Masonry Fire walls
Masonry Fire walls
(OP)
We have a project that includes a fire separation wall. As per architects, the wall construction is this: Each side of the wall must be designed as two separate structures. This is not a problem. The issue is that there is a large bank of doors in this wall. Therefore, a third separation wall is to be placed in between the two other walls, which now have become steel beam and columns in lieu of bearing walls. This middle fire wall needs to remain standing if one or the other sides falls. This means that the wall needs to be designed as a cantilevered wall without accounting for lateral support from either wall.
Does anyone have any experience with such a situation? What have you done in the past? Is there something I am missing here? A 30 feet high cantilevered wall exposed to wind loading requires an unbelievable amount of reinforcing, if possible at all!
Any assistance is appreciated.
Does anyone have any experience with such a situation? What have you done in the past? Is there something I am missing here? A 30 feet high cantilevered wall exposed to wind loading requires an unbelievable amount of reinforcing, if possible at all!
Any assistance is appreciated.






RE: Masonry Fire walls
RE: Masonry Fire walls
I'm not sure I understand why a wall in the middle of steel framing (normally interior) would be exposed to wind, but in any event, the wall and it's foundation can be much lighter than what you would have with a cantilever.
RE: Masonry Fire walls
The reason the middle separation wall would be exposed to wind is that when one structure falls, the middle wall is now an exterior wall, exposed to windward pressures.
Thanks for the information on Factory Mutual - I have heard Hilti may have some help as well.
RE: Masonry Fire walls
I'm sure there are other sources, but the Tilt-Up Concrete Association has guidelines for "construction period" winds. They basically reccommend 70 mph for 135 mph regions and less.
RE: Masonry Fire walls
Thanks,
RE: Masonry Fire walls
http://www.beijingnews.com/courses/g130/g130.htm
In discussions with our architects, their is a UL assembly for a similar situation with "break-away" connections to each wall in apartment construction (wood frame). The thought is that each wall would provide lateral stability, with a clip angle attaching the firewall to each adjacent wall.
However, we can find no such connection/approved assembly for masonry walls (because masonry walls typically don't need such an approved assembly).
Does anyone know of a possible clip that would provide lateral resistance, but in case of failure, would fail before pulling the middle fire wall with it?
Again, any help is appreciated.
RE: Masonry Fire walls
RE: Masonry Fire walls
There are several ways to accomplish break-away connections. Following are two senarios and my solutions:
1. Beam/column framing along wall on both sides: I would hard connect the top of the columns to the wall with clip angles, and bottom bear the beams on column cap plates. Weld unheaded studs to the cap plate installed throuth horizontal slots in the bottom flange of the beam. The length and position of the slots is such that when the beam on the fire side sags under heat, the end will rotate off of the studs. The studs need to be short enough to clear the back of the slot in the beam flange so it can so it can pull free when rotated. The fire side will exert a sag force on the connections on the opposite side of the wall, which they must be able to safely resist. If the connections on the non-fire side are the same connection, the pull would deflect the wall over slightly until the stud reaches the end of the non-fire beam slot, and the wall will be safely held.
Because of roof uplift, it is also necessary to use something like Z-clips welded to the column cap that lap over, unattached, to each edge of the beam flange. They should be placed near the point of rotation so they don't restrict end rotation of the beam.
Diaphragm connections for forces along the wall can be made with the same unheaded studs through oversized holes or short slots in the roof edge angle, with no in/out connection.The edge angle can even be held a little off the wall so it can more easily bend the studs and slip off if the edge angle wants to go with the rest of the falling steel. If possible, I would try to avoid using the firewall as a shearwall, because these "break-away" connections become a little more problematic (unless you have a better idea).
2.Edge joist parallel to the wall: connect a horizontal plate with an short upturned lip to the wall that hooks under and around the top chord of the joist, at intermittent locations along the wall. The clip is light enough (gauge material) that if the roof structure on the fire side starts to sag under heat, the clips will deflect and the joist will pull free. The same clip on the opposite side prevents the wall from being pulled over with the collapse (the clip is strong in tension).
If both of these conditions occured simultaneously, you could probably even justify eliminating the studs at the beams (Z-clips only).
There is no reason why you couldn't use similar concepts while even using the wall as a bearing wall. Joists could be connected similar to what I described for beams, etc.
I can't say that these concepts have necessarily been fire tested, but the concepts are sound and are accepted by the fire insurers, in my experience. I'm sure you can probably come up with some of your own concepts.
RE: Masonry Fire walls
RE: Masonry Fire walls
See the following URL.
http://www.heckmannbuildingprods.com/PFire.htm
You can talk to one of their Tech Reps for more info.
RE: Masonry Fire walls
RE: Masonry Fire walls
You have expressed a concern that I have always wondered about.
I would guess that if the fire is away from the firewall and there is a partial collapse (away from the firewall), that the remaining structure and unmelted anchors would generally be sufficient to prevent the collapse of the firewall.
If the fire is adjacent to the firewall, the anchors would melt on that side of the wall and the unmelted anchors and structure on the opposite side would provide stability to the firewall.
RE: Masonry Fire walls
RE: Masonry Fire walls
The steel framing design to either side of the wall only needs to meet the fire rating design period. What happens after this is not as important as ensuring sufficient time for occupants to get out. Also if the fire wall does its job, then only one side will be subjected to failure whilst the other side supplies stability.
If you have doors in the fire wall, they need to be fire rated and self closing (also incapable of being propped open). If the doors don't meet the fire rating criteria, then you do not have a fire wall. Generally it is better practice not to have any openings in the fire wall.
AS4100 specifies design criteria for steel that needs to be fire rated.
regards
sc
RE: Masonry Fire walls
I was suggesting the use of break away connections for the multi-story applications, not the single story roof applications.
RE: Masonry Fire walls
RE: Masonry Fire walls
I also called my local state plan approval department and they basically said they will review and CONSIDER approval on a case by case basis only. They have not given a blanket approval to any one design detail, with or without the "melt away" anchors. This sounds pretty iffy to me and could entail a LOT of work.
Have any of you actually used these things? I'm sure that there are other ways to handle this, but I haven't found any yet, how about use'guys? Have you seen or used any details that work?
RE: Masonry Fire walls
I have successfully, from an approval standpoint, used connections similar to what I described in my January 23rd response above on at least a half-a-dozen projects.
RE: Masonry Fire walls