Lr (Roof Live Load) Reductions
Lr (Roof Live Load) Reductions
(OP)
I'm not sure if I understand the roof live load reduction method completely. I understand how it might apply to a (flat) roof where there are purlins, beams and columns. Basically take the tributary area of the member and then check Atrib to see if it is greater than 200 ft2. However, I am wondering if it might apply to a a bearing wall as well? I have an interior bearing wall that is resting on a 6" concrete slab. My roof load and wall loads are:
Lr: 20 psf
DL: 15 psf
Wall DL: 10 psf
I have a 12' high wall with 20' of tributary length of roof joists. My load approximately on this bearing wall is: 120 plf + 700 plf = 820 plf ----> NG
The wall is approx. 51 ft. long. The roof tributary to this wall is 1020 ft2.
Can I apply a reduction of R1 = 0.6? which would then bring my load on my bearing wall to 120 plf + 540 plf = 660 plf ----> OK
Lr: 20 psf
DL: 15 psf
Wall DL: 10 psf
I have a 12' high wall with 20' of tributary length of roof joists. My load approximately on this bearing wall is: 120 plf + 700 plf = 820 plf ----> NG
The wall is approx. 51 ft. long. The roof tributary to this wall is 1020 ft2.
Can I apply a reduction of R1 = 0.6? which would then bring my load on my bearing wall to 120 plf + 540 plf = 660 plf ----> OK
A confused student is a good student.






RE: Lr (Roof Live Load) Reductions
A confused student is a good student.
RE: Lr (Roof Live Load) Reductions
I remember where I used to work we used to add a 10,000 lb load on the top of every concrete column presumably for future stories but more likely to take them out of the equation of being overstressed.
RE: Lr (Roof Live Load) Reductions
A confused student is a good student.
RE: Lr (Roof Live Load) Reductions
A confused student is a good student.
RE: Lr (Roof Live Load) Reductions
Jed - I wonder about your method. I can see that adding load is typically a way to increase capacity in members, but for concrete columns the added Pu value sometimes decreases the required reinforcement in the columns.
In many past concrete frame projects, the counter-intuitive results showed that upper, corner columns required more reinforcement than the lower interior columns due to the moments in them.
This can be seen by looking at the column P-M interaction diagrams. If you were originally under the "bulge" in the curve, your column was failing. But if you added axial load the point moved up within the interaction curve and was OK.
So just adding 10,000 lbs. to a concrete column doesn't necessarily add capacity and might actually reduce your required column rebar.
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RE: Lr (Roof Live Load) Reductions
Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.
RE: Lr (Roof Live Load) Reductions
A confused student is a good student.