Question about boundary conditions

[woi123]

As a beginner to Abaqus, I am trying to learn. While watching tutorials on YouTube, I have noticed that when modeling a simply supported beam, a line is used to define the boundary condition. Can someone explain to me why this is the case? In a 3D model, the support should cover an area and not just a line.

 

[FEA way]

Not necessarily, applying BCs to edges of solid models is also fine as long as you know what you are doing. Sometimes we even apply BCs to individual points (nodes) - e.g. when using the 3-2-1 method.

 

[woi123]

Hmm, but when considering a beam supported by two columns, the reaction force from the supports is spread out over an area, not concentrated on a line. Defining the boundary conditions on the edges will result in increased the stresses in the elements, as the reaction forces are not being distributed over the columns area. I am new to this subject and would appreciate any help and clarification

 

[FEA way]

Well, the best way (not only in this case but pretty much always when working with FEA) is to make a simple test and compare the results obtained from analyses based on different approaches. Beams are nice for this because you can easily get an analytical solution for comparison with simulation results.

 

[tham1]

Also if you apply a pinned BC directly over the face of the section it will act like a encastre globally. The pinned face can react a moment through a couple.

 

[buildinggalileo]

In a 3D model, the support would still need to be defined using a line, but the line would be made up of multiple elements to represent the area of the support.