The Big Break: Strength Testing of Glulam Beams

If you’ve ever wondered what 80,000 pounds of load looks or sounds like when applied to a 3-ton wood beam, now’s your chance. Bam! (Hint: keep the volume up around the :53 second mark.)

The largest wood beams ever tested are being studied at the Forest Products Laboratory (FPL).

Made of Douglas-fir, the glued laminated (glulam) beams each measured 72-feet-long and weighed in at 6,000 pounds.

Using FPL’s strong floor system coupled with hydraulic rams, engineers broke 12 glulam beams to determine how much load they could withstand.  The beams were fitted with sensors that recorded the effects of the applied load.

glulam_broken

One big beam, “taken to failure.”

Each test took about 8 minutes to conduct, and the beams bowed as much as 13 inches in the middle before finally snapping under the pressure. The beams withstood a range of loads between 69,000 and 95,800 pounds.

Thanks to the new Centennial Research Facility, FPL is one of the few locations worldwide that has the capacity to test such large wood specimens.  As FPL engineer Doug Rammer explains, that capability is key to determining their strength.

“To get a realistic measurement of how much load these large beams can withstand, it’s important to test them at their actual size,” Rammer says. “Larger beams fail at a lower stress when compared to smaller replicas, so full-scale testing is necessary to obtain accurate data.”

Glued laminated timbers are a manufactured wood product composed of layers of sawn lumber glued together. Glulam beams are typically used in commercial construction to span large open areas, such as in churches or sporting arenas. They make for both an aesthetically pleasing and structurally sound option.

FPL researchers are working in cooperation with the University of British Columbia on these tests. The results will influence building code requirements for the use of glulams in the United States and Canada.

# # #

By James T. Spartz, FPL Public Affairs Specialist