Anchoring Pre-Manufactured Home to Concrete Piers

[rmartinat]

Hello! I am designing the anchoring system of a pre-manufactured home. This is located in the Florida Keys. The manufacturer shared the foundation loads, and as you imagined the anchors need to be designed for uplift and shear. The building is two-story high and is elevated 10' above the ground. Building is 15' wide by 45' long. Per the manufacturer's foundation loading, I have 17kips uplift (0.6WL) and 11 kips lateral (0.6WL) at my governing pier. The piers are 16x16 reinf. conc. The GC sent me a set of plans for a similar structure (same location). The engineer used a 4"x1/4" L-shape flat bar embedded in the concrete 10" and use bolts to connect the bar to the base of the house. I see that being effective for uplift; however, I dont understand how that flat bar be effective for the lateral reactions due to wind. Apparently this is a typical construction detail for this type of houses. I am not sure if I am overthinking this or if I am missing something. I understand the column drifting would dissipate some of that lateral force, which would make that lateral reaction go down some. I am not sure how much, though. Any help would be greatly appreciated. Thanks!

 

[phamENG]

Can you post some images of the proposed detail? By "L-shaped flat bar" I'm assuming you mean a steel angle (which I generally don't think of as flat). I have the opposite sense that you do - I can see how a steel angle embedded in the concrete would resist lateral loads (through bending in the angle) but based on your description it would have essentially zero uplift resistance as the angle gets pulled from the concrete. (Smooth steel and concrete have a low enough coefficient of friction to begin with - zero out the normal force and friction goes to...zero.)

I understand the column drifting would dissipate some of that lateral force, which would make that lateral reaction go down some.

For seismic, yes - codes are based on dissipation of energy through deformations and plastification. Wind is not the same. Seismic is internal to the building and the loads come from inertia of the building as the ground shifts under it. Wind is an externally applied force and that force won't go down just because the building deflects.

 

[phamENG]

1st - probably should have taken a snip of that to post it. I doubt Mr. Campbell gave the contractor permission to share those drawings (ownership of which is typically maintained by the designer), and I'd be very surprised if he gave you permission to share them on the internet along with an image of his seal.

2nd - I see what you mean. That is, indeed, an L-shaped flat bar. I agree that it has very little lateral capacity, but it's not zero. You could always analyze it to see what it can do.

 

[rmartinat]

You are absolutely right. The rush of the moment.

Here is a snip of the requested detail for anyone else that would like to see it.

Yeah, it does offer some resistance. There is friction also between the wood rim joist and the concrete. But I think is minimal compared to the 11 kip lateral wind force acting on that pier. The provided detailed (attached on a snip) is supposed to handle 7.5kip lateral. I doubt it can take that. But again, it seems those "L-shape flat bars" are standard practice. I was thinking maybe embed a C channel with thru bolts in the concrete embedded end. Thanks for your replies.

 

[phamENG]

I bet most of these houses were built using "standard practice." Just sayin'.