The largest live load effect on a pedestrian bridge is likely due to distributed load over part of the bridge. In Example 6.4, we developed the influence line for the axial force in member BH. The maximum likely live load for this bridge results in a distributed load of 500 plf that can act

Question

The largest live load effect on a pedestrian bridge is likely due to distributed load over part of the bridge. In Example 6.4, we developed the influence line for the axial force in member BH. The maximum likely live load for this bridge results in a distributed load of 500 plf that can act anywhere along the bottom chord of the truss. Our job is to calculate the peak tension and peak compression that can develop in member BH due to this uniform distributed live load.

Accepted Answer

Detailed Analysis:
Location where the influence line is zero:
To find where the influence line crosses 0, use similar triangles:(figure 6.50)

[latex]\frac{x}{0.377} = \frac{24 ft}{0.377 + 0.565}\x=9.61 ext{ ft}[/latex]

Peak tension:
Apply the distributed load where the influence line is positive: A to 9.61 ft past B:(figure 6.51)

Calculate the resulting peak tension:(figure 6.52)

[latex]Area = ½(0.377) (24 ft + 9.61 ft) = 6.34 ft[/latex]

[latex]F_{BH} = 6.34 ft(500 plf) = 3170 lb (T)[/latex]

Peak compression:
Apply the distributed load where the influence line is negative: 9.61 ft past B to E:(figure 6.53)

Calculate the resulting peak compression: (figure 6.54)

[latex]Area = ½(-0.565) (14.39 ft + 36 ft) = -14.24 ft\F_{BH} = -14.24 ft (500 plf) = 7120 lb (C)[/latex]

Summary:

Desired Peak Effect	Location of Distributed Load	[latex]F_{BH}[/latex]
Tension	0 - 33.6 ft	3170 lb
Compression	33.6 - 84 ft	-7120 lb

Question 6.9: The largest live load effect on a pedestrian bridge is likel...

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