Learning topic

Structural Element Models

Basic structural models in Strength of Materials: bars, beams, shafts, columns, plates, shells, solid bodies, axes and cross-sections.

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This topic introduces the main geometric idealizations used in Strength of Materials: bars, beams, shafts, columns, plates, shells, and three-dimensional solid bodies, together with the concepts of axis and cross-section.

A real component or structural part is replaced by a geometric model sufficient to describe the mechanics of interest. The chosen element type determines which dimensions, displacements, and internal force resultants are central to the analysis.

One-dimensional members

A bar or member has one dimension, its length, substantially greater than its cross-sectional dimensions. Its geometry is represented by a longitudinal axis and cross-sections.

  • Beam — a member commonly characterized by bending.
  • Shaft — a member commonly used to transmit torque.
  • Column — a compressed slender member for which stability can govern design.

Plates and shells

A plate has a thickness small compared with its other two dimensions and is represented by a middle plane. A shell is also thin but has a curved middle surface.

Three-dimensional solids

When all three characteristic dimensions are comparable and lower-dimensional idealizations do not capture the required mechanics, a three-dimensional solid model is used.

Cross-section

For member models, cross-sectional shape and dimensions determine area and geometric properties that control stress, stiffness, and stability. Internal force resultants are introduced through a cross-section using the method of sections.