Bracing a Building on Pilings

I like this idea of building an open porch under the house, but above the ground...This increases the living space considerably and adds structural stability to the piling supports...

Better to bend, than break....

https://www.fehr.com/1-2-x-1000-ft-6x19-iwrc-stainless-steel-wire-rope-sw19s500-01000

That is a castle compared to what my neighbor has....

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https://www.fema.gov/media-library-data/20130726-1707-25045-4311/chapter6.pdf

This is probably not suitable for just guessing. Wind and seismic loads should be assessed.

Of SE's three examples, the third is the best design, and elegant as well. The first two seem lacking in diagonal strength.

Could you elaborate on this, please?

Essentially the inserted panels become bracing without adding to the static loading.

As others are indicating, for bracing to work, they are in tension and the minimum tension has to exceed the maximum deflection force to be effective.

Bracing with something like simple ply will mean that any movement will become both tension and compression within the sheet.

If the place has been built to correct "code", then it should be structurally safe and this treatment is for "comfort" or "liveability" by reducing the movement that is possible in the flexing piles.

Remember that the more rigid it is made, the more energy will be released when that structural limit is exceeded.

I have seen hangars and built sheds assembled with diagonal bracing, but the real stability comes when the cladding is attached. Any bracing in tension will be adding vector load to the attachment points at either end.

The panels do not need to fill the complete space, but essentially they reduce the effective height of the two adjacent piles. The panels could be perforated to provide a "privacy screen" or breezeway effect, or even only fill the middle 50% of the space, reducing the portion of the adjacent piles that can deflect to be 25% at the top and 25% at the bottom.

You can demonstrate this very simply. Get 4 pieces of timber (say 2 x 1, 2' long) and corner nail them to make a rectangular "box". When you push the diagonals, the box easily collapses. Then get a piece of 3 ply 2' x 12" and nail that across the open box with 3 nails each side. Makes little difference if done at the top, in the middle or at the bottom, though at the top enables you to also nail along that longer edge. (Try it again with 2' x 6" to get some idea of how effective this method can be.)

It seems to me the full panels would add quite a bit of strain from not only wind but tidal flood waters as well, possibly causing loading beyond design capacity resulting in catastrophic failure...not to mention I believe this would be a building code violation...

Cables are used to stay poles against a torsional load but have no effect on compressive forces

Rather than use cables he could employ the method I have seen used here for houses on tall pilings/stumps to reach the prescribed wind loading rating where the cross braces are steel rod in a cross. Instead of crossing the four rods are terminated in threaded ends fitting into a heavy walled round circle such that each can be tensioned individually. Placing these around the building at the corners stiffens the building and removes the swaying as some are always acting under tension and can be easily adjusted. They also make it easy to correct for leaning should ground movement occur.

He also needs to see if the sway is not a rotational sway imparted on the house by unequal wind pressure loadings from the rectangular shape. If so then use the same method to diagonally brace the house just under floor level.

I would suggest triangular gussets at each corner of each piling,if he is looking for a cheap fix.Bolt and glue the gussets to the pilings.I also recommend that he consult a local code enforcement official for advice on this.I presume the purpose of the elevation is to increase durability in storm surges.Another question comes to mind:How deep are the pilings?

The height is for flooding....he lives closer to the Bayou than I do. The Code Authorities passed his design the first time and it still wiggles...

When I see something that could use a brace I weld up a brace and attach with structural fasteners.

I did this a few weeks ago for a friends house. The back porch addition during WW2 (found newspapers) was stable, but literally screwed to the cedar shingles.

This one is made from 3/8" for the body and 1/4" for the diagonal.

These screws are pretty great and come in large sizes.

Cables only work if they are in tension and tension will stress whatever they are attached to. (Wood)

JAE's panel idea seems better all around.

Elevated, Piling and Stilt House Plans - Coastal Home Plans

Then, there's this: Cable Bracing for Steel Buildings | Owlcation may be applicable.

SE: Nice explanation of most of the necessary considerations!

X-bracing looks to me like the way to go. In commercial buildings I think they call this "wind bracing." Yes, definitely in pairs and on all sides of the building. Also consider clearance below the bottom brace pair.

This is exactly what the Planning process is for. In the UK, the applicant in the planning process would be duty-bound to provide the Local Authority a set of calculations by a qualified Structural Engineer as an accompaniment to the planning application prrior to the first hole being dug. The phrase <...has built...> suggests this loop hasn't been travelled, so does the <...neighbor...> tie a horse up to one of the <...pilings...>?

One would assume your neighbour (or anyone building) has gone to the local authorities and they have told him the requirements and he has engaged a professional, so if what he's doing is as instructed and required, so be it.

The fact that his dwelling is swaying in the breeze suggests, though, that he didn't quite play by the rules. Going the wise, and correct, route may not be possible?
You are obviously US (the pound and inches thing) but usually, the authorities for any region are quite thorough. Each region having different guidelines for different prevailing conditions - be they cyclones, snow or whatever - so best he tries google before he hands himself over to a professional.
Having said that, whilst cables may be easier, they only act in one direction and "swaying" is multi-directional. Maybe lattice bracing - "X's" - at each corner would offer a simpler solution.

Has your neighbor actually measured how far his stilt-house moves when it makes him feel uncomfortable? There may already be serious structural issues to address...

If he absolutely has to go that route, then advise him that only internal columns will intrinsically be (nearly) equally load-balanced due to dagonal cabling. All external columns will be un-equally balanced, in the x- and/or y- and z-directions, even if the diagonal cables are tensioned exactly equally.

Starting by using a gage to insure that all the cables are equally tensioned less than, say, 250 psi, is the proper approach. If that still allows too much movement, then incrementally increase each of the tensioned cables a small, but exactly equal, amount, until it doesn't feel uncomfortable.

In any case, be prepaired to equally re-snug the cables a little, one each year...

I understand some home-owners in (earthquake country) do it this way, with satisfactory results, so far...

To clarify for an internal pile, in simplified

horizontal plane PLAN View, ( and ignoring

the continuously long horizontal dashes ),

for any single value of tension T, in pounds-force;

where |+Tx| = |-Tx| = |+Ty| = |-Ty| and

(+Tx)+(-Tx)+(+Ty)+(-Ty) = Tnet = 0 lbf:

_________A

_________| +Ty

-Tx < - - - O - - - > +Tx => load-balanced, in the horizontal plane

_________| -Ty

_________V

but, for an external column,

where |+Tx| = 0, but |-Tx| = |+Ty| = |-Ty| and

(+Tx = 0)+(-Tx)+(+Ty)+(-Ty) = Tnet = -Tx, lbf :

________A______________________________ A

________ | +Ty___________________________ | +Ty

-Tx < - - - O - - - > (+Tx = 0 ) => -Tx => -Tx < - - - O => Tnet = -Tx lbf >< 0 lbf

________ | -Ty ___________________________ | -Ty

________ V______________________________V

Where the the (cables/turnbuckles/others) should be snugged-up once per year...

I would suggest the 15000 tensile more than needed as long as pull is braced

to create a box effect