Bridge design spans product design

Newton, MA--What does the building of bridges have to do with the design of products? If it involves the construction of a composite bridge, the materials used, and the way they are processed, it could have an impact on how design engineers view composites for their future design projects.

First, let's explore what's happening on the bridge-design scene. Researchers at West Virginia University (WVU) have under development a "revolutionary" fiber-reinforced polymer (FRP) composite deck for repair and replacement of bridge decks throughout the U.S. The new product encompasses a corrosive-resistant vinyl ester resin matrix system pultruded into structural shapes required for the bridge-deck design. The researchers claim the design could more than triple the life expectancy of new or existing bridges.

The university and Creative Pultrusions Inc. (Alum Bank, PA) recently signed cooperative research and technology license agreements to formalize their partnership in developing and deploying the new product. The agreements provide for a seven-year commitment by both parties to continue their business relationship and jointly improve and market the product, called "Superdeck."

Hota Gangarao and Roberto Lopez of WVU served as principal investigators on the research project. Creative Pultrusions employed the E-type glass composite engineering process to further improve Superdeck and its cost-effectiveness.

"The new product will allow for bridge decks that are one-third as heavy as those using traditional materials, such as concrete, yet with three to four times the strength," Gangarao reports. This results in less material needed to construct a deck, as well as less costly equipment to erect it. Also, bridge decks built with the FRP material could allow for spans of twice the average length of the longest spans used in today's bridges, Gangarao adds.

An added advantage: durability. Gangarao predicts that Superdeck construction offers a lifespan of at least 50 years, compared to an average of 15 years using concrete materials.

Taking the concept to reality, the state of Ohio recently dedicated a composite bikeway bridge based on Superdeck. Ad'Tech Systems Research Inc. (Beavercreek, OH) designed and built the Shawnee Creek Bridge, located in Xenia, OH. The bridge meets the American Association of State Highway & Transportation Official's IIS20-44 requirement for emergency vehicles. It measures 7.3m long (24 ft) 3 3.7m wide (12 ft, 3 inches). Completing the design is a composite rub rail that measures 4.5-ft high 3 30-ft long. A durable epoxy grit surface treatment, the same used for aircraft carrier decks, provides a non-skid wearing surface for bikers and rollerbladers.

Providing optimal structural performance for highway bridge loads, the Superdeck composite deck performs with six to seven times the load capacity of a reinforced concrete deck at only 20% of the weight (22 lb/ft(super2)), according to Creative Pultrusions officials. Installed in less than five hrs, the maintenance-free bridge "represents the state-of-the-art approach to the repair or replacement of deteriorated bridge structures," the designers report. This contrasts with traditional repair methods--partial-depth deck replacement or complete deck replacement--which can prove costly and tie up bridge traffic for extended periods.

The major obstacle to making this concept a reality nationwide centers on higher initial material costs, a problem that has long plagued composites when competing with other more traditional materials. In a just-released report on the life-cycle cost (LLC) of FRP bridge decks vs. concrete decks, Roberto Lopez-Anido, an assistant professor of civil engineering at the University of Maine, compares the two (see table). FRP came out the winner.

Economical deck repair. The possibilities for cost-cutting composites don't end here. Consider the Construction Productivity Advancement Research (CPAR) project, a 40-month endeavor to improve bridge-deck repairs funded with $1 million in federal money matched by another $1 million from private industry.

The project was capped off at last year's National Bridge Deck Repair Conference in Omaha, NE, hosted by the University of Nebraska and the Army Corps of Engineers. At the event, Liquid Control Corp. (North Canton, OH) Construction Marketing Manager Nick DiDonato demonstrated how his company's drilling, porting, and injection process quickly repairs delaminations on bridges. Liquid Control's Posiratio(reg) Mini Crack injection machine features a new transducer package that allows for kicked-down air pressure to prevent hydraulic lifting of the deck.

Most engineers in the OEM marketplace don't build or repair bridges. Will they reap any benefits from such innovations?

The answer is "yes" on two scores. The composite used on the bridge-deck project has some exceptional properties that may fill the bill for your next design project. And the ultrasonic pulse echo machine that can detect delaminations could add greater reliability to your material tests. Check them out.

COMPOSITES WIN COST BATTLE

COSTS CONCRETE COMPOSITE DECK 1* COMPOSITE DECK 2* COMPOSITE DECK 3*

$/SQ FT $/SQ FT $/SQ FT $/SQ FT

INITIAL CONSTRUC-TION COSTS 41.357.0257.02 57.02

MAINTENANCE COSTS0.660.770.800.80

OVERLAY REPAVEMENT COSTS 6.232.022.61 1.24

REPLACEMENT AND DISPOSAL 12.243.900.000.00

END-OF-LIFE DECK DISPOSAL 0.630.050.330.33

TOTAL COSTS 70.3865.6762.7361.21*Note:

1. Fiber-reinforced polymer (FRP) concrete overlay assumed to last 25 years and the deck to last 50 years.

2. Fiber-reinforced overlay assumed to last 25 years and the deck to last 70 years.

3. Fiber-reinforced polymer overlay assumed to last 35 years and the deck to last 70 years.Source: Roberto Lopez-Anido, Ph.D, P.E., University of Maine.

What this means to you

If your latest design involves any of the following problems, it may pay to check out the advantages of using an E-glass composite as a solution, says Dustin Troutman, design engineer at Creative Pultrusions:c Operates in a corrosive environmentc Demands less weight.c Requires high fatigue strengthc Incorporates high tensile strength. (For example, a solid E-glass rod with roving has a tensile strength of 100,000 psi.)c Must not conductelectricity