Second moment of area about the horizontal axis

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vtaela
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Could someone help me on how to calculate the second moment of area of the beam in the figure below?

Cross-section of a thin-walled beam labelled FIGURE Q3, with 4 mm walls, points 1 to 5 marked, dimensions 100 mm, 100 mm, 400 mm, 120 mm and 150 mm, a 40 kN downward load, and a horizontal x-axis with the shear centre distance e_c marked.


Thank you
 
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my calculations give me 172.8 *10^6 mm^4

is that correct?

thank you
 
vtaela: Excellent work. Your answer is correct.
 
I am trying to find my local variables in order to calculate the shear flow! I have the local variables as shown below! Are my local variables set correct?
Hand-drawn sketch of a cross-shaped thin-walled section with members labelled S1 to S5, arrows showing direction of each member, a 40 kN downward force arrow, and a dashed horizontal x axis.

Thank you
 
I finished with this, look similar to what you got?
 
Attachments
  • Handwritten working on lined paper, rotated sideways, showing shear flow calculations q(S0) = 35.52 + 23.511 + 27.47 = 86.521 N/mm and q(S4) with an integral of 4 x (198 - S4) and a result of 104.67 N/mm, next to a sketch of a stepped cross-section with labelled segments S1 to S6.
    image.jpg
    40.6 KB · Views: 459
Working out of ixx
 
Attachments
  • Handwritten worked calculation of the second moment of area Ixx for a cross-section split into parts 1 to 4, using Ixx = bh^3/12 + Ad^2, with the sum of parts doubled for symmetry, above a dimensioned sketch of the section.
    image.jpg
    25.6 KB · Views: 480
Flow diagram and calculation of s1
 
Attachments
  • Handwritten shear flow calculation for a symmetric cross section with labelled distances s1 to s4, a 40 kN load arrow, and the expression q(s1) = 2.3143 x 10^-4 x 792 s1 with q(150) = 27.49 N/mm.
    image.jpg
    23.7 KB · Views: 449
Calc of s2, s3 and s6. The first picture i posted is calc for s4 and final value. Any idea how to do shear centre?
 
Attachments
  • Handwritten shear flow calculations at points 2, 3 and 6 of a thin-walled section, with integrals of 4 times (300 - s2), (400 + s3) and (198 + s6) and resulting values of 23.511, 13.52 and 35.52 N/mm.
    image.jpg
    24.9 KB · Views: 443

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