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Re: Dead+Seismic for heavy equipment on roof

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I would go along with the 5%, that is what most building departments have limited me to without looking at the lateral impact on the entire some cases they might go as high as 10%, but not very often.
Michael Cochran SE SECB
In a message dated 6/25/2006 2:05:07 P.M. Pacific Standard Time, mbryson(--nospam--at) writes:

I believe the number is 5%.

Michael Bryson, SE

-----Original Message-----
From: Dave Gaines [mailto:gainesengr(--nospam--at)]
Sent: Sunday, June 25, 2006 10:16 AM
To: seaint(--nospam--at)
Subject: Dead+Seismic for heavy equipment on roof


Joe, Neil and Mohammed,


Good points by Neil and Joe.


Lateral force, Fp need not be higher than 4x the forces at ground level for equipment above the roof level, per EQ. (32-3) of section 1632 of the UBC/CBC.  That's a high lateral load for frames above a roof.


Check overturning of the frame/equipment at the base for dead plus seismic for lateral forces in all directions and find the downward jamb force on the roof beams due to overturning.  This may govern over dead plus live.  Design equipment connections through the roof framing to the primary frame for any uplift - dead minus seismic.


If the overall mass of the building is not increased significantly by the weight of the equipment, say over 10% to 15% of the total mass, it may not be necessary to perform a lateral analysis of the entire building.  This is listed in the code for existing buildings.  If the building has poor seismic design, such as older, poorly connected masonry and concrete wall buildings with wood roofs, unreinforced masonry buildings or older steel moment frame buildings, it may be advisable though.  In that case you can recommend it be done (in writing) and list it as not included in your scope of work.


Good luck getting the project,

Dave Gaines

Pasadena. CA

----- Original Message -----

Sent: Saturday, June 24, 2006 6:41 PM

Subject: Re: Heavy equipment on roof


Redesign the new roof beams after they give the exact location of the new equipment.


Follow the vertical loads to ground.


Do the seismic attachment of the equipment to new beams and roof structure.


Do a new lateral analysis for building for new dead loads.


Joe Venuti
Johnson & Nielsen Associates
Palm Springs, CA