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As far as X direction is concerned the difference is minimal and this is understandable as you have the knee braces right below the Tees and that is kind of arresting the lateral movement of the bottom nodes for the Tees and so the support for the Tees in the combined model is behaving similar to a fixed support as used in the separate model. However for the Z direction, the structure is lot more flexible and the base and the top of the Tee are displacing by larger amounts as you are kind of relying on the minor axis bending stiffness and the torsional stiffness of the supporting beam ( underneath the Tee) which is far less than what a fixed support stiffness is. You may consider bracing the bottom of tees in Z direction if deflection is a concern.
Answer Verified By: Anbalagan A
Thanks Sye, I have two more doubt on this subject
1. Even though torsional stiffness of the supporting beam is less, why I am not getting any difference in the strength utility ratio. please clarify ?
2. Is there any other design justification other than that T post is welded to the supporting beam. , for modelling the T post in separate STAAD model.
@Sye :- could you please help on the above soon
You may check the critical condition for design and also the critical load case and that may tell you why the ratios are same. Modeling the T post in a separate model with fixed base is not as accurate as modeling the T post as part of the combined model.