Civil Engineering Reference
In-Depth Information
Cantilever span
Anchor span
Suspended span
A
B
C
D
A1
A2
C2 C3
Shear in panel A1-A2
Shear in panel C2-C3
Moment at A2
Moment at C2
FIGURE 5.17
Influence lines for shear forces and bending moment in anchor and cantilever
spans with panel points.
the effects of unit loads placed at locations A, A1, A2, B, C2, C3, and C (also shown
qualitatively in Figure 5.17).
For long-span railway superstructures it is of further efficiency to utilize truss
spans in cantilever bridges. The influence lines developed in Figure 5.17, in con-
junction with those developed in Sections 5.2.1.2.1 and 5.2.1.2.2, are useful in the
construction of axial force influence lines for cantilever bridge truss web and chord
members. Also, as usual, the consideration of the moving load effect at panel points
simplifies the construction of axial force influence lines. Influence lines constructed
in this manner for axial forces in cantilever bridge truss members are shown in
Example 5.8.
Example 5.8
Construct influence lines for members in panel point 2-3 in the anchor arm
of the cantilever truss bridge in
Figure E5.9.
ByinspectionandplacementofunitloadsatL0,L2,L3,andL6andconsider-
ing the hinge at the end of the cantilever and suspended spans, the influence
linesforaxialforcesinL2-L3,U2-U3,andU2-L3areshowninFigure E5.9.Influ-
ence lines for axial force in other members of the trusses may be constructed
in a similar manner.
