Last week we saw a composite bridge deck. The company that made it, Composite Advantage, also makes complete FRP bridges. These tend to be short span bridges, but they have the interesting property of being fabricated and delivered to the jobsite as a single piece, ready to drop into place.
The Fiberspan Trail Bridge line of products are simple, lightweight beam bridges that can be dragged through a forest by a small work vehicle like a Bobcat and dropped into place. Composite trail bridges like these can span up to about 40 feet. Composite Advantage makes longer spans in their line of Fiberspan Pedestrian Bridges, which can be up to 100 feet long, some of them hydridized with steel as well as FRP.
One of the big advantages of these bridges, as compared to the wooden bridges they often replace, is that they are basically maintenance-free. They are extremely durable, and are impervious to most of the things that break down wooden bridges (insects, rot, and freeze-thaw damage), and equally impervious to the corrosion problems that attack steel bridges and the steel reinforcement in concrete bridges.
Like any bridge, they need a firm footing on either end, but it can be as simple as steel spikes to anchored into solid ground for a temporary trail bridge, or helical piers (giant steel corkscrews) driven into the ground for permanent bridges. In some cases, a concrete abutment must be poured. But the point of these bridges is that they are light enough and rugged enough to be installed in a location that is inaccessible to large construction vehicles.
These modest trail bridges represent something bigger. One of the major areas of study and innovation in the bridge business is rapid bridge construction. The act of replacing a bridge can have wide social and economic impacts because the road that includes the bridge has to be shut down during construction. If the bridge is an overpass for a lower roadway, often that road must also be shut down during construction activities. This means a lot of re-routed traffic; longer commutes, school pickups, and commercial deliveries; traffic diverted from business centers; and other disruptions of private and commercial life. In some cases, it can completely alter the activity of a large portion of a major city, as in the replacement of a bridge on the I-405 freeway in Los Angeles, one of the busiest roadways in America. The complete closure of that road for 48 hours was labeled “Carmageddon,” and made national news.
A great deal of attention has been paid to pre-fabrication of bridges or bridge elements, so road shutdown-time can be minimized. More often than not, the pre-fabricated elemens are gargantuan pieces of reinforced concrete, and installing them involved the use of very big cranes. Composite bridges have the potential to make the “Bridge Replacement Day” faster, cheaper, and far less disruptive. (Whether the entire bridge project would be cheaper is a different issue.)
Composite Advantage continues to expand their capabilities in terms of span and load. This is only the beginning.