Problem 2 . A bridge is composed of the structural system whose configuration is

Question

Problem 2. A bridge is composed of the structural system whose configuration is shown in the following figure. The truss is loaded at its top chord panel points by the reactions from a stringer and floor beam system that supports a roadway slab.

      2.If a fully loaded motorised ore carrier with a total weight of 70 kN crosses the bridge, use either increase?decrease method or trial?and?error method to determine the maximum compressive force in bar BF. Assume the truck can only move from the left to the right.

Explanation / Answer

What they want you to do, is to consider ALL POSSIBLE POSITIONS of the truck on this structure, and draw the plot of the force in Members CF and CE.

While it is important to consider loads in all other members, and it will be part of our initial algebra to calculate accordingly, we only need to actually state our answers for members CF and CE.

I suggest laying out your loads from the truck, as generalized variables.
Load at point A: Wa
Load at point B: Wb
Load at point C: Wc
Load at point D: Wd

These will each be a function of x, the position of the truck along the bridge. Define x=0 when the front tires are above point A. The maximum value for x will occur at x=23 meters.

Set up your point-live load functions, as a function of x. This may require some hand-sketching, to develop them. Each platform gets balanced by two constraint forces, to support the loads on it, so each platform is a statically determinate "two equations, two unknowns".

Regardless of what your point-load functions are, solve algebraically for the member forces in CE and CF, according to Wa, Wb, Wc, and Wd. Keep it generalized, as we will fill in the W-functions when we know them.

I'd recommend using the METHOD OF SECTIONS, rather than the method of joints.

Then it is all a matter of plotting in a computation program of some form or another.

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.