How to derive equation of deflecting curve for a simple beam

In summary: Your M1(x) should be (L/8)q, not (L/8)q(x). Your M2(x) should be (-q/2)(x-L)^2 - (3L/8)q, not (-q/2)(x-L)^2 - (3L/8)q(x-L).In summary, in order to obtain the deflection curve in terms of q, L, and EI, we need to use the second order differential equation of the deflection curve to solve. This means that the M(x) is the second derivative and we integrate twice to get V1 and V2. The moment functions found from the bending moment diagram are (0 ≤ X ≤ 36
  • #1
Blugga
22
0

Homework Statement



Obtain deflection curve in terms of q, L, and EI
fu8i06.jpg


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:
33m98ae.jpg
 
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  • #2
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?
 
  • #3
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.
 
  • #5
If you evaluate your moment expressions, you should get the same values on your bending moment diagram. Your equations don't match the curve.
 

1. What is the equation for the deflection curve of a simple beam?

The equation for the deflection curve of a simple beam is given by:
y(x) = (wx^4)/(8EI) + C1x + C2
where w is the distributed load, x is the distance along the beam, E is the modulus of elasticity, and I is the moment of inertia.

2. What is the derivation process for the deflection curve equation?

The derivation process involves using the Euler-Bernoulli beam theory, which states that the deflection of a beam is directly proportional to the bending moment and inversely proportional to the flexural rigidity. This theory is applied to the differential equation of the deflection curve, and boundary conditions are used to solve for the constants C1 and C2.

3. What are the assumptions made in deriving the deflection curve equation?

The assumptions made include:
- The beam is homogeneous and isotropic
- The beam is subjected to a distributed load
- The beam is initially straight and the deflection is small compared to the length of the beam
- The beam is supported by simple supports at both ends
- The material of the beam is linearly elastic
- The deflection of the beam is in the same plane as the applied load
- There is no transverse shear deformation in the beam.

4. Can the deflection curve equation be used for any type of beam?

No, the deflection curve equation is only valid for simple beams, which are beams with a single span and supported at both ends by simple supports. Other types of beams, such as cantilever beams or continuous beams, have different equations for their deflection curves.

5. How can the deflection curve equation be used in practical applications?

The deflection curve equation can be used to calculate the deflection of a simple beam under a given load, which is important in designing and analyzing structures. It can also be used to determine the maximum stress and bending moment in the beam, which are crucial factors in ensuring the structural integrity of a design. The equation can also be used to compare different beam designs and determine the most efficient one.

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