Live Load Reduction for Bearing Wall & Strip Footing
Live Load Reduction for Bearing Wall & Strip Footing
(OP)
I have a 5-story condo with reinforced CMU bearing walls and hollow-core plank floors. The bearing wall is 72' long, bays are 32' wide, floor-floor is 12'. IBC 2009 / ASCE 7-05
1. Can I use the entire length of the wall to figure At? If so, At=72(5x32)=11,520 sf. I used Kll=2. This allows for the maximum reduction down to L=0.4Lo. Or you could argue that the wall is a one-way slab and the width is limited to 1.5 x the floor-floor height. Then At=18(5x32)=2,880 sf. Now, L=0.448Lo. Your interpretation?
2. Even though I can't get a reduction of the snow load on the roof, I used the roof area as part of the tributary area being supported by the wall and footing. Does this make sense?
The strip footing load is getting very large. I think piles and a grade beam would not work for this project for budget reasons.
1. Can I use the entire length of the wall to figure At? If so, At=72(5x32)=11,520 sf. I used Kll=2. This allows for the maximum reduction down to L=0.4Lo. Or you could argue that the wall is a one-way slab and the width is limited to 1.5 x the floor-floor height. Then At=18(5x32)=2,880 sf. Now, L=0.448Lo. Your interpretation?
2. Even though I can't get a reduction of the snow load on the roof, I used the roof area as part of the tributary area being supported by the wall and footing. Does this make sense?
The strip footing load is getting very large. I think piles and a grade beam would not work for this project for budget reasons.






RE: Live Load Reduction for Bearing Wall & Strip Footing
2. No - you don't use the roof area to reduce floor live loads.
RE: Live Load Reduction for Bearing Wall & Strip Footing
I also wouldn't use the full length of the wall. At most I would only a length equal to how far the wall could clear span without a footing, but would more likely just use a typical bay width
RE: Live Load Reduction for Bearing Wall & Strip Footing
for one-way slabs shall not exceed an area defined by the slab
span times a width normal to the span of 1.5 times the slab span."
RE: Live Load Reduction for Bearing Wall & Strip Footing
Let us consider masonry pier 2'-8" wide with 4'-0" wide openings on each side. For simplicity assume the openings align on all the floors. Tributary area for masonry pier / floor = 6'-8" x (32' / 2) = 107 sft. AT = 4(floors) x 107 = 428 sft.
KLL for exterior column without cantilever slabs = 4.
AL = KLL x AT = 4 X 428 = 1712 sft.
L = 0.61 Lo.
RE: Live Load Reduction for Bearing Wall & Strip Footing
This is similar to what I have on the exterior walls. There are garage door openings with piers.
However, the interior walls have long solid sections. Do you use KLL=2 [Ai/At similar to a beam] and use full length of the wall for AT or use 1.5 times the flr-flr height span of the wall for the AT length?
Everyone,
This may be a little picky. Roof live load is a separate load from roof snow load. Roof live load is reducible but snow is not. You could argue that the roof area could be used in the total tributary area calculation for AT even though snow controls and you take no reduction on the roof. Your thoughts?
RE: Live Load Reduction for Bearing Wall & Strip Footing
RE: Live Load Reduction for Bearing Wall & Strip Footing
I am not calculating the AT for the design of the roof members. I am calculating the AT for the bearing wall and footing that supports all of the floors and the roof.
RE: Live Load Reduction for Bearing Wall & Strip Footing
RE: Live Load Reduction for Bearing Wall & Strip Footing
But no matter what the calculations show, we always design walls on the lower storys for the following minimum live loads.
Exterior loadbearing walls L = 0.60 Lo
Interior loadbearing walls L = 0.50 Lo