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## Robot Structural Analysis

New Member
Posts: 2
Registered: ‎01-02-2012

# quadratic combinations and cable elements

394 Views, 2 Replies
01-02-2012 09:19 AM

Hello,

To calculate a guyed wired mast , the Eurocode requires a dynamic wind analysis. This can be done using patch wind loads.

These patch loads need to be combined with a square root of the sum of  squares combination. You can do this with a quadratic combination. The problem is when using the cable elements the analysis type changes to non linear and the quadratic combination square cannot be checked.

Is there a way to combine a quadratic combination and a non linear analysis? Or is there another way to make a square root of the sum of  squares combination?

Kind regards

Product Support
Posts: 480
Registered: ‎06-23-2008

# Re: quadratic combinations and cable elements

01-03-2012 02:24 AM in reply to: pieterdc

Hello,

the workaround to avoid this limit and to define quadratic combination in non-linear model is to:

1/ run analysis of non-linear model without any combinations,

2/ after completing analysis defining combination(s) without "Quadratic" attribute - in combinations dialogue or on Edit tab of the table of combinations,

3/ opening the table of combinations on Edit tab (if it was not done in step 2/),

4/ clicking right mouse button to open context menu, selecting "Table Columns...", activating "Quadratic combination" in the dialogue and accepting by selecting OK - additional column SQRT will be displayed in the table

5/ selecting YES in SQRT column for appropriate combination(s)

Results for combinations with SQRT attribute set to YES will be calculated as SRSS quadratic combinations of appropriate results of combination components - see the attached screen capture made for simple example.

Opening the Analysis Type window in above case will result in change of the status of results from "available" to "out of date" and results for combinations will become not available (N/A in table of results).

Running analysis again in above case will result in loosing quadratic combination status in combinations it was defined in step 5/.

Additional note: it is important to remember that in case of models containing cables assembling load case (case 1) is automatically considered in other load cases. In case of using the workaround described in steps 1/ to 5/ the assembiling load case (usually by default self-weight) may be considered in combination several times from different combination components.

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Best regards,

Pawel Pulak