Light-framed 3-hour interior load-bearing firewall with large eccentric loads.

[haydenwse]

I have an architect who has specified a 3-hour wall in a light-framed fire station (essential structure in SDS-D). On one side of the wall there is a 2-story living area with 13’ joists and roof trusses bearing on the wall. On the other side of the wall supports 59’ roof trusses. The reaction at the roof top plate from each truss is 560# and 2320#.

The architect has called out the wall as a single 6” steel stud wall with 3 layers of 5/8” GWB on each side. He has shown the trusses bearing on a ledger beam that is through bolted to the wall but this will defiantly not work.

I am not seeing any way to proceed with this concept. It would need to meet the requirements for a tied fire wall and I cannot see that happening.

Has anyone ever done anything like this?

 

[TheCommish]

is it a fire wall or fire separation?

2009 IBC definitions

FIRE WALL. A fire-resistance-rated wall having protected

openings, which restricts the spread of fire and extends continuously

from the foundation to or through the roof, with sufficient

structural stability under fire conditions to allow collapse

of construction on either side without collapse of the wall.

 

[cda]

Welcome,

should get some answers here, just give a few days, since it is the weekend!!!

 

[haydenwse]

is it a fire wall or fire separation?2009 IBC definitions

FIRE WALL. A fire-resistance-rated wall having protected

openings, which restricts the spread of fire and extends continuously

from the foundation to or through the roof, with sufficient

structural stability under fire conditions to allow collapse

of construction on either side without collapse of the wall.

It is a fire wall and I need collapse stability.

 

[cda]

More than likely a little into the project,

Seems like architect missed a code section, seems like the architect should be coming up with a solution

And guess they did not look at non separated mixed use to begin with? Or can it be looked at now?

 

[johnhl]

It looks like this fire station may be in Washington State which requires (WAC 296-305-06507) All sleeping areas in fire stations shall be separated from vehicle storage areas by at least one-hour fire resistive assemblies so the non-separated mixed use is not an option.

 

[TheCommish]

if it is a separation assembly then the collapse stability doe not apply

FIRE PROTECTION RATING. The period of time that an opening protective will maintain the ability to confine a fire as determined by tests prescribed in Section 715. Ratings are stated in hours or minutes.

FIRE RESISTANCE. That property of materials or their assemblies that prevents or retards the passage of excessive heat, hot gases or flames under conditions of use.

FIRE-RESISTANCE RATING. The period of time a building element, component or assembly maintains the ability to confine a fire, continues to perform a given structural function, or both, as determined by the tests, or the methods based on tests, prescribed in Section 703.

 

[Fort]

Where does the 3-hr fire wall come from?

Specifically which occupancies are being separated?

Why is it not just a 1-hr fire restitance rating?

 

[RLGA]

Agree with others; there really isn't enough information provided to be able to respond effectively.

 

[haydenwse]

It looks like this fire station may be in Washington State which requires (WAC 296-305-06507) All sleeping areas in fire stations shall be separated from vehicle storage areas by at least one-hour fire resistive assemblies so the non-separated mixed use is not an option.

John, you are correct. This is for a Washington state fire station.

As the structural engineer on the project I am not knowledgeable in all the fire related requirements; that falls under the scope of the architect. I have been informed by him that there needs to be a 3-hour fire wall that separates the sleeping rooms from the vehicle storage area. On the architectural building section, this wall is shown as a 6" steel stud wall with resilient channel and 3-layers of gypsum wall board on each side. It then shows a load bearing ledger outside of the GWB which supports the trusses on each side of the wall. The truss reaction on the vehicle storage side is 2320-lbs. at each truss.

I know of no way to provide a load path that will meet these requirements with or without the collapse mechanism.

 

[cda]

May be specing a three hour wall

May not have to be that much

If so may only be a barrier and the collapse requirement may not be required??

Maybe ask the ahj if it has to meet collapse requirements ????

The terms used are sometimes wrong and people also are use to calling things by the wrong terms

 

[RLGA]

Per Section 706, a 3-hour fire wall would be required between a Group R-2 and a Group S-2. However, I question the need for a fire wall. I seriously doubt the size of this fire station would require a fire wall to separate it into two buildings. The only reason I could see that the residential portion would want to be separated from the rest of the building with a fire wall is to avoid the installation of sprinkler system--required for the Group R--in the remainder of the building.

If the separated occupancies method is used, then only a 1-hour fire barrier is required, as previously mentioned; thus, the structural stability, as required for fire walls, would be a nonissue.

 

[cda]

http://app.leg.wa.gov/wac/default.aspx?cite=296-305-06507

(1) All sleeping areas in fire stations shall be separated from vehicle storage areas by at least one-hour fire resistive assemblies.

(2) Sleeping areas shall be protected by smoke and carbon monoxide detectors.

[statutory Authority: RCW 49.17.010, 49.17.040, 49.17.050, 49.17.060 and 29 C.F.R. 1910.156, Fire brigades. WSR 13-05-070, § 296-305-06507, filed 2/19/13, effective 1/1/14. Statutory Authority: RCW 49.17.010, [49.17].050 and [49.17].060. WSR 96-11-067, § 296-305-06507, filed 5/10/96, effective 1/1/97. Statutory Authority: Chapter 49.17 RCW. WSR 88-14-108 (Order 88-11), § 296-305-06507, filed 7/6/88; Order 77-20, § 296-305-06507, filed 10/18/77 and Emergency Order 77-24, filed 11/17/77, effective 12/17/77.]

 

[steveray]

Fire rated wall vs. firewall vs. fire barrier vs. etc......a fire wall creates separate buildings and needs the structural independence......Sounds like you only need a fire barrier (separating occupancies) which would not....But would need more information to be sure..................Can you have a "slip track" bearing wall?

 

[haydenwse]

Fire rated wall vs. firewall vs. fire barrier vs. etc......a fire wall creates separate buildings and needs the structural independence......Sounds like you only need a fire barrier (separating occupancies) which would not....But would need more information to be sure..................Can you have a "slip track" bearing wall?

I will get some more info from the architect to try clarifying the issue. I do know that the sleeping areas has sprinklers.

for the sake of discussion, if I do not need to provide for collapse on either side I am still unsure how to provide bearing support for the 2320 lb. truss reaction if the ledger needs to be put outside of the 3 layers of type-X. That is 1.875" of gypsum. It also adds a large eccentricity to the connection that is a problem to resolve into the wall. Can the ledger interrupt the GWB and be placed on the face of the studs?

 

[haydenwse]

Can you have a "slip track" bearing wall?

I am unsure what you mean by a slip track bearing wall. I use slip tracks at the top of wall to eliminate any load from transferring from framing that passes over a non-bearing wall but do not see how it could be used in a bearing condition.

 

[steveray]

Looking quickly I may have confused slip track with resilient channel (My bad, it's Monday after a long weekend for me).....As long as it is not a true firewall or vertical exit enclosure, the framing should be able to interrupt the membrane as long as it can be equivalently protected....

I am unsure what you mean by a slip track bearing wall. I use slip tracks at the top of wall to eliminate any load from transferring from framing that passes over a non-bearing wall but do not see how it could be used in a bearing condition.

 

[MASSDRIVER]

I'm just an idiot carpenter, but believe it or not I built something similar to this a few years back.

Their solution was independent modules. Shear and load was provided by a moment frame on one side that carried the 2 story living area floor and roof, and a taller assembly on the vehicle side that carried the roof. The firewall extended past the roofline as a parapet.

The wall had to be built and rocked first.

As an aside, it sounds like typical firefighter freak out requirement. Surprised they didn't want a 6 hour wall impervious to SR-71 fuel.

Brent

 

[haydenwse]

As long as it is not a true firewall or vertical exit enclosure, the framing should be able to interrupt the membrane as long as it can be equivalently protected....

It is a true fire wall and must have collapse protection. I have brought the architect into the discussion and I have with his permission attached his response to the comments in this thread. I will follow up this post with another that has the architectural building section.

(Arch of record) Great String of responses!!:

All are pretty much correct.

1. This is not a separation wall or the one hour due to occupancy separation.

2. The issue is that the Station is Rural and on a limited (water) well. Per Code we must sprinkle the building, However without capacity to do so (the well limitations) we have to get creative.

3. Discussion with the Building official a Fire wall (creating (2) two “buildings” (3 hour) would be allowed.

4. This is where the (3) three hour wall comes into play. Separation of the R-3 from an S-1. We are sprinkling the Residential R-3 side with a 13d system which the well is capable of handling (hopefully) maybe a tank and pump will be required but this is small (tiny) compared to if we were required to sprinkle the entire building to a full NFPA 13 system.

5. So the 3 hour wall. These are difficult to do, I understand and therefore need your help in design the connection points.

6. The 3 hour wall needs to frame (be rated full height.) And to elevate the “parapet” requirement we will be required to “one hour” the ceiling a min of 10’-0” in each direction. We can use a proprietary GWB (5/8”) product on the lid to accomplish this. (or (2) layers of type ‘x’) right now going with the proprietary rock so we don’t have (2) layers over the entire apparatus bay.

7. Now the difficulty of attachment of the roof trusses and the floor system, yes it’s my interpretation that if one side burns it could collapse but the other side should remain.

8. It’s my interpretation that the wall can be load bearing and support either side of the walls structural components. If a fire was to occur on one side the trusses and other portion of the building would fail Collapse but would not “burn” through the “3” hour wall. I’m not seeing this “3” hour wall failing if one side is burning.

9. This is where the leger we discussed (metal ledger angel) mounted to the studs holding up a wd ledger plate that’s attached to the trusses and floor etc.

10. The extreme case would be to have a wall or bearing separate and on each side of the “3” hour wall but we are trying to solve this more simply and only have the “one” three hour wall do it all.

Not simple! very complex, but we can solve this. Yes I agree that there are additional loading on this wall in the event of collapse we will need to take this into consideration.

 

[cda]

10. The extreme case would be to have a wall or bearing separate and on each side of the “3” hour wall but we are trying to solve this more simply and only have the “one” three hour wall do it all.

Built the three hour wall

Built a non rated wall on each side and build the building??

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[cda]

How many sq ft is this thing???

 

[cda]

More than likely this is going to cost more money than sprinkling the entire building

 

[RLGA]

I understand the classification of a Group R-3 (congregate living facilities with 16 or fewer occupants), but why the classification of Group S-1? Do they plan on performing vehicle repairs in the apparatus bay? If not, classify it as a Group S-2 enclosed parking garage and the fire wall rating drops to 2-hour. Then the type of system that MASSDRVER was describing could easily be done, since there are many 2-hour assemblies like that available.

 

[haydenwse]

I have attached the plan, building section and 3-hour wall section. There is a sleeping area in the 2nd level between grids 1 & 2. One possibility that I am looking at is using the wall on the left side of the hallway for support of the level 2 joists and cantilevering them out to the fire wall so that I do not need any attachment at level 2. This would make the 3-hour wall 18' to T.O.Wall.One of the biggest structural issues I have is how to support the 2320lb truss reaction with the GWB between he wall and ledger. One possibility is to change the studs from heavy gage 6" load bearing studs up to 18' and then use a non-bearing assembly with 1.625" studs between the trusses with the left side aligned. That way I can let the trusses bear on top of the wall and only need to carry the 500lb reaction on the ledger. I assume that I will need to do something to protect the top of wall at the bearing ledge and am not sure how to go about that. Any suggestions?

View attachment 1105

View attachment 1106

View attachment 1107

plan.pdf

building section.pdf

3-hour wall section.pdf

plan.pdf

building section.pdf

3-hour wall section.pdf