Fire protection of steel column in occupancy separation wall

[Yikes]

I have a building that is nonrated (II-B). However, there is a one hour occupancy separation (A-3 vs. S-1) wall inside the building, and there are steel posts inside this wall. These posts support a couple of floors and a roof. The wall construction is 1 layer of 5/8" X gyp board on each side of steel studs.

Question: can I put the steel post inside the wall without any further protection for the post itself?

In other words, is the fire rating only intended to separate the occupancies, and not to protect the steel that supports this wall?

I am concerned that someone might say, "after 30 minutes the fire will break through the Type X gyp board on one side, the steel post will heat up and turn into spaghetti, the wall will then collapse, and therefore your fire separation between occupancies was really only good for 30 minutes, not 1 hour."

What do you think?

 

[JBI]

Re: Fire protection of steel column in occupancy separation wall

I'm thinking the steel post will outlast the steel studs... :roll:

Are we talking concrete filled, hollow or other?

 

[TJacobs]

Re: Fire protection of steel column in occupancy separation wall

If it is an occupancy separation, it's a fire barrier. Since the column is a building component in a non-rated structure, only the wall needs the rating, not the column.

However, the supporting construction for fire barrier walls shall be protected to afford the required fire-resistance rating of the fire barrier supported (IBC 706.5). Hope this wall is on the ground floor slab...

 

[Examiner]

Re: Fire protection of steel column in occupancy separation wall

What you have is a Fire Barrier. The fire barrier (IBC 706) must be continuous from the floor it is bearing on to the underside of the floor above. If the fire barrier wall is bearing on a floor structure then the floor structure has to have the same rating as the fire barrier [ref: 706.5]. You did not state if your fire barrier is on a slab on grade. If it is bearing on a slab on grade then the wall must be rated not the structure that is within the wall IMHO. Unless your structure in the wall is required for the wall’s structural integrity then yes the structure in the wall to the floor deck above must be protected IMHO.

 

[Yikes]

Re: Fire protection of steel column in occupancy separation wall

My main goal was to find out if I was compelled to protect the column for one hour, in order to keep the structure above from collapsing and destroying the one hour occupancy separation. (Obviously, if the structure were to collapse, an occupancy separation would be the least of my worries.)

I suppose that in one sense, almost every non-load-bearing fire wall is dependent on the surrounding structure, below AND above, for its integrity. If the roof or floor above collapses, it is likely to take out the fire wall along with it.

FYI, the reality is that the building is fully sprinklered as required by municipal code (not by building code). I could probably use the sprinkler system as a one-hour substitution for the structure. What's important to me in this post is to learn from you all how to think, in general concepts, about the structural protection as it relates to occupancy separation.

 

[Examiner]

Re: Fire protection of steel column in occupancy separation wall

Let's keep the terminology straight. You have a fire barrier for occupancy separation. Fire barriers do not have to remain in place upon collapse of the building as a firewall would be required. In the IBC there are Firewalls, fire barriers and fire partitions. Only firewalls have to comply staying in place upon collapse of the building on either side. Fire barriers must be supported by construction having the same rating as the fire barrier. There are exceptions to the support requirements of the fire barrier for incidental use spaces. Fire partitions are your walls such as a rated corridor wall.

The structure of the Type II-B is not required to have fireproofing; therefore, the structural columns in the fire barrier do not require fireproofing. The kicker would be if the structure is supporting a fire barrier or is to be part of the fire barrier’s support.

 

[EPrice]

Re: Fire protection of steel column in occupancy separation wall

(Obviously, if the structure were to collapse, an occupancy separation would be the least of my worries.)

That is an important point. One of the differences between type II-B and more restrictive construction types is that the structural frame is not required to be protected. Yes, in II-B buildings, the steel columns will collapse sooner than they would in say a type II-A. The steel column located within an occupancy separation is no more important than the other steel columns, because, as you say, if the structure were to collapse, an occupancy separation would be the least of our worries.

I am concerned that someone might say, "after 30 minutes the fire will break through the Type X gyp board on one side, the steel post will heat up and turn into spaghetti, the wall will then collapse, and therefore your fire separation between occupancies was really only good for 30 minutes, not 1 hour."

My understanding is that the membrane on one side of a 1-hour wall should last 1 hour. The reason that a 1-hour wall rated for exposure from both sides has two membranes, is because we don't know which direction the fire will come from. In theory, the steel column located within the one hour wall should be protected for one hour.

 

[Examiner]

Re: Fire protection of steel column in occupancy separation wall

The fire rating of the wall is based on the burn through time. It takes one hour for the fire to go completely through both sides of the wall, not one side. If the fire is on one side of the wall, say the S-1 side, and that side’s structural framing beyond the fire barrier is not required to be protected then why do you see the need to protect the steel within the fire barrier? The entire structural frame exposed to the fire on either side of the fire barrier could possible fail before the wall is penetrated. IMHO you do not need to protect the steel within the fire barrier.

 

[Yikes]

Re: Fire protection of steel column in occupancy separation wall

My understanding is that the membrane on one side of a 1-hour wall should last 1 hour. The reason that a 1-hour wall rated for exposure from both sides has two membranes, is because we don't know which direction the fire will come from. In theory, the steel column located within the one hour wall should be protected for one hour.

EPrice, I thought that as a general rule of thumb, one layer of 5/8" type X was good for about 1/2 hour...?

 

[Yikes]

Re: Fire protection of steel column in occupancy separation wall

Examiner, what you say makes sense: I could have the column be completely exposed on either side of the occupancy separation wall - - so why shoud I worry about additinal protection when it's inside the wall?

Thanks for the clarification.

 

[EPrice]

Re: Fire protection of steel column in occupancy separation wall

EPrice, I thought that as a general rule of thumb, one layer of 5/8" type X was good for about 1/2 hour...?

Well, if it is a tested assembly, I guess it is hard to say. All we can say is that the wall passed the test for the required amount of time without the steel studs being compromised to the point where they cannot maintain the structure. In the case of load bearing walls, this would include the ability to continue to support the load. It is, however interesting to look at the values used for calculating fire resistance according to the rules of IBC Section 721. I can't find a section in there for steel stud walls, but the section on wood stud walls is 721.6.2. 721.6.2.1 states that the membrane on the unexposed side shall not be included in determining the fire resistance of the assembly. The value given in Table 721.6.2(1) for 5/8-inch Type X gypsum wallboard is 40 minutes, and the time given in Table 721.6.2(2) for wood studs 16 in. o.c. is 20 minutes.

 

[Paul Sweet]

Re: Fire protection of steel column in occupancy separation wall

If the gypsum board fails in less than an hour, the light gauge steel studs will fail and bring down the wall long before the steel column will begin to soften and bend.

 

[EPrice]

Re: Fire protection of steel column in occupancy separation wall

The fire rating of the wall is based on the burn through time. It takes one hour for the fire to go completely through both sides of the wall, not one side.

I don't agree with that. The membrane on the exposed side has to resist the fire long enough that the structural elements will not fail before the required time rating of the wall. In the case of a steel stud wall tested as a load bearing assembly, it seems to me that the steel studs would loose their ability to support the load before the fire burned completely through the non exposed membrane.

 

[Examiner]

Re: Fire protection of steel column in occupancy separation wall

If you want to calculate fire resistance then Tables 721.2.1.4(2) & 721.6.2(1) has values in time for standard Gypsum wallboard or Type X gypsum wall board.

Type X (5/8” thick) is good for 40 minutes. You can get a 1-hour UL non-load bearing wall assembly using 1 5/8” metal studs with one layer of 5/8” type X gypsum on each face of the studs. Per the Tables the gypsum gets 40-minutes per side. Therefore, by calculating the gypsum wallboard failure for the wall would be 80-minutes no counting the stud space. However, the wall is rated for 1-hour (60-minutes) and one side would hold for 40-minutes per the table.

To assume the studs will fail prior to the 1-hour rating just because the gypsum is good for 40-minutes is wrong. These walls are tested assemblies with certification from agencies who perform and certify the whole assembly.

There are tested assemblies for interior / exterior walls as well as bearing and non-bearing walls. We use what the assembly requires to be used. You may not agree with the layers required but the test states the amount listed to be used will result in the required fire resistance or protection.

 

[mtlogcabin]

Re: Fire protection of steel column in occupancy separation wall

The studs do not have to fail in order for a wall assembly to fail a one-hour test ( see below)

Check the link for FREE down loadable manuals from the Gypsum Association

http://www.gypsum.org/download.html

WALL AND PARTITION SYSTEMS

All walls and partitions tested and classified are

required to be at least 100 square feet in area with no

edge dimension less than nine feet. Surface

temperatures on the unexposed side of the test

specimen are measured at a minimum of nine locations.

When load-bearing walls and partitions are tested,

the applied load is required to simulate the working

stresses of the design.

Walls and partitions are required to stop flame or hot

gases capable of igniting cotton waste. The average

temperature of the unexposed surface is not permitted

to increase more than 250°F above ambient nor is any

individual thermocouple permitted to rise more than

325°F above ambient. A duplicate of the system (rated

for one-hour fire resistance or more) is fire tested for

one-half the specified fire-resistance period, but no

longer than one-hour, after which it is required to

withstand the impact, erosion, and cooling effect of a

hose stream.

Openings in walls for fire door frames and