overhead concrete design stuff

[Muckin_Slusher]

Could you DIY one of those concrete-inflatable army tent things? Not sure how to impregnate fabric with concrete. As simply as shovelling and rubbing in cement?





If done right it should give a nice, uniform curve (reducing stress risers).

At work we`ve got an inflatable building looks like this one:

...and the first hit when googling ``ìnflatable building`

 

[[486]]

tensionsing should be done with cables, it needs to be able to stretch pretty good so that it can actually generate some tension.

you sure? one would think a rod would stretch just like a cable
using the rod means I wouldn't need a tube to keep the concrete from sticking
overnight I had another "fuck post tension" thought though so...

Only figuring on maybe three feet of dirt up top, and as much styrofoam as I can find. Just don't want animals burrowing down into my water barrier and foam. Maybe a 6" layer of very low cement content mortar would be a good prevention for that. Something like half a bag of portland to a yard of sand...

 

[Provience]

;n245659]

you sure? one would think a rod would stretch just like a cable
using the rod means I wouldn't need a tube to keep the concrete from sticking
overnight I had another "fuck post tension" thought though so...

Only figuring on maybe three feet of dirt up top, and as much styrofoam as I can find. Just don't want animals burrowing down into my water barrier and foam. Maybe a 6" layer of very low cement content mortar would be a good prevention for that. Something like half a bag of portland to a yard of sand...

rod won't stretch like a cable, i don't know offhand how much tension per foot, but it is a bunch. yeah, ignore tensioning is probably easiest.


yeah sand and portland is probably easy to keep animals out, but i don't think you'll need it

 

[[486]]

yeah sand and portland is probably easy to keep animals out, but i don't think you'll need it

How paranoid do you think I am? Double it.

 

[SLOWPOKE693]

;n245685]
How paranoid do you think I am? Double it.

 

[mrblaine]

#3 bar? For a load supporting structure?

We did a poured in place floor to make a converted movie theater have a basement where the screen used to be. About a 30 foot span at the narrowest, about 120 feet long with 3 columns mid span of the 30 foot direction. 8" thick, two mats of #8 18" on center. The spacing decreased to 12" on center and 6" on center in an 8' square around each column. I don't believe they would have let us use #3 for anything but ties.

 

[stjames151]

;n245659]

you sure? one would think a rod would stretch just like a cable
using the rod means I wouldn't need a tube to keep the concrete from sticking
overnight I had another "fuck post tension" thought though so...

Only figuring on maybe three feet of dirt up top, and as much styrofoam as I can find. Just don't want animals burrowing down into my water barrier and foam. Maybe a 6" layer of very low cement content mortar would be a good prevention for that. Something like half a bag of portland to a yard of sand...

Not the same. Think of breaking a stick vs a bunch of twigs, or a faggot, if you will.

Seriously, cable is stronger and way mor flexible. If rod breaks, you only get one shot. If a strand breaks, theres usually 71 left to back it up.


BTW, you can get n-vented deck, epic deck, and kingspan in curved sections. You just have to order it in advance. I can send you a contact at c-s if you want. 30' sections are childs play.

 

[RusM]

;n245659]

you sure? one would think a rod would stretch just like a cable
using the rod means I wouldn't need a tube to keep the concrete from sticking
overnight I had another "fuck post tension" thought though so...

Only figuring on maybe three feet of dirt up top, and as much styrofoam as I can find. Just don't want animals burrowing down into my water barrier and foam. Maybe a 6" layer of very low cement content mortar would be a good prevention for that. Something like half a bag of portland to a yard of sand...

You pretension rods....

 

[[486]]

Not the same. Think of breaking a stick vs a bunch of twigs, or a faggot, if you will.

Seriously, cable is stronger and way mor flexible. If rod breaks, you only get one shot. If a strand breaks, theres usually 71 left to back it up.

I thought the cable they used for little post tension residential stuff was just 7 strands of something like 1/8" wire
either way, I'm thinking of it like a bolt, bolts certainly stretch quite a bit when you tension them

so far the insights gained from this thread:
I'm gonna die
use #4 for the roof
form the roof with dirt
just buy a couple fucking containers or aged out semi trailers to use as a shed you idiot

 

[arse_sidewards]

Dirt form and pour it all in one shot gets my vote. Doing it this way lets you do a thicker (and stronger) pour than anything that involves you supporting concrete with forms or lifting it piece by piece.

Do two 15ft arches and fill the void between them with gravel, cap it with a thin layer of concrete with a lot of aggregate and then run your roof membrane over that eliminating the water trap in the center.

Using two small arches lets you get arches with more angle which reduces the side load on the outer walls. In a perfect world your arches would be complete semi-circles. Since you are a cheapskate I would avoid any design that requires tensioning things.

 

[Provience]

the only reason i can think of to not use regular forms is cost.

dirt seems like a huge pain in the ass for a large area.

 

[Drummer79]

Forget the arch. Pour the three walls with beam pockets dividing it into 6 bays per side of your center wall. Beams run across the 30' way. Metal deck, weld studs and two mats of rebar. All this can be pretty light stuff because the spans are small.

Metal deck is going to be cheapest when you figure in all the lumber you would use for forms, and the added labor.

Anything this dude says about how to build the most overbuilt badass shop ever I would take as gospel

 

[mrblaine]

;n245933]

I thought the cable they used for little post tension residential stuff was just 7 strands of something like 1/8" wire

That is about how I would describe the couple of post tension residential slabs we've done. The post tension company came out after the forms were up. Drilled holes in the forms, ran the cables in plastic sleeves and stuffed that through the holes with a cone shaped cup pointed to the inside. We poured, let it set up for couple of weeks, they came back with their hydraulic stretcher and cone shaped locks that dropped into the holes in the concrete around the cable ends.

 

[Provience]

That is about how I would describe the couple of post tension residential slabs we've done. The post tension company came out after the forms were up. Drilled holes in the forms, ran the cables in plastic sleeves and stuffed that through the holes with a cone shaped cup pointed to the inside. We poured, let it set up for couple of weeks, they came back with their hydraulic stretcher and cone shaped locks that dropped into the holes in the concrete around the cable ends.

yeah and there is no way you are going to get a rod to hold the same kind of tension that a cable is going to hold.

 

[arse_sidewards]

yeah and there is no way you are going to get a rod to hold the same kind of tension that a cable is going to hold.

How so? You've got the same or more cross sectional area in a threaded rod than an equivalent size cable. You should be able to put the same clamping load on something. It will just take less distance to do it since the rod will stretch less.

 

[Muckin_Slusher]

If you don`t have enough to think about yet, there`s this:

 

[Provience]

How so? You've got the same or more cross sectional area in a threaded rod than an equivalent size cable. You should be able to put the same clamping load on something. It will just take less distance to do it since the rod will stretch less.

because the rod will deform and the cable will try to pull back into shape and hold pressure.

if you were just going to use threaded rod and tighten the ever loving shit out of it, i guess you could give that a whirl but i dunno how tight you'd need to work the fasteners to get the same amount of clamp force that stretching a cable like a spring would get you. i'd imagine it would be shittons

 

[rockdog57]

the only reason i can think of to not use regular forms is cost.

dirt seems like a huge pain in the ass for a large area.

I’ve seen it before on a huge turtle shaped building. They drove full size loaders inside to pull the dirt out. If it will work for that, it would work for something as small as his building. The thing stood up for decades before being torn down to make room for new buildings.

 

[[486]]

because the rod will deform and the cable will try to pull back into shape and hold pressure.

I don't understand how the steel knows what shape it has been formed into
is it like commoncold2019™ where it can tell when you're sitting at a table?

granted a36 is a lot less springy than the sort of steel in cable, but just sub in something like prehard 4140

 

[Dethmachinefab]

because the rod will deform and the cable will try to pull back into shape and hold pressure.

if you were just going to use threaded rod and tighten the ever loving shit out of it, i guess you could give that a whirl but i dunno how tight you'd need to work the fasteners to get the same amount of clamp force that stretching a cable like a spring would get you. i'd imagine it would be shittons

The cable and threaded rod would be the same if they were both the same size and material. The material and forming process of cable strands is different than a steel rod, making for stronger tensile strength. 270ksi cable strands vs a 150ksi rod.

 

[Provience]

;n246061]
I don't understand how the steel knows what shape it has been formed into
is it like commoncold2019™ where it can tell when you're sitting at a table?

granted a36 is a lot less springy than the sort of steel in cable, but just sub in something like prehard 4140

steel knows because cable is twisted so it has a whole lot more actual length to go before you run into plastic deformation, while solid rod doesn't have that advantage.

long thin strands that crush down and tighten against each other under pressure and give a bit of length, so that they are then also trying to force each other back apart, vs a stick that is just trying to resist pulling itself apart.

i dunno how much pressure you can get on a nut or how that would compare.

 

[Provience]

The cable and threaded rod would be the same if they were both the same size and material. The material and forming process of cable strands is different than a steel rod, making for stronger tensile strength. 270ksi cable strands vs a 150ksi rod.

smart answers and stuff ^^

 

[[486]]

steel knows because cable is twisted so it has a whole lot more actual length to go before you run into plastic deformation, while solid rod doesn't have that advantage.

long thin strands that crush down and tighten against each other under pressure and give a bit of length, so that they are then also trying to force each other back apart, vs a stick that is just trying to resist pulling itself apart.

i dunno how much pressure you can get on a nut or how that would compare.

the cable used is nothing like the wire rope on your winch

 

[Provience]

;n246070]

the cable used is nothing like the wire rope on your winch

that is the cable that i am thinking of, see how it is smaller diameter strands that are twisted? pull it, tension it, and because it has so much more length of each strand, vs length of the whole cable, it will be able to move more without hitting plastic deformation vs a solid bar. because it isn't yeilding, it want's to return and stores a bunch of that energy in between all the strands.

i dunno, just how i see it in my head and when they snap and splay themselves open from the tension.

 

[ThePanzerFuhrer]

The cable and threaded rod would be the same if they were both the same size and material. The material and forming process of cable strands is different than a steel rod, making for stronger tensile strength. 270ksi cable strands vs a 150ksi rod.

No the cable would still be way stronger than a solid bar same material and size. In order for a cable strand to yield it must overcome the friction force between it and the neighboring strand. This over coming the friction force allows the cable to be loaded way more than a solid bar. This is the reason why cables are so strong for their size.

I learned this lesson on a bus headed to a tour of South Korean Hyundai heavy industries. The engineering professor was talking about a large ancient bell. The hole that was used to hang is was too small to hold it up with a solid bar. If it was hung on a iron bar it would fail. What the old timers did was hammer a bunch of iron paper thin and roll them up into a wire rope. The friction between the sheets was great enough to allow the bell to be hung without it yielding. Stupid lesson that I haven’t forgotten.

 

[Dethmachinefab]

I think I missed what's getting post tensioned? This is only going to work with roof that has a certain shape, (like a precast bridge section) so the cables can be in the proper place. Pulling cables in a 6" suspended slab will do nothing.

 

[[486]]

huh

So what you're saying is buying a spool of that scrapped guardrail cable and using it instead of rebar is a great idea. c:

 

[[486]]

I think I missed what's getting post tensioned? This is only going to work with roof that has a certain shape, (like a precast bridge section) so the cables can be in the proper place. Pulling cables in a 6" suspended slab will do nothing.

oh no, nothing is getting post-tensioned any more, it was just one of many tangents
This is GCC after all.

 

[Provience]

I think I missed what's getting post tensioned? This is only going to work with roof that has a certain shape, (like a precast bridge section) so the cables can be in the proper place. Pulling cables in a 6" suspended slab will do nothing.

it seems like nothing is going to get tensioned at the end of the day, but for doing a roof if you want a bigger open span, tensioning can help keep the concrete strong.

lightweight tensioning helps reduce cracking associated with shit sub-grade stuff, heavy tensioning helps deal with loads by keeping the concrete in it's strength even if it has a bunch of weight going in the wrong direction. i.e. strong crush from the sides to offset the load from all the dirt on the deck.

 

[Dethmachinefab]

;n246088]huh

So what you're saying is buying a spool of that scrapped guardrail cable and using it instead of rebar is a great idea. c:

I was looking at that stuff to do a cable car but it was too small for what i needed. A bunch of Craigslist adds had it for cheap.