# Concrete and pressure no air nothing more than gravity

• mike232
In summary, the conversation is about the feasibility of building a tall concrete tower using any reinforcements, taking into account only the force of gravity and starting at sea level. The question is whether the tower could be built tall enough for its own gravity to significantly affect it, and whether external gravitational forces from the moon or sun would have an impact. There is also discussion about relevant equations and concepts, such as the gravitational attraction between two masses and the pressure at which concrete will fracture. It is mentioned that the Sears Tower does not use reinforced concrete for its structure and the conversation ends with possible calculations to determine the maximum height of a tower with a 200m base radius.
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?

c
mike232 said:
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?

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 hight 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.

mike232 said:
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?

mike232 said:
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 hight 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?

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?

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

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

## 1. What is concrete and how does it work under pressure?

Concrete is a mixture of cement, aggregates (such as gravel and sand), and water. When these ingredients are combined, a chemical reaction occurs that causes the mixture to harden and form a strong and durable material. Under pressure, the small particles of cement and aggregates are pushed closer together, creating a stronger bond between them.

## 2. How does the absence of air affect concrete under pressure?

Air voids in concrete can weaken its structure and reduce its strength. When concrete is under pressure, these air voids can compress, causing the concrete to crack or fail. Therefore, the absence of air in concrete is important to maintain its strength and durability under pressure.

## 3. Is pressure the only force that affects concrete?

No, gravity also plays a significant role in the behavior of concrete. Gravity causes the concrete to settle and compact, which helps to strengthen its structure. However, too much pressure from gravity can also cause concrete to crack or fail, so it is important to properly design and reinforce structures to withstand these forces.

## 4. How does the composition of concrete affect its resistance to pressure?

The composition of concrete, specifically the ratio of cement to aggregates, can greatly affect its resistance to pressure. A higher ratio of cement will result in a stronger and more durable concrete. Additionally, the size and shape of the aggregates can also impact the strength of concrete under pressure.

## 5. What are some common applications of concrete under pressure?

Concrete is commonly used in construction for a variety of structures that are under pressure. Some examples include foundations, retaining walls, dams, and bridges. It is also used in pavement and flooring, where it must withstand the weight of heavy vehicles or foot traffic.

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