Cyclopedia of architecture, carpentry, and building : a general reference work . minedto see if they are safe in tension,since they are under either tensileor compressive stresses accordingto the direction in which the windblows. The knee-brace for the truss-bent of Article 9 will now bedesigned. The maximum com-pressive stress is 21 440 radius of gyration must be at least 131 -h 120 = Twoangles 3^ by 3 by y^e-inch, placed back to back with their longerlegs J inch apart, will be assumed, since they are the smallest size tobe used with r = or greater. The radius of gyratio
Cyclopedia of architecture, carpentry, and building : a general reference work . minedto see if they are safe in tension,since they are under either tensileor compressive stresses accordingto the direction in which the windblows. The knee-brace for the truss-bent of Article 9 will now bedesigned. The maximum com-pressive stress is 21 440 radius of gyration must be at least 131 -h 120 = Twoangles 3^ by 3 by y^e-inch, placed back to back with their longerlegs J inch apart, will be assumed, since they are the smallest size tobe used with r = or greater. The radius of gyration about anaxis perpendicular to the longer legs is ; and the allowable unit- 110 X 131stress is P= 24 000 = 10 900 pounds per square \^^ . 21 440 inch, the length being 131 inches. TJie requn-ed area is TrTono = square inches. Since this is less than the given area, andsince the angles are the smallest allowed, these angles are suffi-cient. The maximum tensile stress is 8 640 pounds, and the requirednet area is 8 640 -^ 15 000 = square inch. The net area given. Fig. 101. Detail of Knee-Brace andConnections. 290 ROOF TRUSSES 77 by the angles is — = square inches, two |-inch rivet-holes being taken out. This shows the angles to be amply safe intension, and they will therefore be used for the section of the knee-braces. 25. Runway Girders. The runway girders extend from columnto column on each side of the bay in which the girder runs. An
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