Connections for Isolated Footings in Existing Typical Light-Frame Home 4

[b2bm8]

New here and new to structural engineering (when relating to residential construction) and have started with what I thought was going to be a straightforward project so forgive me if the question is too broad...

The structure is an existing conventional light-frame building 18' x 32' almost as simple as it gets except almost nothing is up to code. Modifications have been made to the foundation so that's the focus of our involvement. The owners basically just want us to draw up what they did and stamp it so the county accepts it. But there are issues.

The 'new' foundation is comprised of mostly screw jacks along the entire perimeter installed to level a badly unlevel home that had almost no foundation prior (a remediation typical done in this area by the beach usually w/o the knowledge of the county). Most jacks have a conventionally reinforced (in only one direction) 2' x 2' x 1' deep footing. Various shims in place all over and connections are inconsistent. My goal is to design some sort of connection between the jacks and beams + footings to take lateral loads due to wind and seismic. No risk of overturning and owners really don't want to replace the jacks. They fear continued heavy settlement.

1) Has anyone designed short columns on isolated footings to take lateral loads?
2) If trying to keep these jacks in place is even remotely a good idea, should I use the overstrength factor (2.5) for these connections for horizontal seismic loads? Otherwise, lateral loads due to wind control.

And what makes all of this feel rather pointless is it appears as though there are no floor or roof diaphragms.

 

[Eric C.]

The owners want you to draw up what they did and stamp it? This is an immediate red flag for me. Walk away from this one.

 

[b2bm8]

I'm feeling similar. Although to their credit they mentioned they'd be willing to work with alternative designs just are strongly against pouring a continuous spread footing mostly because difficult access makes it very cost prohibitive.

 

[atrizzy]

I'd echo what Eric said but would first provide the owners with a proposal to review the asbuilt condition and (as required) develop a foundation remediation design to bring it up to snuff with as little work as possible. If they agree to that and sign the agreement, I would proceed with the design scheme. If they won't even entertain that, then walk.

 

[MotorCity]

I am guessing the axial capacity of the jacks is well indicated on the jack itself. How do you plan to determine the lateral strength of the jack (assuming that it is designed to resist lateral load)?

Can you replace the jacks with small concrete piers and/or footings which you can control the design and capacity of?

 

[jayrod12]

I've never seen any of those adjustable jacks that would have any sort of appreciable lateral capacity. Maybe some cable cross braces with turnbuckles would allow for adjustability of the braces to accommodate continued movement.

 

[driftLimiter]

Yes, diagonal bracing is the approach used for this type of support system. The jacks don't take any lateral load.

Here are some ideas to consider for that. Link.

 

[JoshPlumSE]

I looked into something similar to the screw jacks for my house (which has a minor decades old settlement problem). In my case, the screws would have been expensive and overkill. Instead, I just added in some self leveling grout (maybe 1.5" at the deepest). Floor still has a minor slope, but isn't really very noticeable. And, we put down flooring that won't crack (which is what made it so visible in the first place).

I don't think there is anything wrong with the screws in terms of axial capacity. But, I definitely think you want to tie the system into any existing slabs or grade beams or such.

 

[RWW0002]

FYI - many commonly available screw jacks (especially the telescoping type) do not have ICC approval or an evaluation report and are marketed as "temporary supports not intended for permanent or primary support", even for gravity loads. While this does not mean they have no capacity, it is definitely harder to rely on these for permanent support.

There are a couple of brands that do carry code approval and evaluation reports for vertical loads. I know Akron is one (although only some of their products are code-approved)