Pier/footing design
Pier/footing design
(OP)
Hello,
This seems like a dumb question to me but I'm trying to minimize the reinforcing in this pier beam design. The government client has set the parameters of what you see in the attached section I've drawn. There will be a rigid frame column sitting on this beam and I've included the worst load combination for thrust at the top of this beam. I understand how to check stability against overturning. I understand that the beam is being twisted to the left thus producing tension in the right face etc. I typically design true piers to spread footings and this is a hybrid for me and want to make sure I'm attacking it correctly. There is no soils report but I'm assuming 2000psf allowable bearing. Also not sure how minimum steel requirements per ACI affect this structural element? So, in summary, how would you design this member?
Thanks,
Dwayne
This seems like a dumb question to me but I'm trying to minimize the reinforcing in this pier beam design. The government client has set the parameters of what you see in the attached section I've drawn. There will be a rigid frame column sitting on this beam and I've included the worst load combination for thrust at the top of this beam. I understand how to check stability against overturning. I understand that the beam is being twisted to the left thus producing tension in the right face etc. I typically design true piers to spread footings and this is a hybrid for me and want to make sure I'm attacking it correctly. There is no soils report but I'm assuming 2000psf allowable bearing. Also not sure how minimum steel requirements per ACI affect this structural element? So, in summary, how would you design this member?
Thanks,
Dwayne






RE: Pier/footing design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
If designing the pier without a tie beam. It may act as both a column and a beam, adjust phi factors accordingly. Minimum steel will vary as well.
RE: Pier/footing design
This is the boiler plate section this U.S. State uses for all its salt/storage facilities. There are no left out elements, this is what they use. They have dozens of buildings like this and we are trying to break into the market there. I'm not holding out on you, this is what they use and my unfamiliarity with this type of foundation prompted the question.
RE: Pier/footing design
RE: Pier/footing design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
Going by that, I really see no way that the pier that you've shown can possibly hope to resist the imposed forces.
Also, the 16.2kips of thrust looks light for a 100' span with 20' bays - this, however, is just my opinion.
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
I doubt that shed is heated. Ct = ?
If it's government, they may just want it this way. Design a big ass footing.
RE: Pier/footing design
Given the loading and geometry shown (assuming the whole vertical reaction can be used to resist overturning) I figure you need approximately 8' of footing length to provide enough overturning resistance (and that doesn't include any safety factor). Are you comfortable saying that 8-10' of the footing length will contribute to overturning resistance before the top of footing moves laterally? I don't think I am.
RE: Pier/footing design
RE: Pier/footing design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
What I have is Movert=16200x7'-6"=121,500ft-lbs. disregarding soil pressure and surcharge loads like you stated.
Mresis=23,200 x 4'/2 + 4'x7'-6"x8'x150x4'/2=118,400 ft-lbs. (used 8' of beam)
F.S.=118400/121500=0.97
Thus factor of safety is not even 1.0 and I was shooting for 1.50.
RE: Pier/footing design
Ask the State's reviewing engineer's to seal it for you. And then demand calculations that back up their design.
RE: Pier/footing design
I guess I will go back to the salesman and tell him the footing is wholly inadequate for this application and let him decide what he wants me to do.
Thanks guys
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
also, the massive nature of the pier itself will probably cause excessive settlement and induce moments into the frame if there are in fact weak soils present. That's my two cents.
RE: Pier/footing design
RE: Pier/footing design
Well, I sign both building drawings and foundation drawings so my concern is real. I can't say my concern is the same for a foundation by others but when my stamp is on the drawing, I do the work required.
RE: Pier/footing design
Seems pricy to buy all that concrete when it could be done with more efficient layout, but forming and multiple pours can easily push to costs up to where the mass concrete solution becomes workable. I also agree it seems stupid to do all this without a soils report of any kind.
RE: Pier/footing design
RE: Pier/footing design
Any way to tie the grade beam to the 12" slab on grade at the columns?
We could use a PEMB expert on this forum. I hope that you'll come back to help us out with our PEMB issues from time to time.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
The precast panel is continuous, this DOT will never let tie beam penetrate the panel. I've been asked to come up with a new solution, crap, I'm a steel guy, not a concrete guy anymore.:) I don't even know if the DOT will accept my design as it varies from their standard detail and this is all just a bid. Some other SE, might think this works just fine as shown.
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
There is a Butler Manufacturing Company expert who monitors this site and does respond on some PEMB issues and some Butler issues. (Not I).
He has been very helpful on several occasions with information about Butler products and Butler design.
Jim H
RE: Pier/footing design
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
If you take out the step in soil, it calcs out for the loadings specified(not enough known for sliding check). I am willing to bet the step is not what this typical detail was designed for. Not how I would do it, but I think it works under certain circumstances.
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
RE: Pier/footing design
Do you mean the Butler/Computerized Structural Design, Inc. developed "Foundation Design and Construction Manual 2ed" from 1983/1984 or the Butler "Architectural & Engineering Manual" (much more recent but less engineering and more architectural) developed from the older "Product Reference Manual".
Jim H
RE: Pier/footing design
Actually our salesman finds projects like this to bid, in addition to the non-bid market we service. Most often these bids are building only but this was a foundation and building together as a bid package. Our salesman didn't dictate anything regarding the footing, it is just the approved DOT section they want to use. My final result was to redesign this section so it is workable and hope the DOT recognizes the shortcomings of their foundation section when everyone submits their bids. Our salesman is the point man on the project thus my reporting to him on the problem. Historically when we do things like this there is always at least one engineer involved on the DOT side. Whether they choose to take our suggestions, we will find out.
RE: Pier/footing design
The Computerized Structural Design one from the 80's is what I had in mind. In 2004, someone emailed me a scan of an old fax. It contained eight, very useful, pages of the manual. Based on the page numbers, it appears that there are at least 66 pages out there somewhere to be had.
Like SlideRuleEra, I'm a bit of a curator of antiquated structural engineering reference material. The Butler Foundation manual has been on my bucket list for a long time. If you know how I might obtain a copy somehow, I would be grateful to hear about it.
KootK
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Pier/footing design
KootK & jimstructures: Regarding your little side discussion, I have a copy of "Foundation Design and Construction Manual", but it's the first edition. I was with Butler in the 70's, and got to meet with Jim Fisher when he was working on the manual... a little trip on the wayback machine.
RE: Pier/footing design
About 125 to 130 double sided 8 1/2 x 11 pages. I do not have a scanned copy. 250 to 260 separate page sides in all.
We really need to move this to a separate thread.
Jim H
RE: Pier/footing design
The overall concept is not clear.
BA
RE: Pier/footing design
RE: Pier/footing design
If this is a salt storage shed, there will be lateral forces from the salt storage occurring above the floor. yes absolutely, the panel projects another 12' above the floor
•Are the precast panels acting as retaining walls to contain the salt? yes
•If so, are the panels relying on passive pressure from the earth outside the precast panels? Normally when I see panels like this they are not embedded in the ground, they are completely above ground. They are self-stabilizing. Because this one is below ground it can't help but put surcharge load behind it because I know when they compact the soil behind the wall the loads will transfer through.
•If not, what is the purpose of the precast panels? see previous
•Are the precast panels tied to the 12" slab? no
•What is the bulge at the bottom of the precast panels? Not sure what you mean here.
•How do the precast panels terminate at the bottom? These are standard L or T interlocking panels you see in these types of buildings and grain or fertilizer storage facilities as well. They have a flat bottom.
•Is there a concrete slab or footing under the precast panels? No, whether above or below grade, most often these type panels sit on grade and a poured slab is placed around them so there is no lip inside the building to catch the loader bucket on.
The overall concept is not clear.
I pulled this from a standard DOT detail for which they have dozens of these buildings. I understand what they are trying to accomplish, it just doesn't work at all on paper, thus I've proposed a different detail.