Odd Residential Situation

[tradewinds63]

I've a particular design that falls outside my domain of expertice. The project will be located in Hawaii and is not subject to particular energy codes (HVAC) requirements.
The design criteria are rather simple but beyond the realm of conventional residential construction. I've been in residential construction for 28 years but am rather stumped on this one, being I'm more familiar with wood frame and common foundations. I don't think such materials are appropriate for this design.

The structures are simply composed of 4 corner columns cast as round concrete columns in the diameter of 16" with a hight of approximatly 12' from floor on avg. The largest of the structures is merely 24'X24' square with a shed roof @ 1/12 pitch with an EPDM membrane and perhaps common ply roof sheathing.
The floor system is to be raised about 60" from the bottom of the colums thus colums overall hieght will come in around 16' above its footing. Footings are to set upon/within "solid" lava rock and not within common soil.
The trick is this, there is to be no need for lateral support via walls between the colums. In essence the walls are to serve no purpose but that of partitions in the form of glass or single layers of t&g redwood and or sliding glass doors/walls or perhaps veneer (not a brick or common rock but rather 1.5 inch thick lava rock on either hardi or wonder board) lava rock walls.

What I'm looking for is advice on what sort of X/lateral bracing will be neccesary below the floor systems in order to provide for lateral support. Also what sort of roof framing materials would be best suited for this application within the roof system and the floor system framing for that matter.

I've some preliminary 3d design images in a tenative finish goal and can easily provide elevation and floor plan views if neccesary.
The design has been inspired by Bali bale (not hay bales) architecture regarding seperate structures for each room type and all are connected via open air covered walkways. So each room is its own seperate structure and can be predominatly opened all around.
Here's a basic reference:

[Boby]

Hi,

With these footings, it is even more unusual to have a structure without any x-bracing. This also applies when having concrete footings.

You definitely need some kind of bracing against wind and probably a concrete rafter as foundation or at least connecting footings, depending on the geology, to minimize differential settings of the foundations.

Bracing of walls in two directions, as well as roof bracing are necessary. The roof can be stabilized with wooden bracing, as the roof structure is already to be planned out of wood. The wall bracings can be of different types, such as partly or totally made out of reinforced concrete, steel bracings (cables, profiles, etc.), wooden bracings or a mixture.

We do find this design to be not usual and would advise you to check the geotechnical data of the site for the foundations and think about the cheapest alternative to stabilize the buildings against wind by providing bracings in both directions or to statically connect the buildings with each other and stabilize/reinforce the center building against wind.

Regards,
Boby

[tradewinds63]

Thanks Bobby,

Actually I had intended to use X type bracing but not within the wall area. Here's an example of what I had in mind. This structure is 24'X24' square, center of column to center of column. The subfloor framing top is 80" above the footings and the overall height of the highest column from footing to top is 244" or 20'-4". I’ve illustrated a galvanized cross cable system between the columns and it would be tightened via turnbuckles below the floor system to establish the lateral support. A cross member between columns just above the footings may be necessary depending on the columns ability to withstand the applied pull force of the cables at the floor deck elevation. Keep in mind, the soil is solid lava (rock) and the site is fairly level within 3"+/- in 24feet.
Also, the roof beams would all be anchored into the columns top in order to lock their relative positions. Atop all this we’ve to apply the floor and roof sheathing to complete the lateral support on the two horizontal planes between the columns.

Digging in for a footing is not an easy task short of ripping and rolling the site with a D-9 dozer and ripper. Aside from that… we’re after an airway under the house to help establish healthy natural ventilation. This site is located within a jungle and use of stem walls and pads is a very bad idea.

Any help in determing the cable type and required tension acompanied by thoughts regarding connectors and the thickness of the concretecolumns and neccesary embedded steel/rebar would be great.



Thanks,
Mike

[tradewinds63]

The current proposed design calls for a minimum of a 16" diameter concrete column for aesthetic purposes but the column may be increased in diameter if necessary for structural demands although I can’t imagine a greater diameter would be necessary.
Regarding the porte-cochere/drive up carport with overhead deck; is it possible to simply use a pile sort of column considering the soil is solid lava? The lava is only covered by an average of 6 or so inches of common top soil. Under that 6 inches of top soil is solid lava rock, if using a jackhammer head on a mini excavator, it should suffice for excavating a hole deep enough to provide lateral support on those columns; yes, no?
How deep would the holes have to be made?

In case anyone is wondering, this house is to be my personal house and will be an off grid home completely self-sufficient and located in a development called Waa Waa in the lower Puna district of Hawaii.
I’m just trying to iron out some of the details as to not have them blow up when it goes across the engineer’s desk at the city. My final architect may have a few answers but he won’t have them all. Since none of the roof spans are greater than 30’, the state does not require private engineering on them and in this case I don’t want to be playing “patty cake” plans volley with the cities engineer.

Aloha,
Mike

[alabdoetcie]

hi
as you said of a 24'x24' then i built this typpe of structure not in a place as you are but on the mountain & the best way to join up anything if you are good financially, then simply build a raft foundation. For this type of work you don't need to waste your money on barcing or anything like that, your raft should atleast be 15" thick with a double reinforcement & your all problrms will be solved by their ownself step by step. If you use braceing for example: under every roof you will have to use braceings & what garanty is there.

I hope you prefer my idea.

Regards
Abdo

[tradewinds63]

Hello Abdo,

Are you citing something along the lines of the following with concrete between the columns at floor level?

[alabdoetcie]

no nothing like that it will be a simple column & beam (Rcc frame stucture buildinG)

[tradewinds63]

Can you provide a basic scetch or link that illustrates what you're expressing?

Thanks,
Mike

[alabdoetcie]

hi mike
your last pic you uploaded.
you should only provide a beam from column to column under ground level or say inside the foundation
Regards
Abdo

[tradewinds63]

Abdo,
I like your idea regarding its lateral effectiveness, however; I’m trying to minimize ground contact.
Why can’t the beam be placed at floor level as opposed to ground level? I don’t need any rafting with respect to the load transfer. Remember, the ground is solid lava (rock) and there’s no need to convey the load over any additional ground area.
If the lateral qualities can be derived at floor level with the reinforced concrete beam, then it kills two birds with one stone. This could effectively remove the need for a steel or wood beam around the structural perimeter in lieu of the concrete lateral support beam which can then serve a dual purpose as the floor and lateral support.
If a suspended concrete beam were to serve as support for the floor and provide the lateral support, what’s your estimate on the beams thickness and depth? What type of rebar pattern would be most effective? Also, only two of the members would have to support the floor system leaving the other two to merely serve the lateral demands.
Also, and this changes nearly everything, we may bump the floor level to 12’ above grade, remove the exterior perimeter decks and introduce a shaded garden under the house.

Thanks,
Mike

[alabdoetcie]

Hi Mike
yes your beam can be placed at the floor level. the beam that you want to make it as a suspended beam then its size should atleast be 15"x15" useing 3/4" dia bar with a spacing of 6" c/c. keep in mind that fo rthis your column & beam should be of the same size, in that way it will be possible for you to do anything, that of supports or suspended, it will all look one.
Regards
Abdo

[tradewinds63]

Hi Abdo,

Yes, that's more like what I had in mind and that should work out well.
I'll post some details here later when I've got them in place.

Thanks,
Mike

[alabdoetcie]

Hi Mike
thats good to hear i will wait for it

Regards
Abdo