Interesting Trend



A bridge too far?
A bridge too far?
Jun 9th 2005
From The Economist print edition





Materials science: As unlikely as it sounds, plastic is becoming an increasingly popular material from which to build bridges

BRIDGES must always be epic engineering projects involving years of construction work and vast amounts of steel and concrete, right? Wrong. New design and construction techniques mean that bridges can be put together in a matter of days—and they can even be made out of plastic. Consider the InfraCore bridge, a design launched in January by Composieten Team, a firm based in Rotterdam. The designers' goal was to shave months, or years, off the commissioning of new bridges, a process that typically entails lengthy rounds of sketching, specifying and contracting.

Standardising the design and production processes, says Jan Peeters, one of the engineers behind the new design, makes ordering a bridge as easy as buying a car. With a few clicks of the mouse, software adjusts the bridge “recipe” to a client's specifications. The bridge's size, colour, and options such as handrails are chosen on screen, and because engineers no longer need to design each bridge from scratch, the finished product can be delivered within a week. The lightweight plastic even floats, and a two-man crew can install a small bridge in a few hours.


Websites
Composieten Team, Fiberline Composites

This is just the latest example of the growing use of plastics in bridge construction. Bridges made of fibre-reinforced polymers have been around since the late 1990s, and several hundred plastic bridges now dot the globe, mainly in Europe and North America. They traverse everything from rivers and railways to industrial facilities and highways. Some are even tough enough to support a Sherman tank, as was theatrically demonstrated during the inauguration in 2002 of a road bridge in Shrivenham, England. Its 11-metre deck was made by Fiberline Composites, a Danish firm which, like Composieten Team, makes plastic bridges to order.

Plastic bridges have advantages over both concrete and steel ones. They require minimal maintenance during their lifespans (estimated at over 60 years for the InfraCore), whereas traditional bridges often need a costly overhaul after only a decade or two. Plastic bridges are impervious to common problems such as corrosion, frost, mould and insects, which eliminates the need for special coatings. Adding a new composite deck can extend the life of an old bridge that would otherwise not be worth repairing. And plastic bridges can even be made from discarded coffee cups and detergent bottles: a 14-metre span built over New Jersey's Mullica River in 2002 consists of recycled polyethylene and polystyrene.

Technologically, says Mr Peeters, many of the plastic bridges that are now popping up around the world could have been built ten years ago. It has simply taken time for civil engineers—a naturally cautious bunch who are used to building bridges out of concrete, steel and wood—to come round to the idea of using plastic in bridge construction.

But enthusiasm for plastic bridges is now growing. In November, Fiberline supplied the materials for an all-composite traffic bridge in Klipphausen, near Dresden. Indeed, the former East Germany, notes Finn Jerno of Fiberline, was an unsung pioneer of the use of advanced plastics in construction. Five of Klipphausen's wooden bridges were destroyed in the massive European floods of 2002, and replacing the originals would probably have meant disruptive repair work every ten years. After considering the long-term costs, the mayor decided to build the new bridges using Fiberline's glass-fibre-reinforced plastic instead. The plastic design has another benefit, too: the next time catastrophic weather threatens, Klipphauseners can simply disassemble their new plastic bridges at a moment's notice—and then snap them back together once the storm has passed.

Plastic Highway Bridges


by Jennifer R. Griffiths


Overview

Throughout the world, concrete infrastructure reinforced with steel is waging a losing battle against corrosion. Concrete is crumbling, leaving reinforcing steel exposed and subject to rusting. Steel-reinforced concrete bridges are deteriorating from the corrosive effects of de-icing, marine salts, and environmental pollutants. Other factors contributing to the problem are aging, increasing daily traffic, increasing truck weights, more frequent vehicle overloads, and insufficient maintenance and repairs. In the USA, almost 40% of bridges are structurally deficient or functionally obsolete, and the percentage is increasing, according to the Federal Highway Administration.

Plastic reinforced with fibers, a type of composite material, is seen as a possible solution for repair, strengthening, or replacement of an increasing number of substandard bridges. In the broadest sense, composite materials are combinations of materials that have their own distinctive properties. Fiber reinforced plastics (FRP) are composite materials that consist of high strength fibers immersed in a structural matrix such as epoxy or other durable resin. The most common fibers used are glass, carbon, and aramid (trade name Kevlar). Brittle materials such as glass and carbon can acquire enormous strength and stiffness when produced in the form of a fiber. The addition of these fibers to a weak, compliant matrix results in a material that demonstrates a dramatic improvement in performance, producing a material with much greater mechanical properties than its constituents.

Interest in FRP as a solution to the problem of upgrading and replacing these deteriorating bridges is increasing. Various research projects are underway and a number of companies are designing, manufacturing, and installing composite material components for bridges. The applications of FRP for bridge repair and replacement include new bridge decks, strengthening of concrete structures, and internal reinforcement of concrete.

The advantages of employing FRP in new bridge decks include its corrosion resistance, high strength-to-weight ratio, and ease of installation. The composite material can be customized to dimensions of traditional decks and allows the economic reuse of existing support structures.

The USA's first all-composite vehicular bridge deck on a public road was installed in November 1996 by composite manufacturer Kansas Structural Composites Inc (KSCI) of Russell , Kansas, employing a rapid, low-cost replacement system. Using lightweight cranes and factory-built sections, KSCI installed the bridge over No-Name Creek in Russell County, Kansas, in approximately 10 hours. Since then, the Kansas Department of Transportation has gone ahead with two new installations by the same company. KSCI uses a fiber-reinforced plastic honeycomb sandwich construction in fabricating its bridge decks.1

In another project, the New York State Department of Transportation decided to try a composite materials solution for replacement of a deteriorating 25 foot long concrete bridge built in 1926. NYSDOT selected the company Hardcore Composites of New Castle, Delaware, to fabricate the bridge deck. Hardcore employed glass-fiber fabric and vinyl ester plastics in forming the sandwich structure used in the deck, and installed the deck in one day.2

Hardcore Composites, which has manufactured and installed ten highway bridges and bridge decks so far, has been awarded a contract for the first phase of a project to provide composite bridge decks for Project 100 in Ohio.3 Initiated by the National Composite Center in Kettering, Ohio, the project aims to design, manufacture, and install 100 bridge decks throughout the state.4

FRPs benefits of light weight and high strength also make it attractive for strengthening existing concrete bridge structures. FRP can be wrapped like wallpaper around bridge columns and beams to provide additional reinforcement to increase earthquake resistance, durability, and corrosion resistance. The wet lay-up procedure is one technique. High strength fibers are matted or woven into a fabric and then immersed in an epoxy matrix, followed by adhesive bonding of the material to the column.

FRP composites have been used by Fibrwrap Construction Inc. of Los Angeles, California, for a seismic retrofit of the Arroyo Seco Bridge. The bridge, located in Pasadena, California, is a multiple arch structure that spans over 1300 feet of the Arroyo Seco Canyon. The bridges concrete columns were wrapped with glass- and aramid-fiber reinforced epoxy composite. The low-profile composite jackets had a final thickness of less than three-quarters of an inch, yet provided strength comparable to that of full-scale steel jacketing and had minimal impact on the appearance of the historic bridge.5

Composite materials have also been used in the rehabilitation of another historic bridge. This allowed the strengthening work to be done in keeping with the character and aesthetics of the structure. The Tickford Bridge in the UK, built in 1810, is the worlds oldest operational cast iron road bridge. Maunsell Ltd., a civil and structural engineering consulting firm in the UK, recommended that full highway loading could be achieved by strengthening the bridge with a wet lay-up carbon fiber sheet system.6

In another application of FRP, reinforcing bar (rebar) fabricated from either glass-fiber or carbon-fiber reinforced plastic composites is being used to replace steel as an interior structural reinforcement element in concrete. FRP can be used in new structures for reinforcing both cast-in-place and precast concrete. Besides rebar, it can take the shape of stirrups, grating, pavement joint dowels, tendons, and anchors.

The Canadian province of Quebec has built a bridge in Sherbrooke that is innovative in its application of carbon-fiber reinforced plastic (CFRP) reinforcements instead of steel. Part of the Joffre Bridge concrete deck slab is reinforced with CFRP, as well as a portion of the traffic barrier and the sidewalk. Fiber optic sensors were structurally integrated into the CFRP providing a smart structure. Over 180 instruments (fiber optic sensors, vibrating wire strain sensors and electrical strain gauges) were installed at critical locations in the concrete deck slab. These instruments will allow for the remote monitoring and continuous evaluation of the structural performance of the CFRP reinforcements under real-time conditions.7

As an increasing number of bridges require rehabilitation, strengthening, or replacement, interest has grown in fiber-reinforced plastic composites as a solution to the problem of an aging infrastructure. The range of composite materials manufactured for bridge construction and repair is expanding as more installations are undertaken. Soon, a bridge made of plastic may be coming to a highway near you!

© Copyright 2000, All Rights Reserved, C SA

1. Black, Sara, "A survey of composite bridges," Composites Technology, 2000, 6, 2, Mar.-Apr., 14-18.
2. Black, Sara, "A survey of composite bridges," Composites Technology, 2000, 6, 2, Mar.-Apr., 14-18.
3. "Zoltek announces investment in FRP composite bridge builder, Hardcore," Advanced Materials & Composites News, 2000, 22, 10, 15 May, 2.
4. "Ohio bridges gap in deck repairs," Composites Technology, 1999, 15, 4, July-Aug., 6.
5. "Composites seismic retrofit of the Arroyo Seco bridge completed successfully," Advanced Materials & Composites News, 2000, 22, 9, May, 1-3.
back to article

6. "Composite gives new life to bridge," Reinforced Plastics, 1999, 43, 10, Oct., 8.
7. Redston, Jennifer, "Canada's infrastructure benefits from FRP," Reinforced Plastics, 1999, 43, 7-8, July-Aug. 1999, 34-35, 37-38.

http://www.research.uky.edu/odyssey/fall99/newbridge.jpg

Plastic bridges - the way of the future?

By Gloria Chang,

Around the world, city infrastructures are crumbling. You only need to look at a nearby bridge to see the steel reinforcements holding the concrete together baring their corroded and rusty snake arms. The global building boom of the postwar era has given way, resulting in a $900 billion repair problem worldwide. And Canada is leading the way to fixing that problem at a lower cost by repairing and building new bridges with... plastic.

"It's the way of the future," says Dr. Sami Rizkalla, president of Intelligent Sensing for Innovative Structures (ISIS Canada) - one of the Networks of Centres of Excellence created by the federal government last fall. The Winnipeg-based network's job is to develop emerging technologies in civil engineering and construction. University researchers and private industry specialists across the country have been working together and have made Canada a world leader.


To help solve the problem of corroding steel in concrete - a $44 billion problem in Canada - Rizkalla has been working on using new non-corrosive materials to build bridges. They're called Fibre Reinforced Plastic (FRP). Glass or carbon fibres are set in a plastic in the shape of long bars. These are then used to reinforce the concrete in bridges instead of steel, the conventional reinforcement.

"The technology is just the next step in improved materials," says Doug Stewart, manager of structural engineering at Wardrop Engineering in Winnipeg. Using steel bars to reinforce concrete is a century old practice and since then there have been advancements in making the concrete stronger. Stretching the steel before pouring the concrete became a practice about 50 years ago. Then more durable high-performance concrete made its way onto the scene about five years ago. But despite all the improvements, they didn't solve a problem that's rearing its rusty head in cities around the globe: corrosion.

Weather wears away at the concrete until the rain and salt corrode the steel reinforcing the concrete.


Make way for the FRPs, which are up to five times stronger than steel because they are made from hair-thin fibres. "It's a very high-stress material," says Rizkalla. "It's a chemical process so you can produce very fine fibres with very high strength."

At a quarter the weight of steel, these FRPs will become cheaper to use than steel over time predicts Rizkalla, but "it's very hard to put a price at this stage because the material is not produced in mass production. The cost is expensive (now) because it's still in the initial stage of production and is almost always custom-made."


But there is a distinct advantage to using steel. Steel has the capacity of deforming quite a bit when it gets near its breaking strength giving engineers time to respond to deterioration, says John Bonacci, a civil engineering professor at the University of Toronto. He's also on the team of ISIS researchers.

But have no fear: bridges of the 21st century will also be intelligent. Fibre optic sensors located on certain parts of the bridge will tell engineers how the bridge is holding up.


The two technologies seem to provide a perfect, cost-effective solution to our decaying cities, but there is a big challenge to overcome.

"The current problem is that there are no standards and codes for engineers to use. Therefore the engineers are reluctant to use it because they are not aware of how to use it," explains Rizkalla. Stewart suggests "engineers are a conservative bunch, they like to see a good track record."

The composite materials, however, aren't new. They've been around for the last 40 years and are now used extensively in sports equipment like tennis rackets and golf club shafts, not to mention the aeronautic and aerospace industries. The bodies of planes are made from these materials. But they are new to the construction industry.

Fibre optic sensors are attached to the FRPs for a bridge girder (ISIS Canada)
Fibre optic sensors are attached to the FRPs for a bridge girder (ISIS Canada)
To help speed things up, Rizkalla is on several committees around the world to set standards for the use of these materials both in Canada and internationally. Canada should have a code by the end of this year, the US and Japan by the end of next year.

Right now, the biggest benefit of these new materials is in repairing existing bridges, says Rizkalla. The FRPs can be made into sheets and applied like wallpaper to the undersides of bridges (or wrapped around the bridge's columns) to increase its strength capacity by 50 to 60 per cent - all without even interrupting traffic.

"That's the beauty and the promising future of this technique," raves Rizkalla. "It's not only for new bridges, it's mainly for repair, strengthening and rehabilitation of existing structures."

ISIS Canada's current major project is the Headingley Bridge that connects Winnipeg to the Headingly area in Manitoba. "We are getting into a new era of construction of bridges and roads which is quite different from 50 years ago... we're almost starting all over again to build up a new system," says Rizkalla.

http://www.exn.ca/Stories/1997/03/10/06.asp

Wow, that's some fascinating stuff. And it's especially relevant in Canada, since salt is used on the roads here to melt snow and ice. What I'd be curious to find out is what the first major projct will be to use this technology. I wonde if there are any future plans currently under consideration.

I agree with you , I'm fascinated with this technology and there seems to be an environmental angle as well. You're correct it would work very well where rust is an issue. For the moment the projects are small but there is no need to be , just needs a big push from one of the big high tech countries.

I'd be interested to know how well the plastic bridges hold up against continuous tire wear and how long surface finish would last in such a situation.

great....and wonder

From the article and links they've had some bridges for quite a while already. No problem, seems to be more an issue of acceptability rather than technology. Be really great soluiton for out of the way rural areas .