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How do I determine the support reactions at A & E in this example?

Help is much appreciated.

Help is much appreciated.

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- Thread starter smr101
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- #1

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How do I determine the support reactions at A & E in this example?

Help is much appreciated.

Help is much appreciated.

- #2

SteamKing

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Have you tried writing equations of static equilibrium for this frame?

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Have you tried writing equations of static equilibrium for this frame?

How?

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SteamKing

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Have you written equations of static equilibrium for any structure before?

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Have you written equations of static equilibrium for any structure before?

Right I've worked it out.

I've got E vertical as 50kN.

A horizontal as -30kN, vertical as -50kN.

Only problem is the answers have them listed as these values but I have all of the signs wrong.

- #6

SteamKing

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This indicates that the direction in which you assumed the reactions are acting is opposite of the direction in which they act.Right I've worked it out.

I've got E vertical as 50kN.

A horizontal as -30kN, vertical as -50kN.

Only problem is the answers have them listed as these values but I have all of the signs wrong.

- #7

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This indicates that the direction in which you assumed the reactions are acting is opposite of the direction in which they act.

Yeah, I get that, I'm unsure why the answer is in correct.

Here's my working for vertical E:

About A

∑M = (10 x 3) + (20 x 6) - (E x 3)

= 150 - 3E

Ev = 50

The correct answer is - 50

Any idea where I've gone wrong?

Thanks.

- #8

SteamKing

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It helps to write both equilibrium equations. There should be an equation for the forces such that ∑F = 0, just as there is one for the moments, ∑M = 0.

- #9

CWatters

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∑M = (10 x 3) + (20 x 6) - (E x 3)

What SteamKing said. Its much better to write...

I define clockwise as +ve and then

(+10 x 3) + (+20 x 6) + (?E x 3) = 0

Note: I have explicitly written the sign in front of the 10 and 20N. The "+" sign before the E is because I am

Rearrange

?E = - {(+10 x 3) + (+20 x 6)} / 3

?E = - 50

So the unknown sign of E is -ve. That means E acts anticlockwise (eg downwards).

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