Text-book of mechanics . f 7000 pounds, has a section 1 inch by12 inches. Calculate the factors of safety for normal stressand shearing stress. Exercise 77. A wooden cantilever 6 inches long, of rec-tangular section, is to support a steady, uniformly distributedload of 600 pounds. The width is to be 2 inches. Designthe beam for bending and investigate for shear. Exercise 78. Design the beam in Ex. 77 for shear, andinvestigate for bending. I-section with Sharp Corners. — A standard 24-inchI-beam, when the slope of the flanges is neglected andan average depth of flange is used, has approximately
Text-book of mechanics . f 7000 pounds, has a section 1 inch by12 inches. Calculate the factors of safety for normal stressand shearing stress. Exercise 77. A wooden cantilever 6 inches long, of rec-tangular section, is to support a steady, uniformly distributedload of 600 pounds. The width is to be 2 inches. Designthe beam for bending and investigate for shear. Exercise 78. Design the beam in Ex. 77 for shear, andinvestigate for bending. I-section with Sharp Corners. — A standard 24-inchI-beam, when the slope of the flanges is neglected andan average depth of flange is used, has approximatelythe dimensions shown in Fig. 38. The shear at A, the lower edge of the upper flange, is <la=fb%y(±A) =^j(-SS) (7 X .9) =^(),at B, the upper edge of the web, qb- ^ (11-55) (7 )= ^(i45-6), A 70 MECHANICS OF MATERIALS at C, the neutral axis, ff«=§Sy(^) = ^) (nVSS)+() ()1 =4* (). As the variation in the shear follows the parabolic lawin the interval from the extreme fiber to A, also from B. Fig. 38 to C, the variation may be represented by the curve tothe right of Fig. 38. This graph clearly shows that in beams of I-sectionthe material of the web may for practical calculations be STRESSES IN BEAMS 71 assumed to resist the whole shearing force. As already-noted, the normal stresses due to bending reach theirgreatest values at the extreme fibers of the beam, there-fore in practice the material in the flanges alone may beconsidered to resist the bending moment. These con-clusions also hold in the case of built-up girders havingapproximately I-shaped sections. The total shearing force divided by the area of theweb is under these assumptions regarded as the unitshear throughout the web. The distribution of material in these sections isevidently best suited to the case in hand, the materialbeing placed where it will bestressed approximately to itsworking stress throughout. — 40- T W T % Exercise 79. Calculate theshear for the principal points inthe s
Size: 1366px × 1830px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectmechanics, bookyear19
