Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
(OP)
I know, the title is a non-sequitur.
I have an architect who has specified a 3-hour wall in a light-framed fire station (essential structure). 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 I have 59’ roof trusses. The reaction on each truss is 560# and 2320#.
The architect has called out the wall 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? Oh, and just for fun, it is an SDS-D structure.
I have an architect who has specified a 3-hour wall in a light-framed fire station (essential structure). 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 I have 59’ roof trusses. The reaction on each truss is 560# and 2320#.
The architect has called out the wall 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? Oh, and just for fun, it is an SDS-D structure.






RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
What is an SDS-D structure?
BA
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
Not sure how you will get a 3 hour rating unless you have gyp running under your ledger .
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
BAretired, SDS-D seismic design category D. importance factor for seismic = 1.5, for wind, 1.25. in other words, the shear walls have high lateral loads with lots of nails.
The wall assembly is 6" CFMF 20ga minimum with resilient channel and 3 layers of type-X GWB on one side and 3 layers of type-X GWB on the other side. this assembly meets the 3-hour rating but I cannot see any way to support the structural loads and also make it stable with a fire induced collapse on either side.
manstrom. Whehehehat are CH studs?
The architect has shown the 3 layers of type-X GWB under the ledger but then there is no way to support the ledger loads. The reaction of each truss on the 59' bay is 2320lbs. This is not possible over 1.875" of gypsum.
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
(That's not a facetious question, by the way; if it's a requirement I'd like to know about it. Standing by to look dumb(er).)
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
http://www.usg.com/content/dam/USG_Marketing_Commu...
I would recommend 2 separate walls with a CH stud fire wall between them. You should no try to install a ledger spanning over 3 layers of gyp. It just won't work. The separate walls can meet the requirement for one side of the building to fall away and the other to remain (I am unclear on the specific architectural req't. It is either fire "wall" or fire "separation" that must do this. The architect should know)
Archie, I'm finding myself wrapped up in fire rating issues more and more lately. Fire ratings affect structural more than any other specialty. It is important that we have a good grasp on requirements. While the architect *should* know this stuff, it's us who ends up having to fix it.
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
It is the architects responsibility to specify the fire rated assembly and therefore is outside of my scope of work. once he specifies the assembly I need to make sure that it meets the structural requirements of this assembly. As a case in point, the UL assembly that he has specified calls for minimum 20 ga studs but just to carry the design load if it was concentric would require 14 ga 6" studs. in addition to that I need to find a way to get the bearing load into the studs without violating the requirements of the assembly such as (3) layers of GWB continuous.
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.
One thing that I found is that if you use the double wall system, then each of the walls only needs to have a 2 hour rating to get the 3 hour assembly. The problem with the double wall system is that the 59' bay is a single story with 18' plate height and it will need to stand with an 18' unbraced length. That will require some pretty good studs.
CMU may be looking better all the time.
RE: Light-framed 3-hour interior load-bearing firewall with large eccentric loads.