Fireproofing of Rooftop Steel Dunnage.

[TomLeonardPE]

I am the structural engineer for an HVAC project where we are setting a large air handling unit on an existing hospital roof. The roof is over a single story portion of the bulding and more than 20 feet from the nearest three story portion. The steel beams are raised approximately 15" to 24" above the roof line, supported by steel pipe posts that are bolted to the existing roof beams directly above existing columns. Since welding was not permitted in this area, the posts could not be simply welded to the existing columns. Oversized baseplates were used to bolt to the roof beam top flanges.

The existing below the steel is fireproofed and the code official has determined that the dunnage steel must be fireproofed as well per table 601 (IBC 2009). I am interpreting the structure to be a rooftop structure under Chapter 15 and required only to be of non-combustible construction. I can find no reference to dunnage steel in the Code. I have never seen fireproofing required on dunnage and neither has anyone I've discussed this with (fabricators,architects, other code officials). Does anyone know of a section of the code I can refer the local official to. He is requiring this or fireproofing.

 

[jar546]

Great question Tom and welcome to the forum. Let's see what type of responses we get for this one!

 

[Builder Bob]

Does footnote c of Table 601 apply?

c. Except in Group F-1, H, M and S-1 occupancies, fire protection of structural members shall not be required, including protection of roof framing and decking

where every part of the roof construction is 20 feet or more above any floor immediately below. Fire-retardant-treatedwood members shall be allowed to be used

for such unprotected members.

 

[mtlogcabin]

I am interpreting the structure to be a rooftop structure under Chapter 15 and required only to be of non-combustible construction.

It would have to be enclosed inorder to be a rooftop structure

ROOFTOP STRUCTURE. An enclosed structure on or above the roof of any part of a building.

The existing below the steel is fireproofed and the code official has determined that the dunnage steel must be fireproofed as well per table 601 (IBC 2009).

If I am following you correctly all this is is frame work supporting an HVAC unit then 601 does not require the steel to be fire proofe beacause it is not part of the primary structural frame supporting the building, roof or floor



PRIMARY STRUCTURAL FRAME. The primary structural frame shall include all of the following structural members:

1. The columns;

2. Structural members having direct connections to the columns, including girders, beams, trusses and spandrels;

3. Members of the floor construction and roof construction having direct connections to the columns; and

4. Bracing members that are essential to the vertical stability of the primary structural frame under gravity loading shall be considered part of the primary structural frame whether or not the bracing member carries gravity loads.

 

[TomLeonardPE]

Does footnote c of Table 601 apply?c. Except in Group F-1, H, M and S-1 occupancies, fire protection of structural members shall not be required, including protection of roof framing and decking

where every part of the roof construction is 20 feet or more above any floor immediately below. Fire-retardant-treatedwood members shall be allowed to be used

for such unprotected members.

Thanks Bob! Unfortunately the framing is less than 20 above the first floor, so the code official won't let me use this argument.

 

[TomLeonardPE]

Thanks for your response! The Unit on the dunnage is an enclosed, accessible air handling unit which the code official agreed can be unprotected. My argument was the framing was part of the enclosure and he did no concur. Also, section 1509 covers other types of structures such as water tanks, spires, etc. but NOTHING on HVAC dunnage. I also went with the secondary structure argument but he feels that since the posts come down on the existing columns (but are connected by bolting to the beam flanges), they are part of the primary structure. Very frustrating.

 

[mtlogcabin]

Very frustrating

Yes it is

What Type of Construction is the building?

 

[brudgers]

The code official is being obtuse. The purpose of the fire protection is to prevent the building from collapsing. That's not going to be caused by the dunnage getting hot. It's probably got a safety factor of 10 or more...you could probably calculate it's adequacy when exposed to heat.

 

[TomLeonardPE]

The code official is being obtuse. The purpose of the fire protection is to prevent the building from collapsing. That's not going to be caused by the dunnage getting hot. It's probably got a safety factor of 10 or more...you could probably calculate it's adequacy when exposed to heat.

Thanks for all the responses. I have received a written opinion from the ICC that the dunnage is considered to be part of the HVAC unit and does NOT need to be fireproofed. The opinion stated that while this framing is not directly addressed in the code, it can be interpreted from sections 1509.4 and 1509.5.1 which address similar types of rooftop structures. Let's hope we see a black bar and dunnage specifically called out in the next revision.