Designing an elevated concreteslab on pier and beam for a residence

[JOEPE48]

I have been contacted to design a new lakeside home foundation system utilizing a concrete slab supported by a pier (drilled shafts )and concrete beam system. Floor will be elevated approx. 5' above existing ground line. Floor space of 1800 to 2200 Sq. Ft. Hints on slab thickness, reinforcing will be appreciated Wind forces are of little concern. Existing supporting soil is sufficient at about4' deep.

 

[apsix]

It sounds like the ideal design job for a structural engineer.

If you are one, I suggest that you start the ball rolling by giving us your ideas on how to solve the problem.

 

[TXStructural]

Soil condition near a lake will probably NOT be sufficient at 4 ft depth, unless it is eroded to rock. You will need to examine the loads before making this determination, and will need to have a rough design to get those loads. What kind of soil do you have? A geotechnical evaluation will probably be required to know.

The house will be elevated, but will the space underneath be used for anything? Will it be open or enclosed? This will dictate some design decisions, like lateral load resisting system, pier spacing, and ongoing soil weathering, erosion, and wet/dry cycling.

Pier capacity may dictate spacing of piers. Closer spacing means you will have smaller structural members, and lower slab flexural strength requirements.

I'd pick a contractor now and find out what kind of pier/pile and forming system he knows, since that will dictate the structural systems available to you. You will likely have to use a commercial builder, since very few residential builders have the ability to construct an elevated concrete floor with any precision.

Do NOT use any kind of permanent form that is wood or metal if the underside of the slab will be open to weather. You might consider one of the expanded foam floor forms. You could then design beams in the formed shape, with the forms set level on low falsework. You would need to cover or enclose the foam once done.

Be sure you are not reaching beyond your expertise, and hire a structural if you see that happening.

 

[JAE]

Check with ACI - they have design criteria information.

Wind is always a concern.

 

[vandede427]

agree with aspix on needing an SE.

agree with TX about the soil. also, if it IS adequate at 4 ft deep, then why the drilled shafts?

agree with JAE. wind is always a concern.




Just because my diploma says bach of CE, I would never attempt to design a stormwater retention system.

 

[msquared48]

Seems like overexcavating to accommodate a deep spread/strip footing/stem wall scenario would be much more effective here than what amounts to a pile and grade beam system with a structural slab.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask