VB Steel that goes thru 1A Podium

[admiralArchArch]

We have a situation in a IA + VB R-2 building (VB on 3HR podium per IBC 2018 510.2) where a steel column is supporting loads from a beam that is only carrying loads from the type VB construction above. Does the 3HR steel structure protection apply to this column and beam? If so the whole height or only up to the 3HR separation? See a crude sketch below.

 

[Yankee Chronicler]

IMHO, 3 hours, and for the full height of the columns.

510.2 Horizontal building separation allowance. A building
shall be considered as separate and distinct buildings for the
purpose of determining area limitations, continuity of fire
walls, limitation of number of stories and type of construction
where the following conditions are met:
1. The buildings are separated with a horizontal assembly
having a fire-resistance rating of not less than 3 hours.
Where vertical offsets are provided as part of a horizontal
assembly, the vertical offset and the structure
supporting the vertical offset shall have a fire-resistance
rating of not less than 3 hours.

Your situation doesn't perfectly match this code provision, but the intent of a podium building is that the 3-hour upper deck of the podium building creates a new, "virtual grade plane," from which the story count begins anew for the different construction type of the upper portion of the structure.

The intent, therefore, is that the upper building is entirely supported on 3-hour construction.

 

[steveray]

IMHO, 3 hours, and for the full height of the columns.



Your situation doesn't perfectly match this code provision, but the intent of a podium building is that the 3-hour upper deck of the podium building creates a new, "virtual grade plane," from which the story count begins anew for the different construction type of the upper portion of the structure.

The intent, therefore, is that the upper building is entirely supported on 3-hour construction.

I would agree...and code is messy here, but that is the intent.....

 

[Yankee Chronicler]

I don't feel like chasing down the full code path and then trying to dredge up the discussions from when the podium building concept was introduced, but philosophically it can be argued that irrespective of fireproofing, that column extending up from the footing through the 3-hour slab to support the second upper story shouldn't be allowed at all.

 

[steveray]

I don't feel like chasing down the full code path and then trying to dredge up the discussions from when the podium building concept was introduced, but philosophically it can be argued that irrespective of fireproofing, that column extending up from the footing through the 3-hour slab to support the second upper story shouldn't be allowed at all.

I'm not sure that I would go that far as they allow the stair to pass through.....

1. 3.Shaft, stairway, ramp and escalator enclosures through the horizontal assembly shall have not less than a 2-hour fire-resistance rating with opening protectives in accordance with Section 716.
   
   Exception:Where the enclosure walls below the horizontal assembly have not less than a 3-hour fire-resistance rating with opening protectives in accordance with Section 716, the enclosure walls extending above the horizontal assembly shall be permitted to have a 1-hour fire-resistance rating, provided that the following conditions are met:
   1. 1.The building above the horizontal assembly is not required to be of Type I construction.
   2. 2.The enclosure connects fewer than four stories.
   3. 3.The enclosure opening protectives above the horizontal assembly have a fire protection rating of not less than 1 hour.
2. 4.Interior exit stairwayslocated within the Type IA building are permitted to be of combustible materials where the following requirements are met:
   • 4.1.The building above the Type IA building is of Type III, IV, or V construction.
   • 4.2.The stairwaylocated in the Type IA building is enclosed by 3-hour fire-resistance-rated construction with opening protectives in accordance with Section 716.

And to defeat the OP's proposal, I would use 510.2:
2.The building below, including the horizontal assembly, is of Type IA construction.

But I would also be concerned about the "penetration" but likely grout could solve that....

 

[redeyedfly]

I don't feel like chasing down the full code path and then trying to dredge up the discussions from when the podium building concept was introduced, but philosophically it can be argued that irrespective of fireproofing, that column extending up from the footing through the 3-hour slab to support the second upper story shouldn't be allowed at all.

???

By what reasoning? What if you split the column with a top and base plate bolted together at the 3hr deck? Obviously only the bottom column could need to meet the IA requirements and the top column VB requirements. Now what if the engineer decided to full pen weld the column instead of the plates? What's the difference between that and a continuous column fireproofed within the IA only?

 

[Tim Mailloux]

On the podium projects I have worked on, the podium / 3 hour rated horizontal assembly was designed with sufficient structural capacity so that the upper type V construction can bear right on the structural podium (hence the term podium). No need for additional columns / structure to support the 5B construction above.

 

[Yankee Chronicler]

But I would also be concerned about the "penetration" but likely grout could solve that....

Where you have a rated member passing through a rated assembly, I would want to see a listed penetration seal assembly.

 

[Yankee Chronicler]

I'm not sure that I would go that far as they allow the stair to pass through.....

But the stairs do not support the upper building.

 

[steveray]

But the stairs do not support the upper building.

They support the upper stairs which are part of the upper building....

 

[Yankee Chronicler]

They support the upper stairs which are part of the upper building....

Arguable. They certainly aren't part of the primary structural frame of the upper building.

 

[admiralArchArch]

Good discussion, seems like there is 50/50 split on what is necessary based on code intent.

 

[steveray]

Good discussion, seems like there is 50/50 split on what is necessary based on code intent.

I would say more like 25/25/25/25.....

 

[Yankee Chronicler]

I think there's good consensus that the column as designed has to be fireproofed to 3-hours. There's no consensus as to whether or not the column should be allowed to penetrate the 3-hour podium slab at all.

 

[redeyedfly]

I think there's good consensus that the column as designed has to be fireproofed to 3-hours.

In the Type I portion. No fireproofing in the VB section.

 

[admiralArchArch]

I think there's good consensus that the column as designed has to be fireproofed to 3-hours. There's no consensus as to whether or not the column should be allowed to penetrate the 3-hour podium slab at all.

Does this sway us in any direction?

602.1.1—Minimum Requirements: A building or portion thereof shall not be required to conform to the details of a type of construction higher that that type which meets the minimum requirements based on occupancy even though certain features of such a building actually conform to a higher type of construction.

 

[Yankee Chronicler]

Does this sway us in any direction?

Not really. That basically says if you can meet the height, area, and egress requirements for your design with type II-B construction, you don't have to make the entire building Type II-A even if you elect to fireproof certain elements.

A podium building is different. It's not one building, it's two building, one constructed on top of the other. The top of the lower structure (the "virtual grade plane" for the upper building) has to be 3-hour rated construction. That means that everything supporting it also has to be 3-hour rated. We can argue that by fireproofing that column to 3 hours the upper structure is still supported by 3-hour construction, so it's okay.

BUT -- that column extends through the 3-hour slab, which is supposed to be a complete separation between two separate buildings. The upper building is supposed to be built on top of the 3-hour slab, not supported through it.

 

[redeyedfly]

The upper building is supposed to be built on top of the 3-hour slab, not supported through it.

There is no material difference.

 

[steveray]

Arguable. They certainly aren't part of the primary structural frame of the upper building.

And they are also fire rated...

Does this sway us in any direction?

that would be general and 510.2 is specific….

 

[Yankee Chronicler]

And they are also fire rated...

The stairs aren't. They are enclosed in a fire-resistance rated enclosure (shaft).

 

[jar546]

I would love to keep this thread alive and get some more people involved. This is an excellent real-life question.

 

[wwhitney]

BUT -- that column extends through the 3-hour slab, which is supposed to be a complete separation between two separate buildings. The upper building is supposed to be built on top of the 3-hour slab, not supported through it.

To echo the thoughts in post #6, suppose you cut the column off at the top of the slab. Can the resulting penetration through the slab from the rest of the column be made with the requisite 3-hour rating?

If so, and that is done, what difference does it make if the upper portion of the column is supported by the lower portion of the column via being integral parts of the same member, rather than via a construction joint made up in the field?

Cheers, Wayne