Testing reveals higher design values for glulams

A S o result of extensive industry.CLwide testing of full-scale glulam beams, certain design values for glued laminated timber have increased.

Whether the beams are manufactured using visually or mechanically

I Glulam l{orizontal Shear Values

Glulam reportedly is the most cost competitive glued engineered wood beam product available. Based on recent market surveys in the Western U.S., laminated veneer lumber costs up to 257o more than glulam depending on sizes and applications, according to APAThe Engineered Wood Association. Glued LVL and parallel strand lumber can be as much as 357a higher.

Higher Horizontal Shear Values

The model building codes recognize APA EWS graded lumber, this translates into expanded design capabilities and improved product performance, at no added cost. glulam design values through NER486. Recognizing that traditional horizontal shear values for glulam were very conservative, APA and its relat- ed corporation, Engineered Wood Systems (EWS), developed and administered an innovative full size horizontal shear beam testing program at the APA Research Center in Tacoma, Wa. As a result, horizontal shear values published in NER-486 for Douglas fir glulam have been increased by over 257o and southern pine values have increased by 357o. Other species have similar increases (see Table I at left).

Increased Reverse Moment Gapacity

Often it is desirable to use an unbalanced glulam beam such as a 24F-V4 Douglas fir in continuous span floor beam or cantilever applications. However, the traditional allowable bending stress for this layup when the top of the beam is loaded in tension (commonly referred to as reverse tension) was only 1200 psiessentially preventing such uses.

APA evaluated the "reverse ten-

24F-Vs/SP sion" performance of unbalanced glulam beams, using a computer strength prediction model, recognized in NER486, to predict performance. An additional testing program of full size 24F-V4 Douglas-fir beams loaded in

Recognizing the

need to improve glulam performance and increase compatibility with l-joist floor systems, the glulam industry has made several recent advancements.

an "upside down" orientation followed. Test results verified the performance predicted by the computer model and, as a result, the "reverse tension" value has been increased by over S)Vo-from 1200 psi to 1850 psi.

Other unbalanced layup combinations have realized similar increases (see Table 2 above). These higher "reverse tension" values which are included in NER-486 make it more efficient to design cantilevers or continuous span floor beam applications using an unbalanced layup.

Gompatibility with l-Joist Framing Systems

The use of I-joists to frame residential floor systems continues to gain popularity. Recognizing the need to improve glulam performance and increase compatibility with I-joist floor systems, the glulam industry has made several recent advancements.

Glulam stress grades ranging from 24F-1.88 for Douglas fir to 30F-2.1E for southern pine are available for use in I-joist compatible (IJC) residential floor framing systems.

To achieve compatibility with standard residential I-joist depths, EWS member producers are manufacturing glulam beams in depths of 9ll2" . Il-7 /8" 14" and 16".

Traditional glulam depths in multiples of l-712" for western species and l-3l8" for southern pine are also available for use in these systems when an exact I-joist depth match is not required.

To provide width compatibility each can vary depending on market locale. When camber is desired, most builders and engineers agree that the 3500-ft. radius introduced by EWS is just the right amount of camber for nearly all residential applications (see Table 3 below). For IJC floor system applications, most manufacturers supply a zero camber glulam.

Readily Available

Engineered wood products distributors carry a full line of glulam and provide prompt shipment to local dealers and contractors. Local distributors inventory beams in a wide range of widths and depths and in lengths up to 66 feet. Stock beams are cut to specified lengths and delivered with the framing package. Custom orders of straight beams are routinely supplied in one to two weeks from EWS member milis.

with 2x4 and 2x6 dimension lumber framing, EWS member producers are manufacturing glulam in net widths of 3-l/2" and 5-l/2". These should be specified in accordance with the new EWS Framing Appearance designation.

Camber Gonsiderations

Glulam stock beams are available with either zero camber or 3500-ft. radius camber- although availability of

- For technical assistance or a list of EWS glulam manufacturers, contact the APA help desk line ar (253) 620-7400 or e-mail help@ apawood.org