Product(s):	RAM Elements
	Version(s):	Any
	Area:	Analysis; Modeling

 

 

How can I assign a member to be tension-only?

In the Spreadsheet, go to Members - Axial behavior and for any tension only braces select Axial rigidity = "Tension only" or use the Ribbon menu tool "Tension only" once you have only the desired members selected.

Normal, linear biaxial behavior is "Full".

"Compression only" or "Cable" options are also available.  

In prior versions this was included on the Member - Hinges spreadsheet. The first field was for "Axial rigidity".  

Why is my tension-only brace failing in bending?

There are three typical reasons why a tension-only member will induce bending.

1. If the member ends are fixed, a tension-only member can still develop an end moment. Tension-only members are typically hinged at both ends in both M3 and M2 axis, if not also torsion.
2. If self-weight loads are applied this will cause the member to bend or sag under its own self-weight. To alleviate this issue we suggest using a weightless, zero density material for tension only member. An "A36 weightless" material is provided out of the box for this purpose.
3. If the tension-only member intersects other members and the Finite Element analysis option to "Add intermediate nodes at member intersections" is checked, then there will be intermediate points of connection (without hinges) leading to force transfer and potentially bending. 

We suggest not using this option for models with tension-only braces. If there are other places where you really want joints at member intersections, manually segment those portions using Process - Segment selection.

Why are my combined forces not equal to the sum of the load case forces?

When you run a P-Delta analysis, or a tension-only analysis, or compression-only analysis, each combination is solved directly. We do not use addition, or superposition, to calculate combined effects since a member that might not be in compression due to one load may be in compression due to that same load combined with another.

Under Process - Analysis - Condition tab the user can select which cases or combinations to include.

See Also

RAM Instability In Finite Element Analysis

RAM Frame - Tension Only [FAQ]

Ram Elements Load Combos [FAQ]