Continuous Beam Support Loads

[JLKDS]

Hello all,

I am trying to calculate the support loads on a 10m I-beam that will be fixed at 1m intervals. There are 4 point loads representing trolleys but I will not be treating them as live loads at this point. I am using SimXpert 2012 to try and model the beam by meshing a straight curve and then using the Beam function in 1D properties. The results are attached ok but when I try and display results as a FBD to show constraint forces, I get the following message:

"The selected result does not contain [Grid Point Forces, Constraint Forces] and [Grid Point Moments, Constraint Forces] data for plotting constraint forces"

I'm pretty sure I must be constraining the beam incorrectly. Could anyone advise me on the correct way to do this. I have attached a screen shot of what I've done so far.

Many thanks,

Pete

 

[rb1957]

you are over constraining the beam. are there really axial constraints at each support ? the LH end (looks like fully fixed) should not be constrained in the memonet that is reacted by the beam support reactions. but that shouldn't stop the run from working, it'll just mess with your reasults.

maybe your run failled, and that's why there's no data. your beam 1D property includes I right ?

 

[JLKDS]

Thanks for your reply rb1957

Using one point which is fully fixed allowed the calculation to run, I can see deformation and bending stress results but not loads.

If I just have the beam constrained in the vertical, Nastran won't run and In get this message in the log:

USER FATAL MESSAGE 9050 (SEKRRS)
^^^ RUN TERMINATED DUE TO EXCESSIVE PIVOT RATIOS IN MATRIX KLL

I have included the correct geometry of the I-beam cross section.

Any thoughts?

Cheers,

Pete

 

[rb1957]

yes, if you constrain just in the vertical direction, then you are restraining only two (Fz, My) of the six rigid body motions. so you need to restrain the other four on the model.

i don't know your software but if you can read the f06 file (your error message looks like NASTRAN) you can find the reactions.

you can also deduce the reactions by the change in shear in the beam elements either side of a support. maybe plot beam forces ?

but both these methods are too difficult for today's easy to use packages. i think you're missing something.

 

[JLKDS]

I'm sure I have all six motions constrained, yet I still get the same fatal error (9050) in the Nastran f06 file, saying that it is not constrained correctly. I can't find what is wrong with my model nor can I figure out what I'm missing.

Here is the model at present:

Can anyone see anything blindingly obvious. Really don't fancy taking on continuous beams by hand!

Cheers,

Pete

 

[rb1957]

this looks different from your first pic ... the LH support looks pinned (before it looked fixed) ?

if it is pinned, there's nothing taking out torque.

before the model was running, right?, and your problem was seeing the reactions ?
the message said something like "no GPF", so maybe you need to evaluate Grid Point Force balance to get constrinat forces ??

 

[JLKDS]

Yeah it runs fine when fixed at one end, I guess I didn't understand the difference between fixing and pinning in all three directions but I understand it now.

I think you're right that my main problem is the GPF, I've been trying to find how to evaluate it but can't find it.

Apparently it's in the model browser > simulations > nastran job > load cases > output request

However, load cases is the last item in the tree and I cannot find output requests anywhere. Is there another way to modify the GPF balance? Or is the reason I can't see the file part of a the larger problem I am experiencing?

Cheers,

Pete

 

[JLKDS]

Wait, forget that, found it now. My apologies!

Pretty new to SimXpert if you couldn't tell

Pete