Why is the design status of all the steel members unknown after running a Design? I am using the United States (ACI/AISC) Head Code.

Tekla Structural Designer
Not version-specific
Tekla Structural Designer
design
resistance
code
combination
ASD
LRFD
unknown
steel
status
unknown status
results
Environment
USA

Issue

I am using the United States (ACI/AISC) Head Code and after running a Design the design status of all the steel members is Unknown or Not yet designed.  Why is this?

 


Answer

Mismatched Resistance Code(s) and Design Combinations

A common cause of this issue is when the load combinations defined do not match the chosen Resistance design code. Go to the Home ribbon > Model Settings then to Design Codes and select the Resistance Codes tab. The design code for Steel Design and Composite Design are specified here.
 

Image
Combinations.jpg

 



Under the Load ribbon open the Combinations interface to see the load combinations being considered in your model. TSD will perform the design checks required per AISC using either the ASD or LRFD procedures. For example, if the LRFD Design Resistance Code option is selected in the Model Settings, there must be at least one LRFD combination defined in order for the program to perform a design. If there is not, there are no combinations to check and the status of each steel member will therefore be unknown.  Note that if the Resistance Code is modified, all load combinations will be removed from the model and you will need to recreate the load combinations.

 

 

 

Image
Combinations(1).jpg

 

 



Any changes made to the Model Settings under the Home ribbon are specific only to the current model being worked on. The default settings for all future models created in TSD can be modified under the Settings menu in the Home ribbon.

Design Process Terminated due to Mechanisms/ Excessive Deflections

If there are excessive deflections from analysis - which are commonly caused by mechanisms - the Analysis & Design process will terminate before the design stage is run.  Hence the design status of members will be Unknown or Not yet designed

Check the Process Window for any error messages such as, "Analysis error - structure unstable, review deflections" and "Design failed due to analysis errors".  If you see these you should investigate the cause of excessive deflections - we recommend you proceed as follows:

  • Run 1st Order Linear Analysis directly from the options on the Analyze tab of the ribbon.
  • Review the Solve messages in the Status Window - there will commonly be warnings about mechanisms and/ or excessive deflections.
  • Review both the shape and magnitude of deflections, these should guide you to understanding the nature of the modeling error(s) causing excessive deflections, such as missing supports or too many releases etc.
  • For more advice on resolving such issues see the article Guide to Resolving Mechanisms.

Do not attempt to run Design until you have fixed the model problem(s) and have reasonable deflections for all load combinations.

 

 

Was this helpful?