Week8_1 - Looking into FBD (b), you get ENGR210, Fall 2011...

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ENGR210, Fall 2011 1 Two-force members (re-visit) It is important to recognize two-force members in a system to solve problems efficiently. But is it absolutely necessary? Illustrative example: Determine the support reactions at A and C.
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ENGR210, Fall 2011 2 (The solution using the two-force member approach) Member BC is a two-force member. So, the FBD is There are 3 unknowns, so you can solve for the reactions. Done!
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ENGR210, Fall 2011 3 If you fail to recognize the two-force member and draw a FBD like There are 4 unknowns, and you cannot solve for these. (Therefore, if you leave your FBD like this, you will have a trouble.)
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ENGR210, Fall 2011 4 However, if you separate the system into and Then, you have 6 unknowns and 6 equations (good).
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Unformatted text preview: Looking into FBD (b), you get ENGR210, Fall 2011 5 These relations (Bx, By, Cx and Cy) means that the FBD (b) is equivalent to Therefore, in summary, even if you dont recognize two-force members in a system, you CAN solve for unknowns IF you separate the system into subsystems (like (a) and (b) above). However, if you use a whole system without knowing two-force members, you have often difficulty solving for unknowns (like ( ) above). Note that drawing FBDs for two-force members (without knowing two-force members), writing equilibrium equations with extra unknowns and solving for the unknowns take more time. So, be efficient , by identifying two-force members. ENGR210, Fall 2011 6 ENGR210, Fall 2011 7...
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Week8_1 - Looking into FBD (b), you get ENGR210, Fall 2011...

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