June 22nd, 2012

BACKPACK ADVENTURE

Optimize Mobility, Preserve Infrastructure, Strengthen the Economy, by Catherine Higgins.

UDOT will use an innovative hybrid bridge system that combines the durability of concrete with the strength of Fiber Reinforced Polymer.

The system, called Bridge in a Backpack, uses stiffened FRP tubes that are shaped into aarches and filled with concrete. While design of the brides varies, the arches are typically attached to a concrete footing and covered with corrugated decking then covered with compacted soil. The new bridge, which is being designed, will be built in Ogden Canyon on SR 39 near Huntsville.

Hundreds of the tubular structures have built in the United States, although the building method is fairly new. The arches were developed by the University of Main. FHWA has developed an implementation strategy and is funding part of the construction costs of the new bridge.

Advantages of the Bridge in a Backpack system include:

  • Fast construction which benefits the driving public.
  • Light weight components that can be transported easily.
  • Potentially lower maintenance costs over the life of the bridge – FRP is not susceptible to road de-icing chemicals as is steel.

UDOT has used FRP in other structures. UDOT’s Beaver Creek Bridge on US-6 near Soldier Summit has a deck that is reinforced with FRP bars. The bridge is instrumented with sensors that measure strain. Researchers are collecting data that will show how the deck holds up under traffic.

UDOT will also build a bridge with hybrid-composite beams near Beaver. The design uses an FRP box to with a concrete arch inside that gives the beam compressive strength. More than just a covering, the box “provides shear strength and encapsulates the tension and compression elements,” according to the HCB Company website. The arch structure inside the beam is surrounded with low density foam core. A prestressing strand provides additional strength and steel shear connectors provide stiffness. Along with being very strong and durable, the beams are also light and easy to lift and place.

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