6x6 Elevated on Concrete Pier

[XR250]

I have a customer who wants to support his 7 ft. long deck post on a 5 ft. tall 12”Ø concrete pier on top of a square spread footing. The footing has already been placed and is 8” below grade. The deck is braced by the house so there are no lateral loads on the post. My experience is that these systems don’t like to stay plumb and are very sensitive to the soil conditions. The soil in this spot is reportedly hard-pan clay. What overturning design loads would you design for? For starters I was going to use 2% of the column axial load as a lateral load at the top of the pier. Then I was going to assume some reasonable amount of eccentricity. In the past, I have always just shown a huge footing. In this case, a 24x24 footing already exists. I may just tell them “NO” and run the darn post down to the footing or use a very short pier.

Thanks

 

[KootK]

I'd typically go at least 5% for something like this acknowledging tolerances surely crappier than generic steel. I also feel that 2'x2' is questionable for the application. Is there any way to detail it to get a nominal moment connection between the pier and the post?

 

[phamENG]

XR - to KootK's point, I'd spec a Simpson moment post base between them.

 

[dik]

We used to use 'U' shaped straps cast into the concrete pier and secured with double headed nails so the beams could be adjusted in future and shimmed.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[XR250]

I agree, 2'x2' seems a little puny for this. I like the idea of the moment post base. Being that an Arch. is involved, I imagine that will get veto'ed (she likes the Simpson CPTZ's). I'm happy to veto the whole idea, however. I guess I could also run the post down to the footing and cast the Sonotube around it for aesthetics knowing that it will likely crack. Maybe nail some expansion joint around the post first.

 

[dik]

wood in concrete -> rot...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik