Applies To
	Product(s):	STAAD.Pro
	Version(s):	ALL
	Environment:	ALL
	Area:	Analysis
	Subarea:	Direct Analysis
	Original Author:	Sye Chakraborty, Bentley Technical Support Group

 

I am running a DIRECT ANALYSIS but have some tension only members in my model. When I run the analysis I get the warnings like

 

**WARNING: TENSION/COMPRESSION SPECIFIED WITH PDELTA KG OR

DIRECT ANALYSIS. SO TENSION/COMPRESSION IS SWITCHED OFF.

 

**WARNING: DIRECT OR PDELTA KG ANALYSIS REQUESTED.

SO TENSION/COMPRESSION ANALYSIS IS NOT ALLOWED.

 

Seems like the MEMBER TENSION is being ignored by the program when DIRECT ANALYSIS is carried out. Is there any way for me to run a DIRECT ANALYSIS with MEMBER TENSION in it ?

 

As of now, STAAD.Pro does not allow Tension/Compression members to be used in a DIRECT ANALYSIS or with a PDELTA KG ANALYSIS. If TENSION/COMPRESSION is assigned in either of these type of analysis, these attributes are turned off and the members are simply treated as TRUSS members which can take both tension/compression. The warning messages specified above, are indicative of that.

It may be worth noting that the iterative PDELTA analysis, namely PDELTA nn ANALYSIS is the only second order analysis that supports MEMBER TENSION ( or COMPRESSION ) specification.

 

As a workaround, you can do one of the following.

 

Workaround Option 1

Run a DIRECT ANALYSIS with these members specified as TRUSS members instead of MEMBER TENSION. Check the member forces to find out for which load cases the axial forces in these members come out as compressive. Use the INACTIVE MEMBER command to deactivate these members for these cases and rerun the DIRECT ANALYSIS. The members can be active for other cases for which they develop tension force.

 

For details on how to run a DIRECT ANALYSIS with INACTIVE MEMBER specification click here

 

Workaround Option 2

Use a PDELTA nn ANALYSIS, which supports MEMBER TENSION, in lieu of using DIRECT ANALYSIS.

 

The same workaround applies for PDELTA KG ANALYSIS as well.