Learning Forum

[DIWAS2441]

Hello, I have analysed a single column(BEAM189) with following conditions:

Material: Structural Steel NL with BISO, yeild strength: 250MPA and tangent mod: 0;

Model: Rec Tube: (500*500-thickness 30); length: 5000mm; Orientation: vertical

BC: Fixed Rotation at both end, displacement: along X- direction with cyclic displacement

No damping condition.

Solution: Force Reaction(Displacement BC)-Deformation plot 

Problem: The force deformation plot is nowhere near expected results. 

Done a separate modal analysis also.

But when I choose a fix support at the bottom and displace the top using the same displacement the results are OK. 

I expected the result somewhat to be like this which I got from the fix support analysis.

[peteroznewman]

Applying a sawtooth displacement-time history in a Transient Analysis means accelerations approach infinity at each peak and valley as the time step approaches zero. This makes the analysis noisy and time step dependent.

You can apply a sawtooth acceleration-time history without harming the solution quality.

In your Modal analysis, you have to drag and drop the Fixed Support from the Transient above onto the Modal. It doesn't pick that up by itself.

I assume you don't have a Modal as a Pre-analysis in the Initial Conditions for the Transient because that creates a MSUP analysis which is linear where plasticity is ignored.

 

[DIWAS2441]

@peter, the drag and drop lesson, hats off... thankyou very much... I am still trying one the time-step trick you gave in another post to reduce the sinusoidal effects. I will apply and come back here quickly for more response. Thankyou very very much. Hope it works.