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RE: beam camber...[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: beam camber...
- From: Reza Dashti Asl <rezadashti(--nospam--at)hotmail.com>
- Date: Tue, 1 May 2007 12:08:14 -0700
I have not run the numbers but if the DL deflection will be (2.14-1.75=0.39") then all deflections seem to be OK. The natural frequency could be about 5 (Considering that you don't use all the live load for frequency calculations) which is not that bad but still a second or third harmonic of foot steps to cause resonance. Depending on the floor bays the acceleration could be somewhere between OK and 3 times the allowable! So I suggest either you or the other engineer check the floor as per AISC steel design guide 11 for vibration.
Reza Dashti P.Eng
Date: Mon, 30 Apr 2007 17:46:53 -0700
Subject: Re: beam camber...
Does it have an inverted WT welded to the bottom that may not be showing on the plan? I see that one quite a bit and the WT terminates a few feet from the columns/girders to allow for HVAC duct runs.
It does appear to be too flimsy at first glance and a quick check I did appears to show it's not even close. Those TL deflections are obviously unacceptable. I think your numbers are about right...I doubt with LL reductions it will work either (I didn't do the reduction)
On 4/30/07, David Fisher <dfisher(--nospam--at)fpse.com> wrote:List members:
We are currently designing a multi-story office building in Florida.
We have been shown a "prototype" by another engineer with the following
Purlin: 40 ft span
100 psf LL
5" composite slab (2"+3" NWT)
Beam spacing: 10'
W18x35 Fy = 50 ksi with 52 shear studs
Camber <1 ¾">
DL deflection: 2.14" L/224
LL deflection: 1.25" L/386
TL deflection: 3.39" L/142
My staff and I think this doesn't even come close to working, even with the camber.
David L. Fisher SE PE
Cape Cod Grand Cayman Holdings Ltd. - Cayman
Fisher+Partners Structural Engineers Ltd. - Cayman
980 North Michigan Avenue #1640 Chicago 60611
75 Fort Street Georgetown Grand Cayman BWI
319 A Street Boston 02210
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