Non linear Relaxation Factor FAQs

For a small number of models that are mostly symmetrical, and rely on tension only braces for lateral stability, you may find that for gravity only loadcases and combinations, a first order non linear analysis will fail to solve. This is often due to all braces becoming inactive during the analysis, rendering the structure unstable. Relaxation factors allow the analysis to complete successfully, by determining the state of each brace gradually, over the course of the non linear analysis. This is achieved by altering the stiffness of each brace during the iteration process

Should the model fail to solve due to symmetry we need to introduce an element of randomization to the process to allow the model to settle/sway/deflect in one direction or an other. The range between the min & max settings is the extent of the randomization used to automatically generate the relaxation factor for each brace.

The min and max settings are limited to between 0.001 and 0.999, but the chosen default settings are arbitrary values found to work with all of our existing test cases.

You may choose to alter the min & max settings, however we suggest you only do this if you encounter a model that fails to solve with the defaults, but please bear in mind the following

• Increasing the max will result in larger relaxation factors being applied to the braces and will tend to cause a failure to get convergence because the given brace does not become active or inactive quickly enough.
• Decreasing the max will lead to smaller factors being applied which will speed up convergence however too small and all braces will become inactive - exactly the problem we are trying to avoid.

For a brace that already has a relaxation factor applied setting the relaxation factor to 0 will force the relaxation factor to be determined automatically next time. Should you wish to influence which brace stays active, give the brace a higher relaxation factor and it will tend to remain active whereas setting a lower factor makes it more likely the brace will go into compression and eventually become inactive.