Drilling Holes in Joists 1

[drawoh]

We are trying to work out an optical alignment mount on a mezzanine up close to our ceiling. We are looking for attachment points to which we can attach a rigid fixture, preferably one not attached to our floor. Our floor is plywood and not very rigid. People should be able to walk around without affecting our alignment.

One possibility is that we attach cross braces to our ceiling joists. The cross braces keep the lower parts of our ceiling joists from moving side to side. The joists are rigid up and down. We attach our fixture!

I am mechanical, not architectural, but as far as I can tell, the joists are standard ones, welded from steel angle and bar.

How safe is it to drill 1/4" holes in the joist flanges?

JHG

 

[cap4000]

Do Not drill any holes anywhere on a joist. Depending on the Joist Specs you typically can only connect small loads to its Panel Points at the Diagonals. Consult a Joist Manufacturer in your area before you do anything. Any changes made should be in writing and done by a Licensed Structural Engineer.

 

[drawoh]

cap4000,

Thanks.

JHG

 

[Lutfi]

4000 pounds is a serious concentrated load to add to a joist especially if it was not designed for it. Drilling holes reduces the gross area of the joist chord. If the load is located away from the panel point, then you are introducing bending into the bottom or top chords of the joist which are theoretically are designed to carry axial loads (tension and compression).

I recommend that you get a hold of the joist tag (usually a thin and small aluminum strip) attached via a wire to the end of joist. It should have identification of the joist size, manufactures and joist mark number. Also measure the depth of the joist and the span. Also make free body diagram of the joist locating the concentrated load.

Call th joist supplier and provide them with the above data. They will give you a reading if you can add the load, or if you have to beef up the joist and they should provide you with details.

Another simple solution is to hire a local structural engineer and have him run all of this down for you.

Good luck

 

[haynewp]

I think you are asking if it is alright to put in add'l cross bridging to stabilize the ceiling joists above the mezzanine area. Can you put down mats over the floor and weld the bracing instead?