Manufactured Building Tie-Downs

[spats]

Does anybody have any experience designing tie-downs for a manufactured building? I'm interested in the analysis and design procedures, not product literature. I'm in Florida, where wind is a real issue.

Also... I started reseaching it, and find all kinds of code requirements related to mobile homes. Are manufactured buildings and mobile/manufactured homes considered to be the same thing? This is a commercial building I'm dealing with, not a place of residency.

 

[rowingengineer]

spats,
I don't understand the lingo, sorry. are you designing a mobile building that needs to be tied down to the footings?


Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that they like it

 

[Ron]

Most of those buildings are required to have Florida Product Approval. Check there first. If you are helping a manufacturer to gain approval, then you'll have to explore several methods of tie-downs, including anchorage into a base slab, helical anchors, and small drilled piers.

Keep in mind that one of the most significant loads you have to resist with these buildings is the overturning moment. Further, assuming these are "utility, garage, or storage buildings, they will likely need to be designed as partially enclosed structures.

 

[southard2]

FHA loans now require a permanent foundation. Google it and you should be able to find their permanent foundation guide. Most mobile homes are still just tied down with the helical anchors but that is not a permanent foundation. I like to think of it this way. If you can pick up and carry away the foundation it is not permanent. Ahhhh heck here is the link.

http://www.hud.gov/offices/hsg/sfh/ref/sfhp1-9d.cfm

I would think the physics of tying down a commercial mobile home would essentially be the same.

If you are having one of those concrete prefabbed buildings usually a typical spread footing can be used with minimal doweling because the weight of the concrete building is so much.

John Southard, M.S., P.E.

http://www.pdhlibrary.com

 

[JedClampett]

When you say manufactured building, I think Pre-Engineered Metal Building (PEMB). If that is the case, the engineer or manufacturer will define uplift loads at the columns or walls. These loads are transferred into the foundation system. This is like any other building.
The hold downs you're worried about are only required for mobile type structures. If it's not driven to the site in one (maybe two) piece, you don't have to worry.

 

[spats]

Thanks for the comments, everyone.

This particular building is a 28' x 70' double wide "trailer", basically. It is constructed using wood framing, sheathing, etc. on a permanent steel I-beam frame. These types of structures are very common, and are often used for "portable"/temporary classrooms and construction trailers. In this case, it is a small office for a trucking operation. To the best of my knowlege, it is not considered to be a permanent building, nor is it a place of residency.

I have found some info on the web, most notably local & state codes that pertain to mobile homes. For instance, Florida Administrative Code (F.A.C.) Rule Chapter 15C-1 has installation/tie-down requirements per the Florida Department of Highway Safety & Motor Vehicles for mobile/manufactured homes. Would such rules apply to a commercial building as well?

The standards set forth in the Florida mobile/manufactured home requirements allow supports to be dry-stacked concrete blocks (2 or 3 courses) on small poured or precast footings, spaced at 8' max o.c.. A wood cushion block is used on top of the pier to support the steel frame. Metal straps connected to the frame are normally anchored with 48" to 60" helical anchors with stabilizer plates at the top of the anchor. Straps are to be angled at 40 degrees minimum from the horizontal to laterally stabilize the building on the dry-stack blocks.

In my case the owner wants a base slab, which I could use to anchor the building, as opposed to using helical anchors. However, to get lateral stability, I would have to extend the slab quite a bit beyond the structure, or I would have to also provide the helical anchors and use the slab for gravity only. That would be a waste.

Getting back to my original post, I'm most interested in analysis and design procedures. These structures are 18" minimum to the frame above grade, which means the wind can get under them, in addition to roof uplift. The lateral stability is a real issue for me, in addition to uplift. I'm sure they'll think I'm crazy if I ask them to mortar and reinforce the piers... again, it's not a permanent structure.

Any insights would be greatly appeciated.