Live Load Reduction in IBC 2015

[CURVEB]

In the IBC 2015 table 1607.1, what is the purpose of footnote 'm' on live loads of 100 psf or less? We are having some internal discussions about whether or not you can reduce these loads. Although footnote m states that these loads cannot be reduced, it goes on to say "unless specific exceptions of 1607.10 apply".

We read 1607.10.2 #1 to say that live loads of 100 psf or less may be reduced.

In other words, if we have an occupancy of Residential/Public Rooms, the Lo is 100 psf. It cannot be reduced by footnote m, but if you use section 1607.10.2, it allows reductions in live loads of 100 psf or less.

The previous iterations of the IBC had an exception that Group A assembly occupancies could not be reduced, but we always interpreted that to only apply to loads under the "Assembly" area of table 1607.1. The 100 psf loads that show up under other primary occupancies could still be reduced as long as the other exceptions are met.

Any thoughts or different interpretations?

 

[ahypek]

I would always refer back to the ASCE 7-10 for anything vague in the IBC;

Footnote "a" says "Live load reduction for this use is not permitted by Section 4.7 unless specific exceptions apply."

4.7.3. Heavy Live Loads: Live loads that exceed 100 psf shall not be reduced.

Exception: Live load for members supporting two or more floors shall be permitted to be reduced by 20 percent.​

This applies to Passenger Vehicle Garages also.

Assembly uses are not allowed to be reduced in any case.

My interpretation: If the LL is > 100 psf and the loaded area is not an assembly, then I can only reduce a column carrying 2+ floors by 20 percent at most.

But, I don't personally use live load reduction ever.

 

[JoshPlumSE]

And, if you look at most of the cases where the m footnote is given for a load of 100psf or less it is for places that can be termed public assembly. They might be extending that definition out a bit farther than before.... hence the switch to a footnote to make it apply for some of those borderline cases.

 

[CURVEB]

What about dining rooms? Not really an assembly area - tables take up a lot of space and don't weigh that much. I'm surprised that this would be considered an nonreducible live load.

Also, I find it strange that all of the corridor and exit live loads that are 100 psf are considered reducible. I feel that these are the areas MOST likely to see the full required live loading.

 

[JoshPlumSE]

Yeah, some of the items seemed a little odd to me too.

But, to play devil's advocate.... weren't there a couple well publicized failures of ballrooms at weddings a few years ago? They move the tables out of the way and then start dancing. That may not take up the entire floor, but it can be pretty tight spacing at some areas.

I honestly didn't look at the m cases that closely, but at first glance it seemed to be mostly areas of public assembly or areas the code writers might have specific concerns about reducing the load.

 

[wannabeSE]

CurveB
Dining rooms are usually classified as Assembly Group A-2 (see IBC chapter 3).