Concrete Pan Joists
Concrete Pan Joists
(OP)
Is the concrete pan joist system still an economical system for concrete structures?
It seems like it was widely used in the past, but it is not as popular today. Is a flat slab and beam system more economical? Seems like you would save a lot of formwork.
It seems like it was widely used in the past, but it is not as popular today. Is a flat slab and beam system more economical? Seems like you would save a lot of formwork.






RE: Concrete Pan Joists
This system seems to be more prevalent in the southern US. In Texas where I used to work it was very common.
RE: Concrete Pan Joists
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Concrete Pan Joists
I think its drawback is that it is labor intensive--and labor is more expensive than materials these days.
DaveAtkins
RE: Concrete Pan Joists
From a material point of view, it seems like an extremely economical system but, unless a contractor can get repeated use of pans which he has purchased, he must rent them from others. This, together with high labor costs has more or less ruled out the pan joist and waffle slab system in my locale.
BA
RE: Concrete Pan Joists
RE: Concrete Pan Joists
I only got to help out on one, seems like a very interesting system and if you are going concrete this is a pretty economical way to do it.
RE: Concrete Pan Joists
It is a bit more labor intensive than flat plat, and takes taller floor-to-floor heights, due to the depth of the joists. Where there are height restrictions and more columns are not a problem, flat plate is attractive.
The first project I designed was wide module, and I see projects using it all the time.
See http://crsi.org/index.cfm/engineering/floor
RE: Concrete Pan Joists
As far as the OP's question regarding economics versus beam and slab system. It depends on the column layout/spans. We ran several framing scenarios for estimation, in last project, with beam and slab systems versus the wide module system. The wide module system ended up cheaper per square foot.
RE: Concrete Pan Joists
RE: Concrete Pan Joists
RE: Concrete Pan Joists
In the skip pan system, I assume you could vary the joist width to suit requirements, so it could be 56" + 6" for a 5'-2" c/c spacing. Or perhaps 56" + 8" for a 5'-4" c/c spacing?
The waffle slab has eye appeal and should be very economical for a two way system. Again, it would be nice if the pans could be larger than those I have seen.
BA
RE: Concrete Pan Joists
I'm not seeing offhand why it saves material. Is there a structural reason why? Maybe for longer spans the flat slab becomes too thick?
Why exactly is this? It seems like the structural depth of the floor would still be governed by the beam depth, which using the same grid for comparison, shouldn't vary much in depth between systems, right?
Thanks all for the responses. Do the pans come in standard spacings/modules?
RE: Concrete Pan Joists
That's right, flat slabs and flat plates, when they get quite thick for long spans, have a lot of concrete that is not needed, and dead load that is detrimental. Thus the voids in pan systems. I saw an old variation on this theme recently, in Turkey. A common method of construction there is to build a flat form, build sections of clay tiles where the concrete is not required for strength, then place the reinforcement and concrete ribs. They leave the clay tiles in place, so don't get much benefit of reduced dead load.
RE: Concrete Pan Joists
So maybe for spans > 25 feet the flat slab becomes excessive in thickness and a concrete pan joist system could be more feasible?
RE: Concrete Pan Joists
RE: Concrete Pan Joists
RE: Concrete Pan Joists
A somewhat belated response: I worked for one of the US's largest concrete subcontractors for many years. My observation is that the refinement of post-tensioned concrete has nudged one-way (pan) and two-way (dome or waffle) slab construction out of the picture for many applications. It is simply a matter of economics - P/T flat slabs require less labor overall.
Pan or dome slabs still have their place - typically in structures requiring very stiff floors. Custom dome slabs showed up on several semiconducter projects we were involved in, as the floor of a chip plant must be as vibration-free as possible - I believe the floor thickness was 36" overall - 30" deep domes with a 6" topping. Columns were massive and on a very tight grid (20' or so). Joist spacing varied to suit the projects and were spaced around 6 feet centers.
Most of the metal forms for one-way systems do NOT produce a finish suitable for being exposed in the finished structure. New FRP or steel dome forms can produce an attractive structural system, but little is being designed utilizing them.
Ralph
Structures Consulting
Northeast USA
RE: Concrete Pan Joists
The newest thing is "voided slabs" with a flat bottom and top, but using any of a variety of void-forming components inside. This is similar to the filigree systems of the past. One-way systems use hollow tubes, two-way systems use spheres or such in the middle-middle portion of a conventional 2-way design - with the intent being to remove unneeded dead weight.
RE: Concrete Pan Joists
Funny how some concepts cycle through over the years.
Ralph
Structures Consulting
Northeast USA