IEBC Allowable 5% Gravity Increase on Total Load or Load Type? 2

[waytsh]

My understanding based on previous editions of the IEBC is that the 5% increase was based on the total gravity load. The wording in the more current versions, however, could be read as 5% of the load type, i.e. dead, live, or snow.

“Any existing gravity load-carrying structural element for which an alteration causes an increase in design dead, live or snow load, including snow drift effects, of more than 5 percent shall be replaced or altered…”

How do you guys read this?

 

[Nick6781]

Note that it's the effect of the load. Think in axial, shear, moment, and overturning, etc.

 

[lexpatrie]

I've always viewed the "origin" as being intended for a lightweight roof overlay. That would lend to the "solo" 5% increase that would net, in some load combinations, 15%. I would NOT read it that way without signoff from the building official and disclosure on the drawings/letter that that's what is being done. (a la Florida 'violating' the code or standards).

Were it my project, logically, the 5% overstress would apply to a load case or a load combination under the appropriate code, and I suspect there've been a few code change proposals (that I also presume failed) that would have clarified that.

Further, the 'overlay' in my mind, would typically be shingles, not all that typical with the "current" vogue for flat roofs. This would technically be a dead load, but unless there's some kind of offsetting effect, a change of occupancy (i.e. live load increase), adding weight (like solar), and changing insulation (higher snow load), these all "eat" from the same trough of allowable 5% increase.

I'd also add something about roof slope. We've seen enough roof collapses in the media, better to try to avoid them on the design/repair side, if possible.

Mike Mike - code change proposals are "free". No need to go the drastic step of joining the organization... I've gotten one approved. That or just call that Reid Middleton guy who writes a hundred code change proposals a week, he can squeeze yours in, I'm sure.

EZ building - I've referenced that provision in several damage reports calling for engineering to satisfy those requirements. One was a residential, the other was a poured gypsum roof from 1970. It shows up in Hurricane damage projects with structural and roof damage, there's a dollar limit in the FBC/FEBC for residential and a precedence lists, and I often see public adjuster estimates that include renailing of the diaphragm (for uplift), as a precautionary measure. T.L. Smith discussed that some years ago. And What's SID, anyway?

 

[RWW0002]

I've always viewed the "origin" as being intended for a lightweight roof overlay. That would lend to the "solo" 5% increase that would net, in some load combinations, 15%.

I am not following the math here. Can you give me an example of how 5% increases in loads can lead to a load combination of anything over 5%??

My opinion is that the letter of the "new" wording is more restrictive and more conservative than previously. It seems that you are implying that it is less conservative than previous codes from your statement.

I agree with you though that the 5% has always in my mind applied to the total gravity load effect in the past.