AXIAL LOAD DUE TO GRAVITY LOAD NOT LATERAL LOAD

Dear all

 

Greetings.

 

I have model here contains of the main frame "rafter +column" (for gravity load +lateral load) + the lateral system (strut pipe +x bracing).

my question is :-----design output shows the highlighted member fail due to gravity load(dead +roof live load) not due to the  lateral load as it suppose , is there any way to let the program to analysis the model by applying the lateral load “wind " on the highlighted member then the load will transfer to the bracing .

 

In other way can i let the program to ignore the axial load from gravity load..

 

 

Is my load path assumption as described above is correct?

 

 

Note : i believe the members fail from the local deflection that occurred because of the gravity load ( is that correct ? 

 

 

Thanks. 3005.3D.std

Parents
  • You have already declared these as TRUSS members and there are no loads directly applied on these members. So whatever axial forces you are seeing in these members are due to the framing effect. You can always use a separate load list and a separate design command block to design these members only for certain specific cases  but I would not advise doing that as these members are going to experience these loads in your real structure and unless you have any special arrangement to prevent that from happening, you should make sure that these members can actually carry the loads. You did not include any DFF command and so deflection is not being checked here. The design failures are either strength failures or slenderness failures for some cases.   



Reply
  • You have already declared these as TRUSS members and there are no loads directly applied on these members. So whatever axial forces you are seeing in these members are due to the framing effect. You can always use a separate load list and a separate design command block to design these members only for certain specific cases  but I would not advise doing that as these members are going to experience these loads in your real structure and unless you have any special arrangement to prevent that from happening, you should make sure that these members can actually carry the loads. You did not include any DFF command and so deflection is not being checked here. The design failures are either strength failures or slenderness failures for some cases.   



Children
  • Thank you Mr.Sye  for your reply but i have more queries : 

    1- you mentioned that i declared these member  as truss, should i  specify them as something else? i assumed these member are going to transfer the lateral load and make the structure stable  in the direction of bracing .

    2- you mentioned that there is no direct load on the member ..should i but a direct load on the members as per attached instead of modeling the whole structure together (gable frame with the front column  +main frame   .?

    3-you mentioned that i can separate the analysis & design of these member . a) can i do it at the same model ? kindly explain in detail if it possible ?.     b) how can i  eliminate there contribution  in the stiffness from other load cases without making my structure unstable ?

    4- DFF command  Dj1 Dj2 suppose to be from column to column am i right  ? "what is the lateral drift value for column , i have table for vertical displacement but for horizontal i do not have, kindly advice .

    5- is the FRAMING SYSTEM and load path assumption for the model from your EXPERIENCE  &YOUR POINT OF VIEW . GOOD ENOUGH OR NEED IMPROVEMENT. 

    6-  i quoted you" these members are going to experience these loads in your real structure and unless you have any special arrangement to prevent that from happening" is there any arrangement can , or tis what is going to happen in real life .

    Thanks a million