| Shear stress: | (english) Stress acting parallel to an imaginary plane cut through an object. |
| Shear modulus: | (english) The ratio of shear stress divided by the corresponding shear strain in a linear elastic material. |
| Stability: | (english) Stability is best defined as the opposite of instability, which is the occurrence of large structural deformations which are not the result of material failure. |
| Statically equivalent: | (english) Two force systems are statically equivalent when their resultants are equal. Physically, this means that the force systems tend to impart the same motion when applied to an object; note that the distribution of resulting internal forces in the object may be different. |
| Stiffness: | (english) This is a general term which may be applied to materials or structures. When a force is applied to a structure, there is a displacement in the direction of the force; stiffness is the ratio of the force divided by the displacement. High stiffness means that a large force produces a small displacement. When discussing the stiffness of a material, the concept is the same, except that stress substitutes for force, and strain substitutes for displacement; see modulus of elasticity. |
| Strain: | (english) The intensity of deformation at a point in an object. See normal strain and shear strain. |
| Strength: | (english) A very general term that may be applied to a material or a structure. In a material, strength refers to a level of stress at which there is a significant change in the state of the material, e.g., yielding or rupture. In a structure, strength refers to a level of level of loading which produces a significant change in the state of the structure, e.g., inelastic deformations, buckling, or collapse. |
| Stress: | (english) The intensity of internal force acting at a point in an object. Stress is measured in units of force per area. See shear stress and normal stress. |
| Structural model: | (english) An idealization for analysis purposes of a real or conceived structure. A structural model includes boundaries limiting the scope of the analysis. Supports occur at these boundaries, representing things which hold the structure in place. |
| Support: | (english) A support contributes to keeping a structure in place by restraining one or more degrees of freedom. In a structural model, supports represent boundary entities which are not included in the model itself, e.g., foundations, abutments, or the earth itself. For each restrained translation degree of freedom at a support, there is a corresponding reaction force; for each restrained rotation degree of freedom, there is a reaction moment. |