Hand Calculations vs Simulation Results - Please h

Hi All,

Been attempting to validate simulation results against hand calculations, have been a hit and miss.

It seems the simulation results is somewhat similar with hand calculations when a test specimen with short span length is used.
Increasing the span length 10 times and the results from simulation doesn't tally with calculations.

Does anyone have similar occurrence?

Please critique my simulation setup and findings below:

TEST SETUP

1) Formula used: Taken from engineersedge

2) 2nd Moment of Area: Taken at, Lxx = 35.815316cm^4

2nd Moment of Area.png

SPAN of 600mm

3) Simulation Results: Average of 20.743 MPa

Hand Calculation: 21.51MPa

Avg. Von Mises Stress.png

4) Simulation Results: Displacement in Y Direction Average of 0.077587mm

Hand Calculation: 0.07813mm

Avg. Displacement Y Dir.png

SPAN of 6000mm

5) Simulation Results: Average of 108.38 MPa

Hand Calculation: 215.10MPa

Avg Von Mises Stress.png

6) Simulation Results: Displacement in Y Direction Average of 25.663mm

Hand Calculation: 78.125mm

Avg Displacement Y Dir.png