Zero length element

[jonade]

I wanted to assign material for zero length element only in the z rotation. I know opensees is unitless but for rotation, I am not sure how opensees works. How will opensees determine the rotation is in degrees or radian?

[Prafullamalla]

uniaxialMaterial Steel02 $SpringM2Tag $M1 $MTheta 0.001 18.0 0.925 0.15;
element zeroLength 1 1 2 -mat $SpringM2Tag -dir 3

Here M1(Nmm) is moment and MTheta is slope of moment and rotation curve(radian)

[jonade]

Thank you

[selimgunay]

Rotation does not have a unit, and moment units should be consistent with the remainder of the model

element zeroLength 1 1 2 -mat $SpringM2Tag -dir 3

If you do this, you will have zero stiffness springs in all the other dof. If you want the other dof to be rigid, you should use equal displacement

[jonade]

Thank you selimgunay. so if rotation is unitless does it mean I need to make the rotation unitless, if moment and rotation curve of the material is specified in knm and radian respectively. Since I am recording the deformation of the zerolength element i need to know which unit it is using.

[Prafullamalla]

Thanks
Since your unit of Force is kN, and displacement is mm, your deformation will be in mm

[selimgunay]

That is not correct. Rotation should be unitless and moment should be in kNm if the force and displacement units in the remainder of the file are kN and m respectively

[jonade]

i am grateful for your swift replies. But I still can't understand how I can make my rotation unitless.i have from experiment the dampers Moment(Knm) vs Rotational(radians) curve. And I want to use this data to model it as a zero-length element in opensees. So how can I specify the material properties in opensees? how can I make the rotation unitless? I had previously used the experiment result to define the moment in knm and the rotation in radians. and I thought the recorded results would also have the same unit.

[selimgunay]

That is correct, if you defined the moment in KNm and the rotation radians, recorders will have the same units

[jonade]

Thank you very much selimgunay