Structural Steel at Mechanical Equipment Screen

[MKALLAY]

On a project for a university building, an exterior wall is provided to enclose an area with rooftop mechanical equipment. The project is Type 2A under the 2018 IBC. The structural steel does not support any floor, roof, or equipment, but only provides lateral support for the enclosing walls (see highlighted elements in the image below).

Would such framing be considered part of the primary structural frame, and therefore require a fire resistance rating? Fire separation distance is not an issue.

 

[Yankee Chronicler]

2021 IBC:

[BG] 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.
4. Members that are essential to the vertical stability of
the primary structural frame under gravity loading.

[BG] SECONDARY STRUCTURAL MEMBERS. The
following structural members shall be considered secondary
members and not part of the primary structural frame:
1. Structural members not having direct connections to
the columns.
2. Members of the floor construction and roof construction
not having direct connections to the columns.
3. Bracing members that are not designated as part of a
primary structural frame or bearing wall.

The highlighted members in the graphic appear to be for the purpose of providing wind bracing for the screen walls. It's really up to the structural engineer-of-record to say whether they are primary or secondary but, based on the code definitions, I'd say they are secondary.

 

[MKALLAY]

Thanks, this is consistent with what I was thinking. Also, from the 2018 IBC definition of "Primary Structural Frame":

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.

Since these members are essentially lateral support for the (unrated) enclosure walls and contribute nothing to the stability of the primary frame, I believe they are excluded.

Good point to have the Structural Consultant confirm!

 

[klarenbeek]

Can the HVAC equipment under it be replaced? 2021 IMC:
306.1 Access for maintenance and replacement. Appliances, controls devices, heat exchangers and HVAC system components that utilize energy shall be accessible for inspection, service, repair and replacement without disabling the function of a fire-resistance-rated assembly or removing permanent construction, other appliances, venting systems or any other piping or ducts not connected to the appliance being inspected, serviced, repaired or replaced. A level working space not less than 30 inches deep and 30 inches wide (762 mm by 762 mm) shall be provided in front of the control side to service an appliance.

 

[MKALLAY]

Any large-scale equipment that needs replacement would be removed and replaced by crane.

 

[klarenbeek]

Any large-scale equipment that needs replacement would be removed and replaced by crane.

I understand that, but looking at the drawing it looks like the beam is directly above the equipment. Unless its modular equipment that can be slid out from under the beam in sections, the beam prevents removal of the equipment.

 

[MKALLAY]

Yes, modular units (air cooled chillers) are indicated at this location; but I'll pass on note to the PM to verify installation will be achieved with the steel as shown (Structure will be in place prior to equipment, so units will need to be installed the same way they will need to be removed).

Thanks for the note!

 

[ICE]

is the equipment operation reliant on airflow?

 

[MKALLAY]

Presumably yes - clearances, louvers, etc. have been coordinated per the MEP consultant.