Why will the analysis not complete when my model has tension only bracing?

Problem

Tension only bracing requires non-linear analysis, since a model with tension only bracing is fundamentally non-linear in nature. 

Non-linear analysis may have problems with some less common problematic geometry and or loading situations, where most or all braces undergo compression during analysis and become inactive, producing an effectively unbraced and thus unstable structure.  This instability can prevent an analysis solution from being found, especially for 2nd order non-linear in which an unbraced structure will be susceptible to buckling behaviour.
 

Resolution

Tekla Structural Designer 2017 has introduced Relaxation factors, as a means of resolving this issue.

Relaxation factors control an amount of nominal compression, that tension-only braces can undergo while remaining active during analysis iteration. When converged, these tension-only braces will still have only either zero or tension force. The process is entirely automatic by default and it is anticipated the factors will not require manual editing for most circumstances.

Relaxation factors are not activated by default as it is anticipated they will not be required for the majority of models. In addition, since the solution process is more complex, their use can increase the analysis time to a degree.

If you find that you have issues, you can turn on Relaxation factors by;

1. Accessing the Analyse ribbon > Options command
2. Selecting the Non-Linear analysis you are attempting to perform
3. Checking the option Use relaxation factors for tension only bracing

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If the model still fails to converge when using relaxation factors, expanding the allowable range (by changing the above minimum and maximum values) may produce convergence.  For more about this see the related article Non linear Relaxation Factors FAQ