Section 509.2 (2009 IBC)

I have a project that is utilizing Section 509.2 of the IBC. So far, the building completely complies with the requirements of that section with Type IA for the single story below the 3-hour horizontal separation and Type VA for the four stories above (total of five stories).

The building is a typical U-shape. At the open end of the "U" at each story is an open, connecting bridge. Centered at the bridge is an exterior (not enclosed) stairway. I don't see where this would be a problem, but the issue has to do with the fire resistance of the bridge structure. Would the structural frame supporting the first bridge be required to have a 3-hour fire-resistance rating (for Type IA) and the rest of the structural frame have a 1-hour rating (for Type VA)? And, would the bridge at the second story (i.e. in line with the 3-hour horizontal assembly) also be required to have a 3-hour rating? Or, could it all have a 1-hour rating?

Ron Geren RLGA Technical Services Phoenix AZ
Original Post
3104.3 Construction. The pedestrian walkway shall be of noncombustible construction.
1. Combustible construction shall be permitted where connected buildings are of combustible construction.
2. Fire-retardant-treated wood, in accordance with Section 603.1, Item 25.3, shall be permitted for the roof construction of the pedestrian walkway where connected buildings are a minimum of Type I or II construction.

I thought about that section, too; but I was concerned about the use of "separate structures" as indicated in Section 3104.2.

Although the building is really two separate structures using a horizontal separation, the pedestrian walkway doesn't really connect separate buildings unless you include the stairway as a part of the pedestrian walkway.

I'll fly that by the building official.

Any other approaches/views out there?

The concept is that the building above the podium deck is a separate structure. The use of a pedestrian walkway would not be appropriate if the building above the deck complies as one building.

The "bridges" would only have to comply with the one hour fire rating for Type VA constrcution.

Chuck Daleo
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