Temperature deformation in construction stage

Question:

Hi all,

please consider the model attached.

It is a simple cantilever beam subjected to a temperature load (stage 1, -176°C) and a compression axial force (stage 2, 1000 kN).

At the end of the stages we expect this axial displacement:

Stage 1) DL1 = alfa x DT x L = 5.45E-6 [1/°C] x 176 [°C] x 1000 [mm] = 0.9592 mm

Stage 2) DL2 = DL1 + N/EA x (L - DL1) =0.9592 mm + 1000000 [N] / (200000 [N/m2] x 100 [mm2]) x (1000 [mm] - 0.9592 [mm]) = 0.9592 mm + 49.952 mm = 50.91124 mm

Note that we considered the new length of the beam for the calculation of the dispalcement due to the force. The length is different beacuse of the temperature load in the previous stage.


Midas civil gives an another value: 50.9592 mm.
We noted that it doesn't update the new length of the beam:
Stage 1) DL1 = 0.9592 mm
Stage 2) DL2 = DL1+ N/EA x L = 0.9592mm + 50mm = 50.9592mm

So it seems that the construction stage analysis is a simple linear combination of effect and not consider the updates of the geometry of structures.

Can you check it or explain us why?
Thank you very much

 
Answer:
Hello,

Thank you for sending your question.
In midas Gen, linear analysis of beam element is based on the assumption of the small strain-small rotation. Therefore, the strain caused by temperature load of step1 is ignored in the deformation calculation of the step2.
Thank you.

Best regards,
Jihong Hwang

Thank you for your reply.

Even setting the analysis as non linear, the results don't change:





Why Midas does not take into account axial large displacement?

Thank you
regards




Hello,

Thank you for your patience.

Generally, in case of actual structure behavior, buckling occurs in the structure before axial large displacement occurs. Therefore, in midas Gen, nonlinear analysis of beam element is based on the assumption of small strain-large rotation. To consider axial large displacement, further development is required . However, it is difficult to develop right now.
For the work-around, program can consider the axial large displacement by using the plate element. However, for the plate element, the construction stage is not applied, so define the load sequence function.
Thank you. :)

Best regards,
Jihong Hwang
Creation date: 7/24/2018 10:46 PM (dklee@midasit.com)      Updated: 7/25/2018 8:17 AM (dklee@midasit.com)
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