Cyclopedia of architecture, carpentry, and building : a general reference work . ope. Fig 46 represents such a truss. The weight of the truss itself can be esti-mated by means of the formula of Art, 10. Thus if the distancebetween trusses equals 12 feet, the weight of the truss equals 32 W == 12 X 32 ( -^ + 1) = 875 pounds. The weight of the roofing equals the product of the area ofthe roofing and the weight per unit area. The area equals 12times the sum of the lengths of the members 12, 23, 34, and 45,that is, 12 X 304^ = 438 square feet. If the roofing weighs 10pounds per square foot, then t
Cyclopedia of architecture, carpentry, and building : a general reference work . ope. Fig 46 represents such a truss. The weight of the truss itself can be esti-mated by means of the formula of Art, 10. Thus if the distancebetween trusses equals 12 feet, the weight of the truss equals 32 W == 12 X 32 ( -^ + 1) = 875 pounds. The weight of the roofing equals the product of the area ofthe roofing and the weight per unit area. The area equals 12times the sum of the lengths of the members 12, 23, 34, and 45,that is, 12 X 304^ = 438 square feet. If the roofing weighs 10pounds per square foot, then the weight of roofing sustained byone truss equals 438 X 10 = 4,380 pounds. The total dead loadthen equals 875 + 4,380 = 5,255 pounds; 209 76 STATICS and the apex dead loads for joints 2, 8, and 4: equal: -J- X 5,255= 1,314 (or approximately 1,300)pounds;while the loads for joints 1 and 5 equal -—- X 5,255 = 057 (or approximately 650) pounds. The snow loads for the joints are found by computing thesnow load on each separate slope of the roof. Thus, if the snow 2loo , looolbs. - \Rfl74olb9. Fig. 46. weighs 20 pounds per square foot (horizontal), the load on the portion12 equals 20 times the area of the horizontal projection of the por-tion of the roof represented by 12. This horizontal projection equals8 X 12 (= 96) square feet; snow load equals 96 X 20 (= 1,920)pounds. This load is to be equally divided between joints 1 and 2. In a similar way the snow load borne by 23 equals 20 timesthe area of the horizontal projection of the roof represented by 23;this horizontal projection equals 8 X 12 ( = 96) square feet asbefore, and the snow load hence equals 1,920 pounds also. Thisload is to be equally divided between joints 2 and 3. Evidently the loads on parts 31 and 45 also equal 1,920pounds each; hence the apex loads at joints 1 and 5 equal 960pounds and at joints 2, 3 and 4, 1,920 pounds. 210 STATICS 77 The wind load must be computed for each slope of the roofseparately. The angl
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