footing question

[astidham]

Hello all,
i started digging the holes for my 24"x24" footings for piers, after 6 hours i got 1 hole 22" deep by 12" dia.
new plan tuesday i have a backhoe comming out to dig 2 strips 16" deep x 18" wide x 29' long for a continuous footing.
i will stub up some rebar for my piers.
the piers will be 12" dia ~12" to 18" tall with a simpson 6x6 post bracket installed.
I will bring 6x6 pt post up to level out my foundation support beams.
any suggestions or problems stand out?
Thank You

[Redoverfarm]

Been there and done that.  You could just bulkhead the footings within the trench.  The footings are mainly for downward pressure so if you have solid ground at the base of your footings you should be alright with this modifications. There is some lateral forces but you could always extend the width to compensate to say 36" long X 18" wide X16" deep and at the location directly under the pier just have him dig an extra 12"X12".    Not real sure where your location is but 16" deep might not be enough for colder regions where the frost/freeze level is 24"+.  The bottom of the footings should be below that area common in your area.  That is a lot of concrete to pour in a continuous footing that will not actually be used unless you decide to enclose the crawlspace later with block.

[astidham]

Thanks for the advice redoverfarm, the frost depth in this area of oklahoma is 16".
do you think running the concrete the total 29 feet would help with lateral support?

[Don_P]

That is why it is typically a code requirement in a prescriptive (non engineered) foundation. It will also make it easier to fill in curtain wall segments to laterally brace the piers (the second part of the prescription). Bending a 90 in the rebar thet comes up for the piers makes that connection FAR stronger. Actually just about any time you can hook the end of rebar makes alot of sense. I've tipped sonotube piers right off the footings withdrawing non hooked, wet stabbed, rebar.

[astidham]

If each of the footings are 16" deep x 18" wide and 36" in length with the rebar bent to a L shape protruding in the area of the sonotube pier,do you think this should be strong enough?

[Don_P]

Beats me. The vertical load and resistance is easy to figure. Stepping outside of the code for lateral resistance is really an engineer's territory. How are you bracing the 6x6 posts? Walls or wall sections or diagonal bracing are steps in the right direction

[astidham]

Im going to triangle brace the 6x6 post to the laminated beams by using wood, probably 2x6.
Anyone have an answer to my previous question?
"If each of the footings are 16" deep x 18" wide and 36" in length with the rebar bent to a L shape protruding in the area of the sonotube pier,do you think this should be strong enough?"

[John Raabe]

When you ask questions such as "is this strong enough" you need to be asking a professional who knows your local conditions and how your specific building will be built. One way to find out if you need to spend money on engineering calculations is to take your plans to the building department or to an experienced local builder.

What are you using for plans? Our CP plans have beam and pier layouts for most of the houses that will work in "standard" soil and climate conditions. These can be modified for local wind and earthquake specifications and there is usually a footing chart for modifications in different soils. Most of the pier and beam houses shown in the Owner-builder Gallery have used these plans.

If you are working from one of our plans you can ask your question in the Plans Support forum.

[astidham]

I am working from the 20x30 single story house plans fron this website, the plans call for a 24" x 24" x 12" footing.
my question is 18" wide x 16" deep x 36" in length as sufficient.

[John Raabe]

Rereading your posts I see that you are planning a 29' long continuous strip footing down each side of the house. On top of this you will be placing the 8" concrete piers. Is that correct?

[Redoverfarm]

John I think where the confusion is that he originally was digging the plans called for footings but was having difficulty and switched to having someone come in and dig a trench footing the length of of 29' X 18"W and 16" deep on both sides in lieu of individual peir footings.  The 36" came from me in an effort to lessen his concrete cost by pouring a continuous footing.  I also stated that he should have the backhoe operator to dig a 12" X 12" approx where his peir locations would be situated centered in the 36" long bulk headed footing.  The 36" was in lieu of his narrower footing and assist in some lateral movement with in inclusion of the 12" deeper pocket. IMO there was no need to pour a continuous footing unless he was later going to block up or build off of it for underpinning.   

[John Raabe]

John: So you were suggesting the strip footings be chopped into 36" long sections to serve as spot footings? With a couple of rebar laid in them to tie it all together there would certainly be enough bearing area - more than a 24" square footing.

[Redoverfarm]

astidham there is an alternative available to digging the plan footings with a little less effort.  I ran into the same problem recently digging footings for piers on my deck through shale.  After several hours of using a digging iron I had only dug 1 footings.  I had 8 more to go and figured there has to be a better way.  I rented a Bosch "Brute" electric jackhammer for about $50 a day and it tremendously helped.  It can be run off of a generator without any problems.  I used the 4" spade bit and was able to get them true to the demensions that I needed and only had to shovel the loose shale out of the hole.  Most rental centers should have one and at the rental price it sure beats a backhoe @ $50-60 an hour and you would not be disturbing the surrounding ground which would assist in the lateral movement of your piers/footings.

This is the tool that I was referring to:  http://www.cpotools.com/bosch-11304-brute-breaker-hammer/bshn11304,default,pd.html?start=2&cgid=bosch-breaker-hammers

[astidham]

Thank you guys for your help, the difference in cost from the 36" footers and the complete 29' strips for both is about $180.00 im not sure it its worth the extra money or not. also i will be extending upward with 12" sonotube.

[astidham]

thank you redoverfarm,the guy who is digging for me has a huge backhoe and is charging me $270.00 total. i will keep that in mind for when i make my addition and deck.

[John Raabe]

Tying you 12" dia. piers into a continuous footer with rebar in both will add extra rotational resistance over spot footings and also decreases the chance of differential settlement.

[astidham]

thanks John, Thats great news.
tomorrow we will dig, i will submit pictures in the owner builder forum.