Metal Building Foudnation Design
Metal Building Foudnation Design
(OP)
Recently I was awarded two small projects from two end users. The projects consisted of the design of some metal building foundations. In each instance the columns rested on a knee wall that was approx. 3’-0” high with a required frost depth of 4’-0”. In each instance I have approximately 15.0 kips placed at the top of the wall. I designed the foundations and sent them off to the client only to get irate phone calls back about the size of the foundations I selected. The issues at play could have easily been mitigated by making minor modifications to the building during the design but this is not what I was hired to do. I see foundation designs with similar loads (15 kips applied 8’ above the footing) and 4x4 footings being used. I know there is no possible way an engineer can justify their design.
I am beginning to realize that doing work on this end of my industry just isn’t worth the hassle (end user metal building foundation design). The clients can’t really grasp the idea of the forces at play and never really appreciate the difficulty of the problems that were solved.
I am beginning to realize that doing work on this end of my industry just isn’t worth the hassle (end user metal building foundation design). The clients can’t really grasp the idea of the forces at play and never really appreciate the difficulty of the problems that were solved.






RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
I usually work with contractors and rarely end users however, recently someone I used to work with became a sales rep for a metal building company and he is sending his clients my way. While I appreciate the thought and am flattered by the recommendation, I am beginning to realize that this might not be worth the effort.
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
Perhaps the depth of the footing is what they are crying about? If I was the designer and they wanted an engineering stamp, then I would have to design to the frost depth, period.
RE: Metal Building Foudnation Design
I don't know a solution for this. Maybe if everyone puts their foot down and won't design these foundations, the PEMB engineers will have to get involved to stay in business. Or owners will realize that the building needs to be on a foundation and you need to consider its price, too. But someone is always willing to take the money, put in a 4' by 4' foundation and be on their way.
RE: Metal Building Foudnation Design
I don't design these anymore either =- too much hassle for the money.
RE: Metal Building Foudnation Design
12' x 3' x 36" thick footings on the side walls. T.O.F. = 100'-0"
7'-0" x 7'-0" x 18" thick footings at the corners. T.O.F. = B.O. grade beam.
- 33" long anchor bolts.
- With footing centered on anchor bolts, the portion of footing outside the perimeter is below grade.
8'-6" x 8'-6" x 24" thick intermediate footings. T.O.F. = 99'-4".
These footing sizes are to resist excessive uplift.
This is not uncommon for me, especially with grade beam foundations.
Fortunately, I work with a very reasonable general contractor client. I do at least one PEMB foundation every month.
SteelPE... I'd also be concerned about the thrust on top of the 3' high knee wall. What was your thrust? Did your pier V-Bar account for this?
RE: Metal Building Foudnation Design
This complaint was more of a general complaint, not about a specific project. We usually check the vertical bars in the pier for the thrust. The can be an issue as we try to keep the bars a small as possible, so we will tend to use more bars vs larger bars in the peir.
Good news is that I was able to meet the client and I went through the problems with him and he seems to understand.
I don't mind doing these designs with contractors I work with. The projects are usually small and I can make decent money squeezing them in-between larger projects.
RE: Metal Building Foudnation Design
Examples:
Owner: "My last building having the same spans used only a 7 in. slab, yours is way too thick at 8 in." . . . but he fails to mention his 7 in. slab was post-tensioned, while the current design is conventionally reinforced . . . and he also says nothing about the design loading.
or
Contractor: "I've built many retaining walls of this height and not one of them had a base that large." . . . but he fails to mention none of them had a 1:1 sloping backfill which the current design considers.
I suspect your Metal Bldg owner is not presenting the whole picture. Perhaps his building with 4x4 footings used "hair-pins" or cross-slab connecting rods and yours does not?
Usually when owners and contractors make these accusations of over-design they're not comparing apples to apples.
RE: Metal Building Foudnation Design
DaveAtkins
RE: Metal Building Foudnation Design
From SteelPE's description, the columns are resting on piers that have tops that are 3' above the floor slab. Thus, you've got 3*thrust (kip-ft) of moment to take down to the footing.
RE: Metal Building Foudnation Design
DaveAtkins
RE: Metal Building Foudnation Design
While I understand the concept and I used to use hairpins before, I no longer use them (this is at the advice of some colleagues/mentors). We just find that they are too unreliable especially since they typically rely on the WWM to transfer the loads to the other side of the building. When we did use them in the past we would limit their allowable design capacity to around 10-12 kips
In the instance you give of forming a couple, the load on the hairpin will actually increase due to prying action (using passive resistance will only make the situation worse as the lever arm below the hairpin will actually be less than it is if you assume bottom of footing). In the instance I have given (3' knee wall and 4' frost depth) a 1k thrust at the top of the wall will 1.86 kips in the hairpin (assuming the hairpins are placed at the center of a 6" SOG). So it doesn't take much thrust at the top of the wall to negate the effects of a hairpin.
Just my $0.02
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
DaveAtkins
RE: Metal Building Foudnation Design
In regards to tie rods, if you have 40 kips of thrust do you just size the rods to resist this load or do you place some additional reinforcing to account for the elongating of the rods? If this load could be resisted by 1 square inch of steel(which is plausible) the elongation of the rod would be 0.0165 inches/foot of length. So for a 80' wide building you are looking at an elongation of 1.32 inches.
My colleague/mentor was the chief engineer for a very large metal building manufacturer and knows Jim very well, he still refuses to use them. Also in regards to tie rods, his theory is that by the time you are done trenching and placing the rods and encasing in concrete you might as well just make the footing bigger, then you don't have to worry about the elongation of the rods under load (which can be significant).
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
Seems like trying to deal with the overturning created by a 40k thrust (on each side of the building) would be significantly harder that just doing some trenching and adding alot more steel. There ain't no free lunch.
RE: Metal Building Foudnation Design
Dik
RE: Metal Building Foudnation Design
It seems that often the cost of the PEMB takes precedent and the cost of the foundation (and foundation design) is an afterthought.
Owners are sold on the notion that the "building" is so much cheaper but they (owners) don't know enough to ask about the foundation cost implications.
RE: Metal Building Foudnation Design
RE: Metal Building Foudnation Design
It gets even skinnier... I've had occasion to work with a PE that came from a family PEMB business. They would apparently shop suppliers for steel elements that just barely satisfied the lower limit of a certain gage, and then buy railcars of it by the ton