Hi, I'm doubting my answer to this simply supported beam task.

The beam is 22m long, it is simply supported at both ends (R1 & R2) It has a point load of 8kN 5m from the left and another point load of 4kN 5m from the right. It has a UDL of 3kN/m acting along 17m from the right.

My calculations are:

UDL = 17 x 3 = 51 kN

R2 = (8 x 5) + (51 x 13.5) + (4 x 17) = 796.5 N = 79.65 kN

R1 + R2 = 8 + 4 + 51 = 63 kN

R1 = 63 - 79.65 = -16.65 kN

I'm confused why I have a negative reaction force at R1, is this possible or have I messed up somewhere?

Any help would be amazing thanks!!

The beam is 22m long, it is simply supported at both ends (R1 & R2) It has a point load of 8kN 5m from the left and another point load of 4kN 5m from the right. It has a UDL of 3kN/m acting along 17m from the right.

My calculations are:

UDL = 17 x 3 = 51 kN

R2 = (8 x 5) + (51 x 13.5) + (4 x 17) = 796.5 N = 79.65 kN

R1 + R2 = 8 + 4 + 51 = 63 kN

R1 = 63 - 79.65 = -16.65 kN

I'm confused why I have a negative reaction force at R1, is this possible or have I messed up somewhere?

Any help would be amazing thanks!!

Original post by mqb2766

In the R2 "equation", youre taking moments about the left so its not equal to a force or R2. If youre taking moments about the point where R1 acts, then it should be

22*R2 = ...

to get clockwise = anticlockwise moments. Also the 796.5 N = 79.65 kN doesnt make sense.

22*R2 = ...

to get clockwise = anticlockwise moments. Also the 796.5 N = 79.65 kN doesnt make sense.

Thanks for your reply. Yep you're right, I had written down on paper 796.5 (10) not N. So I had 796.5/10 to get 79.65N I'm still completely lost though, it wouldn't let me upload a picture of the actual beam either ☹️ going to have to abandon it for tonight I think!

Original post by Becklaa7

Thanks for your reply. Yep you're right, I had written down on paper 796.5 (10) not N. So I had 796.5/10 to get 79.65N I'm still completely lost though, it wouldn't let me upload a picture of the actual beam either ☹️ going to have to abandon it for tonight I think!

It sounds a fairly basic moments question. Your main mistake is that you write

R2 = sum of moments

which is wrong as you have

force = moments

I suspect you should have 22*R2 on the left (assuming youre taking moments about R1), then R2 would be about 35kN and ...

Original post by mqb2766

It sounds a fairly basic moments question. Your main mistake is that you write

R2 = sum of moments

which is wrong as you have

force = moments

I suspect you should have 22*R2 on the left (assuming youre taking moments about R1), then R2 would be about 35kN and ...

R2 = sum of moments

which is wrong as you have

force = moments

I suspect you should have 22*R2 on the left (assuming youre taking moments about R1), then R2 would be about 35kN and ...

https://www.youtube.com/watch?v=lrs4V7CQDbw I've done exactly as this video shown for a practise one, the beam is exactly the same set up except the length and forces are different acting upon it. I cannot figure out where I've gone wrong at all ☹️

Original post by becklaa7

https://www.youtube.com/watch?v=lrs4V7CQDbw I've done exactly as this video shown for a practise one, the beam is exactly the same set up except the length and forces are different acting upon it. I cannot figure out where I've gone wrong at all ☹️

In that example they have R2 multplied by 10. You need to multiply your R2 by 22 (third time of saying this) because you need to have a moment = moment sum equation. You have a force = moments sum equation, which is wrong.

(edited 6 months ago)

Original post by mqb2766

In that example they have R2 multplied by 10. You need to multiply your R2 by 22 (third time of saying this) because you need to have a moment = moment sum equation. You have a force = moments sum equation, which is wrong.

Ok thank you I see where I've gone wrong now

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