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The aluminum door is lighter and less expensive than steel door.
Steel reinforced concrete is concrete with rods of steel running through it.
Steel is heavier than concrete for the same volume, however steel buildings are generally lighter. This is because steel buildings utilize high strength of steel, so volume of steel in steel buildings is much smaller than volume of concrete in concrete buildings. In another words in steel buildings much less volume of material is needed for the same strength compared to concrete buildings.
because concrete is unpredictable than steel
Concrete can be reiforced by using steel; steel can not be reinforced
I think you are talking about embedding steel rods (rebars) in concrete, right? This would make the concrete much stronger. It is called reinforced concrete, and you can make all sorts of structures with it, something that you can't do with ordinary concrete. Though, I am not even sure anyone is using non-reinforced concrete nowadays.
The aluminum door is lighter and less expensive than steel door.
Steel reinforced concrete is concrete with rods of steel running through it.
The steel rods are there to strengthen the concrete - making it reinforced concrete.
Advantages of steel frames include the fact that they are durable and strong. Disadvantages are that they are heavy and difficult to move. They are also hard to manufacture.
The advantage is that it is strong and can stand up to many types of weather. Disadvantage is that it will get rusty easy.
how calculate steel in concrete
The basic matetrials were steel and concrete.
Concrete is much more fire resistant. This is shown by the design of reinforced concrete structure where the steel is placed within the concrete. A major reason is that the concrete protects the steel from any fire. Steel only construction requires the steel to be covered in a fire protection material.
Steel is heavier than concrete for the same volume, however steel buildings are generally lighter. This is because steel buildings utilize high strength of steel, so volume of steel in steel buildings is much smaller than volume of concrete in concrete buildings. In another words in steel buildings much less volume of material is needed for the same strength compared to concrete buildings.
Concrete is unpredictable compared to steel...
Mainly re-enforced concrete (concrete that's been set around steel rods). The cables are made from many long strands of steel.