## influence lines (structural engineering)

The concrete highway bridge show in Figure Q3a is supported on
columns at B and E, and abutments at A and F. The bridge has joints
at C and D, which can be modelled as pins. Figure Q3b shows an
idealised model of the bridge deck.
Draw influence lines for:
i) the shear force across joint C;
ii) the axial force in column E;
iii) the bending moment in the beam over column B.

I attempted part (i) and got: when x<15m shear force at C=0, when 15m<x<30m shear force at C=(30-x)/15 and finally when x>30m shear force at C=0. I assumed the moments about joints C and D will equal 0 as they are pinned. Can anyone tell me if I'm correct?

Parts (ii) and (iii) are puzzling me though.
Could anyone give me some advice/tips on how to get an expression for the axial force in column E and bending moment over column B for the influence line?

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 Haris, I believe you need to include the weight, 100kN, in your equations. Also, for part i, you should have 3 equations, one with the front axle on the center span, one with both axles and one with only the rear axle on the center span. Once you get that you might move on to the other two. You'll have to expend some pencil lead to complete them. S