Bar Joist Deflection

[EngineeringEric]

Looking for some inputs.

I have a 36'-8" span supporting 4" NW Concrete. I am working with some tight constraints with depth and spacing and wondering what you guys would recommend for deflections tolerances? Mainly what would you recommend for a maximum deflection for similar span, for smaller spans we limit everything to 1/2" but that is unreasonable for this situation?

With the shallowest joist I am getting 1-1/8" LL deflection and 2" TL. which seems bad but it is less than L/360 and does not account for any rigidity or load sharing from the concrete slab.

Thank you,
EW

 

[mijowe]

You can camber to take care of the DL portion. L/360 is fine for a typical floor, especially if it will never see the full live load anyhow.

 

[a2mfk]

Be careful with deflection compatibility such as long span adjacent to a short span or joists next to load bearing walls. Many times we will reduce the spacing of the first couple of joists or otherwise play with the joist size if they are next to load bearing walls to limit deflection, this can play a big role in the steel deck installation.

 

[UcfSE]

What do you have below that would warrant an absolute deflection limit of 1/2-inch? Typical interior partition walls can have slip connections handling 3/4-inch without an issue. Do you need to use a stricter limit?

 

[EngineeringEric]

I might have worded the poorly. When designing shorter spans for commercial/residential projects.

As always, Thanks for the inputs!

 

[Triangled]

Almost all my floors are wood deck commercial industrial mezzaninesa so that is a big difference, the mass of your floor surely contributing to comfort. For my wood decks, I don't look to l/360 much once I get beyond typical spans for 2x floor joists. I could be totally wrong here, but I see l/360 as I kind of relic from days gone by. I'd be looking closer to the 1/2" you stated, could settle for 3/4”. I like the full live load and deflection compatibility considerations of mijowe and a2mfk above and would definitely take those into account. A 50 psf live load generating L/360 for a longish span bothers me. If I design the entire office floor for exit corridor live loads and L/360, then with mijowe's full live load considerations, knowing my offices will really never even see 50 psf live load, and therefore L/720, I'd probably call it good.