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Re: 25% of Live Load added to Lateral[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: 25% of Live Load added to Lateral
- From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
- Date: Tue, 22 Jul 2008 22:29:27 -0700
Attics and other areas of homes for residential storage need only be designed for the LL of the rest of the house (40psf) typically. Then you get your architect clients who are doing there own houses and want to make little offices in their ceiling space under the ridges (actually it's usually a photo emailed to you with a "so whatcha think?)
Live load sign postings are usually only required in designated storage areas and mezzanines in my experience.
While it is true that any floor could be used for any type of load condition or occupancy, the code (as was once explained to me in the City of Los Angeles) limits the original design of the floor live load which used to be required to be posted. However, based on original design, the only provision that I know of in commercial buildings that could be misused is the live load required in corridors that would change if the layout of the offices were modified to change the location of the corridors.
Simply put – the building official required a percentage of live load to be used for the design of the lateral load, but since it was not possible to anticipate the possible change of where the live load was applied on a specific level, the percentage was added to the entire level. The same held true in a remodel of a building that was converted from office to warehouse as the existing building now triggered the provision of adding the percentage of live load into the lateral force and making sure that the building was capable of resisting the additional mass that occurred at higher levels.
If one level is originally designed to be a warehouse, then the type of warehouse loading and the limits added to the lateral load generally became part of the original design indicated on the application for permit under occupancy and usage. The city may require the warehouse load to be posted on each level as was the case when I lived in L.A. The city was not expected to maintain or track what portion of the level was used for storage and what part was used for offices – they figured that the original design was applicable to the entire level.
My question was not originally intended to bring up the question of portions of a level but to question if the total storage load percentage was added to the entire building or only to that specific level.
Life gets complicated – or maybe I'm just getting old :>)
But, Dennis, isn't it also true that a storage area's floor system would need to be designed to carry the larger live loads, and that the owner/occupant *could* expand the storage use into the non-storage area, thus possibly greatly overloading the "weaker" floor framing.
And, to be extreme about it, couldn't the owner also decide to add a story to the building and in doing so also compromise the existing lateral-force-resisting system? :)
In other words, if we try to anticipate EVERY possible harmful act of an irresponsible owner we'll never stop "improving" the structure.
Sort of like designing the WTC towers for, well, you know what.
Ralph Hueston Kratz, S.E.
Richmond CA USA
In a message dated 7/20/08 12:14:59 PM, dennis.wish(--nospam--at)verizon.net writes:
It is safer to assume the more conservative lateral load applied to the entire diaphragm at that level than to try and restrict it when there is not means in place (other than placard) to restrict compliance to the load restriction.
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