Mezzanine Lateral Stability

[palk7 EIT]

Hi,

I have an interior mezzanine (4 sides rectangular box). The framing goes like this with Steel beam, columns and Open web steel joist running perpendicular to the beams. As far as the lateral stability is concerned I can do moment frame in the beam to column lines on two sides, however in the Joist direction spanning direction, could I consider that a tie-joist at the column locations will provide stability to the structure in that direction? No exterior loads other than seismic base shear (will be very minimal as not in a seismic zone).

My question is since I dont have beams in the joist spanning direction could I consider the tie-joist (bottom chord connected to columns) to provide lateral stability to the mezzanine in this direction?

 

[KootK]

You could use the joists at the column lines for this purpose if, and only if, they're designed for that purpose. The tie joist business is for erection stability and would not, on its own, be sufficient to ensure the strength and stiffness that you need to stabilize the mezzanine. For that purpose, the bottom chord of the joist may well require more onerous bracing than the common joists do. You'd probably also want your columns to run all of the way up to the joist seat elevation such that the beams would tie into the sides of the columns rather than running over top of them.

 

[palk7 EIT]

Thank you KootK! I 've seen in some of the drawings where the Engineers noted that the tie joist to be designed for 5 or 10 Kips axial load, could I use this case and provide the note for the forces I would get in this scenario, it would be somewhere around 5 kips or less

 

[JLNJ]

You might consider using cantilevered columns. That way there is no need for moment frames which incorporate joists.

 

[XR250]

...or just add some beams in the other direction

 

[phamENG]

It's not just axial load, it's also moment on those joists aligning with the columns if they're going to form a moment frame.

How big is the mezzanine? Is it worth it to use OWSJ? I heard the other day some contractors around here are still having trouble sourcing them for small jobs. Might want to check that.

 

[KootK]

... could I use this case and provide the note for the forces I would get in this scenario, it would be somewhere around 5 kips or less

Yeah, more or less. Some of the things that you'll want to ensure happen:

1) Joist gets designed for the axial couple in the top and bottom chords implied by the end moment.

2) Somebody specifies the joist bracing to ensure that the bottom chord doesn't buckle when in compression.

3) Axial loads in joist chords are successfully delivered to the column at the connections.

4) The joist get designed to be not just sufficiently strong but, also, sufficiently stiff to preclude P-delta flop.

If there's still time to switch the affected joists to beams, that may be advantageous. At the least, it would be simpler and easier for you to manage. If the design requirements for the affected joists would make them a different product from the common run, they'll likely be less economical than the common run. That said, I don't know that they have to be different from the common joists for a small scale application. You may well be able to use a common joist and just brace the snot out of it.