# Calculate bending moment of a beam and the size of the beam to be used? Answered

Please refer to the uploaded images. (there are two images) When the right of the weight is lifted up, I need to know the formula to calculate the bending moment of the beam according to the rest of parts I have and how to calculate the suitable size of the beam to be used. I appreciate your help very much...

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Thanks kelseymh and frollard for your helps. To frollard, As the bending moment is at its maximum when one of the weight is lifted out of the sea, the rest of the bending moment measurements are not neccessary for me to find out. I could only know how to calculate the easy question on bending moment. This one is too tough for me.. Let's assume the buoyancy force is 40N.. Volume of buoyancy is 1000m3

**please refer to my latest image for clearer view

Relevant equations
M = Force x distance
Volume of buoyancy is 1000m3
buoyancy force is 40N
Mass = 40kg

The attempt at a solution
Moment of Mass = 40kg *9.81 m/s-2* 30m = 11.72 KNm
Moment of the structure (horizontal, above water)= 10 * 9.81 * 45 = 4.41 KNm
Moment of the structure (vertical, above water) = 10 * 9.81 * 40 = 3.92 KNm
Moment of the structure (horizontal, under water)= 10 * 9.81 * 22.5 = 2.21 KNm (how to deduct the buoyancy force??)
Moment of the structure (vertical, under water)= 10 * 9.81 * 22.5 = 2.21 KNm (how to deduct the buoyancy force??)

Total M = 12.75KNm

In this case, how do I relate to the size of the stainless steel to be use ? what is the suitable diameter?

Hi frollard, Please refer to the added image, the volumes of buoyancy is unlimited as it is considered as under the sea. There lengths and delta height of movable weight are added.

Thanks kelseymh and frollard for your helps.

To frollard,

As the bending moment is at its maximum when one of the weight is lifted out of the sea, the rest of the bending moment measurements are not neccessary for me to find out.

I could only know how to calculate the easy question on bending moment. This one is too tough for me.. Let's assume the buoyancy force is 40N.. Volume of buoyancy is 1000m3