In order to design the splice for the bridge girder in Example 6.2, we need to know the peak moment generated at that splice as well. Therefore, we need to construct another influence line.

Question

Accepted Answer

Detailed Analysis:
Identify locations for the unit load:
Reaction locations: A, C
Point of interest: B

Calculate the moment, MB, due to each unit load:
Unit load at A:
FBD:

Apply equilibrium:

[latex]+\circlearrowright \Sigma M_C = 0 = A_y(30 \mathrm{~m}) - 1(30 \mathrm{~m})[/latex]

[latex]A_y = 1(+\uparrow)[/latex]

Note that the reaction is the same as when we generated the shear influence line. The reaction is not a function of where we calculate the internal force.

Cut at B:

Apply equilibrium:

[latex]+\circlearrowright \Sigma M_{\mathrm{cut}} = 0 = 1(22 \mathrm{~m}) - 1(22 \mathrm{~m}) - M_B[/latex]

[latex]M_B = 0[/latex]

Unit load at B:
Cut at B:
Note that we actually cut the beam at either [latex]B^-[/latex] or [latex]B^+[/latex],but it does not matter to the value of the moment at the cut.

Apply equilibrium:

[latex]+\circlearrowright \Sigma M_{\mathrm{cut}} = 0 = 0.267(22 \mathrm{~m}) - M_B[/latex]

[latex]M_B = 5.87 m[/latex]

Unit load at C:
Cut at B:

Apply equilibrium:

[latex]+\circlearrowright \Sigma M_{ ext {cut }} = 0 = 0(22 \mathrm{~m}) - M_B[/latex]

[latex]M_B = 0[/latex]

Table of points:

Location of Unit Load	[latex]M_B[/latex]
A	0.00 m
B	5.87 m
C	0.00 m

Create the influence line:

Question 6.3: In order to design the splice for the bridge girder in Examp...

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