. Strength of materials: a practical manual of scientific methods of locating and determining stresses and calculating the required strength and dimensions of building materials . Fig. 2. STRENGTH OF MATEEIALS stress. The stresses in beams are usually complex. There are otherterms used to describe stress; they will be defined farther on. 4. Unit=Stress. It is often necessary to specify not merelythe amount of the entire stress which acts on an area, but also theamount which acts on each unit of area (square inch for example).By unit-stress is meant stress per unit area. To find the value of a
. Strength of materials: a practical manual of scientific methods of locating and determining stresses and calculating the required strength and dimensions of building materials . Fig. 2. STRENGTH OF MATEEIALS stress. The stresses in beams are usually complex. There are otherterms used to describe stress; they will be defined farther on. 4. Unit=Stress. It is often necessary to specify not merelythe amount of the entire stress which acts on an area, but also theamount which acts on each unit of area (square inch for example).By unit-stress is meant stress per unit area. To find the value of a unit-stress: Divide the vjJtole stress hythe whole area of the section 0)i which it acts, or over which it isdistributed. Thus, let P denote the value of the whole stress, A the area on which it acts, and S the value of the unit-stress; then P S=-^, alsoP-=AS. (i) Strictly these formulas apply only when the stress P is uniform,. Fig. 3. that is, when it is uniformly distributed over the area, each squareinch for example sustaining the same amount of stress. Whenthe stress is not uniform, that is, when the stresses on differentsquare inches are not e(]^ual, then P-^-A equals the avcnKje vat hoof the unit-stress. 5. Unit-stresses are usually expressed (iu Americ;;) inpounds per square inch, sometimes in tons per square incli. ]fP and A in equation 1 are expressed in pounds and S([u:ir(inches respectively, then B will be in pounds per S(|uare inch; .-mdif P and A are expressed in tons and square inches, S will bo intons per square inch. Exrfi/ijdc.^. 1. Suppose that the rod sustaining- the load inFig. 1 is 2 S(piare inches in cross-section, and that the load pounds. What is the value of tlu unit-stress ? 6 STEEXGTH OF :\IATEPJALS Here P = pounds, A= 2 square inches; hence. S = —^— = 500 pounds per square inch. 2. Suppose that the rod is one-half square inch in cross-sec-tion. AVhat is
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