Concrete and pressure no air nothing more than gravity

[mike232]

So I'm looking for how tall I could make a tower of concrete, using any reinforcments, in an environment of only gravity starting at sea level. Could it get so tall it'll own gravity would effect it, the moons, or the sun's gravity, or would the bottom give out will before that?

 

[berkeman]

c

So I'm looking for how tall I could make a tower of concrete, using any reinforcments, in an environment of only gravity starting at sea level. Could it get so tall it'll own gravity would effect it, the moons, or the sun's gravity, or would the bottom give out will before that?

What do you think? What would be the Relevant Equations/Concepts that would help you calculate this? One Relevant Equation is the gravitational attraction between two masses -- are you familiar with that equation yet? And how can you calculate under what pressure the concrete will fracture?

 

[mike232]

I have about a Jr level physics knowledge. So my guess would be that the base of the tower would give out before the towers gravity effected anything to a significant degree, but I don't know. So before I went into the math behind the material science I am hoping someone knows if just conceptually we could ever make a concrete tower that its own gravity is significant, in the described environment.

For my guess on relevant equations and stuff, probibly a lot of trig in the design on the support structure. So a lot of triangles forming polygons making framework. But I also disn't initially give a base so I guess theoretically I could have a 70 mile radius at the base and then the height would potentially be enormous. I was thinking more realistic though like a normal kind of magnitude for a tower we have made. So I guess I'm asking for the max height of a tower with the base roughly the same as the sears tower or many like a 200m base radius. But I'm more looking for gestamates like order of magnitude.

 

[berkeman]

I have about a Jr level physics knowledge. So my guess would be that the base of the tower would give out before the towers gravity effected anything to a significant degree, but I don't know. So before I went into the math behind the material science I am hoping someone knows if just conceptually we could ever make a concrete tower that its own gravity is significant, in the described environment.

What would any external gravitational attraction do? Would it pull the tower down sideways? Would it unload the base pressure some? What is your thinking about how this would modify the base crush pressure calculation?

For my guess on relevant equations and stuff, probibly a lot of trig in the design on the support structure. So a lot of triangles forming polygons making framework. But I also disn't initially give a base so I guess theoretically I could have a 70 mile radius at the base and then the height would potentially be enormous. I was thinking more realistic though like a normal kind of magnitude for a tower we have made. So I guess I'm asking for the max height of a tower with the base roughly the same as the sears tower or many like a 200m base radius. But I'm more looking for gestamates like order of magnitude.

The Sears Tower does not use reinforced concrete for its structure. Why not?

 

[mike232]

So is this called a base crush load calculation? I was only showing a parallel in the size of the base with the sears tower, I'm taking about a 200m ish radius concrete tower, and was thinking that if the tower could be tall enough its gravity could interact with other fields and like you said cause to fall or take pressure off the base. But how can I find out if the tower could even get tall enough at that magnitude base so that I would even have to start thinking about gravity?

 

[stedwards]

With a very deep foundation The Himalayas reach a few miles. Should your tower be slimmer?

 

[billy_joule]

A quick Google tells me:
high strength concrete has a compressive strength of 130 M Pa (Mega pascals, or Mega Newtons / square metre)
And a density of 2400 kg / m ^3

Along with 'g', you can calculate an upper limit for the tower height from these values.. (assuming a prismatic tower)
And: P = ρgh