Hello!
I'm a CE student and im trying to design a structure made up of steel.
I would like to know what connection do I actually use for the support on trusses, and on STAAD.Pro do I place the truss on my structure or do I analyze the structure by two parts first the truss then transfer the loading to the steel columns?
Thank you!
The reason you are getting these zero stiffness warnings is that you have certain nodes where there are no stiffness associated with certain degrees of freedom. For example if you look at the node 10, all the members connecting to that node are trusses lying in the XY plane. So if there is a load in the Z direction at that node, there is no way for the structure to resist that load which is why you get the zero stiffness warning at that node for direction 3 ( which represents translation in Z ). In addition since all the members at that joint are trusses, there is no rotational stiffness about any of the global directions ( 4, 5 & 6 ).
In your model there are no abnormal displacements and the static check seems to be satisfied. So as far as I can see, the zero stiffness did not have an impact on the analysis.
You find more on zero stiffness at the following wiki
https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/29020/zero-stiffness-warning
Instructions on uploading files in Bentley Communities forum is available at
https://communities.bentley.com/products/ram-staad/w/structural_analysis_and_design__wiki/28129/how-can-i-upload-files-in-the-bentley-communities-forum
Dear Mr Sye,
I have some warning from STAAD as :
ZERO STIFFNESS IN DIRECTION 3 AT JOINT 10 EQN.NO. 51LOADS APPLIED OR DISTRIBUTED HERE FROM ELEMENTS WILL BE IGNORED.THIS MAY BE DUE TO ALL MEMBERS AT THIS JOINT BEING RELEASED OREFFECTIVELY RELEASED IN THIS DIRECTION.**WARNING - THERE WERE MORE THAN 12 DOF WITH ZERO STIFFNESS.
Should I be worried about it? I applied TRUSS spec to only to intermediate truss element whereas not any spec to top and bottom chord as suggested by you.
Second, for the truss member, Does the member orientation ( beta angle ) affects much? I suppose truss has compression and tension only .. so I didn't care much about the rotation of each truss element ... will that be alright...?? My truss elements legs are parallel to global axis thus I applied BETA ANGLE, However, the orientation of unequal angle seems to be opposite.
I tried to upload my file here but doesn't know how.?
https://drive.google.com/open?id=0Bx8YDHIrp3cXMHBNYUw1Y0dsNzQ
Yes that should work.
Thank you Mr. SYE.. Thats seems to be the solution. One more thing, Since my roof truss has attributary area little bit complex for hand calculation of wind load from roof covering to the member. I am thinking to make plate member with zero stiffness and apply the wind pressure to the plate member. Will this be the correct way of doing it ??? Once again thanks.
Since your truss support is 15 cm high, why don't you model these supports using short vertical members. These would connect your truss and the base frame.