Permissible stress design (in USA construction more commonly called allowable stress design) is a design philosophy used by civil engineers. The designer ensures that the stresses developed in a structure due to service loads do not exceed the elastic limit. This limit is usually determined by ensuring that stresses remain within the limits through the use of factors of safety.
The permissible stress design approach has generally been replaced internationally by limit state design (also known as ultimate stress design, or in USA, Load and Resistance Factor Design, LRFD) as far as structural engineering is considered, except for some isolated cases.
In USA construction, allowable stress design (ASD) has not yet been completely superseded by limit state design except in the case of Suspension bridges, which changed from allowable stress design to limit state design in the 1960s. Wood, steel, and other materials are still frequently designed using allowable stress design, although LRFD is probably more commonly taught in the USA university system.
Famous quotes containing the words permissible, stress and/or design:
“Fences, unlike punishments, clearly mark out the perimeters of any specified territory. Young children learn where it is permissible to play, because their backyard fence plainly outlines the safe area. They learn about the invisible fence that surrounds the stove, and that Grandma has an invisible barrier around her cabinet of antique teacups.”
—Jeanne Elium (20th century)
“In the stress of modern life, how little room is left for that most comfortable vanity that whispers in our ears that failures are not faults! Now we are taught from infancy that we must rise or fall upon our own merits; that vigilance wins success, and incapacity means ruin.”
—Agnes Repplier (1858–1950)
“What but design of darkness to appall?—
If design govern in a thing so small.”
—Robert Frost (1874–1963)