PDelta(large)_1(Converge).stdPDelta(large)_1(Iteration).std
Hello,
Firstly, thanks to all of you reading this.
I tried to understand what they(number of iteration, converge) do of P-delta analysis.
As per the help of STAAD(C:\Program Files\Bentley\Engineering\STAAD.Pro CONNECT Edition\Help\std_dls_P-Delta_Analysis.html)
- "Number of iteration" make perform analysis for the specified number of iteation whether or not converges.
- "Converge" make perform analsysis for the speicfied number of iteration. But if the convergence made, then the analysis will be stoped.
I thought that there should be no difference if there is no difference of numbers.
As you could find out the attached files, the only difference of command is that usage of "converge" or "number of iteration".
The numbers are same "3". and the they both did 3 times iteration.
So, I assume that the results will be same.
However the some results are different as follows:
1. Support reaction at Node 1.
1) Iteration : Fx=-2 kN
2) Converge : Fx=-7.712 kN
( It is obvious that, the "converge" makes the moment equlibrium of support reaction from the second order moment(77.12kN-m) )
2. All Relative Displacement at 5m height of Beam 1
1) Iteration : y = 282.148 mm
2) Converge : y= 75.106 mm
(I could not find out what this means)
3. Node Displacement at Node 2
1) Iteration : x = 1504.790 mm
(if, this function do not care about convergence, it shoud be 390.24mm = PL^3 / 3EI = 2.0 kN * 10m^3/ (3*2.05*10^8kN/m^2 * 8.33*10^-6m^4) )
2) Converge : x = 1504.790 mm
(From simple manual calculation - 1504.790mm = PL^3 / 3EI = 7.71 kN*10m^3/ (3*2.05*10^8kN/m^2*8.33*10^-6m^4)
As you could see above mention, not like the STAAD help explanation,
Not only the "convergence check" is added by the "converge function".
However there are no "detailed explanation" of them.
To sum up, Could anyone kindly tell me
1) What "number of iteration" and "converge" are ?
2) What "number of iteration" and "converge" do differently ?
For subscribers, I herewith post the response from the [Service Request] as below:
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I would like to inform you that the issue you have reported was logged for our developers:
Defect 1069490:[Engine] "PDELTA CONVERGE is defective and needs to be removed" -
PDELTA CONVERGE, Note that the STAAD program is making a SRSS comparison of the full system displacement vector for 2 consecutive iterations.
Convergence is not tested for iteration 2 to allow a more reliable vector to compare with.
This procedure is rarely successful without trial & error, hence not recommended. Particularly because enforcing a fixed number of iterations is just as reliable.
I will set this Service Request to Open - Defect Filed.
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Answer Verified By: Ko, JungMo