Effect of Variation of Elastic Characteristics on Static Unknowns

As is well known, the values of statically indeterminate quantities are influenced by the elastic characteristics of the structure, such as cross-sectional areas of compression and tension members, moments of inertia of flexural members, and moduli of elasticity. The actual magnitudes of these elastic characteristics are likely to differ somewhat from the values assumed in analysis because of inaccuracies and accidents of manufacturing and construction, and these may result in deviation of the actual stress values from the quantities used in the design. A proportional change in an elastic characteristic in different parts of the structure in most cases will not affect the values of static unknowns, but a random variation of cross-sectional area, moment of inertia, or modulus of elasticity from point to point may influence the results considerably, depending on location, magnitude, and sign of the variation.