# Homework Help: Vertical reactions and UDLs

1. Sep 4, 2008

### Ry122

I have to calculate the vertical reactions at point A and C.
I know that the sum of all vertical forces is equal to zero but i can't solve the equation since there's two variables.
http://users.on.net/~rohanlal/Q3.jpg [Broken]
Bv=50
Cv=55
Dv=45
w=80

Last edited by a moderator: May 3, 2017
2. Sep 5, 2008

### tiny-tim

Hi Ry122!
general rule … when you have a unknown force you can't get rid of, take moments about a point (strictly, an axis) through the line of that force.​

(Alternatively, find the point about which the moment of all the given forces is zero )

3. Sep 5, 2008

### Ry122

Is this correct for the vertical reaction at C?
0=((15/2)*80)-(50x5)-(55x10)+(Cyx10)-(45x14)

4. Sep 6, 2008

### tiny-tim

Hi Ry122!

Yes … you've taken moments about A …

and everything's correct (except you need a minus in front of the 15/2*80 )

(I suggest you take moments about C also, just for practice … but of course, as I expect you've noticed, you don't need to, because you already know the total reaction for A and C together )

5. Sep 8, 2008

for the UDL wouldnt the moment created about point A be the load (80) multiplied by the distance it covers (15m) then multipied by the half way point (7.5m) giving you a moment of 9000 KN/M about point a?

rather than what you have with 7.5 x 80 giving you a moment of 600 KN/M about point a?

6. Sep 8, 2008

### tiny-tim

Welcome to PF!