- #1

lazypast

- 85

- 0

## Homework Statement

Hi. See attached, I need to determine the forces in all members.

## Homework Equations

Sum of forces in X, Y & Z all equal 0.

Sum of moments in X, Y & Z all equal 0.

## The Attempt at a Solution

I've drawn the reactions at each support, A, B and C in my 2nd attached

ƩFx=0 ∴ 8+3-R(ax)-R(bx)-R(cx)=0

ƩFy=0 ∴ R(ay)+R(by)+R(cy)=0

ƩFz=0 ∴ 20+20+20-R(az)-R(bz)-R(cz)=0

After taking moments from various places and about various axis, I get Reactions at:

A-x= 8

y= 0

z=20

B-x= ?

y= 0

z= 9

C-x= ?

y= 0

z= 31

All in kN. The workings are just long winded so I'll put the important bit in - the unknowns R(bx) and R(cx).

Taking moments at A about the Z axis

0.866R(bx)+0.866R(cx)+0.866(3)+0.5R(cy)-0.5R(by)=0

R(cy)=R(by)=0 & dividing by 0.866

The equation becomes:

R(bx) + R(cx) = -3kN

I would say 3kN is shared equally between point C and B, but I have no proof, i.e. I can't see an equation that shows R(bx)=R(cx). Can I just assume 3kN is shared equally and R(bx) = R(cx) = 1.5kN