Understanding loads on concrete floors 1

[madmantrapper]

I spent most of my career designing production machinery for a manufacturer. I am sort of retired now and am trying to understand loads on concrete. If you are designing a elevated slab which has a few steel beams supporting it on columns to a footer, how do you figure the loads. You have the dead load from the concrete which will be cured before the live loads are placed on it. How would you go about figuring the deflection? Do you figure the deflection from the dead load concrete and then the live load deflection after it is cured? How do you figure the added strength of the concrete to the live load deflection? I guess you can tell I am very confused.

Thanks,
Paul

 

[fegenbush]

For the design of the concrete slab itself, it is required to use factored loads per ACI 318 (assuming USA construction). An example of factored loads are 1.2*D + 1.6*L. For the deflection calculation of the concrete slab, service loads are used. An example of service loads are D + L.

The deflection calculations take into account the dead loads, including the self weight of the concrete as well as the live load for the most stringent location of that load.

The concrete strength is not a (direct) factor in deflection calculations just as in steel construction. The modulus of elasticity (which is partially determined by concrete strength) and the moment of inertia are the determining factors.

 

[a2mfk]

I would suggest reading these two books if you are curious about structural engineering, they are good reads for SE and non SEs alike....
Why Buildings Fall Down
Why Buildings Stand Up
Levy and Salvadori

 

[Bagman2524]

When the slab is poured there should be adequate shoring left in place until the concrete has reached it's design strength. I believe deflection is not considered for this curing phase. Enough shoring is used to ensure the concrete is not supporting any appreciable load. Once the concrete is reaches it's design strength dead loads and live loads are combined using factors specified in codes such as IBC or ACI-318 to determine design stress and deflections

 

[madmantrapper]

Folks thanks for the info. Last night a buddy of mine gave a book called Simplified Engineering for Architects and Builders by Parker and Ambrose. I had time to thumb through it today and I learned a lot from it. I will try to locate the two books that were mentioned here.

 

[hokie66]

If you can explain electricity to me, I can explain reinforced concrete to you. But since we are both "sort of retired" now, I don't think we have enough time left.

 

[TDIengineer]

Good questions. Never too old to learn. And trust me, you are gonna love statics!

I often feel like more of an accountant than an engineer.. tracing loads. We are building accountants! That crossed with a lawyer to interpret the ever changing design codes.
Good luck with your studies. This is a great site for questions, come back when you have more.

 

[madmantrapper]

I have acquired some deck pan left over from a bridge job in NJ. I have the measurements and am trying to find the specs on them. I have looked thru manufacturers data and can not find a match. Does anyone know of a way to figure this out? I have not undone the bundles to see if there is some type of manuf. stamp, I try that tomorrow.

Thanks,
Paul

 

[TDIengineer]

Measure the height of the flutes. Measure the spacing between flutes. Measure the low flute width and the high flute width. From that, engineers on this site may be able to steer you in the right direction.

See attached sample from a decking catalog showing the dims typically provided that define the deck.

 

[madmantrapper]

Ht of flutes 2 1/2 "
8" repetition
top flute 3 1/2 " wide
bottom flute 2" wide
1 1/4" vertical between flutes

Hope this helps

Thanks
Paul

 

[madmantrapper]

I don't know if there is a way to edit a post.
Anyway the pans are 36" wide and 7' long.

 

[IsaacStructural]

I took a quick look through my Vulcraft manual and didn't see a deck type matching those you've described. If you can find a logo that would obviously help, otherwise you have to kind of go brute force, and just look at each manufacturer. Most manufacturers have their decking catalogs available online, and these include dimensions as well as geometric properties, like moment of inertia.

Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[madmantrapper]

Isaac,
Thanks for looking. I looked thru a few websites trying to id but no luck. I will look tomorrow and see if I can find any clues, I'll also try to get the gauge.

 

[CANPRO]

Just out of curiosity, are you actually trying to design/build something with this steel deck?

 

[madmantrapper]

I'm thinking on it. I have time on my hands these days and I have a slope out back that I am thinking of building a parking area on. I just acquired the deck pans for free.

 

[TDIengineer]

If you can find the gauge, I would say you could safely assume design values for a W2 deck..

You can get as much as 400 psf capacity depending on how thick you go. If it is even 20 gauge you can make it work for a parking surface. You'll just have to control your purlin spacing and thickness of cover.

I always like those stories where someone gets about 500$ of free construction materials, and then spends $10,000 just to use it.

 

[madmantrapper]

OK it mic's at about .039, must be 20 gauge.

 

[madmantrapper]

What are the chances of a company roll forming deck pans for one job? I can't find anything even close to the dimensions I have. The job must have been rather large because I have about 900 square feet of pan. I've compared ASC, Vercodeck, and Vulcraft. Can anyone recommend others to try?

 

[civeng80]

madmantrapper
Good on you. Its good to be semi retired and planning projects.
Incidently those books mentioned will not explain reinforced concrete, there just an introduction to structures, probably useful as an introduction to structural engineering in general.
Hang in there, the basics of rinforced concrete are not that hard to learn.