T Thermally treated to produce stable tempers other than F, O, or H. This designation applies to products that are thermally treated, with or without supplementary strain hardening, to produce stable tempers. The T is always followed by one or more digits. *Recommended by the Aluminum Association. A digit after H represents a specific combination of basic operations, such as H1strain hardened only. H2strain hardened and partly annealed, and H3strain hardened and stabilized. A second digit indicates the degree of strain hardening, which ranges from 0 for annealing to 9 in the order of increasing tensile strength. A digit after T indicates a type of heat treatment, which may include cooling, cold working, and aging. There are economic advantages in selecting structural aluminum shapes more efficient for specific purposes than the customary ones. For example, sections such as hollow tubes, shapes with stiffening lips on outstanding flanges, and stiffened panels can be formed by extrusion. Aluminum alloys generally weigh about 170 lb / ft3, about one-third that of structural steel. The modulus of elasticity in tension is about 10,000 ksi, compared with 29,000 ksi for structural steel. Poissons ratio may be taken as 0.50. The coefficient of thermal expansion in the 68 to 212
F range is about 0.000013 in / in

F, about double that of structural steel. Alloy 6061-T6 is often used for structural shapes and plates. ASTM B308 specifies a minimum tensile strength of 38 ksi, minimum tensile yield strength of 35 ksi, and minimum elongation in 2 in of 10%, but 8% when the thickness is less

Drainage Access Probability of nonuniform settlement: Masonry walled structure Framed structures Smokestacks, silos, mats 1530 cm (612 in) 3060 cm (1224 in) 2.55 cm (12 in) 510 cm (24 in) 830 cm (312 in) Tilting Stability against overturning Tilting of smokestacks, towers Rolling of trucks, etc. Stacking of goods Machine operationcotton loom Machine operationturbogenerator Crane rails Drainage of floors Depends on H and W Differential movement High continuous brick walls One-story brick mill building, wall cracking Plaster cracking (gypsum) Reinforced concrete building frame Reinforced concrete building curtain walls Steel frame, continuous Simple steel frame L  distance between adjacent columns that settle different amounts, or between any two points that settle differently. Higher values are for regular settlements and more tolerant structures. Lower values are for irregular settlement and critical structures. H  height and W  width of structure. Source: G. F. Sowers, Shallow Foundations, ch. 6 of Foundation Engineerings, ed. G. A. Leonards, McGraw-Hill Publishing Co., New York. The Use of the Structure. Even small cracks in a house might be considered unacceptable, whereas much larger cracks in an industrial building might not

Mohrs circle an also be plotted when the principal stresses are not known but the stresses x, y , and vxy , on any two perpendicular planes, are. The procedure is to plot the two points representing these known stresses with respect to the and v axies (points C and D in Fig. 5.10). The line joining these points is a diameter of Mohrs circle. Constructing the circle on this diameter, we find the principal stresses at the intersection with the axis (points A and B in Fig. 5.10). For more details on the relationship of stresses and strains at a point, see Timoshenko and Goodier, Theory of Elasticity, McGraw-Hill Publishing Company, New York. Forces that cause a member to twist about a longitudinal axis are called torsional loads. Simple torsion is produced only by a couple, or moment, in a plane perpendicular to the axis. If a couple lies in a nonperpendicular plane, it can be resolved into a torsional moment, in a plane perpendicular to the axis, and bending moments, in planes