Daily and annual variations of atmospheric temperatures, especially those caused by the heat of the sun, produce a wide variety of temperature gradients in hardened concrete that are known to cause stress within a structure. In designing structures that will be subjected to such conditions, the codes of design engineers should include recommendations for prevention of these resultant stresses and, thereby, the cracks or even structural failures they can produce. Internal restraint of deformation develops under certain conditions when changes of ambient temperature occur and produce a temperature gradient across the cross section of a structural member. In addition to being a function of time, the temperature distribution across the section depends on thickness of the member and on thermal properties of the material. Where external restraint of deformation is present, as is the rule in statically indeterminate structures, additional stresses due to temperature gradients are produced which are superimposed on the internal stresses. In contrast to the stresses attributable to internal restraint, integration of the stresses from external restraint is present over the cross section and the structure is subjected to stress resultants depends on the nature and degree of temperature variation, type of structure, and the degree of the tensional stiffness of the different members. The stresses due to temperature gradients as described here are those due to inner to outer restraint and thus their magnitude depends largely on the thickness or stiffness of the structural members. When cracks occur stiffness decreases considerably, leading to a corresponding decrease of the temperature stresses. Thus it is not necessary to provide reinforcement for the full amount of stresses as calculated for the uncracked section. Nevertheless, a sufficient amount of non prestressed reinforcement must be provided . In addition to reinforcement, measures recommended for reduction of the magnitude of tensile stresses would include the avoidance of thick members and- in the case of hollow-box sections- avoidance of joining thin members to thick members. To minimize longitudinal tensile stresses at the bottom fiber of continuous beams near intermediate supports, it is recommended that the builder use small radii of curvature for prestressing tendons.