John D Wagner: The Overlooked Glulam
Advantages as to why glulams are the no-brainer choice.
BY: JOHN D WAGNER
Okay, admit it, you sometimes forget about glulam, don’t you? You don’t pay it much mind, like that dependable, competent, middle “dream child,” who is smart and obedient, yet forgotten because he’s not screaming about who gets to sit in the front seat of the car for the ice cream run.
Fact is, glulams are one of the original engineered wood products (EWPs), and they are still around because of their remarkable utility, ease of use, and how easy they are to order. Plus, glulams are among the greenest EWPs out there (more on that in a sec). I’m reminded of glulams by a recent push by APA-The Engineered Wood Association to educate dealers and end users on their capabilities, supported by cool downloads at http://bit.ly/ZmMOt7.
Used as a structural item on everything from long-length garage door headers to massive curve rafters for large open spaces (think hockey arenas), glulams are one of the few EWPs that designers will leave exposed—“architectural grade” as opposed to “framing grade”—because glulams can look great when finished or polyurethaned. Yet, they are just as efficient when used behind drywall in structural applications. Stock glulams come in widths that match standard 2×4 and 2×6 wall construction, including typical widths like 3-1/8, 3-1/2, 5-1/8, 5-1/2, and 6-3/4 inches, and some stock glulams are also available in I-joist-compatible depths, too.
As for glulam’s remarkable structural ability compared to steel, it may seem counterintuitive, but wood has a greater tensile strength relative to steel: 2X times as much on a strength-to-weight basis. And wood has a greater compressive resistance strength than concrete, also on a strength-to-weight basis. (In case you didn’t get the hint, APA—The Engineered Wood Association offers a free download (http://bit.ly/1s3syJT) of a 44-page “data file publication” that shows glulam equivalents for steel and solid-sawn beams.)
As for spans, stock glulam beams can easily span up to 28 feet. With all the talk about the clear spans (especially for large windows) offered by moment frames from Simpson and MiTek’s Hardy Frame, glulams may be the original “moment frame,” if only because they are an easy-to-install wood product that allows for large clear-span openings.
What’s more, glulams can be ordered with a camber to help fight against deflection under load. Stock beams are typically supplied with zero camber, which is a camber radius of 3,500 feet— a very big circle indeed, which means a very small curve in the glulam beams.