Masonry Firewall

[drewtheengineer]

So I'm at a meeting the other day when the client tells me I need to spec out a "break away bolt" at the firewall bracing connection. First, is there a such thing as a break away bolt and if so, how does it work. The detail is as follows.

An 8" cmu firewall fits in between a unit separation wall (2x4 bearing walls). Within the floor framing is an LSL rim bolted into the cmu, floor sheathing nailed to the top of the LSL. On both sides of the wall, the floor system runs perpendicular to the wall and are at the same level (no vertical step).

Assuming there is such a bolt designed to be good in tension but poor in shear, I don't believe this would help anything. Say the bearing wall on the opposite side of the unit were to fail, this would impose bending (tension, not shear in the bolt).

Any thoughts?

 

[ishvaaag]

It seems mere steel inserts are quite safe respect passing fire from one side to the other. You may want to check this freely available article

Electronic Journal of Structural Engineering, 1 ( 2001)

Fire behaviour of steel members penetrating concrete walls
I. D. Bennetts and C. C. Goh

It is a pdf file.

I agree in that except that you design the connections for the circumnstance of failure, you will see unwanted imposed moments at the connection. I think these things more properly be used following some kind of previous test, or sustaining code.

 

[Taro]

Perhaps the client meant "melt-away" instead of "break-away". The intent would be that a fire would melt the bolt so that collapse could occur on one side of the wall without dragging the other side down. I've never used this method, but have heard of people using nylon bolts that melt at 500 degrees Fahrenheit for this purpose.

 

[jec67]

This is a link to an earlier thread. It might be of some help to you.

http://www.eng-tips.com/gviewthread.cfm/lev2/21/lev3/68/pid/507/qid/84879

 

[valleyboy]

I work as an engineer in the UK, where out terminology is a little different from yours, so I may be well off the mark here, but bear with me.........

In firewalls in the UK formed in steel cladding, it is common practice to provide slotted connections between sheeting rail cleats and the sheeting rails. During construction, a combustible washer is inserted before the bolted connection is completed.

This washer combusts at temperature, effectively loosening the bolted connection. The resulting thermal expansion in the sheeting rails is dealt with by the slotted connections at the cleat. This means that there is no buckling of the sheeting rails, and the integrity of the firewall is maintained.

Is this the situation you have?

 

[shepherd]

Here's something along these lines i've seen by heckmann building products

BREAK-AWAY FIREWALL ANCHORS

Several building codes now require masonry walls to be secured, but to break-away in the event of a fire. To accomplish this we offer our non-wire anchors to be manufactured from Rolled Strip Zinc Alloys. The physical and mechanical properties are listed below. These anchors will melt at temperatures over 800 degrees Fahrenheit. The Rolled Strip Zinc Alloy is available in 1/8" or 16 gage. The chart below lists the physical and mechanical properties of the zinc strips and comparisons to other metals.

Shepherd