Patrick Baxter November 09, Tags : breyer design structures wood. Posting Komentar. I find my self comparing it to the design value under the 86 NDS. Breyer I use ASD. I think LRFD makes more sense for a material like steel, where something like an adequately braced beam fails by the formation of a platic hinge, or for concrete.
I am not familiar with LRFD for wood, but am skeptical that it would add anything other than increased complexity. With that said, I'm sure the academic community will embrace it and try to shove it down everyones throat. If I'm wrong I'll have a nice helping of humble pie.
You can't go wrong learning both, I suppose. Breyer I still use ASD in my day to day work. I think, for example, LFD of concrete structures is fine. I also thing LFD design of steel can be fine, but you should still perform the servicability checks. This is one of my greatest concerns with LRFD.
The community is telling me that you no longer have to check deflections and stuff like that. I say BULL! In wood, I'd accept some sort of LFD design theory so that a larger Factor of Safety could be applied against live load, but it is still a basic solids of mechanics type material, so I'm going to treat it that way. Breyer Dinosaur, if deflections aren't being checked with LRFD that sounds like a recipe for disaster. In my experience deflections often control for steel and for longer engineered lumber like LVL.
I'm just skeptical the LRFD will provide a tangible benefit for the design of wood structures, and that it's mostly something the academics will like. If they take the same approach that AISC did in having a unified spec, that could be ok.
Chapter 4 Solutions Page 4 of 19 4. Chapter 4 Solutions Page 5 of 19 4. Chapter 4 Solutions Page 6 of 19 4. Chapter 4 Solutions Page 7 of 19 4. The shorter the duration of load, the higher the strength of a wood member. CB DB is the multiplier that adjusts the reference design value from normal duration 10 years to other durations for ASD.
See NDS 2. Higher moisture contents require reduction of design values by CB MB. See NDS 4. When three or more wood members are spaced not more that 24 in.
This is a 15 percent increase over single member bending design values. The CB rB adjustment recognizes that failure of a single member in a repetitive application will not mean failure of the overall system. The load will be distributed to other members. Chapter 4 Solutions Page 8 of 19 4. Dry service conditions are defined as: a. Reductions in strength caused by heating up to degrees F are generally reversible when the temperature returns to normal.
Reductions in strength may not be reversible when heating exceeds degrees F. Reduction in strength occurs when the member is subjected to the full design capacity.
When a wood member is consistently heated above degrees F and is subjected to the full design load, an adjustment for temperature effects will be required. This may occur in an industrial plant, but reductions are not normally required in ordinary roof structures. Chapter 4 Solutions Page 9 of 19 4. Reference design values apply directly to preservative treated wood, and an adjustment factor is not required unless the member has been incised to increase the penetration of preservatives.
Fire-retardant-treated wood has much higher concentrations of chemicals than preservative treated wood. At one time a 10 percent reduction in reference design values was specified. However, the reduction in strength varies with the treating process, and the NDS refers the designer to the company providing the fire retardant treatment for appropriate reduction factors.
Subjects Building, Wooden. Structural design. Strains and stresses. Engineered wood. Laminated timber. Axial loads. Wood bending. Shear walls. Timber joints. Diaphragms Structural engineering Wood fasteners. Bolts and nuts.
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