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posted by  edelpink on 11/4/2009 9:28:37 AM  |  status: Closed  |  Earned Karma: 60

Problem 5.144

Course Textbook Chapter Problem Needs by
Mechanical Engineering Vector Mechanics for Engineers Statics, 9th edition, Beer, Johnston, Mazurek, Chapter 5 5.144 11/5/2009 at 8:00:00 AM
Question Details:
A beam is subjected to a linearly distributed downward load and rest on two wide supports BC and DE, which exert uniformly distributed upward loads as shown. Determine the values of wBC and wDE corresponding to equilibrium when wA= 600N/m



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posted by Mobiusdick on 11/4/2009 2:08:39 PM  |  status: Live
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Response Details:
For the system to be in equilibrium, the total torques need to be equal from both directions.

As for the top, this can be broken down into a square whose center of gravity is at the center of the beam, and a triangle whose centroid is located 2 m from the right side of the beam.

Fblock = 600N/m * 6m = 3600 N @ 3 m from right
Ftriangle = 1/2 (600)*6m = 1800 N @ 2m from right

as for the bottom supports, they are both squares whose center is at their center.
Fbc = Wbc * .8m = .8Wbc @ 5m from right
Fde = 1m* Wde = Wde @ 1m from right

Now, from point F, we set up all of the torques (clockwise is positive, counter is negative, sum must be 0)

0 = .8Wbc*5m - 3600N * 3 - 1800 N * 2 + Wde
So, we find Wde = 14400-Wbc

Now, setting Wbc's center as the pivot point, we find
3600*2m + 1800*3m = Wde*4
Wde = 3150
Wbc= 14400-3150 = 11250



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posted by walken on 11/4/2009 3:18:36 PM  |  status: Live
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Response Details:
The above answer is correct.
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