Simply supported beam with 2 point loads and a UDL.
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!!
Reply 1
21
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.
Reply 2
Becklaa7
OP
2
Original post
by mqb2766In 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!
Reply 3
21
Original post
by Becklaa7Thanks 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 ...
Reply 4
Becklaa7
OP
2
Original post
by mqb2766It 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 ☹️
Reply 5
21
Original post
by becklaa7https://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 1 year ago)
Reply 6
Becklaa7
OP
2
Original post
by mqb2766In 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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