7. Lee's Frame Problem

Lee's frame is a simple frame structure subjected to large displacements and rotations. The B2000++ model defined in file frame.mdl follows the original geometry and loading, and it is clamped at both ends. Analysis is performed by means of the B2.S.RS Reissner-Simo beam element. The test also checks the beam local coordinate system orientation option (defined by a reference node or by a reference orientation vector).

Lee frame: Beam model and load (dense mesh).

Figure 32. Lee frame: Beam model and load (dense mesh).

Two tests are executed, one with applying a force as shown in the above picture, and another with a 'displacement loading' instead. Solver options (see case command in input file) for the force case are

analysis               nonlinear
increment_control_type hyperplane
step_size_max          10 # To get a curve with some points...
ebc                    1 # zero constraints set
nbc                    1 # applied force set
join                   0 # Needed because more than one epatch

The structure deforms until it reaches an unstable state, after which a new stable state is reached. Using the continuation processor, the complete static solution can be obtained as displayed in the load-displacement plot below.

Lee frame: Load-displacement response point A (continuation).

Figure 33. Lee frame: Load-displacement response point A (continuation).