Live load required for two-way post-tensioned slab - office space
Live load required for two-way post-tensioned slab - office space
(OP)
I have the structural plans for 2 adjacent office buildings that are almost identical structurally.
They are both 8.5" two-way post tensioned slabs with the same mild reinforcing and column grids.
The plans state that both buildings were designed for 100PSF LL (reducible as allowed by code).
I checked the capacity of a column strip on the first building and for a trib area of 900 ft^2, I can reduce the LL 40% to 60 psf
Everything checks out and the strip is good for 100PSF Reducible LL.
Then I check an identical strip on the second building, the mild reinforcing is the same, spans are the same...everything is the same except there are about 50% less tendons in the strip on the second building.
I have to use a 50 psf LL reducible, which reduces 40% to 30psf to get the strip to work.
The original architectural plans show "open office space" in the area im checking...
I still can't figure out how on a set of plans that show 2 buildings on one sheet how there can be such a disparity in floor capacity. Possiblly the buildings were done by two different engineers...one designing for 100psf reducible and the other 50psf reducible???
Now the new owner wants to change the floor space...from an open office space with a bunch of cubicles...to office space with areas of light storage and corridors, etc.
We have typically designed office space LL for 100 psf for concrete buildings and 70-75 psf for steel framed buildings
Do any of you design office spaces for 50 psf? how do you handle the 80psf for corridors above the 1st floor..and light storage @ 125 psf?
Thank you!
They are both 8.5" two-way post tensioned slabs with the same mild reinforcing and column grids.
The plans state that both buildings were designed for 100PSF LL (reducible as allowed by code).
I checked the capacity of a column strip on the first building and for a trib area of 900 ft^2, I can reduce the LL 40% to 60 psf
Everything checks out and the strip is good for 100PSF Reducible LL.
Then I check an identical strip on the second building, the mild reinforcing is the same, spans are the same...everything is the same except there are about 50% less tendons in the strip on the second building.
I have to use a 50 psf LL reducible, which reduces 40% to 30psf to get the strip to work.
The original architectural plans show "open office space" in the area im checking...
I still can't figure out how on a set of plans that show 2 buildings on one sheet how there can be such a disparity in floor capacity. Possiblly the buildings were done by two different engineers...one designing for 100psf reducible and the other 50psf reducible???
Now the new owner wants to change the floor space...from an open office space with a bunch of cubicles...to office space with areas of light storage and corridors, etc.
We have typically designed office space LL for 100 psf for concrete buildings and 70-75 psf for steel framed buildings
Do any of you design office spaces for 50 psf? how do you handle the 80psf for corridors above the 1st floor..and light storage @ 125 psf?
Thank you!






RE: Live load required for two-way post-tensioned slab - office space
50psf (2.5kPa) for office space is very restrictive, the loading code I use specifies a minimum 60psf (3kPa) for office space with many property managers requiring a minimum 80psf (4kPa) floor design so that the office space can rented as "premium office space".
RE: Live load required for two-way post-tensioned slab - office space
Why would you design an office building for a different live load based on the material the building is constructed out of (concrete v steel)?
RE: Live load required for two-way post-tensioned slab - office space
RE: Live load required for two-way post-tensioned slab - office space
I will have to disagree here about the application of the LLR here. It does get tricky though when combined with alternate loading scenarios. Tricky does not mean that it should not be used, just used carefully and judiciously.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com