Can we bend concrete?

 

Can we bend concrete? 

We can bend concrete, but there is a problem. Let us try to understand by using hands.

 (as above)

Just imagine that two hands clasp together just like a concrete beam.

(As shown in the above picture)

 With a great big load acting on hands. What happens is this will bend down. Hands would bend down and can see on top of the hands that the skin of hands is scrunching up which means that we have compression at the top of the beam 

and if the hands are turned upside down we have tension because the skin of hands is stretching. 

What that means is with that compression on top of any concrete can take that compression easily you've seen that from the bare essentials of concrete, but unfortunately all that tension at the bottom is the problem that's where concrete is not strong, and so what will happen is the concrete will crack and it will collapse immediately.

Why don't concrete beams in buildings or bridges fall down?

The problem is concrete has no tensile capacity. So Structural Engineers wrestled with this problem and thought how on earth can we put tensile strength into concrete?

The solution found in steel bars. We all have seen that steel used in great & big structures example of the Golden Gate Bridge is an example where the steel is in tension between two great big towers steel is brilliant in tension 

Golden Gate Bridge

It's wonderful and concrete is wonderfully in compression. We put the two together, we create a new material and that new material is reinforced concrete.

Why don't concrete beams in buildings or bridges fall down?