lees frame
The Lee's frame is shown as follows.
The model can be downloaded. lees-frame.supan
Model Setup
Since this is an elastic analysis, we use EB21
element to model this problem. To suppress axial deformation, a large area of is assigned. The node and element definitions can be established as follows.
node 1 0 0
node 2 0 1
node 3 0 2
node 4 0 3
node 5 0 4
node 6 0 5
node 7 1 5
node 8 2 5
node 9 3 5
node 10 4 5
node 11 5 5
element EB21 1 1 2 500. 1. 1 1
element EB21 2 2 3 500. 1. 1 1
element EB21 3 3 4 500. 1. 1 1
element EB21 4 4 5 500. 1. 1 1
element EB21 5 5 6 500. 1. 1 1
element EB21 6 6 7 500. 1. 1 1
element EB21 7 7 8 500. 1. 1 1
element EB21 8 8 9 500. 1. 1 1
element EB21 9 9 10 500. 1. 1 1
element EB21 10 10 11 500. 1. 1 1
material Elastic1D 1 10
fix 1 1 1 11
fix 2 2 1 11
Both snap-back and snap-through are involved in this example, the arc length method shall be used. A reference load of magnitude is applied on the DoF 2 of node 7.
refload 1 0 -1 2 7
step arclength 1
Here the magnitude of reference load matters. A proper selection of reference load may help to converge. By default, the algorithm automatically scale the arc length until a stopping criterion is met.
To control the solving strategy, one can control arc length by using
set ini_step_size .5
set fixed_step_size true
set max_iteration 1000
The above command uses a fixed arc length of . By default, a maximum of sub steps are allowed, this may not be sufficient, to change it the set
command can be called.
criterion MinDisplacement 1 7 2 -3.8
With the above criterion, when the negative displacement of DoF2 of node 7 reaches , the analysis stops.
Now the model can be analyzed.
analyze
Result
The sign of vertical displacement is flipped.
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