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RE: higher loads or better details.[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: higher loads or better details.
- From: "Bill Allen, S.E." <bill(--nospam--at)allendesigns.com>
- Date: Fri, 4 Sep 1998 15:08:50 -0700
Roger, which would you rather have: A. a structure where the members are 20% overstressed, or B. a structure missing 20% of its connections? IMO, those who are inexperienced at providing a lateral load path from roof to foundation (shear collection and transfer) are more dangerous than those who underestimate the design loads as well as codes that provide too low of a design load. Regards, Bill Allen -----Original Message----- From: Roger Turk [mailto:73527.1356(--nospam--at)compuserve.com] Sent: Friday, September 04, 1998 2:48 PM To: seaint(--nospam--at)seaint.org Subject: Re: higher loads or better details. Ralph Hueston Kratz wrote: . > In a message dated 9/4/98 9:47:04 AM, Roger Turk wrote: . > . > <<Proper loads and details go hand-in-hand with each other. A "good" . > detail for an inadequate load will have the same result as a bad detail . > for a proper load. >> . > . > I don't agree. I feel that proper connection details are much more . > important than design for precise loads, at least when it comes to seismic . > design. I believe that a properly tied-together building designed for . > half seismic loads will perform better than an inadequately-connected . > structure designed for double loads (if there were such a thing as . > adequate design with inadequate connections). . > . > I'd certainly prefer a building that deflects a lot under seismic loads, . > but doesn't collapse, to one that has plenty of bracing, but isn't tied . > together than thus may "fall apart." . > . > This may apply to gravity design too: Would you rather have an undersized . > beam with adequate bearing (thinking of wood), which will sag and provide . > warning before failure, or an adequately-sized beam with inadequate . > bearing (which could fail catastrophically)? . > . > There's an old architectural saying: "God is in the details." He (She?) . > may also have been thinking of engineering. . > You certainly do want a structure or structural element to deflect like a sway back mule before it *collapses*. At this point (sagging like a sway back mule), the structure or structural element is long past failure. [Failure is when a structure or structural element cannot support the loads or function in the manner as it was originally intended.] While I referred to "proper" loading in the referenced post, I never mentioned "precise" loading. I learned long ago that there is never anything "precise" in determining loading; in fact, there is nothing "precise" in structural engineering as we start with assumptions and proceed exactly from there. A design live load of 20 psf for a storage floor would not be a "proper" load. The code required live load of 125 psf for light storage may never be reached, or it could be exceeded by more than 50 percent. Go into some apartment buildings that are under construction and you will find drywall stacked 4 feet high is loading the floor closer to 150 psf (48 inches X 2 X 1.5 psf) than it is to 40 psf, and it is stacked in the middle of the room so that workers can maneuver around it. A. Roger Turk, P.E.(Structural) Tucson, Arizona
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- Re: higher loads or better details.
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