ABSTRACT
The response of a structural member subjected to heating (or cooling) is an expansion (or contraction). The expansion, or contraction, can in turn produce stresses if
1. External forces constrain the expansion, or contraction 2. The shape of the structural member is incompatible with the tendency to expand or contract
The thermal behavior under the first condition may be represented, for example, by a uniform, straight bar held at the ends and subjected to a constant temperature gradient. The case corresponding to the second condition can be best illustrated with reference to a cylinder having a temperature gradient across its wall. Although in this case no external forces of constraint are applied, thermal stresses are produced because the strains are incompatible with the free thermal deformation. The two cases outlined above can also be characterized as those structural systems, which are governed by external or internal constraints.
