BROOKINGS, S.D. - After simulating a glulam bridge and applying 32,000 pounds of force, researchers at South Dakota State University found that glulam timber bridges are a viable and cost-effective option for replacing bridges in low traffic areas.
The tested glulam girder bridge, made of Southern Yellow Pine, showed satisfactory performance and minimal damage under cyclic loading equivalent to 75 years of service.
“To our knowledge, this is the first time that full-scale testing has been done on glulam timber bridges,” said civil engineering professor Mostafa Tazarv, structures lab coordinator and co-principal investigator for the project.
Glulam, short for glued laminated, means the structural members are made of layers of wood strips held together with glue.
Fifteen fully loaded trucks per day typically cross a low-traffic county road bridge. To simulate this, the researchers applied a 32-kip, or 32,000 pounds-force, load to the middle of the bridge at a rate of one load per second.
The tested bridge, supplied by Gruen-Wald Engineered Laminates, was 50-feet long and 9.5-feet wide - approximately equal to one lane of traffic. The bridge was composed of 13 deck panels connected to three girders using a strong epoxy adhesive, said the University.
Fifteen fully loaded trucks per day typically cross a low-traffic county road bridge, according to Tazarv. To simulate this, the researchers applied a 32-kip, or 32,000 pounds-force, load to the middle of the bridge at a rate of one load per second.
“This ages the bridge in a short period of time,” Tazarv said. The bridge withstood half a million load cycles, which equates to 90 years of service."
With initial construction costs 25 to 50 percent less than a conventional bridge, glulam timber bridges could be a viable alternative. Tazarv says bridges could be installed in one day, and without the need for specialized equipment or specially trained personnel.
The project was co-sponsored by the U.S. Department of Transportation through the Mountain Plains Consortium and the South Dakota Department of Transportation. The aim was to provide alternatives to conventional precast double-tee bridges, for which there is only one local supplier in South Dakota. This research gives counties and townships more options when designing a new bridge or replacing an old one.
Source: South Dakota State University