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Temporary bridge designed to save time and money

Posted on 02/23/2017
Temporary bridge designed to save time and money

by Rachel Ehnert, Weld County Communications Specialist

In 1996, the Weld County Department of Public Works began an ambitious project: replacing all 68 of the county’s remaining load restricted bridges. These bridges, often in rural areas over irrigation ditches or small creeks, were typically easy to rebuild—the Public Works team would simply fill the ditch or creek area with dirt and culverts to allow small amounts of traffic to pass while old bridge was destroyed and the new bridge constructed. This was a solution that the team used for years—in fact, this process was working so well that by 2011, the county was down to only 14 load restricted bridges to be replaced.

Unfortunately, the success of this process would be short lived. Weld County, like many other areas in Colorado, experienced a massive population boom in this time, resulting in a surge of traffic levels across county roadways. This meant that the dirt-and-culvert, low-traffic-levels-only bridge construction technique was no longer a viable plan—they’d have to revert to closing down entire roadways to finish replacing these bridges.

Crews installed a temporary bridge at WCR 50.5 last fall in order to make necessary repairs. However, as it turned out, closing these roadways for bridge replacement resulted in another, even more problematic issue. As Public Works narrowed their sights on the last few bridges, they discovered that these bridges (and the roadways they connected) were the only way many residents had to access their homes. If the team couldn’t find a way to replace these bridges without shutting down the road, many residents would be landlocked in their properties, with emergency crews unable to access them.

To make matters worse, 2013 saw one of the worst floods in Weld County memory—bridges and roadways across the county were damaged as a result of overflowed ditches, creeks, and rivers. Public Works needed a way to repair bridges without closing roads, and fast.

Ron Graves, the Public Works Bridge Foreman had an idea: why reinvent the wheel? He, along with some Weld County engineers and the rest of the Public Works team, devised a plan for temporary bridge structure that wasn’t too dissimilar from permanent bridge structures. Instead of concrete, however, they’d use gravel. Instead of welding beams together, they’d chain them (and weld a few high-stress areas). Instead of using tons of costly materials, they’d reuse materials they already had in storage. The result? A bridge with all the strength and functionality of a permanent bridge, only quicker to assemble. Never again would Public Works have to fill a ditch or land-lock a resident due to bridge construction operations!

The temporary bridge’s design consists of several I-beams chained together (and welded selectively) which are covered in four-six inches of gravel (this is the driving surface.) Work on the temporary bridge at WCR 50.5.This surface rests on four steel H-beams and pilings at each corner of the bridge, with the two outermost I-beams fitted with guardrails. It can be used to span distances of 30-60 feet, with materials being reused whenever possible. Design for this bridge was completed entirely by Weld County employees, including the program used to calculate how much weight the bridge could safely withstand.

Although durable enough to accommodate for Weld County’s increase in traffic numbers, this temporary bridge is designed to withstand low speeds, and is intended for use in construction zones only.  

Thanks to this temporary bridge, Weld County, in 2017, is down to only 3 load restricted bridges. Public Works anticipates the county to be free of these outdated bridges by the end of next year. 

Portions of this article were published in the Winter 2017 issue of Colorado Public Works Journal.