G'day welcome back to build some what I want to show you today in this video is
the strength and weakness of
concrete and steel and how we use them together as
reinforced Concrete to
provide or to form a very strong
structural member of our building
so essentially
This is our slab of concrete and concrete is very strong when it's compressed
Or pushed together
So I think about a force being pushed it on the line of these arrows pushing the concrete together
The Concrete is going to stand up pretty well
It's not going to want to crack or anything, and it's it's very strong in compression
However if We do reverse the situation and try and pull the concrete apart
Then the concrete is going to break reasonably easy
So concrete is very strong in compression very weak in tension
Steel and like our reinforcing Rod however is the opposite it is
Incredibly strong in tension
So I think about a tug o'war with a steel Rod even if you tied two cars to the to the rod you
know need a fair bit of force to cause any damage to the Rod, so it steel's very strong in tension
however if we were to try and compress it it would very quickly deform and buckle and
get out of shape, so
Steel has the exact opposite
properties as a concrete, so
That's why we can form them
together but the thing is
You know concrete slabs just sitting there. How is it ever going to be placed under
compression or tension
So what happens especially with them suspended slabs if the slabs supported on both ends such as this one
And then there's a load placed in the middle and that could be
the self weight of the concrete or any live loads or dead loads you're going to put on top
But then what is effectively, what's trying to happen is
That the slab is being pushed or trying to be pushed into that shape
So what that does is because it's now our concave shape the top of the slab has actually been
compressed
By the by the load and the bottom half of the slab is
now in tension because it's actually been made longer
So this is where the structural engineers come into play and this is how they work out where they're going to place their reinforcement
so we need to place reinforcement in the areas of the slab that are going to be placed under tension, so
in this case the bottom half of the slab is going to be in tension
So we need to put our reinforcement in the bottom half of the slab
I'm not right on the bottom because we have to allow for our cover and
not right the ends again for cover, but in the bottom half of the slab
now as I said before this is where structural engineers make their money because
There's going to be lots of different situations
where we're going to have different loads and
different scenarios
so in this instance such as a cantilever, got a load down in the middle and
Again, we're going to have the self weight of the slab plus anything else
We're going to put out here on this end of the slab
Causing a load out here. So there's actually going to be a bend
over that support and a bend in
here as well, so
This is where our structural engineers can advise us
where to place our steel and
Yeah, what size it needs to be
so hopefully that shows you the relationship between
the Concrete and the reinforcement in a reinforced
concrete member and
That we are using the best properties of both materials
to form a highly efficient and a very popular building component