Statically indeterminate beam question

Join the discussion
Registration is free. Start your own thread to ask a follow-up.
6 replies · 8K views · last reply
georgeburton
Messages
4
Reaction score
0
I have been trying to solve this question using the superposition method, but cannot seem to get the correct answer. Can anyone help?
Question & formulae are attached.
Cheers, G
 
Physics news on Phys.org
here are the files
the answers are;
Ra=0.33 kN
Rc=2.67 kN
Mc=-1.27 kN
Mb=0.49 kN
 
Attachments
  • Exam figure of a propped cantilever beam ABC, fixed at C and pinned at A, with 1.5 m between A and B and 1.5 m between B and C, carrying a uniformly distributed load of 2 kN/m over BC.
    Screen Shot 2011-12-23 at 20.03.51.jpg
    33.7 KB · Views: 1,274
  • Table 1 summarising beam loadings and deflections, with columns for case number, type of load diagram, maximum moment, slope at end, deflection equation and maximum deflection, covering six cases.
    Formulae table.jpg
    40.9 KB · Views: 10,807
Seems a simple enough propped cantilever.

Do you realize you have to add some ficticious forces (loads) to complete this by superposition? If you do this all the necessary parts are tabulated in your second picture.

You need to show us some of your own working (even if wrong) before we can help further.
 
To solve this, i would state that the deflection of the beam at A equals 0.
I am just unsure how to calculate the deflection due to the distributed load using the table. This is because the table doesn't offer any deflection equations for beams that have distributed loads on only parts of the beam rather than all of it.

If the distributed load was on the first half of the beam i would have no difficulty solving it. It's just that the point i am trying to calculate deflection for (i.e. point A) does not lie within the distributed load.

Any advice?
 
Does this sketch help?
 
Attachments
  • Hand-drawn free-body diagram of a horizontal beam fixed at the left wall at point C, with moment Mc and reaction Rc shown there, a downward distributed load labelled 2kN/m along the top, a support triangle at the right end A, and an upward distributed load labelled 2kN/m over the segment from B to A.
    gbeam1.jpg
    5.7 KB · Views: 822
Hi, thanks for the help so far, but i am still unsure of how i would calculate the deflection at 'A' due to the load that you have drawn underneath the beam.
As the distributed load is not at the built in end, i don't know how to calculate the deflection due to it.
 
It is difficult to know what advice to offer since I don't know what beam methods you have covered. You would not usually do this by superposition alone.

Perhaps these examples will help
 
Attachments
  • Worked beam example with a 40 kN/m uniformly distributed load on a fixed-support beam, showing shear force and bending moment diagrams, with results Ra = 160 kN, Qa = 160 kN, Ma = -320 kNm, and at section K Qk = 60 kN, Mk = -45 kN m.
    gbeam2.jpg
    12 KB · Views: 730
  • Textbook worked example 5.3 for a cantilever beam with a 40 kN/m uniformly distributed load over 4 m, showing a beam diagram, shear force diagram (SFD) and bending moment diagram (BMD) with reactions and values at section K.
    gbeam3.jpg
    14.2 KB · Views: 771