STAAD.Pro Interactive LEARN Session: Direct Analysis and AISC 360 Specifications

During the SIG session this morning someone was asking about the Tau-b reporting. Just wanted to mention that information on Tau-b are printed as part of the analysis output file. If such messages are not required to be printed, one can turn those off by using the following SET command as part of the command file.  

STAAD SPACE

START JOB INFORMATION

ENGINEER DATE 16-Nov-08

END JOB INFORMATION

INPUT WIDTH 79

SET NOPRINT DIRECT

UNIT FEET KIP

JOINT COORDINATES

...

During the SIG session this morning, some of the users wanted to know more about the 18 warnings obtained during the analysis. I am checking the model now and these were being caused by the fact that there were zero stiffness at certain locations in the model for example at the intersection of the X braces. Since the braces were specified as TRUSS members, at the intersection there was no ability to carry an out of plane force. These zero stiffness were causing high displacements at the nodes which were eventually causing the direct analysis to diverge leading to additional warnings. Working on the model right now. Will upload it shortly ...

Here is an updated version of the model used in the SIG session. The warnings are now taken care of. Had to add a couple of X braces to add to the lateral stability of the frame. I noted that some of the members are failing in design but of course that is expected as there are no design parameter definitions in the file. One can always add parameters like UNT UNB to specify the correct unbraced lengths and the model can also be refined further but even without these, this model may serve as a useful practical example for users using the Direct Analysis feature.

Plant-Bldg3-US-Direct-Analysis-2010-SIG_modified.std