We have cases for the Analysis and Design of Structural steel members as noted below and in the attachment. Please advice with the algorithm, the possibility of simulating the inputs in the Staad Pro to match the conditions as below to get the structural behavior in the Analysis and Design.
Case 1: Beam with Pinned / Fixed ends
1) The member ends will be with pinned support initially, and the dead loads are applied with this stage, so the internal forces in the members and deflection due to dead loads are locked.
2) During this stage, member ends support are to be converted as fixed ends, then the pinned supports to be removed, and then the live loads and other loads are to be applied to the deflected shape of the structure caused by point 1 (case 1).
Case 2: Portal frame (two columns and a beam connecting the columns at top, with pinned/fixed base for columns)
1) In the portal frame, the beam member end releases will be with pinned support initially (beam to column with shear connections – simple joint), and the dead loads are applied with this condition, so the internal forces in the members and deflection due to dead loads are locked.
2) During this condition, member ends support are to be converted as fixed ends (member end releases to be removed, beam to column with moment connections – Rigid joint), then the pinned supports to be removed, and then the live loads and other loads are to be applied to the deflected shape of the structure caused by point 1 (case 2).
K. Mahesh Kumar
Regarding the Case -1
Lets compare your condition with the real life situation .
Take a beam whose ends are pinned and load it will load DL . After attaining a deflected shape , lets somehow lock the pinned supports or grout the end fixity and then add more load and then analyze the structure .
As far as I know , there is no such direct way to model such condition in Staad .
However, indirectly you could simulate such situation .
First , analyze the beam model (pinned ends) with Dead Load (DL) . From the out-put files or post-processing mode, note down the deflected shape and internal forces like moment , shear etc .
Now, model another structure in seperate Staad file of the same beam . But this time , model the beam whose shape is almost same as that of the deflected shape you noted down from the first case . Assign the end supports with fixed end support condition (inclined support may be opted ) , then apply the LL load here and run the analysis .
You would get the deflected value and the end forces of the new structure .
Eventually , add the deflected values and internal forces reported from both the models to know the actual result .
If the above suggestion suffice your requirement then you can use it for the Case 2 .
Thank you, for the indirect approach to solve the issue. This concept may be workable for the structure involving less number of members. But for the structures involving more than 700 members this concept will be very much time consuming work, that to, to combine with the lateral loads.
Are there any other way in the Staad Pro to deal with these kind of requirements by using the existing commands like Change, inactive, Second Order Analysis like imperfection analysis, etc...?
We have to analysis the structure initially with the dead load cases alone with pinned ends at the end of the structure, the deformed shape and the internal forces due to this case to be carried over to the subsequent stages by adding the other loads, change the end supports. Basically, the matrix arrived for stage 1 (Point 1) to be retained and to be used in the stage 2 (Point 2) along with the other changes at this stage.
The condition that you have cited is a very different and extremely rarely case . Staad has the ability to handle nonlinear analysis like P-Delta analysis ,Imperfection analysis ,Direct Analysis . But there is no such option available to instruct Staad to change the support condition amidst the analysis ,where the structure after attaining a deformed shape under the first loading , the support condition could be modified and new loading pattern would be applied on that deformed model in a single model .
By using the CHANGE command , although you can change the support condition and re-analyze the structure , but that would not serve your requirement as this command would completely reset the stiffness matrix and the previous deflected shape could not be captured for next set of analysis .
if the support condition is same , then you could opt for P-Delta analysis .