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1. L

L
W
M ?

How to determine Design moment for a
Rectangular slab using Yield lineAnalysis

2. Virtual work method
L

L
Work done by external load in undergoing small virtual displacement is equal to
the internal virtual work done in rotations along Yield line.
W

3. L

L
/ 2
L / 2
L
/ 2


Internal Energy = External Energy
Internal Energy = Moment * rotation * length of projected yield line
External Energy =Area * Load * Average moved distance for each right half slab
W

4. L

L
/ 2
L
/ 2


Internal Energy = Moment * rotation * length of projected yield line
/ 2

 
/ 2
L
2 / 2
tan
L
 

/ 2
L
2 2 / 2
small angle, tan
L
For  



2 / 2
L
 

4
L
 

Internal Energy 4M
 
4
Internal Energy *
M * L
L



W
? ?

5. L

L
/ 2
L
/ 2



/ 2
L
W
External Energy =Area * Load * Average moved distance for each right half slab
2
External 2*[( * ) * ( ) * ( )]
2
Energy L
L W
 


6. L

L
/ 2
L
/ 2



/ 2
L
W
Internal Energy = External Energy
2
2* [( * ) * ( ) * ( )]
2
4M L
L W

 
 
2
8
M WL
