Finding Element Stress of Space Frame Stiffness Method

[earthlink]

Hi all

If I have interconnected frames, when using stiffness matrix for frame I can find the reaction at each node of the space frame.
So now I have these reaction forces at each node.

Then lets say there is this node A connecting 3 frame elements a, b and c.
I know the reaction force at A equal x.
So the value of x would be the sum of reaction forces of element a, b and c at end point A.

But what would be the reaction (moment, torque, axial, shear) at node A with respect only to the element a?
, what would be the reaction at node A with respect only to the element b?
and
, what would be the reaction at node A with respect only to the element c?

I need this value to find the stress components of each member a, b and c at point A.

Thank you in advance.

 

[bowlingdanish]

If you post a well annotated sketch I'm sure someone could help you.

...Probably not me though

 

[IDS]

The output from the stiffness method is the deflections and rotations at each node. You then apply those deflections and rotations to both ends of each beam, which gives you end actions of each beam. So you set up the stiffness matrix for each beam and multiply it by the displacement vector of the two end nodes.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[rb1957]

1) what s/ware are you using that doesn't give element loads ?

2) the load at the node is going to be shared between the elements according to stiffness. I would calculate the stiffness of each element (axial only ?) then project into the three global axes (that match the nodal loads). Three elements (or less) into a node are solvable, more than three are redundant (but you may be able to use other nodes to infer the load in one, or more, elements and so solve these too.

3) get a better FE s/ware !

another day in paradise, or is paradise one day closer ?