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glulam definitions 1
- Thread starter swm99
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AITC 117-2004 is a recommended reference for designers, building officials, laminated timber manufacturers, and quality assurance agencies. free download
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- #5
ThePioneer
Structural
Go to the American Institite of Timber Construction (AITC) for this type of information:
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1
- #7
The 26F refers to the allowable bending stress at the "bottom" face of the beam. The V4 or similar is the combination symbol and is critical to your specification.
"V" indicates Visual grade for strength and has nothing to do with the architectural appearance of the beam.
Architectural appearance is determined by the following terms and has nothing to do with strength: "industrial appearance, architectural appearance, premium appearance"
A glued laminated beam consists of multiple laminations, each of which, consistent with its final manufactured location in the glulam section, experiences a different load demand upon it. for example, only the outermost lamination on the bottom face of the beam will experience the demand of the 'extreme fiber in tension' under bending loads. The lamination at the neutral axis will not experience that load demand, and therefore need not be capable of resisting the same load as the outermost lamination. the glued laminated industry has defined the strength of the laminations at each place throughout the depth of the beam so that the design values exhibited in the codes are truly there. The location and load capacities of each of these laminations must be combined in an exact order in order to insure the design capacities for the complete glulam section. Hence the term "combination symbol".
For example, a 24F-V4 DF/DF and a 24F-V8 DF/DF both provide for 2400 psi extreme fiber in bending tension at the bottom face of the beam. But the V4 is intended for a simple span beam and consequently provides only 1200 psi extreme fiber in bending tension at the top face of the beam. So, should the beam be installed upside down, or should the beam be used in a cantilevered condition, the maximum bending will not be 2400 psi but 1200 psi.
The V8 combination is intended for a cantilevered condition and therefore the 2400 psi extreme fiber in bending is available at both faces.
Consequently, one can see also, a notch in the bottom face of such a beam is even more critical. Not only is the depth of the beam reduced, but the allowable extreme fiber in tension may well be reduce too, depending how deeply the notch extends into the laminations.
"V" indicates Visual grade for strength and has nothing to do with the architectural appearance of the beam.
Architectural appearance is determined by the following terms and has nothing to do with strength: "industrial appearance, architectural appearance, premium appearance"
A glued laminated beam consists of multiple laminations, each of which, consistent with its final manufactured location in the glulam section, experiences a different load demand upon it. for example, only the outermost lamination on the bottom face of the beam will experience the demand of the 'extreme fiber in tension' under bending loads. The lamination at the neutral axis will not experience that load demand, and therefore need not be capable of resisting the same load as the outermost lamination. the glued laminated industry has defined the strength of the laminations at each place throughout the depth of the beam so that the design values exhibited in the codes are truly there. The location and load capacities of each of these laminations must be combined in an exact order in order to insure the design capacities for the complete glulam section. Hence the term "combination symbol".
For example, a 24F-V4 DF/DF and a 24F-V8 DF/DF both provide for 2400 psi extreme fiber in bending tension at the bottom face of the beam. But the V4 is intended for a simple span beam and consequently provides only 1200 psi extreme fiber in bending tension at the top face of the beam. So, should the beam be installed upside down, or should the beam be used in a cantilevered condition, the maximum bending will not be 2400 psi but 1200 psi.
The V8 combination is intended for a cantilevered condition and therefore the 2400 psi extreme fiber in bending is available at both faces.
Consequently, one can see also, a notch in the bottom face of such a beam is even more critical. Not only is the depth of the beam reduced, but the allowable extreme fiber in tension may well be reduce too, depending how deeply the notch extends into the laminations.
msquared48
Structural
Note that the "bottom" is the tension face whether it is on the top or bottom.
It is possible to use a 24FV4 in lieu of a V8 for a cantilever if you mount it upside down, and the tension face of the back span does not exceed 1200 psi. This is assuming the cantilever mopment is greeater than twice the backspan moment.
Contrarily, it is also possible to ues the same member with a 24FV4 rightside up if the cantilever moment is less than half of the backspan moment.
You just have to play the numbers game.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
It is possible to use a 24FV4 in lieu of a V8 for a cantilever if you mount it upside down, and the tension face of the back span does not exceed 1200 psi. This is assuming the cantilever mopment is greeater than twice the backspan moment.
Contrarily, it is also possible to ues the same member with a 24FV4 rightside up if the cantilever moment is less than half of the backspan moment.
You just have to play the numbers game.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
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