Floor Framing Systems on Concrete Drilled Piers

[RareBugTX]

Hello:

Am designing a 5000 sf home in NW Dallas metroplex. Soil turned out to be expansive from soil report. Geotech recommended raised concrete slab on piers. Am new to drilled piers but upon looking at some projects that I have seen in the past I was wondering why it has to be a raised concrete slab. Floor plan is not a rectangle and am sure a cip slab and beams is going to be very pricey. I dont see a valid reason why a steel frame with metal deck and concrete topping can not be a floor framing system. Your input will be appreciated.
Rarebug

 

[jayrod12]

I would say you should be free to choose whichever floor framing type you want. If it were here (Canadian Prairies) we would likely do a wood floor supported on piles. Although to be fair we have full height concrete basements 95% of the time.

 

[KootK]

Structurally, I agree, steel satisfies the same soil/structure separation requirement that steel would. That said, keep an eye on:

1) Other possible requirements such as durability, fire protection etc that might affect costs.

2) The steel system will probably be a good deal deeper than the concrete. The skirt or whatever may cost real money.

3) I doubt that the concrete is all that expensive if done properly. It's still rough work, kinda like SOG. They seem to do a lot of this in Australia so it must make some sense.

4) I thought that the stock answer to this in TX was the post-tensioned SOG: Link



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Yes, there are a lot of options. If you use a slab supported directly by the piers, you would likely require void formers to protect against the swell. If it is to be conventionally formed, then you need a fair bit of clearance in order to get the formwork out. With permanent forms or with the steel solution, consider corrosion above the crawlspace. I have used the steel with metal deck and concrete solution, especially when the external grade varies significantly. I found that the use of short spans, with square hollow section posts, and channel beams, provided an elegant design. All my steel was hot dipped galvanized.

 

[thaidavid40]

If the floor framing is to raised above the top-of-grade maximum (swelled) elevation, why not frame the entirety of the floor with wood (either sawn lumber, glulams, etc)? That would obviate the need for a separate steel erection crew, and allow the work to proceed with just the carpentry framers. This is assuming that a suitable crawl space depth will remain below.
Dave

Thaidavid

 

[BUGGAR]

I suggest a clarification from the geotech. "Raised concrete slab" could be a slab poured on void forms. The slab is supported by the piers and the void form is not structural beyond supporting wet cement.