Risk Category - Building Addition

[KHoff]

I am working on an addition to a research facility at the local university. Based on the applicable building code (IBC 2012) the building is Risk Category III if the occupant load is 500 or more. The original building has an occupancy of approximately 300, and the addition has an occupancy of approximately 400.

1. Does the addition have to be designed to Risk Category III due to the combined occupancy for the entire building?

2. The original building was designed for Risk Category II. Does the existing structure have to be reviewed to resist increased loads based on Risk Category III importance factors?

 

[mike20793]

Expansion joint or hard attaching to existing? If expansion joint, I vote Risk Category II since they are essentially separate structures. If hard attached, then Risk Category III.

 

[KHoff]

The structures are isolated with an expansion joint. However, there are corridors that allow occupants direct passage between the original building and the addition, so I am not sure how the code would define the occupancy.

 

[jakeh76]

I think if you look close it's 300 ppl in an area ... not total occupancy of the building. Don't quote me on this but I think this was a difference in the IBC and ASCE-7

 

[EngineeringEric]

didn't ASCE 7-10 remove the number of occupants... ASCE 7-05 used to list the 300 people rule. If my late night foggy memory serves me.

If you are a research facility and a university that has gathering rooms or auditoriums you may need to be III regardless of the gross number. Honestly what is 15% increase in load as long as we are in the Schematic phase and this isn't to save you from redoing weeks of work

 

[KHoff]

The exact verbiage in the 2012 IBC is as follows:

Buildings and other structures containing adult education facilities, such as colleges and universities, with an occupant load greater than 500.

In addition, the 2012 IBC states the following regarding public assembly:

Building and other structures whose primary occupancy is public assembly with an occupant load greater than 300.

I interpret that to mean that an assembly of 300 people for any type of building falls under Risk Category III. For building specifically used as adult education facilities, I take that to mean a total building occupancy of 500.

That being said, I am leaning toward designing the addition as a Risk Category III structure. I just want to be sure it isn't necessary I review the original building structure for increased loads due to the Risk Category III importance factors.

 

[Archie264]

>>>didn't ASCE 7-10 remove the number of occupants...<<<

Engineering Eric, it's in there in the commentary in the form of Figure C1-1, which is shown as a logarithmic scale. And if you track down or create a logarithmic scale to determine the cutoff between "Occupancy Category" and "Lives Placed at Risk" the transition from II to III appears to be 250, which, incidentally, I thought was the cutoff in ASCE 7-05, not 300. I might be wrong, though. And I'm not sure how ASCE 7-1516 addresses it.

KHoff, As I read it, per IBC Section 1613.1 there is the option of deferring to ASCE 7. If you were to do that then the Risk Category would be determined per the occupancy in a specific area; not per the whole building. If you haven't already I encourage you to read ASCE 7 Commentary Section C1.5.1.

At least, that's how I interpret our bowl-of-spaghetti-like building codes on this particular issue. If I'm wrong on it I look forward to being set straight.

 

[KHoff]

Archie264 - The way I interpret 1613.1 is that ASCE 7 can be used in lieu of Section 1613 (Earthquake Loads), and therefore that statement wouldn't apply to the Risk Category.

It seems the Risk Category is somewhat open to interpretation in this case.

 

[Archie264]

KHoff, I see it now, no interpretation required. It was added to Section 1604.5 of the 2015 edition of the IBC.

 

[EngineeringEric]

well i appreciate the corrections! i still like how the older one cleary said the number. I am an engineer i don't want to have to do math

 

[JLNJ]

I think you would look at it the same as the architects do. If they have it as one building, then you should too. If they break it into separate occupancies with fire walls, then you might be able to break it up as well.