Modular bridge replacement fits to existing piers, abutments

Case Studies
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With a focus on protecting the natural environment, Thousand Trails is the largest private system of RV campgrounds and outdoor preserves in the U.S. When a concrete truck caused an aging timber bridge structure to collapse at its Yosemite Lakes Preserve in California, it was critical to both the park operator and the Department of Fish and Game that its replacement would have minimal environmental impact on the waterway.

The department was adamant that the existing piers not be removed or disturbed.

The concrete truck made it across the older, glue-laminated beam bridge before it collapsed. Otherwise, the environmental impact of the failure might have been much worse. The bridge is located in the middle of the busy RV park, so a fast replacement was paramount. The client, Thousand Trails NACO, considered a “stick-built” steel bridge with a timber deck system, but it was concerned about the high cost and lengthy construction time.

The engineering teams at Big R Bridge proposed a two-piece modular steel bridge design that was value-engineered to fit the existing piers and abutments perfectly and to save the client more than $90,000—and a great deal of time—in the process.

Big R custom designed and fabricated bearing plates and pads to work with the existing piers and special spacers to accommodate the steel beams on the piers and abutments. This was a key aspect of solving the problem for the client and the project’s success.

To get the overall weight to match that of the failed bridge, the company’s solution used a treated-timber wearing surface. The company was also able to design a combination vehicle/pedestrian rail system to suit the healthy mix of traffic at this location.

Natural weathering steel finish was recommended for the structurals and rail system. Weathering steel saves maintenance dollars and reduces environmental impacts because it requires no painting and has a 100-year maintenance-free design service life.


Since weathering steel does not need to be painted, the emissions and future removal of volatile organic compounds from oil-based coatings are eliminated from the environment. Plus, the steel alloy composition of weathering steel develops a vibrant rust coating, or patina, that gives the appearance of age in keeping with the natural beauty and architectural features of the park. Made from high-quality American recycled steel, it gave a little extra help to the overall environment.

The bridge (72 ft 6 in long by 20 ft wide) was pre-engineered and prefabricated at the Big R Bridge plant in Greeley, Colo., and shipped in two modular sections. It installed snuggly onto the existing piers and abutments on the same day it was delivered, just weeks after the order was placed.

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