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# 50% live load reduction factor ?

## 50% live load reduction factor ?

(OP)
Hi again,

For that 30 story building, the negineer has used a 50% live load reduction.  The National Building Code of Canada has a formula to calculate this reduction factor and the reduction I calculate comes to 78%......

Is there some empirical design formula that I may be missing here ??

Thanks

### RE: 50% live load reduction factor ?

At the time of design the building wasn't fully leased.

50 years ago the allowance for simultaneous live load distribution was treated much simpler. I think the Loading Code was a small 30 page handout.

Johnp.Rz
http://www.mets.net.au

### RE: 50% live load reduction factor ?

I think IBC limits LL reduction to 20%

### RE: 50% live load reduction factor ?

Playing devils advocate, how are you determining the reduction? Is it plainly stated that a 50% factor is used? Is this factor plainly show across the entire building?

Away from that, I have never know of a reduction that great.

If it is concrete, I hope the contractor is ready to shore the building to grade for most of its duration...

Daniel Toon

### RE: 50% live load reduction factor ?

LLRF is covered under cl.4.1.6.9 in NBCC in particular sentence 2 applies to areas other than assembly occupancies.  If the tributary area is greater than 20m^2 (215 sft) the load is multiplied by 0.3+(9.8/B)^.5.  For example if columns are spaced 20ftx20ft grid (TA=400sft or 37.1m^2),LLFR=0.81.  For a 30 storey bldg with same grid TA=30*37.1=1113m^2, therefore LLRF=0.39.

### RE: 50% live load reduction factor ?

Other countries also use a 50% LLRF:

Australia; AS/NZS1170.1:2002; LLRF = 0.5 (min.) for supported area > 225 m2 (not applicable for certain load types). The formula given is virtually identical to "0.3+(9.8/B)^.5" as pasted by Calculor, but with the 0.5 limit.

UK; BS6399:Part 1:1996; reduction in live load = 50% (max.) for columns etc. supporting > 10 no. floors.

### RE: 50% live load reduction factor ?

In the UK a 50% LLRF can be used to calc the forces in COLUMNS ONLY, when the number of floors is greater than 10.

Another reduction factor of up to 25% can be used for live load on beams depending on the area of floor that the beam supports.

### RE: 50% live load reduction factor ?

patswfc
By "columns etc" I meant the elements as listed in Clause 6.2; "columns, piers, walls and their supports and foundations".
From a theoretical viewpoint it could be argued that transfer beams can be included if they support columns carrying a number of floors. Common practice may indicate otherwise.
The above is based on the 1996 edition, please ignore if it has been amended since.

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