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RE: beam camber...

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 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
Vancouver, BC

Date: Mon, 30 Apr 2007 17:46:53 -0700
From: gmse4603(--nospam--at)
To: seaint(--nospam--at)
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)> 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
Senior Director
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
312.573.1726 facsimile
312.622.0409 mobile



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