The next generation of bridges in country roads could be made of glulam – structural timber made of layers of wood strips bonded with glue.
Researchers from the J. Lohr Structures Lab in the USA built a full-scale glulam bridge – a 15 metre long single lane bridge – and tested it to simulate decades of service.
According to Assistant Civil Engineering Professor Mostafa Tazarv, Structures Lab Coordinator and Co-principal Investigator for the project, the girder bridge tested (which was made of southern yellow pine) showed satisfactory performance and minimal damage under a cyclic loading equivalent to 75 years of service.
The aim of the project was to provide alternatives to conventional bridges, providing more options when designing a new bridge or replacing an old one.
The initial construction costs for a glulam timber bridge can be anywhere from 25 to 50 percent less than a conventional bridge, according to Professor Tazarv. Typically, the bridge can be installed in a day without the need for specialised equipment or specially trained personnel, which shortens the road closure time.
Glulam manufacturers can layer the wood to reduce material variability that is inherent in natural wood and increase strength by placing higher quality material where the stress demand is greatest.
Testing the girder bridge
The bridge was composed of 13 deck panels, connected to three girders using a strong epoxy adhesive.
Fifteen fully loaded trucks per day typically cross a low-traffic county road bridge, according to Professor Tazarv. To simulate this, the researchers applied an equivalent force to the middle of the bridge at a rate of one load per second, “aging” the bridge and testing its service life.
Source: Phys.org, South Dakota State University
