# pro mechanica hardship

IM desperately trying to get pro mechanica to give me reliable stress
analysis.
Basically im trying to analyze a simply supported beam with a single
load at the center. It gives me stresses at the ends but bending
stresses should not exist.
distrabution does not make sense when I check by hand. Ive made
complete restraints at the ends of any reactions or translation.
Thanks!
...Did you mean "should" exist?
How are the constraints applied to the ends? (e.g. If you completely constrained both end surfaces of the beam in all axes, it's not a "simply supported beam" simulation).
Your correct on not being a simply supported beam. But having fixed ends on a beam (translation and rotation) and one force in the middle means no moment on the ends and maximum monent in the middle. Picture a T and the force is applied at the bottom. Its a surface load. All rectangular tubing.
In the original post you stated; "but bending stresses should not exist." However if you've fully constrained both ends of the "T" and you're applying a surface load at the "bottom branch" of the "T" then, I would fully expect to see stresses at the ends & bending in the middle (or intersection of all "branches" of the "T") among other things. It's difficult to tell exactly what the problem is with such little information...
Here's some advice that might help: It's a common mistake is to over-constrain a ProMechanica structure model. That makes the structure model too ridged and does not allow the structure to flex as it should under load during the analysis. Also if a model is under-constrained, the analysis can provide unrealistic results or fail altogether. Those problems can be avoided if you perform the application of constraints as follows:
Apply the least amount of constraints necessary to; 1) react to the load as expected (free body constraints) & 2) prevent unwanted rigid body motion (rigid body constraints).
First apply the free body constraints to simulate how the structure will be secured in the real world. Then check for any unconstrained "rigid body" degrees of freedom and apply minimal constraints to prevent unrealistic motion of the model in "virtual space".

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