FEAP User Forum

FEAP => FEAPpv => Topic started by: rkiseral on January 10, 2014, 12:53:27 PM

Title: unexpected reactions when running a simple cantilever beam test case
Post by: rkiseral on January 10, 2014, 12:53:27 PM

Hello Dr. Taylor and FEAPpv Admins

I am using FEAPpv to run a simple cantilever beam test case and an finding unexpected results in the computed reactions.  Basically, the model is a round bar along the Y axis loaded at its tip with a force in the Z direction.  The nodes are constrained to only allow Y and Z deflection and rotation about X.

At the fixed end, I get the expected reaction force in Z and the expected moment reaction about X.  At the free end, I get the expected values for deflection and rotation that match hand calculations from Roark & Young's handbook.

However, at the fixed end I also see a large reaction force in X and a large reaction moment about Z that I didn't expect.  Since there was no X force input, I don't see where these reactions came from.  Although I am a novice w/ FEAPpv, I don't see that I have made any modeling errors or assumptions.

Have I made some huge freshman-year blunder here or is something else going on?  I have attached a copy of my test case input file for your perusal.  I would very much appreciate any help in getting to the bottom of this.  I am using FEAPpv 3.1  64 bit version.

Thanks in advance for your attention,

Robert Kiser, PE

Title: Re: unexpected reactions when running a simple cantilever beam test case
Post by: FEAP_Admin on January 10, 2014, 04:13:27 PM

I think the problem is that your area moment of inertia tensor has a non-zero off-diagonal element.  Thus you are are getting coupled two-axis response -- or in other words your force is not aligned with a principal axis of the cross-section and this is generating unexpected couplings.  Try:

Code: [Select]

CROSs, SECTion,    0.7854,  0.04909,  0.04909
The ordering can be found on page 58 of the FEAPpv user manual.