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). 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). When we did use them in the past we would limit their allowable design capacity to around 10-12 kips 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. 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). RE: Metal Building Foudnation Design DaveAtkins (Structural) 13 Apr 17 15:39 Usually when owners and contractors make these accusations of over-design they're not comparing apples to apples. Perhaps his building with 4x4 footings used "hair-pins" or cross-slab connecting rods and yours does not? I suspect your Metal Bldg owner is not presenting the whole picture. but he fails to mention none of them had a 1:1 sloping backfill which the current design considers. and he also says nothing about the design loading.Ĭontractor: "I've built many retaining walls of this height and not one of them had a base that large.". slab was post-tensioned, while the current design is conventionally reinforced. Owner: "My last building having the same spans used only a 7 in. I find they're usually leaving a piece of the design out in their comparisons. Many of us have received this over-design rant from an owner or contractor at one time or another. RE: Metal Building Foudnation Design XR250 (Structural) 12 Apr 17 17:56 But someone is always willing to take the money, put in a 4' by 4' foundation and be on their way. Or owners will realize that the building needs to be on a foundation and you need to consider its price, too. 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. I have to be the bad guy, similar to your experience. They'll give me four anchors with just enough area to meet the steel tension allowable, and no recognition of the concrete design. Four anchors, spaced on a 4 inch grid, sure, what the heck! I've tried multiple times and in multiple ways to get the PEMB supplier or the GC to do the anchorage calculations, and they've slithered out of it each time. It's like the PEMB designer is purposely making the foundations, and my favorite, the anchorage, impossible to design. SteelPE, if you do a search on my threads, you'll see this is a common complaint with me. RE: Metal Building Foudnation Design JStructsteel (Structural) 11 Apr 17 17:50 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). I know there is no possible way an engineer can justify their design. I see foundation designs with similar loads (15 kips applied 8’ above the footing) and 4x4 footings being used. 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 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. In each instance I have approximately 15.0 kips placed at the top of the wall. 3’-0” high with a required frost depth of 4’-0”. In each instance the columns rested on a knee wall that was approx. The projects consisted of the design of some metal building foundations. Recently I was awarded two small projects from two end users.
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