# Shear force and Bending Moments

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#1
Can anybody tell me if my calculations for the questions are correct? If not can you show me how you would work it out.

Much appreciated if someone can help me asap.

Thanks
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4 years ago
#2
Cordero31 I think you have made a mistake in calculating your shear forces: you seem to have not included the UDL.
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#3
(Original post by Smack)
Cordero31 I think you have made a mistake in calculating your shear forces: you seem to have not included the UDL.
I thought so, but I'm confused on how to include it in my calculations. Would you be able to help me? I've looked online for guides but still no help to me as I don't quite understand it.
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4 years ago
#4
(Original post by Cordero31)
I thought so, but I'm confused on how to include it in my calculations. Would you be able to help me? I've looked online for guides but still no help to me as I don't quite understand it.
I'm not really that familiar with how to explain it, sorry, but I would encourage you ask your lecturer or keep looking on the net.

I found this:

http://www.engineeringintro.com/mech...upported-beam/

May be helpful. Remember that for a UDL the SF diagram won't be flat like with a point load, the the BMD will be curved where the UDL is. For working out reaction forces I think you can consider the UDL to be a point load, where the weight is concentrated in the centre of the UDL, and weighs the same as the entire UDL.
1
#5
(Original post by Smack)
I'm not really that familiar with how to explain it, sorry, but I would encourage you ask your lecturer or keep looking on the net.

I found this:

http://www.engineeringintro.com/mech...upported-beam/

May be helpful. Remember that for a UDL the SF diagram won't be flat like with a point load, the the BMD will be curved where the UDL is. For working out reaction forces I think you can consider the UDL to be a point load, where the weight is concentrated in the centre of the UDL, and weighs the same as the entire UDL.
I've tried looking at that but still completely stuck on how to include the UDL. thank you tho!

Any one else have any suggestions on how to use it? Much appreciated ! really stuck on this and how to draw the shear force diagram and the bending moments >.<
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4 years ago
#6
(Original post by Cordero31)
...
To start off, you need to analyse each of the four discrete sections of the beam in a piecewise manner. So, start from the left and take a virtual cut in the beam in the first segment.

Since you know all the reactions, you can do a shear force and bending moment equilibrium to obtain an expression for the shear force and bending moment strictly valid for that segment only. So very importantly, your expressions for the shear force and bending moment distribution will be piecewise continuous.

Then repeat for the other three segments.
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4 years ago
#7
(Original post by Cordero31)
I've tried looking at that but still completely stuck on how to include the UDL. thank you tho!

Any one else have any suggestions on how to use it? Much appreciated ! really stuck on this and how to draw the shear force diagram and the bending moments >.<
Do what pleasedtoyou has recommended above. That is the first step then...

Remember that a UDL can be represented by a single force acting at the centroid of that section. Don't forget to multiply that force magnitude by the total length leading up to that section of the beam.
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4 years ago
#8
(Original post by Cordero31)
I've tried looking at that but still completely stuck on how to include the UDL. thank you tho!

Any one else have any suggestions on how to use it? Much appreciated ! really stuck on this and how to draw the shear force diagram and the bending moments >.<
On your shear force diagram, the UDL should be represented by a sloped line from the start of where the UDL acts to the end of where it acts. The difference in the height of it from start to finish is given by multiplying the N/m value by the full length that the UDL acts on.
Transferring that UDL to the bending moment diagram means calculating the area between the slope and the zero line just like the other sections. However as other folk have said, the UDL is a steady curved line on a bending moment diagram
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4 years ago
#9
(Original post by Cordero31)
I thought so, but I'm confused on how to include it in my calculations. Would you be able to help me? I've looked online for guides but still no help to me as I don't quite understand it.
Ok apologies cos this is rough lol, it your reaction forces are wrong cos the UDL is not included at all. I've got them as 18.25kN for R1 and 30.75kN for R2
Knocked up a quick shear force diagram there.
Just realised now how pointless this reply is cos of age of the post hahahha. Hope you're having better luck, I'm 1st year HND at nescol at the moment and I've only just started getting decent at statics lol. the only thing im not 100% on with this 1 is the 8kN force on the end there, but the maths and the diagram works out so......
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