Separate from the computational and problem solving classes, are classes for building models (termed ModelBuilder classes). The Version 0 release of OpenSees includes a general model-builder for creating three-dimensional frame and continuum models using TCL. Users can generate models using TCL procedures, and are encouraged to share these generation procs with others! Additional ModelBuilder classes suited to a particular type of model may also be developed.


  • Beam-column -- 3D elements with the following integration rules
    • Linear elastic material (closed form),
    • Concentrated plasticity integrated over specified hinge lengths, or
    • Distributed plasticity integrated along the element length.
    Beam-column plasticity is described by section models. Each element can use the following geometric transformations
    • Linear -- first order geometry,
    • P-Delta -- second order "leaning truss" transformation, or
    • Corotational -- large displacement transformation.
  • Zero length -- 3D element which uses multiple uniaxial materials to model the element force-deformation relation.
  • Truss -- 3D element with material non-linearity modeled by
    • Uniaxial material stress-strain integrated over cross-sectional area, or
    • Section force-deformation relationship.
  • Quad -- 2D bilinear isoparametric element which uses ND materials at each of its integration points.

Uniaxial Materials

  • Elastic -- linear elastic material tangent with optional linear damping tangent
  • ElasticPP -- elastic-perfectly plastic
  • ElasticPPGap -- one-sided EPP with an initial gap
  • Hardening -- bilinear model with combined linear isotropic and kinematic hardening
  • Steel01 -- bilinear steel model with linear kinematic and exponential isotropic hardening
  • Concrete01 -- concrete model with Kent-Park envelope, degraded linear unloading/reloading, and no tensile strength
  • Hysteretic -- trilinear backbone with pinching, damage, and degraded unloading stiffness
  • Parallel -- multiple uniaxial materials in parallel
  • Series -- multiple uniaxial materials in series
  • BiLinear -- bilinear hysteretic model with degradation
  • Clough -- Clough type hysteretic model with degradation
  • Pinch -- pinching hysteretic model with degradation

ND Materials

  • ElasticIsotropic -- plane stress and plane strain formulations for use with the quad element.

Section Models

  • Elastic -- uncoupled axial and bending response.
  • Fiber -- discretized by fibers which collectively define section response. The fiber models available are
    • Uniaxial2d/3d -- associates with a uniaxial material and enforces the Bernoulli beam assumption for axial and uni/bi-directional bending
  • Generic1d/Nd -- map stresses from uniaxial and ND materials to section stress resultants. For example, a uniaxial material can be used to model section moment-curvature behavior, or an ND plasticity model can be used to model section moment-axial-shear interaction.
  • Aggregator -- combination of a section and multiple uncoupled uniaxial materials used to define additional section force-deformation relations. For example, a fiber section can be combined with an uncoupled shear force-deformation relation.