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Re: LRFD, ASD, and USD

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I agree with Mel, I design mostly wood-framed residential and small commercial
buildings, and if I need to use steel or concrete, the quantities are small. I
use steel beams where wood beams are too deep to fit within the depth of the
joist system and for lateral resisting sytems, and usually, deflection
governs. I haven't used LRFD and I use USD only on big footings and heavy
grade beams.

I think serviceability(or deflection limits) should be personally evaluated..
I designed a long span wood roof beam a long time ago and the framers called
me and said the beam is sagging excesively and bouncing like a diving board. I
checked my calcualtions and everything works fine(understressed  based on
design loads and within the code deflection limits). I went out to the jobsite
and checked it out and they're right, I would not want that kind of beam if
this was my building. And I learned my lesson. They ended up adding a post at
the midspan of the beam. And this is only a roof where only the framers can
see and feel it. What more for a floor system?

My point is, don't just design for minimum code requirements, design for what
you and the ultimate user of the building think and feel is a safe structure.

Ernie Natividad