# influence lines (structural engineering)

• May 7th 2010, 12:41 PM
Haris
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?
http://img294.imageshack.us/img294/1...luenceline.jpg