OpenSees Substepping Methods

A python Library for adding Substepping methods to your models in OpenSeesPy

Sub-stepping is a procedure that is adopted from the Finite Element Method in order to achieve the dedicated state without knowing if the selected timestep or load increment can be handled from the solver. OpenSees is an open source finite element solver, where you can simulate you structural engineering problems. Until a couple years ago, OpenSees was available only through the Tcl programming language. Nowadays, OpenSees is available also with Python language. Taking advantage of the opportunity, a small library with predefined sub steps is implemented in a python library. In order to use the library a sort example is listed below. In case you would like to download the library is available to pypi.org.
Just execute in the terminal

pip install OpenSeesPySubStepping

Example in python


import openseespy.opensees as ops
from OpenSeesPySubStepping import DispControlSubStep
from OpenSeesPySubStepping import LoadControlSubStep

def main():
    """
    Create a Cantilever Problem
    """

    ops.wipe()
    ops.model('basic', '-ndm', 2, '-ndf', 3)
    height = 5.0
    nElem = 20

    ElemLength = height / nElem
    nodeID = []
    Ycoord = 0
    for i in range(nElem + 1):
        nodeID.append(i)
        ops.node(i, 0.0, Ycoord)
        Ycoord += ElemLength
    IDctrlNode = i

    ops.fix(0, 1, 1, 1)
    ops.geomTransf('Linear', 1)

    concrete = 'Concrete04'
    steel = 'Steel02'

    matTAGConc = 319
    matTAGSteel = 312
    fcc = -20000
    ec2c = -0.002
    ecu2c = -0.0035
    Ec = 30000000
    fct = 2200
    et = 0.001
    fy = 500000
    E0 = 200000000
    b = 0.01
    ops.uniaxialMaterial(concrete, matTAGConc, fcc, ec2c, ecu2c, Ec, fct, et)
    ops.uniaxialMaterial(steel, matTAGSteel, fy, E0, b, 20, 0.925, 0.15, 0, 1, 0, 1, 0)

    # Core Fibers
    ops.section('Fiber', 105)
    ops.patch('rect', 319, 11, 11, -0.20, -0.20, 0.20, 0.20)
    # Cover Fibers
    ops.patch('rect', 319, 15, 2, 0.250000, 0.200000, -0.250000, 0.250000)
    ops.patch('rect', 319, 15, 2, 0.250000, -0.250000, -0.250000, -0.200000)
    ops.patch('rect', 319, 2, 11, -0.250000, -0.200000, -0.200000, 0.200000)
    ops.patch('rect', 319, 2, 11, 0.200000, -0.200000, 0.250000, 0.200000)
    # create corner bars
    ops.layer('straight', 312, 4, 0.00025450, 0.200000, 0.200000, -0.200000, 0.200000)
    ops.layer('straight', 312, 4, 0.00025450, 0.200000, -0.200000, -0.200000, -0.200000)
    ops.beamIntegration('Lobatto', 100, 105, 3)

    for i in range(len(nodeID) - 1):
        ops.element('forceBeamColumn', i, nodeID[i], nodeID[i + 1], 1, 100, '-iter', 10, 1e-6)

    # Add Vertical Load at Top
    ops.timeSeries('Linear', 101)
    ops.pattern('Plain', 100, 101)
    ops.load(IDctrlNode, 0, -500, 0)

    # Solve Gravity First
    ops.system('UmfPack')
    ops.numberer('Plain')
    ops.constraints('Transformation')
    ops.integrator('LoadControl', 0.1)
    ops.test('RelativeTotalNormDispIncr', 0.001, 100, 2)
    ops.algorithm('Newton')
    ops.analysis('Static')
    LoadControlSubStep(10, 0.1, True)

    # Displacement Control Analysis(Pushover)
    ops.pattern('Plain', 200, 101)
    ops.load(IDctrlNode, 1, 0, 0)
    ops.system('UmfPack')
    ops.numberer('Plain')
    ops.constraints('Transformation')
    ops.test('RelativeTotalNormDispIncr', 1e-2, 500, 2)
    ops.algorithm('Newton')
    ops.analysis('Static')
    DispControlSubStep(100, IDctrlNode, 1, 1.0)

if __name__ == '__main__':
    main()