Combining analysis command

Question

Hello, 
 
 1) If after P-delta analysis i got an output that the problem is divergence for a particular load case, does this mean the structure has collapsed. And if so, do I need to resize the members or remodel the whole or part of the structure to make it more stiff? 
 
 2) If i combine two analysis, say: Buckling analysis and P-delta analysis with CHANGE COMMAND in-between them, the results of displacements, Moments, that will be displayed in the post-processing belongs to which of the analysis? 
 
 3) If bucking analysis shows that the buckling factor for the first mode is less than 1, then i move on to perform p-delta analysis and the analysis converges, does this mean if i proceed to design with the moments and forces in the post-processing i have done the right thing as long as those members pass? Does this mean the p-delta analysis is to give us much more ideal results (forces and moments) for a structure which is closer to buckling so that we can design it with these results rather than the results of linear analysis? 
 
 Thanks

DSANJU · Answer

Here is my response- 
 Answer to Q-1. This indicates that the stiffness of the structure should be increased. Yes, you need to increase the section size. 
 Answer to Q-2. You need to create two seperate files for these two type of analysis. Say, after Load case 1 you have buckling analysis command followed by a change command and after load case 2, you have p-dealta analysis command. Results of load case 1 will be buckling analysis and 2 will be of P-delata analysis. Please note that if you perform a buckling analysis,the post processing results are not meaningful rather you should look into the buckling factors and buckling mode shapes. 
 Answer to Q-3. If you get buckling factor < 1, this indicates that the loads are higher than that f buckling loads for the structur. In this case, you need to increase stiffnss of the stuctue before you go for 2nd order analysis.

DSANJU · Answer

Answer to Q-1. P-delta post-processing results are meaningful and it considers 2nd order anlysis effect. 
 Answer to Q-2. Please note that P-delta analysis needs to be perforned to capture 2nd order effect for combined vertical and horizonal loading. 
 Answer to Q-3. In such a case, whichever is the 1st type of analysis command, the program will honour that. As I mentioned earlier, buckling analyss is performed to check if the stucture can withstand the loading applied to be without buckling. On the other hand, for the design purpose, P-delta analysis needs to be carried out.