How to derive equation of deflecting curve for a simple beam

AI Thread Summary
To derive the deflection curve for a simple beam in terms of q, L, and EI, the second-order differential equation of the deflection curve is utilized, requiring integration of the bending moment function twice. The bending moment equations for the two segments of the beam are presented, with M1(x) = 1800*X for the first segment and M2(x) = -100(x-72)² - 5400(x-72) for the second segment. The discussion highlights a discrepancy between the calculated moment functions and the expected results from the bending moment diagram. Participants emphasize the need to verify the moment functions to ensure they align with the bending moment diagram for accurate integration. The conversation underscores the importance of accurate calculations to derive the correct deflection curve.
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Homework Statement



Obtain deflection curve in terms of q, L, and EI
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Homework Equations



Use the second order differential equation of the deflection curve to solve.
Meaning that the M(x) is the second derivative and you integrate twice to get V1 and V2

The Attempt at a Solution


From the bending moment diagram I've found that:
(0 ≤ X ≤ 36) → M1(x) = 1800*X which is [(L/8)q](x)
(36 ≤ X ≤ 72) → M2(x) = -100(x-72)2 - 5400(x-72) which is
(-q/2)(x-L)2-(3L/8)q(x-L)

From the back of the book, I can see that the answer is going to be the same as the table values (just for the opposite side). I Have tried, but can't get the right answer. Can anyone help me?
Table values:
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You have shown the back of the book answer, not your own calculations. How can we see what is wrong with your calculations if we don't have them?
 
SteamKing said:
You have shown the back of the book answer, not your own calculations. How can we see what is wrong with your calculations if we don't have them?

yes that is what we're supposed to get, but I'm not getting close to it. Pretty much all I have to do is get the moment of the beam as a function of x for the first half of the beam and the second half. From there, we take the integral twice.

Anyway, I think my first question is, are the moment functions right? Then we can go from there. Thanks.
 
If you evaluate your moment expressions, you should get the same values on your bending moment diagram. Your equations don't match the curve.
 
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