SAP2000 Buckling, P-delta, P-delta+ large different results
SAP2000 Buckling, P-delta, P-delta+ large different results
(OP)
Dear all,
I've posted this thread in "STR engineering and other topics" and I had no Response
So Iam posting it again here since this forum is dedicated for SAP2000; hopefully I might get any response.
I have the following problem. I am trying to find the buckling load for the beam in attached SAP file. The following are the strange results I’ve got:
Eigen Value buckling (buckling analysis) = 39X1 tons
P-Delta Non-linear analysis = 9 tons
P-Delta + large displacement Non-linear analysis = 72 tons
Though I know that the buckling load is near the 39 tons , the more important question why is there so much difference between the difference analyses, and even more important why is there a difference between P-delta and P-Delta + large displacement
Note: the file may take a bit while running also refer to the plot function of joint 393
I've posted this thread in "STR engineering and other topics" and I had no Response
So Iam posting it again here since this forum is dedicated for SAP2000; hopefully I might get any response.
I have the following problem. I am trying to find the buckling load for the beam in attached SAP file. The following are the strange results I’ve got:
Eigen Value buckling (buckling analysis) = 39X1 tons
P-Delta Non-linear analysis = 9 tons
P-Delta + large displacement Non-linear analysis = 72 tons
Though I know that the buckling load is near the 39 tons , the more important question why is there so much difference between the difference analyses, and even more important why is there a difference between P-delta and P-Delta + large displacement
Note: the file may take a bit while running also refer to the plot function of joint 393





RE: SAP2000 Buckling, P-delta, P-delta+ large different results
Please explain your criteria for determining buckling with the P-Delta and P-Delta with large displacement cases.
Also, I believe your "Axial" load is 4.4 Kips, not 1 ton, so your Eigen buckling factor would be 39 X 4Kips, not 39 X 1 ton. You appear to have double-assigned joint loads for the Axial load pattern. Your joints have two load assignment for the same load pattern. When you assign loads, you have choices to Add, Replace, or Delete existing loads
RE: SAP2000 Buckling, P-delta, P-delta+ large different results
thank you for your response
and This is embarrassing, you are right about entering the axial load. I don't know how it slipped.
The Axial load then becomes 1.999 tons.
Which now , Wow, makes the Eigen -Value results equal to the P-delta+ large displacement i.e. 39*1.999 = 78tons
the problem then seems to be be with the P-delta only.
to answer your questions , its as follow:
1-I tried the Eign analysis with the lateral load (actually as rest of the cases 0.01 * lateral) it did not affect the buckling analysis much.
2- The difference between the two scaling factor between the P-delta and P-delta + large Is
if I assigned the 40 scale factor for the P-delta, the analysis runs forever (i.e cannot find an answer) that is the the buckling or convergence load is small that the load step cannot capture it
If I assigned the 5 scale factor for P-delta + large, the analysis does not reach the buckling load and the plot function is still linear
therefor I had to make trial to reach the convergence or instability (buckling) load
3-for the joint I've answered it above
the problem now is with the P-delta analysis results