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Building with Glue-Laminated Beams

Construction How-To June 30, 2003 admin



 

Glued-laminated timber constitutes an ever-increasing percentage of the framing materials used in residential construction. In 2002, 65 percent of the approximately 338 million board-feet of glulam found its way into North American homes.
Much of this growth is attributed to the fact that glulam beams are available from building material dealers and distributors in stock sizes (typical widths: 3 1/8, 3 1/2, 5 1/8 and 6 3/4 inches). Like all engineered wood products, glulam beams are resource-efficient with highly predictable structural performance. As headers, floor beams and columns, the materials are easy to specify, even easier to work with, and the timeless aesthetics of wood remain unchallenged by other building materials.

Glulam is an engineered stress-rated product created by bonding together individual pieces of lumber having a nominal thickness of 2 inches or less. Individual pieces of lumber are end-joined together to create long lengths referred to as laminations. These laminations are then face-bonded together to create the finished product. On a pound-for-pound basis, conventional glulam can achieve allowable strengths equivalent to steel. Glulam is also among the most versatile of the engineered wood products. It can be shaped into forms ranging from straight beams to complex curved members. Typical residential applications include garage door headers, floor girders, ridge beams and purlins, cantilever beam systems and columns.

 Garage Openings

APA EWS-trademarked (Engineered Wood System) glulam beams are supplied with either zero camber or a very flat factory built-in camber, which makes it easy to connect glulam with other wood frame components. Figures 1 through 5 illustrate some of the many simple connection details that can be used with glulam residential garage door headers.

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Installation Recommendations – Notching and Drilling

Since glulam timbers are highly engineered components manufactured from specially selected and positioned lumber laminations, an improperly cut notch or a hole drilled in the wrong place can seriously affect the load carrying capacity of the member. Field notching, cutting or drilling of a glulam beam, particularly on the tension side of the member, should be avoided. Field conditions may require making a cut, notch or hole that was not originally anticipated. In some instances, these can be made in areas of the glulam, which are not highly stressed and will thus have minimal effect on the structural capacity of the member.

APA Sturd-I-Frame

One of the most challenging design areas in a home is the narrow wall adjacent to the garage door opening. This short wall section must withstand the same lateral forces that bear on other, larger wall and roof sections of the home. The APA Sturd-I-Frame system gives builders and homeowners a design solution that allows for the narrow walls while providing the necessary strength and stiffness. The connections in the frame allow the Sturd-I-Frame to act as a moment-resisting “portal frame” that resists lateral loads from winds or earthquakes. Glulam beams are readily available in the long lengths that are needed to extend the header over the adjacent walls. The vertical wall segment is wood structural-panel sheathing that overlaps the glulam header and is attached with nails in a specified grid pattern. At the base of the wall, a hold-down connector attaches the wall segment to the foundation (see Figure 6). These two moment-resisting connections, combined with the bending capacity of the vertical segment and glulam header, provide the lateral resistance normally facilitated by shear walls or braced wall sections of a substantially greater width.

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Floor Beams

Homeowners appreciate the natural beauty of wood and the warmth it brings to interior spaces. They also enjoy the consistent, long-lasting performance of wood. Unlike large solid sawn or built-up timber beams, glulam, which is manufactured from kiln-dried lumber, will exhibit minimal shrinkage and warping, which ensures a level floor surface. In addition, floors have minimal nail popping and fewer squeaks. Framers find that glulam floor beams are easier to work with than comparable steel beams. Plus, it’s easy to connect other wood floor-framing components to glulam because the wood-to-wood connections can be made with standard carpentry tools and fasteners. Nailers are not needed as they are with steel beams, and nail-on joist hangers can easily be accommodated. Since the framing crew can install glulam floor beams, it’s not necessary to schedule a second trade crew for steel work.

Glulam beams can span long distances using lighter-weight members with minimal need for intermediate supports, opening the design possibilities in a host of applications. Everyone, from homeowner to homebuilder to home designer, can appreciate the expanded design flexibility of wood.

Hybrid Beams Offer New Design Options

In response to market demands for increased structural performance, APA EWS worked with its member manufacturers to develop a new high-strength “hybrid” glulam beam. This beam uses laminated veneer lumber (LVL) as the outermost top and bottom laminations. The beam has a balanced layup, eliminating the concern about losing structural value if the beam is installed upside down. The hybrid glulam is rated at 30F – 2.1E* as compared to the traditional 24F – 1.8E glulam. Since these high-strength hybrid beams are often used to support wood I-joist floor framing, they are typically supplied in I-joist-compatible (IJC) sizes. This means the depths match the typical residential I-joist depths (9 1/2, 11 7/8, 14 and 16 inches) and the widths match conventional 2-by-4- and 2-by-6-inch wall framing. Hybrid glulam beams are only available in a framing or industrial appearance classification for use where appearance is not of primary concern.

Glulam floor beams can be installed within the floor joist cavity if a concealed application is desired. Many stocking distributors inventory IJC glulam for use with I-joist framing systems but most standard-depth stock beams can easily be used in a concealed floor application with minimal furring. They can also be partially concealed in the floor joist cavity or left completely exposed below the floor framing, adding increased aesthetic value to the room below. Below, the illustrations illustrate a variety of simple floor-framing details incorporating glulam beams.

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APA publishes a wide variety of load design charts, substitution tables and connection details for glulam beams and columns, most of which are available online at www.glulambeams.org. For technical guidance on design and connections call APA’s help desk at (253) 620-7400.

* 30F – 2.1E is a structural classification, which refers to a beam with an allowable bending stress of 3000 psi and a modulus of elasticity of 2.1×106 psi. An E denotes mechanically graded lumber whereas a V denotes visually graded lumber.

Editor’s Note: Special thanks to Kevin Hayes of APA – The Engineered Wood Association for contributing this article. For more information, visit www.apawood.org.