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

It sounds like the Residential side is fairly straightforward from the structural side, with the bigger concern being how to adequately carry the S-1 roof and maintain the integrity of both the rating and the structure. Could a heavy steel structure accommodate the load of the bay roof only? Might be more practical (and carry more weight) than another full length steel stud wall. Build an I-beam on columns sized for the load on the inside of the bay.
 
The 2nd floor framing for the residence side is straight forward but the architect wants a single wall to the roof. His concept was that both spans would need to be supported by the wall which would need to be designed as a tied wall. This would require that both sides have the lateral capacity to support the maximum axial force developed by the trusses during collapse (what ever that is).
 
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Could 8" solid filled CMU's be used for the 3 hr. rated wall & roof

trusses loading, and light-frame the Residential side ?



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steveray said:
One firewall cannot support both buildings.....Period....
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According to NFPA 221 it can.

Section 6.4 Tied Fire Wall

6.4.1 Placement - Tied fire walls shall be centered on a single column line or constructed between a double column lines.

6.4.2.1 - Structural framing on either side of the wall shall line up horizontally and vertically and shall support the roof.

6.4.2.2 - The framework on each side of the fire wall shall be continuous or tied together through the wall.

6.4.2.3 - The framework on each side shall be designed so that it resists the maximum lateral pull that can be developed due to framework collapse in ta fire on the opposite side.

6.4.2.4 - Tied fire walls shall be supported laterally by the building framework with flexible anchors.

This is what I think the architect is trying to accomplish but it would greatly increase the lateral load on the walls between grids 1 & 2. It would also require the use of interior shear walls on both levels to reduce the aspect ratio of the diaphragms.

The problem is that there is no clear guidance as to how to determine the loads for section 6.4.2.3. The failure mechanism due to fire for metal plate connected wood trusses is burn-through of the tension chord which may or may not also reduce the section of the top chord. Initially the top chord would have outward lateral translation until the ridge dropped to level. This would likely all go into toppling the grid 4 wall. After that, the top chord would go into tension but I have no idea as to how to quantify it.
 
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haydenwse,

I would recommend contacting a reputable truss manufacturer

and ask if they can assist you in performing the calculations of

the lateral loads of the chords.......It will be their product that

[ will potentially ] fail in a fire event.

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I would not calculate anything, that is the job of the RDPs. the architect just draw pictures, the structural engineer should be designing the wall and the connections for the loads in play
 
TheCommish said:
I would not calculate anything, that is the job of the RDPs. the architect just draw pictures, the structural engineer should be designing the wall and the connections for the loads in play
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I think he is the SE......
 
Re: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.

TheCommish said:
I would not calculate anything, that is the job of the RDPs. the architect just draw pictures, the structural engineer should be designing the wall and the connections for the loads in play
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Don't think much of architects? I agree the RDP should provide the calculations and details.

I looked briefly but can't find a UL or USG detail that included a single wall for bearing with a penetration.
 
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I think the architect thinks he is simplifying the design by going with the single wall. But it's just expecting too much from the poor little thing.

Load carrying modules are actually the simple solution, and faster to build.

I can see however where the door placement might interfere.

That wall is going to be 2 feet thick if it has to do all that.

Brent.
 
And what rating does any door and other openings have to be ???

Or is any opening allowed in a three hour wall???
 
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Any door(s) would have to be a 90 minute rated, and yes, ...openings

can be in a 3 hr. rated wall assembly.

Albeit, they're not typical because of the costs, but they are allowed !



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north star said:
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Any door(s) would have to be a 90 minute rated, and yes, ...openings

can be in a 3 hr. rated wall assembly.

Albeit, they're not typical because of the costs, but they are allowed !



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And if they want a glazing in the 3 hour wall to we the fire trucks???

Three hour glass????? Or rated shutters?
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In the `12 IBC, ...please refer to Table 716.5 for "opening protectives"

[ i.e. - glazing in fire rated doors ].

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To install rated glazing in a rated wall assembly , see Section 716.2

in the `12 IBC........Also, the glazing would need to be part of an

tested & approved wall assembly [ i.e. - Factory Mutual, ...U.L.,

or as approved by the Code Official ].

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2009

Looking at table. 715.5.

Does not look like they can have a window????

And does not appear you can put a window in any fire wall???
 
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