ANALYSIS!!

[helpplease]

I have programmed Analysis of Plane Frames using Direct Stiffness approach i.e. regular procedure consisting of Discretization,applying member properties,defining member loads,joint loads,applying boundary conditions,computing stiffness matrix,assemblage of stiffness matrix,computation of equivalent joint loads and finally computing joint displacements,stress resultants(shear force, bending moments).I have use a beam element(two noded)Now the stress resultants are computed at the nodes. If length between adjacent nodes is "L"and i want the stress resultants , displacements at a distance L/10 intervals can anyone suggest of a procedure?

 

There are several things you can do.

1) You can revamp the beginning of your program to insert extra members and nodes where you want them for 10th point ( etc ) output. If you always want output at those extra points, this is a decent efficient method. However... it does require you to code an algorithm that creates extra members and nodes that your user will never see... a little more difficult than it sounds in the beginning.

2) Once your ouput at the user specified nodes is completed, you can get forces at point x on each member by summing up the left node force on the member and all the applied forces on the member left of point x ( ie, basic equilibrium stuff ). Getting displacements is slightly more difficult but not too bad. The advantage to this method is that your (already written ) code doesn't need too much altering... ie, mainly, you only need to add some additional routines. You will have to be sure that your current code stores all data about your members and their loadings to use at this last stage of calculations though.

3) After your existing program calculates your member end results... you take the member you are interested in and "reanalyze" it. ie. you create a new model existing of that one member broken up into multiple members. It's plus and minuses are similar to 2) above. One additional possible minus... you may have to alter your original code so that it reinitializes a lot of stuff to zero ( or whatever ) so that it can do the second, third, etc. rounds of analysis after the analysis of the large model.

4) Other methods exist. ( there are ways to do stuff that is sort of a combination of 2 and 3 above. )

Let me know what you ultimately decide to do ( and why ).

Dan
dan@dtware.com

http://www.dtware.com

 

[ram1]

Hi,
displacement within the element can be found
using shape function(interpolating function).

u=nq sigma=dbq

u=displacement fn.
n=shape fn
b=element-strain displacement matrix
d=bending stiffness
q=nodal displacement

bye cheers.