Providing Longevity

Sika installed its first composite bridge reinforcements in 1991. “We have gone back and looked at a lot of these early projects, and they don’t show any signs of degradation,” White says.

In 2007, Sika worked on the Sunshine Skyway Bridge in Tampa, Fla., which had opened in 1987 but showed some concrete cracking after just 20 years. “They decided to repair the cracks and wrap them with a carbon fiber material to provide a barrier and to keep the moisture and chlorides out of the inside of the bridge,” White says. The composite wrap, installed in 2007, has performed well and looks almost new.

The demonstrated durability and resiliency of composite materials in these applications has encouraged bridge builders to find other uses for the material.

White notes that composite rebar is currently being installed in new bridge decks. Contractors are also cutting grooves into existing decks and adding composite rebar to provide extra reinforcement before they are repaved. On some smaller bridges, designers are replacing pre-cast concrete deck slabs with pre-cast FRP panels. “They are just as strong as pre-cast concrete and much lighter in weight,” Scott says.

Designers are also employing composite components to prevent the collapse of suspension bridges. The vibrations caused by high winds can cause these bridges to ripple, bounce and eventually fall apart. (The best-known example is the Tacoma Narrows Suspension Bridge in Washington State ‒ Galloping Gertie ‒ which buckled and fell in 1940.)

To avert a similar disaster, bridge owners began adding weight to their structures, using concrete and steel to stabilize them. They also installed triangular wind fairings to deflect the wind from the bridge. While bridge fairings are usually made with steel, composite fairings are a better choice in some instances.

Composite Advantage built 50 FRP wind fairing panels for the Bronx Whitestone Bridge in 2003. “They had added mass to the bridge back in the 1940s and 1950s, but as traffic loads got heavier the bridge was beginning to show fatigue. They decided they needed to get all the extra weight off and come up with a new solution, which was fiberglass fairings,” says Scott Reeve, the company’s president.

The designers of the new Sarah Mildred Long Bridge, which connects New Hampshire and Maine, also chose FRP fairings for their structure’s lift span. “If it wasn’t a lift bridge, they might have added concrete and steel if they were concerned about wind loads causing vibrations,” Reeve adds. “But when you’re talking about a lift bridge, that weight has a huge effect on the structure and on the mechanisms that are lifting that bridge up. If you make that bridge heavier, you have to make mechanisms more robust and more costly.”

Lighter weight fairings are not needed for many bridges. “But when you do have the need, it’s a place where fiberglass is pretty much the only solution. That’s where we provide the value,” Reeve says.