8.12.2.13. Graph the Load and Response History
This verification technique may be considered to be a graphical combination of two other techniques:
checking for reasonableness, and reviewing the iteration history. POST26 graphs of load and response
histories should agree with your informed expectations about your structure's behavior. The results of
interest (displacements, reaction forces, stresses, and so on) should show relatively smooth response
histories. Any non-smoothness may indicat e that too coarse of a time step was used.
8.13. Example Nonlinear Analysis (GUI Method)
This example runs a nonlinear analysis of an elastic-plastic circular plate under the action of a dead load
and a cyclic point load. You define a kinematic hardening plasticity curve, as well as load step options,
the maximum and minimum number of substeps for a load step, and the various load steps that describe
externally applied loads. You also learn how to interpret the monitor file that the program writes for a
nonlinear analysis.
The program uses an incremental solution procedure to obtain a solution to a nonlinear analysis. In
this example, the total external load within a load step is applied in increments over a certain number
of substeps. The program uses a Newton-Raphson iterative procedure to solve each substep. You must
specify the number of substeps for each load step, since this number controls the size of the initial load
increment applied in the first substep of the each load step. The program automatically determines the
size of the load increment for each subsequent substep in a load step. You can control the size of the
load increment for these subsequent substeps by specifying the maximum and minimum number of
substeps. If you define the number of substeps, the maximum and minimum number of substeps all
to be the same, then The program uses a constant load increment for all substeps within the load step.
8.13.1. Problem Description
Use an axisymmetric model for the plate, using four-node PLANE182 elements with the axisymmetric
option to mesh the model. Perform a geometrically nonlinear analysis. Specify the kinematic constraints
as follows: The nodes located at the center of the plate are constrained to have zero radial displacement.
The nodes located at the outer edge are constrained to have zero radial and axial displacement. Apply
the dead load in load step 1 and the cyclic point load in six subsequent load steps. See Problem
Sketch (p. 274).
Specify 10 substeps for the first load to ensure that the increment of the dead load applied over the
first substep is 1/10 of the total load of 0.125 N/m^2. Also specify a maximum of 50 and a minimum of
5 substeps to ensure that if the plate exhibits a severe nonlinear behavior during the solution, then the
load increment can be cut back to 1/50 the total load. If the plate exhibits mild nonlinear behavior,
then the load increment can be increased up to 1/5 the size of the total load.
For the subsequent six load steps that apply the cyclic point load, 4 substeps, with a maximum of 25
and a minimum of 2 substeps.
Monitor the history over the entire solution of the vertical displacement of the node at the location
where the point cyclic load is applied and the reaction force at the node located at the bottom of the
clamped edge.
8.13.2. Problem Specifications
The circular plate has a radius of 1.0 m and a thickness of 0.1 m.The following material properties are
used for this problem:
Release 15.0 - © SAS IP, Inc. All rights reserved. - Contains proprietary and confidential informationExample Nonlinear Analysis (GUI Method)