Metal Building Foudnation Design

[SteelPE]

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.

 

[XR250]

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).

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.

 

[dik]

I put the horizontal ties in the slab... usually as hairpins. If the thrust is too high, then I encapsulate the frame anchor rods with a plate with holes in it and use 'real' tie rods going across the slab to the opposite leg of the frame.

Dik

 

[HouseBoy]

I have limited experience with PEMB but have worked in offices where others have done many.
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.

 

[dhengr]

While the owner did pay a fair amount of money for their new all metal bldg., those PEMB s.o.b’s. cut every corner they possibly can to minimize the apparent cost of their product. And, their price looks pretty good at first glance, the initial price for walls and a roof over your head. They cut the code requirements to something below the bare bones, using their own design criteria, software, etc., and the bldg. may show distress or fail if it is ever really loaded to normal code loads. This combination of loads isn’t statistically very likely, so they are almost safe on that account. If you ever want to add a small load to the bldg. or make some changes, it is almost impossible for a real world engineer to justify the original design, let alone the changes. The long term deterioration caused by skimpy design and detailing doesn’t usually show up until after their warrantee has expired, so they are off the hook there too; and the way their self interested design and detailing screw everyone else in the construction chain for a bldg., well that’s someone else’s problem to deal with and explain, since the PEMB Co. already have their money. You invariably have to have this discussion with the owner and contractor, with little hope of convincing them that these large cost overruns aren’t all your fault.

 

[mbullism]

We've lost clients to the 4x4 footing guys... good riddance. No fun be admonished for doing it right.

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