Joints represent points of connection between structural elements. Joints are automatically created at the ends of line objects (frames, cables, tendons, links) and at the corners of area and solid objects. Joints may also be added manually, to capture localized behavior, or to simulate restraint supports. Constraint conditions are also applied to joints to establish correlation among their displacement DOF.
Joints are fundamental to numerical solution in that stresses and strains are resolved according to joint displacement. First, an object-based model is created by drawing structural objects which are connected by joints and subjected to loading.
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Software then generates a finite-element model according to structural geometry and individual-member properties. Users have additional control over mesh refinement and intersecting-object connections. Analysis then proceeds according to the FEM model, and useful results are reported in terms of the object-based model.
Element mass and distributed loading are automatically transferred to joint locations during analysis. Users may assign additional mass to joints. During dynamic analysis, users should also assign mass moment of inertia (MMI) to joints such that inertial forces may relate to joint acceleration. MMI formulation is presented in the
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[_Analysis Reference Manual_] (page 41), and guidelines for dynamic-analysis acceleration are presented in the Time-history output-acceleration accuracy article.