Constraints on beam nodes.

kent

If I have just a horizontal beam, simply-supported at each end, and subject to a mid-span vertical load. How do I constrain the two ends in a FEA? The first node can be fixed in all three translations and two rotations, but the other end must not be fixed in longitudinal translation and the in-plane rotation.

Victor

Use displacement and node rotation constraints to allow you individually constrain each direction.

In the attached picture, I accidentally put in a redundant Z constraint which I removed from the liml file.

kent

Victor - many thanks for your explanation. Problem solved.

I have been using Strand7 for the past few years, so my brain found it difficult to change from that program's way of applying restraints (In Strand7, for each selected node, all required restraints are applied from one single pop-up pane), to Mexway's way. (Applying each restraint in turn to all applicable nodes).

I was confused by the red lines in the icons for restraints in the Outline Tree. I thought the red lines indicated a warning or fault.

I am also still confused by the restraint pop-up windows. If I select say the “X” button, then a “1” appears in the entry-box below, and zeros appear in the other two entry boxes. I would have expected a zero, for zero displacement, to appear in the “X” direction box, and the other two entry-boxes to be blank, for no restraint. According to the Manual, Section 10.5 – Displacement, the displacement for a total restraint must be zero.... Could you please explain why a “1” appears?

Even with my confusion over restraints, I am very impressed with mecway, and the User Manual. It has been very easy to learn to use it.

Victor

Thanks for telling me that about the red line. I never considered that possibility before! It's not an error, though when the text is red, that is an error. Right click it to see the error message.

In Mecway, each displacement (or node rotation) constraint is only in one direction, unlike Strand7's 3 directions. A reason for this is that Mecway isn't limited to only 3 constraints per node and they don't all have to be orthogonal to each other. The solver automatically reduces an arbitrary set of constraints to the equivalent 3-axes + rotation like what Strand7 has. I believe this way of defining them is more natural and flexible. It's not so bound to the internal details of how FEA works.

The first 3 boxes aren't constraints in 3 directions like Strand7 has. They're the components of a vector that defines the direction of the single constraint. So for the X direction, they'll be (1,0,0), for Y, they'll be (0,1,0), etc. If you wanted it at a 45 degree angle, use something like (1,1,0). To do that in Strand7, you'd define a coordinate system for it. In Mecway, you specify the direction directly. So if you're only doing constraints parallel to the global axes, just click X,Y or Z and let it fill in the 3 boxes automatically.

The 4th box is the amount of displacement in that direction, which is the same as one of the 3 "Translational" values you can enter in Strand7.

The "must be 0" in the manual refers to nonlinear and dynamic analysis with the internal solver. You can get around that by using the CCX solver.

kent

Hi Victor,
Many thanks again. for your very lucid explanations. All is now sweetness and light. It is now Hello Mecway, bye bye Strand7 for me.

How about incorporating your explanations in any future update of the Mecway Manual, for other "newbies"? (Although the Mecway manual is already probably the "easiest-to-understand" and best technical manual I have ever read.)

Victor

I'm trying to keep the manual fairly minimal and factual. Targeting a broader audience is more difficult to get the balance right.