Coastal Home Construction

In that old pic, the cross bracing isn't really doing much, it's almost cosmetic IMO (I'm not a mech eng... I'm a cat).
Real crossbracing would be from base of one column to top of the other.
So, to me the new code looks like a simplification more than a real change.
Del

I don't know the Texas Building Code (hey, I'm a Damn Yankee LOL), but from a Structural Engineering vantage point I can say that a majority of your guesses are pretty much on the money.

First off, those braces are commonly called "knee-braces", not x-bracing or diagonal bracing. They add stiffness to the connection between the beams (or girders) and the columns. They also lessen the unsupported lengths of the beams and the unsupported height of the columns. Some people refer to theses columns as piers, or stilts, and even sometimes pilings.

I believe the reason the minimum height was raised to 16 feet above grade so as to allow the storm surge to pass underneath the structure as much as possible, thus minimizing the lateral forces acting on the building. Naturally, the column minimum cross-sectional size was correspondingly increase due to the increased unsupported height of the columns; had the column sizes not been increased the slenderness ratio of the member would have increased accordingly, resulting in a lesser allowable load carrying capacity.

I suspect that the inclusion of knee-bracing type of framing allowed designers and builders to "skin the cat" (so sorry Dell!) in terms of beam and column sizes. The new requirements now force the designer to "beef-up" both members, based on the actual unsupported spans and heights. Please note that the use of knee-bracing allow the designed to apply lesser unsupported beam (or girder) spans, and lesser unsupported heights of the columns. Another problem with the use of knee-bracing or X-bracing is that have to resist the surge forces as well as the impact of debris pushed by the tidal surges and the "snagging" of said debris, which would greatly impact the structure.

Now, with the inclusion of hurricane clips and anchors together with the blocking of beams, the new method of framing is much more robust than the older method of beam-to-column connectivity. Also, I suspect that there are more columns along a given beam or girder line than previously used, thus the lateral loads (and resulting bending moments due to portal frame & frame rigidity action at the joints) are carried by the multiple columns more efficiently. The new design, IMPO, allows the entire framing of the house to "flex" against the applied lateral forces of the wind and/or the tidal surge, much like the analogy of a "tree bending in the wind".

Without me personally viewing the new TX Building Code requirements, together with performing a visual observation of the new house framing, that is all I can offer at this time.

Yes, the guys building a new one showed up this morning with the architect!!!

Exactly the reasons Del and Moosie mention.

It's weird, though, walking around in the houses - almost like walking on a really tall scaffold that sways too much. The floor moves an inch with every step. Sink water sloshes, coffee stirs itself...

But, these guys say the houses will survive a Cat 4 direct hit... We'll see come september/october!!!!

Hey Tex, nice to see that you're back! LTNS as they say! Whatcha been up to lately, vacation possibly, or just the typical work overload?

Hmmmm, the house sways around too much huh? Sounds like something is missing or not tightened down in a lot of places. It should be solid as the Rock of Gibraltar! What did the 'Archie' say about that?

The builder and the archie both said it was to be expected. The 10x10 posts are 8 feet in the ground on bell bottom piers, and 18 feet from the base to the beams. They said if they did not sway they would snap at the base in the wind and storm surge.

The floors are all glue-down laminate fake wood like pergo. Owner, builder and archie all said nothing else will stay put except carpet and of course that's nuts for a beach house.

I'm surprised there's no sheetrock cracks. I did notice the pre-cast bathtub surround and shower surround are set with a thick bead of silicone, no grout. And the kitchen cabinets are falling off the walls and the doors don't fit right - it's a bit like cooking on a coleman stove on a bass boat in 2 foot chop.

I know if I was having to live here, I would need something more stable, or I'd have to move farther inland - I love boating but when I am in the house I'd like my milk to stay in the bowl at breakfast!!!

Wow Tex, that house construction is a tad scary to say the least! Sounds like very bad workmanship, and the Archie (w/ Owner's nose in tow) goes with this? Bad Bad Bad!!!!

Ya know, instead pressure treated columns I would have opted for precast concrete piles driven to refusal. They're easy to obtain, as they use them down your way quite a bit for supporting all of those expensive concrete bridges that Texas DOT like to design and have built. Heck, they use them on every coastline in the states, even up here! Those puppies ain't going nowhere I can assure you of that if driven correctly.

I have some doubts about the milk staying with your morning Corn Flakes my friend with those wooden columns rattling about.....

I saw some concrete columns today!

I was wondering about how they would drive them to refusal without having them shatter.

Plus - how to get them all the same height... I guess they could be saw cut after driving?

And one more thing - they say these wood posts are costing about $600 a piece, so it seems possible that the concrete would be better and cheaper.

It's gotta be a little harder to work with the wood beams and attachment, but if the beams were through-bolted to the concrete - "that ain't going nowhere" right?

Tex, no problem driving those concrete pilings as they are typically cast with high strength concrete and heavily reinforced. Additionally, some pre-casters usually install a structural steel cap atop the piles for ensuring durability.

I have yet to see a precast concrete pile shatter in sand.....only seen them fail when there was a buried boulder in the way. If it is known that ledge rock or bedrock is down there, they usually cast a steel driving shoe on the pile base or switch to HP steel piles.

Typically, the tops of precast concrete piles are not cut for sake of structural integrity. Yes, you could saw-cut off the extraneous top portions of the concrete piles, but I wouldn't recommend it. Personally I would not allow such practice on my project(s). Most often than not, the piles are driven below the required datum elevation and then capped-off with high strength cast-in-place concrete up to the desired elevation, typically the bearing seat level of beams and girders that are part of the floor system that they would be supporting. During the cap-off steel anchors and structural steel shapes like angles (side clip angles) are embedded into the top of the work to provide a secure anchoring point for the follow-on framing resting atop the pilings, whether it be concrete, steel, or timber framing. I don't like to side bolt floor framing members to concrete pilings unless absolutely necessary because it's a real bear to align cast-in bolts (or bolt holes) with the bolt holes, both vertically and horizontally, in the beam webs.....I'd rather the floor beams rest atop the top of the piers and shimmed if required. Sometimes even a 1/4-inch steel leveling plate with non-shrink/non-metallic grout under it is required. No big deal actually, because you can field weld beam side clips (with through bolts to attach it to the beam ends) to this!

Well, if it were my beach house I would go with a continuous reinforced concrete wall directly under where the floor girders would have been, to support the floor joists. These would be much like a bridge abutment. Of course they'd have to extend down 8-feet below grade and the upper 4 feet said embedment would be protected with heavy angular stone rip-rap scour protection. I know it sounds like overkill, but storm surge and it's scouring/erosion effects can do a real number on the supporting foundation and surrounding soil mass, thus promoting undercutting of the footings. That is why you see piles being driven at bridge abutments, marine docks, river locks and other heavy Civil Works along water ways and coastal improvements, even if there is sufficient bearing capacity of the underlaying soil structure. Protection against undermining of foundations is very crucial.....big capital investments in infrastructure require these upfront installations for protection sake.

Recently, my first cousin, a very well off Dentist in Florida, contacted me regarding the protection design for his second home located on the beach in Key West Florida. His concern, a very valid one, was that someday they'll lose the very expensive beach house to a hurricane. The house is only around 10 or 12 years old, and BTW cost several $M to build. I can just imagine what it is worth today, being that it is on Key West and waterfront property, it is probably worth many times what he built it for and improved upon over the last decade. I've never been there, but he did forward digital pics to me for an initial eng evaluation and commentary/critique.

Initially, he only wanted to install a stone sea wall of sorts. Somehow I don't think that the state of Florida would allow such a thing...maybe, maybe not. Basically, I told him to have the house temporarily moved and have tall concrete piles driven to support the house at a much higher elevation so that the house could ride out the storm surge. Also he needed to have hurricane clips installed throughout the entire structure to resist the hurricane wind forces. I also informed him to obtain a Florida-licensed Structural Engineer (I'm not licensed in FL, so I cannot legally design this work for him) that is highly qualified to design and oversee construction of said work. And not to shop for the lowest cost engineering services either, because you get what you pay for (He has a family habit of being very cheapo). Either that, or sell the house and get the hell away from the coastline! So far, nothing has been done.....

Moosie, one further complicating factor here in Texas, the Texas Open Beach Act states that all land seaward of the vegetation line belongs to the state, so when a hurricane comes through and the vegetation line moves past your build line, you lose your house to the state. There is a clause about waiting a certain amount of time to see if the vegetation comes back (I forget how long.) but you can't plant vegetation to help it along. so even if the house is still standing and in good shape, if the vegetation line moved past your house, you no longer own it, so there is an incentive to not build too terribly sturdily because it might just be throwing money down a hole. To my knowledge, Ins. will not reimburse you for your losses if the state takes your house due to movement of the vegetation line. A lot of people plant Kudzu on their property because it grows so fast and is dang near impossible to kill in the hopes of stabilizing the vegetation line for that reason.

Sounds exactly what the State of S. Carolina does.....them and their damn "Sea Oats" on the dunes stance! ACKKKKK!!!!!!

Environmentalists running amok IMO!

You have to draw the line somewhere. In the UK, I think it's the high water mark.
If you don't then people will build islands shaped like palm trees and maps of the world before you can blink. Not to mention polders...
Del

Hmmm, like the peeps (errr the King) in Dubai with their 'palm tree-shaped" islands that are quickly (a relative term actually) eroding away?

I just have to ask, who takes responsibility for the insurance on the first wave of such a dramaticly different building satandard? What if these houses don't make it through the first storm? Is it the home owner's insurance, or the contractor's that eats it? Or better yet the building inspector who approved the mess who should be held personally responsable?

I bet putting ceramic tile on those floors without something like DITRA is a lost cause....

In addition to the other excellent posts something to keep in mind, those old photo 'knee braces' provide little to the structure BUT are excellent trash catchers and a storm surge is a little water and a lotta debris.

surely if storm surge is an issue you would have fewer posts , make them stronger and put 2/3 rd X bracing on the back and side walls ( 3 sides ) , then you can still park vehicles underneath the dwelling ?

storm surge is the ENTIRE problem. imagine a 28' sailboat floating on an 18' tidal surge being slammed under your house....

Many years ago- I forget which year and which storm, a hurricane went through the Corpus Christi/Rockport area after property developers had been in and built a number of "modern" houses (usually with glass walls facing the ocean). These, in certain areas, were interspersed between these century-old rock fortress like homes, that had no windows facing the sea (obviously originally built with storm survival in mind). Touring the area after the cleanup crews had been through, nearly every one of the modern-built structures was gone. The old stone houses still stood and were still owner-occupied- most of them having survived several direct hits over the years.

Some of these modern construction practices don't seem to bear comparison to some of the older construction practices, from back before we had building codes...

Maybe (Nature) was trying to tell people something back in 2008...

Now, I actually agree with Del, Capt Moosie, et al, but if I were actually going to try to live in such a house, I would take their advice even farther...

It would be even better to install (non-continous, pvc-covered, metallic) cross-cabling between each of the bays in the x-, y-, and z-directions, at a minimal tension, so as to achieve a more systematic and distributed resistance to the surge of the water.

In fact, it would be even better to install similar cabling to the house's walls, ceilings, and rafters, as well, in order to stiffen the resistance of the entire structure.

Also, about 16' of column, plus about 8' more of wall height, plus maybe 6' more of gable height, at the ends of the house, would take the structure height up to about 30' above ground level, where the wind starts to exert even more force than it would down at ground level...

(Water + wind + rain) tends to equal (damaged-wooden-structures) pretty quickly, last I time heard...

By the way, are any of the Developers currently residing in any of these (houses)?...

pvc coated cabling actually corrodes faster than galvanized or stainless cable because it traps salt laden moisture in the crevices. Stainless cables work best in that environment.

The stilt type construction was once fairly common in Australian coastal towns since it made the house cooler in summer and let fewer snakes get into the kitchen.

The amount of swaying that you described does seem seriously wrong.

Does it do it in X and Y directions?

I also would have installed horizontal X-bracing in to plane of the floor at the bottom of the floor joists for stiffness, especially if the house was built unsymmetrically. Ditto at the underside of the roof trusses. Also, install x-bracing in every exterior wall + add shear walls at the interior partition walls.

You also have to minimize the breaching of the exterior envelope construction, such as windows, exterior walls and the roof. Once the higher wind pressures intrude into the building interior, then all bets are off and the building will suffer catastrophic failure, usually by uplift failure mode (like that seen with failures due to tornados). Plywood sheathing used throughout the walls and roof attached to the structural framing members with high strength/high quality wood screws and not those damn pneumatically/electrically driven cheapo staples and nails, which are totally useless in a structural sense. Also, the inclusion of hurricane anchors and clips like those made by Simpson Strong-Tie (and others) are absolutely required, top to bottom of the structure for integrity.....roof trusses tied to wall studs tied to floor joists tied to beams & girders tied finally to the supporting columns.

We constructed a little experiment for the kids using our fishing poles and some weights.

We duplicated the pendulum length of the post length, and then made some shorter "harmonics" lengths.

The weights sway in time with the building.

They also swing in a circle, which is what the floor is doing. It does not move only x or only y, but rather in an ellipse.

Tex, don't buy that house! LOL

Seriously, if it moves like that it's in serious trouble!

actually I understand large buildings have pendulum counterweights designed to counter the harmonics of the structure...

Yes, that is correct Rorschach, they are installed to lessen sidesway dynamics in tall skyscrapers due to wind and seismic events.

If you had ever had the pleasure of being on the Observation Level of the old World Trade Center buildings (before the 9-11 attacks, of course) during a very windy day, then you would have experienced a lot of sidesway, as those towers did not employ such countermeasures. At the roof level they could laterally sway as much as 3 feet horizontally on windy days! A literal "PUKE FEST"! I kid you not!!!

Please note that not all "anti-sway mechanisms" that are installed in tall buildings rely on a pendulum device.

As i understand it...

It's not the pendulum effect that's assisting in stopping the sway. The pendulum is there to provide a plumb reference for hydraulic dampers to work against. The sway heats up the dampers and the sway's energy radiates away.

Is that right Dr Moosie or does the pendulum do more than this?

A couple of wobbly new bridges were retrofitted with dampers weren't they?

I was going to suggest to txmedic that some automotive dampers could be rigged up as bracing at the post/bearer joints. Still give but the swaying would diminish. Would give the house that whole redneck look too...sweet.

http://www.nd.edu/~nathaz/journals/%281999%29Mitigation_of_Motion_of_Tall_Buildings_with_Recent_Applications.pdf

Wal, there's several types of Tuned Mass Dampers (TMD) being utilized around the world in skyscrapers and bridges.

Although I have never had the pleasure to design a TMD for a skyscraper, you assumption/statement is essentially correct in regard to the pendulum-hydraulic rams/damper interaction. The chief aim of these devices is to change the natural response frequency of the building in resisting wind and seismic induced oscillations, as well as to reduce the overall amount of steel used throughout the building.

Yes, there are several bridges (mainly suspension bridges and cable sway bridges) around the world that employ TMDs, but most were designed that way from the onset....bridges in Japan, but some in the USA, China, Singapore and the "Millennium Bridge in London UK.

Here's a URL link that includes a very good article about TMDs that was in the American Institute of Steel Construction some time back:

http://www.civil.umd.edu/~ccfu/ref/TunedMassDampersCompositeFloor.pdf

The bottom line should be that the Recreational Vehicle in the background of the first picture illustrates the most reasonable approach to the situation. (ie: If you absolutely have to live in the subject area, just buy a parcel without a house, and spend the money saved on a durable, dependable RV, and pay attention to storm reports so you can gather up your goods and drive to safety at the first warning of any storm...)

The workmanship of the (house offerings) just does not justify any financial investment...

By the way, you might want to know that the Categories of wind levels are:

LEVEL--v(mph)---P (in-hg)-------IMPACT----------------------------------------P(v) (psi)

__1____>_74___<_28.94_"very dangerous winds will cause some damage"___873

__2____>_96___<_28.50_"Extremely dangerous winds...extensive damage"_1,469

__3____>111___<_27.47_"Devastating damage will occur"_______________1,964

__4____>130___<_27.88_"Catastrophic damage will occur"_______________2,694

__5____>136___<_27.17_"Catastrophic damage will occur"_______________2,949

(ie: velocity values should be read as "greater-than-or-equal-to")

(ie: in-Hg values should be read as "lesser-than-or-equal-to")

(ie: psi values should be read as ("greater-than-or-equal-to")

Yeah, but that's hardly what I'd call tall.
Simple wire cross bracing should do the trick... or maybe just all move about very s-l-o-w-l-y on tippy toes
Del

problem with wire cross bracing is twofold, first it will catch all the flotsam and jetsam in the tidal surge and the salt environment will corrode dang near everything... I suspect they were built this way to minimize the financial loss when they blow away again in 7-12 years...

Having lived through a half dozen BIG storms and a whole bunch of minor ones as well as some near missess whre the wind stayed 75mph and above for several hours......I can say that there is NO such critter as a hurricane proof or even resistant homebuilt directly on the Coast.

If you park your truck on the railroad tracks, you're going to get hit.

If you build and re-build a home in a coffee cup like New Orleans ( 15' below sea level) you're going to get drowned.

If you want to live on the coast, get used to buying a new house every so many years.

Storm surge comes in and its a lot of water and some mud....the further away from the beach the water turns to thick mud and debris. when that chevy truck, being pushed by 8' of black mud and water hits your home...its going through your home.

Building you house 8',10', 12' off the ground just lets more air get under you and gives you a better chance of Lift Off later during the night.

wind blows one way for hours, then turns the other direction for hours again. Ever wiggle a fence post out of the dirt?

Storm surge pushing tons and tons of debris at 1-2 mph has the impact of a 1/2 dozen bull-dozers hitting your pilings or concrete foundations. Its going over people....it ain't going to hold up.

You know what DOES survives every hurricane?

A steel barge.

Buy one, rennovate the inside.It can look just the canal barges in Holland except no windows.

Put your solar units and AC on the deck and live inside.

Haul it on your lot and bury 8- 20 ton pyramidal shaped mooring anchors about 20' deep, all around.

Attach 4" Dyneema Braided line to everything.

Put in a doube set of tractor tire snubbers with 4' of slack on the halters to EVERY mooring.

Allow yourself 30' of slack line from barge to the surface shackle of every mooring anchor.

You might have a chance.

Just my opinion.....

actually in Holland, they have a variation on this theme. they drive steel pipe to refusal on the corners of the raft (which their house is built on), fill the pipe with concrete, and the raft is captive on the pipes. it can go up and down but not side to side. as the water comes in, the raft/house floats. as the water goes back out it settles back down on top of whatever gets trapped underneath....

HA HA HA a Jack-Up-Barge house!

....at least there won't be any of those midnight alarms going off when one of the 'legs' looses hydraulics and the whole dang thing starts listing .......