This is continuation of video of raft foundation with
drop in foundation
In Part-1, we discussed about modelling & analyzing
In Part-2 we discussed about reinforcement design of
drop using strip method
In this Part-3,
we will look into design reinforcement of Raft
foundation using FEM Finite Element Method
I will drop link of previous parts
PART-1 & PART-2 connecting to this video
in description with some other video links.
First go to Run ---> & Click on Run Analysis & Design
After designing,
go to display ---> & click on Show Slab Design
Check on "Impose Minimum Reinforcing"
so that if no reinforcement need in any area of
foundation,
design will show minimum reinforcement required
according to code
Select "Finite Element Based" in Design Basis
Choose Direction-1 Bottom Rebar
that is x-direction bottom reinforcement
Choose "Typical Uniform Reinforcing Specified Below"
in Show Rebar Above Specified Value
Let's say we are using #5 @ 5" c/c
bottom reinforcement
Click on Apply
This is contour color diagram showing
extra bottom reinforcement of x-direction needed
after #5@5"c/c reinforcement
Since all extra reinforcement coming in location of
drop foundation of raft
which we already design using STRIP method,
so no extra reinforcement required after placement of
#5@5" c/c reinforcement
Now choose Direction-2 Bottom Rebar
that is y-direction bottom reinforcement.
Click on Apply
This is contour color diagram showing extra bottom
reinforcement of y-direction needed
after #5@5"c/c reinforcement
Same result as we get for x-direction reinforcement
no need of extra reinforcement
after #5@5"c/c
Now choose Direction-1 Top Rebar that is
x-direction top reinforcement
Let's say we are placing #5@5" c/c top reinforcement
Click on Apply
This is contour color diagram showing extra top
reinforcement of x-direction needed
after #5@5"c/c reinforcement
Look at this point
We need 0.23 in2/ft or can say 0.3 in2/ft
extra reinforcement required in top x-reinforcement.
Calculation of this extra reinforcement is
Reinforcement required = 0.3 in2/ft
we are using #5 bar
Area of #5 bar = 0.306 in2
Spacing will be is equal to
12 / reinforcement required that is 0.3 in2/ft
divided by
area of rebar
that is 0.306 in2
We get the value 12.24 inch
So we will provide
# 5 @ 10 " c/c
at location of extra rebar intensity contour diagram
because main reinforcement is on 5" c/c
so this extra reinforcement
will be place in between 
two main reinforcement alternate.
Now choose Direction-2 Top Rebar that is y-direction
top reinforcment
Click on Apply
This is contour color diagram showing extra
top reinforcement of y-direction needed
after #5@5"c/c reinforcement.
Look at this, we need 0.24 in2/ft
or you can say 0.3 in2/ft
extra reinforcement required in top y-reinforcement
Calculation of this extra reinforcement is
Reinforcement required = 0.3 in2/ft
We are using #5 rebar
Area of #5 rebar = 0.306 in2
so spacing will be
equals to 12 / reinforcement required
that is 0.3 in2/ft / area of rebar
that is 0.306 in2
equals to 12.24 inch
So we will provide # 5 @ 10 " c/c
at location of extra rebar intensity contour diagram
This is how we calculate extra reinforcement
using Finite Element Method.
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