Steel Floor Deflection

[asixth]

Hi, I am designing a steel floor system of dimensions 8000mm x 8000mm (27' x 27') where the deflection criteria is span/500.

Basically I have 360UB's (14in. deep I-sections) framing into 530UB's (21in. deep) which are supported by columns.

Should the span/500 be applied to each element independently, i.e. the 360UB spanning 8m should be limited to 16mm relative to the 530UB's it spans between, likewise the 530UB's should also be limited to 16mm spanning 8m between columns.

Or should the span/500 deflection limit be applied to the diagonal panel span. That is, the digonal span of the floor is 11300mm, so the deflection should be limited to 22mm, whereas in the above scenario, my total panel deflection amounted to 32mm.

 

[Lion06]

to each member individually.

 

[Lion06]

assuming it is JUST deflection you are checking. The girder's contribution to deflection does need to be considered when checking vibrations.

 

[civilperson]

The deflection limitation is for all components' deflections added together using live loads only.

 

[csd72]

L/500 is very stringent, is this supporting brittle finishes?

 

[Lion06]

civilperson-
I disagree. I don't know anyone who adds the simple span deflection of a filler beam to the deflection of the girder at the point where the filler beam frames in to get the "total" deflection of the filler beam.
You could end up with a square bay say 30' x 30' and have an allowable LL deflection of L/360 (or 1").
Using your method, you would have varying deflections for the beams depending where they frame into the girder (since the girder deflection varies along its span)? And you would limit the deflection of the beam at midspan of the girder to 0.5" since the girder could be deflecting 0.5"?

 

[csd72]

A little bit more info may be required:

You make a valid point regarding the diagonal deflection, this is something that most people overlook.

If this deflection limit is based on support of walls then the diagonal deflection may not be relevant unless you have diagonal walls as it is the curve of the floor under the line of the wall that is important.

 

[asixth]

Without giving too much away, the floor is supporting mechanical equipment with a relativley "light" live load of 2.5kPa.

I guess what I am trying to get at is a limit for the overall deflection of the floor.

I have seen in two-way flat slab systems that the diagonal span should be used when considereing the overall panel deflection and was pondering whether this philosphy of diagonal panel span has any merit in steel-floor design.

 

[Lion06]

I've never seen anyone consider it for one way slab systems in steel structures, but I've only been around for 2 years.