OpenSees Command Interface

Overview

Almost all OpenSees commands are encapsulated in the .opensees module. All commands use the same input format as OpenSees and OpenSeesPy. For example:

opsMat = OpenSeesMatlab();  % Get Instance
ops = opsmat.opensees;  % Get the OpenSees command interface

ops.wipe();
ops.model('basic', '-ndm', 2, '-ndf', 3);
...
ops.node(1, 0.0, 0.0);
ops.node(2, 5.0, 0.0);
ops.fix(1, 1, 1, 1);
ops.element(...);

For details, please refer to their official documentation, You can call it in the same way.

OpenSeesPy

OpenSees

OpenSees Command Manual

Usage Tips

• ✨ Both char and string inputs are supported. However, using char is recommended.

• ✨ Most commands accept scalar arguments only and do not support passing a numeric array directly. Please pass scalar arguments one by one.

  To unpack a cell array, use {:} expansion:

  ops.node(1, coords{:});         % coords is a cell array
  

  To unpack a numeric array, convert to cell first:

  coords = num2cell(coords);
  ops.node(1, coords{:});
  

  The following commands are exceptions and do support numeric array and cell array inputs, which are flattened automatically (Since OpenSeesMatlab v3.8.0.1):

  node, element, eleLoad, geomTransf, uniaxialMaterial, nDMaterial, equalDOF, equationConstraint, rigidDiaphragm, rigidLink, fix, fixX, fixY, fixZ, section, fiber, layer, patch, load, mass, rayleigh, ShallowFoundationGen, block2D, block3D, setNodeDisp, setNodeVel, setNodeAccel, frictionModel, region, setElementRayleighDampingFactors, setElementRayleighFactors, recorder , and timeSeries (Path type only: numeric array accepted for -values and -time )

• ✨ Commands with return values will return MATLAB data. If a command has no return value, an empty array [] will be returned.

• ✨ The additional post-processing provided by OpenSeesMatlab may be slow or buggy. If you think so, you can use only the OpenSees command interface and use recorder or other output commands to post-process the analysis results.

Example

The following is an example of Nolinear Truss Pushover Analysis:

First, instantiate the OpenSeesMatlab interface class. This class provides native OpenSees commands, as well as additional visualization, pre/post-processing, and utility methods.

opsMat = OpenSeesMatlab();
ops = opsMat.opensees;  % OpenSees command interface

Create model

ops.wipe();
ops.model('basic', '-ndm', 2, '-ndf', 2);

% variables
A = 4.0;
E = 29000.0;
alpha = 0.05;
sY = 36.0;
udisp = 2.5; 
Nsteps = 1000;
Px = 160.0;
Py = 0.0;

% create nodes
ops.node(1, 0.0, 0.0);
ops.node(2, 72.0, 0.0);
ops.node(3, 168.0, 0.0);
ops.node(4, 48.0, 144.0);

% set boundary condition
ops.fix(1, 1, 1);
ops.fix(2, 1, 1);
ops.fix(3, 1, 1);

% define materials
ops.uniaxialMaterial('Hardening', 1, E, sY, 0.0, alpha / (1 - alpha) * E);

% define elements
ops.element('Truss', 1, 1, 4, A, 1);
ops.element('Truss', 2, 2, 4, A, 1);
ops.element('Truss', 3, 3, 4, A, 1);

% create TimeSeries
ops.timeSeries('Linear', 1);

% create a plain load pattern
ops.pattern('Plain', 1, 1);

% Create the nodal load
ops.load(4, Px, Py);

Start of analysis generation

% create SOE
ops.system('ProfileSPD');
% create DOF number
ops.numberer('Plain');
% create constraint handler
ops.constraints('Plain');
% create integrator
ops.integrator('LoadControl', 1.0 / Nsteps);
% create algorithm
ops.algorithm('Newton');
% create test
ops.test('NormUnbalance', 1e-8, 10, 1);
% create analysis object
ops.analysis("Static");

Finally perform the analysis

Analysis results data are returned directly from the OpenSees domain:

data = zeros(Nsteps + 1, 2);

for j = 1:Nsteps
    ops.analyze(1);
    data(j + 1, 1) = ops.nodeDisp(4, 1);
    data(j + 1, 2) = ops.getLoadFactor(1) * Px;
end

Plot

You can visualize it directly in MATLAB.

figure;
plot(data(:, 1), data(:, 2), 'LineWidth', 1.5);
xlabel('Horizontal Displacement');
ylabel('Horizontal Load');
grid on;