Question: Consider the given figure with a force acting at D . Draw the free - body diagram of member ABD. Determine the reactions at A
Consider the given figure with a force acting at Draw the freebody diagram of member ABD. Determine the reactions at A and
Strategy. The figure shows a simple machine. Note that drawing a FBD of the structure completely attached together would allow you to see two reactions at pin A and at pin For a twodimensional problem, we can only solve up to three unknowns for any freebody diagram. We need to reduce the number of unknowns or draw multiple FBDs we have not covered how to do this yet for machines Identifying twoforce members will reduce the unknowns by one. Identifying threeforce members will also reduce the unknowns by one. This problem has one of each. The unknowns should initially be: and since there are two pins.
Task Identify the twoforce member. It is attached at no more than two places and has no additional forces applied to it Draw a FBD of the member itself, knowing the line of action of the forces at the ends pass through both attachment points. Draw this member in compression. Note that instead of both and at the pin at there is only one unknown, the magnitude of the force at The unknowns have been reduced. The unknowns should now be: and
Task Identify the threeforce member. The sum of attachment points and applied forces on the member is exactly three. Draw a FBD of the member. The lb applied load has a known line of action. By identifying member as a twoforce member, we know the line of action of as well. Draw pointing at from Locate the intersection point of the force and Instead of writing and at point we know the third force must pass through the same intersection point as the other two forces. Define the line of action for the force at The unknowns should now be only: and
Task Use the FBD to apply equilibrium and solve for the two unknowns. Express your answer as a force and small angle from the horizontal axis.
Further. With known reactions, can you find the values for the initial four unknowns: and
After identifying the twoforce member, there were three
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