Your design experience with heavy warehouse floors-Discussion request 7

[IJR]

Pals

I once came across a heavy warehouse floor, the type that DHL, TNT,FEDEX would use. Spans are typical 15m(45ft) and live loads are 5metric tons/m2 (250 psf).

In my first experience we used heavy steel girders in box shape, and made sense yet was heavy.

I saw one being desined using waffle slabs and heavy RC beams. Beams are 160cm(5.3ft). Makes sense but back-of-the-envelope calcs shows contractor will face heavy reinforcing.

Any other efficient system?

respects
IJR

 

[jechols]

Maybe post-tensioned beams and slabs? Not sure for that heavy loading and long span.

j

 

[DaveAtkins]

The industrial buildings I work on typically use composite steel deck with VERY thick concrete topping (total slab thickness = 8", for example), with steel beams and girders.

DaveAtkins

 

[SlideRuleEra]

Concur with DaveAtkins. Permanent steel decking with thick reinforced concrete supported by framed structural steel members is typical for operating floors at electric generating stations.

http://www.SlideRuleEra.net

 

[msquared48]

Heavy composite was my first thought too.

Mike McCann
McCann Engineering

 

[rapt]

IJR,

Post tensioned beam and slab would work well. Wide flat beams, probably 2 way beams for that span and loading, and preferrably bonded PT to get a better structure but that is sure to be ignored in USA.

It would be partially prestressed with significant extra reinforcement top and bottom for strength and crack control.

 

[DaveAtkins]

My problem with PT has always been the inevitable future remodeling project. PT severely limits where you can cut openings through a floor.

DaveAtkins

 

[hokie66]

Dave, that limitation really only applies when you don't grout the tendons. With grouted, fully bonded tendons, the problems of cutting openings is not substantially different than in a conventionally reinforced structure.

I think the most practical solution would be one of the two suggestions above, with the decision probably coming down to what is done in your area.

 

[shin25]

45' span with 250 psf live loading, seems like will require decent amount of prestressing. Design needs to consider long term camber, otherwise,floor may not look or ride well!

 

[jike]

We have done many poured in place conventionally reinforced, 12" thick flat slabs on 28 foot square grid for 400 psf live load plus fork trucks. I agree that 45 foot span will definitely need to be a PT slab.

 

[rapt]

Shin25,

That is a logical part of the design. The idea of using bonded PT and partial prestress will reduce the amount of PT required as long as all deflection conditions are checked properly (upward and downward) and it is easier to cut holes in as hokie66 pointed out. In fact, if hole cutting is a requirement, a secondary beam system could be included to give much smaller slab bays and the slabs would then be RC only with PT beams. Then the whole slab panels could be cut out later if required.

If they use decent software (I am not allowed to mention brand names but the one I am talking about does not come from the USA) that incorporates all of these checks properly to design it then transfer as well as long term deflection is one of the checks.

 

[H57]

In an industrial mezzanine that I was a part of the design was thick conc. slab on metal decking on steel joists and joist girders. It was designed for 250 psf and spanned ~70 feet. The joist girders were ~6' in depth and spaced at 24' o.c. to make this happen.

We didn't even consider using PT or reinforced conc.

 

[kslee1000]

H57:

Good point. Did you guys checked vibration?