and construction of civil engineering structures.
Fibre reinforced polymer is a manufactured material in which fibres with very high strength such as glass, carbon or aramid, are encased in a polymer (plastic) resin. The resin provides the shape of the product, which can be reinforcing bars or structural members.The resin also protects the fibres from moisture, ultraviolet light and corrosive chemicals.
Benefits for civil engineering
Fibre-reinforced polymer composites are one-fifth the weight of steel and up to six times stronger. They are completely resistant to corrosion, non-magnetic, and easily tailored to a wide range of designs. Their high strength and light weight, and the fact that they can now be formed into very thin sheets, means they are an attractive and economical solution for strengthening existing concrete bridges and structures to increase ductility, flexure and shear capacity.
Fibre-reinforced polymers can be used for longer, unsupported, spans, or where a reduced overall weight could mean greater seismic resistance. A lightweight FRP-reinforced structure can reduce the cost of columns and foundations and can accommodate heavier truck loads.
In new structures, the material is used for reinforcing both cast in-place and pre-cast concrete. It can take the shape of rebars, stirrups, grating, pavement joint dowels, tendons, anchors, and more. In rehabilitation projects the fibre-reinforced polymer serves either to confine concrete subjected to compression or to improve flexural and/or shear strength as an externally bonded reinforcement.
Until now the composite material was not feasible for civil engineering applications because the manufacturing procedures were expensive. Advances in manufacturing systems such as pultrusion and filament winding have brought costs closer in line with steel, concrete and masonry. Although fibre-reinforced polymer is still more expensive initially, in the long run it can bring substantial savings. The design service life of a structure reinforced with FRP is estimated conservatively at 75 years, compared to 50 for conventional structures.
While some of ISIS Canada’s field applications use fibre-reinforced polymer only where economically viable, there are others such as in marine environments and in bridge decks where price is not a factor. In these cases, it is the non-corrosive property of FRP that gives it a distinct advantage over steel. Suppliers continue to improve the ability of the fibres to withstand harsh chemical environments, and so far FRP has no rivals.
High tech monitoring
Fibre optic sensing (FOS) is a natural outgrowth of aerospace research where the technology is used to monitor aeronautical and space structures composed of composite polymers. The sensors have the advantage of being immune to electromagnetic interference and are lightweight. The evidence that fibre-reinforced polymers have long-term stability is another factor in their use.
ISIS Canada research generated at the University of Toronto’s Institute for Aerospace Studies has been setting new standards with sensors that gather localized information and absolute measurements. They can take into account temperature corrections and differentiate between the parking and passage of a vehicle.
The fibre optic sensing technology provides an unintrusive way to monitor traffic flows and excess loads. It can also measure the long-term health of structural components rehabilitated with fibre-reinforced polymer wraps, vibration frequency and seismic response. The technology can help reduce the tendency of engineers to over-design structures. It can also enable them to monitor the actual load history of a structure, and to detect internal structural weaknesses before erosion becomes critical and the structure becomes unsafe.
Field applications using fibre optic sensing systems are a recent innovation. Besides the applications in Canada, there are a highway bridge and a concrete dam in Germany and a few bridges in Vermont outfitted with such systems. In Switzerland, researchers are monitoring the behaviour of geological structures around pilings and tunnels using fibre optic sensing.
ISIS Canada’s field applications cover a range of designs and different challenges. A few of the projects are shown here, and each is a collaborative effort of owners, engineers, constructers, suppliers and researchers.
Field applications are ISIS Canada’s trophies. The successful completion of one project generates sufficient data to initiate another application, and each in turn serves to gain the confidence of the design and construction community and prove the technology’s long term performance. The data collected to date shows that this material has had an excellent record in more than 10 bridges since 1993.
St. tienne de Bolton Overpass
Engineer: Ministre des Transport, Quebec
This landmark restoration project on Highway 10 in Quebec was completed in a mere three weeks by the Quebec Ministry of Transportation. Out of 18 circular columns, 12 were severely deteriorating because the steel rebars were in an advanced state of corrosion. Nine of t
he damaged columns were repaired using fibre reinforced polymers (five with carbon FRP and four with glass FRP) while the remaining three were repaired using conventional materials and methods. For each column, one layer was first installed with the FRP fibres aligned vertically. A second layer was applied with FRP fibres placed circumferentially.
To validate this method of repair, fibre optic sensors were installed on four of the columns to measure reactions to extreme temperature variations, corrosion and loading. The project proved that the significant savings in labour outweigh the increased expense of fibre-reinforced polymers. Because the materials are so lightweight and the installation method so easy to learn and apply, construction time and the size of the work crew are reduced compared to conventional methods. In addition, no form work is required and traffic flows as usual.
Consulting engineer: Le Groupe SM
The City of Sherbrooke undertook to revitalize the 37-year-old Webster Parkade in the fall of 1996. The project was done through the Canada-Quebec Infrastructure Program, which since 1966 has enabled a variety of civil engineering projects to incorporate new technologies.
The project team used glass and carbon fibre-reinforced polymers to rehabilitate and reinforce columns which had lost their initial capacity over the years due to corroding steel rebars, and to protect column bases exposed to de-icing salts during the winter. The FRPs were used to strengthen beams that didn’t conform to current standards concerning their bending and/or shear capacity. The team also installed an integrated structural sensing system to monitor the behaviour of the parkade under loading variations. Infrared rays were used to determine the success of the bonding between the FRPs and the concrete surfaces.
This project won the Innovation Award from the Quebec Ministry of Municipal Affairs in recognition of ISIS Canada’s contribution to the preservation of infrastructure.
Engineer: St. Lawrence Seaway
In October 1996, Jacques Cartier and Champlain Bridges Inc. selected glass fibre-reinforced polymer to repair one pier of the Champlain Bridge in Montreal. The base of the bridge pier is submerged and subjected to a strong current, and because it is located at the confluence of two parts of the St. Lawrence River it is particularly vulnerable to ice collisions during the winter and early spring.
Nine layers of glass fibre composite sheets were wrapped around the pier base giving an overall thickness of 10 mm. A special reel device was used to help in applying the nine layer glass FRP envelope. The sheets were wrapped around a reel, unwrapped and saturated in a resin bath, then rewound on a reel at the opposite end of the apparatus. This device was then transported to the site for the installation. This procedure saved considerable time, as well as saving workspace, which was critical because the material was being handled over the water.
The FRP wraps provide strengthening as well as added protection against damage from both ice collisions and corrosion. So far, the pier has been subjected to some of Quebec’s worst winters on record and it has shown excellent performance.
Consulting engineer: Teknika Inc.
Early in August 1997, the province of Quebec began constructing a bridge in Sherbrooke that was innovative in its use of carbon fibre-reinforced polymer reinforcements instead of steel. For the first time in the world, fibre optic sensors for remote monitoring were structurally integrated into the FRP reinforcement, as opposed to being attached to the FRP reinforcement which is embedded in concrete.
A portion of the Joffre Bridge concrete deck slab is reinforced with carbon fibre-reinforced polymer, as is a portion of the traffic barrier and the sidewalk. The bridge is outfitted extensively with different kinds of monitoring instruments including the embedded sensors. Over 180 instruments (fibre optic sensors, vibrating wire strain sensors and electrical strain gauges) are installed at critical locations in the concrete deck slab and on the steel girders to monitor the behaviour of the FRP reinforcement under real-time conditions. The instrumentation is also providing valuable information on long-term performance. All the sensors transmit data to a telephone line for remote monitoring of the structure’s behaviour.
Consulting engineer: Wardrop Engineering
The two-lane, 165 metre-long, structure has four out of 40 precast girders reinforced with carbon fibre-reinforced polymer stirrups. These girders were prestressed with carbon FRP cables and bars. Glass FRP also reinforces portions of the barrier walls.
As a demonstration project, it is vital that the new materials be tested under the same conditions as conventional steel reinforcement, so only a portion of the bridge was designed using FRP. The bridge boasts a complex embedded fibre optic structural sensing system that allows engineers to compare the long-term behaviour of the two materials.
Two of the four girders were reinforced for shear using two different types of carbon FRP stirrups. The other two beams were reinforced for shear using epoxy coated steel rebars for comparative purposes.
The deck slab is reinforced by indented leadline bars similar to the reinforcement used for prestressing. Glass FRP reinforcement produced by Marshall Industries Composites Inc. was used to reinforce a portion of the Jersey-type barrier wall, while double-headed, stainless steel tension bars were used for the connection between the barrier wall and the deck slab.
Bishop Grandin Boulevard
Consulting engineer: UMA Engineering
Approximately 26,000 vehicles a day travel along Bishop Grandin Boulevard in Winnipeg and over the test site for the first Canadian field application of fibre-reinforced polymer dowels in concrete pavement. In this project, a joint project of the City of Winnipeg, UMA Engineering and ISIS Canada, 780 glass FRP dowels were used in concrete joints instead of the conventional epoxy-covered steel dowels.
Generally, concrete pavement failures are due to the expansive forces caused by the oxidation of conventionally used steel dowels. Tests conducted in the laboratory at the University of Manitoba prior to the field installation indicated that the glass FRP dowel joints would be more effective because they are non-corrosive.CCE
Nanni, A., “CFRP Strengthening,” Concrete International, Vol. 19, No. 6, June 1997, pp.19-23.
Karbhari V., Seible F., “Advanced Composites Build on Success,” Civil Engineering, August 1996, pp. 44-47.
Neale, K.W. and Labossire, P., “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. 25-40.
Rizkalla, S., Mufti, A. and Tadros G., “Recent Innovation for Concrete Highway Bridges in Canada,” Proceedings of the 42nd International SAMPE Symposium and Exhibition, May 1997.
Tennyson, R.C., Installation, Use and Repair of Fibre Optic Sensors, University of Toronto, pp. 3-12.
Dunker, K.F. and Rabbat, B.G. “Why America’s Bridges are Collapsing,” Scientific American, March 1993, pp. 66-72.