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Bridge testing gives engineers cost-effective options

Glulam full-scale bridge testing

Glulam full-scale bridge testing at the Jerome J. Lohr Structures Lab gives engineers data to make decisions that will help state and local governments stretch their bridge-building dollars. That testing has shown that the counties and townships can consider using glulam timber bridges and inverted bulb-tee precast concrete bridge options for replacing bridges on low-traffic county and township roads.

The research is part of a two-year, more than $160,000 project that investigated the feasibility and performance of two glulam timber bridges and a fully precast concrete inverted bulb-tee bridge for use on local roads. The project was co-sponsored by the U.S. Department of Transportation through the Mountain Plains Consortium and the South Dakota Department of Transportation.

Gruen-Wald Engineered Laminates of Tea donated the two timber bridges, while Gage Brothers of Sioux Falls supplied the inverted bulb-tee bridge. The aim was to provide alternatives to the conventional precast double-tee bridge, for which there is only one local supplier in the state.

The initial construction costs for a glulam timber bridge can be anywhere from 25 to 50 percent less than a conventional bridge and other timber structures showed satisfactory performance and minimal damage under cyclic loading equivalent to 75 years of service. The bulb-tee bridge, which costs about 10 percent more than the same size conventional double-tee concrete bridge, withstood loading equivalent to 119 years of service. In addition, multiple companies make the bulb-tee bridge precast components so counties can choose a supplier that is closer to the bridge site, thus reducing transportation costs.

This research gives counties and townships more options to choose the optimal type of material and design for each situation—and to make the best use of taxpayers’ money.