# 4.2.8.1. Tri31 Element¶

This command is used to construct a constant strain triangular element (Tri31) which uses three nodes and one integration points.

element('Tri31', eleTag, *eleNodes, thick, type, matTag, <pressure, rho, b1, b2>)
 eleTag (int) unique element object tag eleNodes (list (int)) a list of three element nodes in counter-clockwise order thick (float) element thickness type (str) string representing material behavior. The type parameter can be either 'PlaneStrain' or 'PlaneStress' matTag (int) tag of nDMaterial pressure (float) surface pressure (optional, default = 0.0) rho (float) element mass density (per unit volume) from which a lumped element mass matrix is computed (optional, default=0.0) b1 b2 (float) constant body forces defined in the domain (optional, default=0.0)

Note

1. Consistent nodal loads are computed from the pressure and body forces.
2. The valid queries to a Tri31 element when creating an ElementRecorder object are ‘forces’, ‘stresses,’ and ‘material $matNum matArg1 matArg2 …’ Where$matNum refers to the material object at the integration point corresponding to the node numbers in the domain.