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RE: Vibration - Office Floor Guidelines

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Harold,

Thanks for the feedback.  I really appreciate it.

If the joist spacing's are increased to 5-6 feet, the total load can easily
exceed the 550 plf of a K series bar joist system.  Are joists now not
feasible for office floor construction?

Rich


-----Original Message-----
From: Harold Sprague [mailto:spraguehope(--nospam--at)hotmail.com] 
Sent: Monday, July 31, 2006 1:24 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Vibration - Office Floor Guidelines

Rich,
To start with, contact your local steel fabricators in the area.  They will 
be able to zero you in on the most economical structural system.  You will 
have to add in the concrete costs yourself.

I do not know your project (bay spacing, live load, flr to flr height, 
etc.), but the use of 9/16 form deck and bar joists at 30" has not been the 
most economical system in most areas for many years.  The composite decks 
and increase in joist spacing for bar joists of 5 or 6 ft is generally a 
more economical soution.   It will make your joist girders work out better 
too.  Once you increase the span to 5 or 6 ft, your system stiffness and 
mass will increase, but your cost per square foot will decrease.  Your 
bouncy floor problem will take care of itself with a more economical 
structural syste.

Reducing piece count is generally considered more economical

Regards,
Harold Sprague

>From: "Rich Lewis" <seaint03(--nospam--at)lewisengineering.com>
>Reply-To: <seaint(--nospam--at)seaint.org>
>To: <seaint(--nospam--at)seaint.org>
>Subject: Vibration - Office Floor Guidelines
>Date: Mon, 31 Jul 2006 08:30:22 -0500
>
>I am designing an office building, something I used to do a lot in the 
>past.
>My typical design for buildings that do not require a fire rated floor
>assembly is to use steel bar joists at about 30 inches on center, 9/16
>corrugated form deck and a 3 inch total slab thickness.
>
>I'm using AISC Design Guide 11, ""Floor Vibrations Due to Human Activity"
>and having a hard time coming up with a system that satisfies the 0.5% g
>value for office floor vibrations.  In my study girders seem to have a
>greater influence than the joists.  My girder sizes were getting extremely
>large.
>
>Are there typical slab thicknesses and joist spacing that others have found
>that make it easier to meet the 0.5% g value?  I know a lot of the 
>vibration
>influence has to due with the spans of the joists and girders.  Should
>girders be having such a large impact on my design, or is it possible I'm
>doing something wrong in my calculations?  Do others find that girders are
>the main influence in vibration?  I was wondering if a different slab and
>deck configuration, along with joist spacing is more conducive to reducing
>the '%g' vibration value.
>
>Thanks for your help.
>Rich

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