**Discretization** refers to the process of translating the=
material domain of an object-based model into an analytical model suitable=
for analysis. In structural analysis, discretization may involve either of=
two basic analytical-model types, including:

**Node-element model**, in which structural elements are r= epresented by individual lines connected by nodes. In a 3D system, each nod= e has six degrees of freedom, each either constrained or free. The geometri= c and material properties of structural elements are then characterized by = line elements which simulate their physical behavior by following mathemati= cal relationships. Through application of the direct stiffness method, load= ing at node locations translates into displacement and stress fields which = indicate structural performance.

**Finite-element model**, in which a meshing procedure creates a network of line elements conn= ected by nodes within a material continuum. Each line element simulates the= geometric and physical properties of the local material. Given the loading= and boundary conditions of the whole system, numerical formulation of stru= ctural response may advance through the computational model. The discretiza= tion of a finite-element model will have some degree of refinement, produci= ng either a coarse or fine mesh. A node-element model is technically a fini= te-element model in which a single line element represents the structural e= lement. Node-element modeling, however, follows the direct stiffness method= , whereas finite-element modeling follows the fin= ite-element method (FEM). The SA= PFire =C2=AE Analysis Engine implements an efficient finite-element = approach when performing structural analysis.

While the discretization of an object-based model is always critical (in=
that discretization facilitates analysis), there are conditions in which i=
t is also important to **divide frame elements** into multiple=
segments such that accurate results are generated.

It is useful to subdivide frame elements for the following analysis type= s:

- Buckling analysis - To capture hig= her modes.

- Dynamic analysis - To better capt= ure mass distribution, since mass is assembled at joint locations.

- P-Delta (P-=CE=B4) effect - = To better capture local column deformation for assessment of equilibrium co= nditions about displaced configuration.

- Displacement accuracy - To create joints at locations where accurate di= splacements are needed, otherwise values are interpolated from the nodes at= either end of the frame element.

- For shell elements, discretization ma= y be refined through auto meshing (Assign > Area > Automatic Area Mes= h) or area dividing (Edit > Areas > Divide Areas).

- For frame elements, auto meshing at i= ntermediate points is specified by default. Frame discretization is then co= nnected to that of shell elements at each applicable joint.