Multi linear Elastic Link Tension Only


Hi Midas 

My intension was to understand the thermal interaction behavior between two parallel elements. 

Model Description:

Two simple rectangular beams are modelled having vertically 500mm spacing. Both beams are simple supported, one end translationally fixed other end sliding. Only bottom beam a  uniform thermal load of 350C is applied. There are multilinear spring between the two beams @1m interval are exist. The multilinear spring stiffness defined as a tension spring only, as per the below screenshot. 

However, in the result, there is no axial load in either of the beam. but I can see the bottom beam is axially deforming. 

May I ask if the multilinear spring definition is not correctly defined. Please find attached .mcb file for reference. 



The displacement diagram for spring 1 and spring 2 is shown below.
The local x-direction of elastic link is upwards, hence the positive direction for the link displacement is upwards.
Spring 1 and spring 2 are the one defined in earlier example by you.

Now, when the point load is applied on lower beam, the lower beam deflects downwards. So, j-th end of the elastic link(upper beam node) has relatively moved away/ moved up with respect to i-end of elastic link(lower beam end). 
In spring 1, when deflection is positive, the elastic link provide stiffness to movement, hence load is transferred to upper beam.
While in spring 2, for positive deflection, there is no spring stiffness or no load is transferred. 
So, it depend on the direction of local-axis of the spring and defined multi-linear spring table data.
In original example, where temperature load was applied, the deformations are
As temperature load is applied in lower beam, the lower beam moves in +z direction of the elastic link. 
Now, as the j end of the elastic spring(upper node) is behind/moved in-z direction with respect to i-end of the spring(lower node), the relative displacement will be negative. So, the model in which spring is defined with negative function, will transfer the load.

Creation date: 6/4/2021 3:55 PM      Updated: 6/4/2021 3:55 PM
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Multi Linear Tension Link.mcb
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multi linear spring_tension.avi
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Multi Linear Tension Link_Model 2.mcb
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