Manual of military engineering . ELe\aJLiorv To foll<ryv pbxte 79 CHAPTER XX.—FRAME BRIDGES, ETC. 113 295. When round timbers are used the groundsills and capsills Framedmust be adzed to give a square bearing surface for the trestles ofuprights. Ipund When there are two or more tiers, it will be best for the ^^ ^^upper tiers not to have groundsills. The uprights may restdirectly on the capsills of the tier below {see PI. should be wedged up after fixing ; to keep the trestletogether while it is being raised, a light timber or board maybe spiked to the sides of the uprights near thei
Manual of military engineering . ELe\aJLiorv To foll<ryv pbxte 79 CHAPTER XX.—FRAME BRIDGES, ETC. 113 295. When round timbers are used the groundsills and capsills Framedmust be adzed to give a square bearing surface for the trestles ofuprights. Ipund When there are two or more tiers, it will be best for the ^^ ^^upper tiers not to have groundsills. The uprights may restdirectly on the capsills of the tier below {see PI. should be wedged up after fixing ; to keep the trestletogether while it is being raised, a light timber or board maybe spiked to the sides of the uprights near their feet. 296. Formula for Use in Suspension Suspen-sionbridges. Length of cable between piers = a +-— W cr W=. uniformdead load ony cables perun of Tension in cable, Tq Tension at piers, Tg Pressure on piers = W a J Height of frame d •= -\- h (length of centre sling) + camber (1 in 30) For a concentrated load, such as that brought by a traveller, without Adroadway, safe load on the cable = — x working- strength of cable. (5289) u lU CHAPTER XX.—FRAME BRIDGES, ETC. 297. The followinf;^ table will be found useful for calculating stressesdue to uuiform loads on suspension bridges ; in it the load is \Vx a :— 1- 2. 3. 4. 5. 6. Dip. Tension atlowest point. Tension athighestpcint. Length ofcable. Depression at centre due to an elongation of cable of 1 inch. Ta^ue ofJK. a10 1-25 X lead 1 -346 X load 1 -027 X span 1 -875 inches 2o SK all 1 -375 „ 1 -49 1 -022 2 -0625 „ 2-75 „ a12 1-0 1 -58 1 -0185 2 -25 3-0 a13 1 -625 „ 1-7 1 -0158 2 -4875 ,, 3 •25 „ a14 1 -75 „ 1 -82 „ 1 -0136 2-65 3-5 „ a15 1 -85 1 -94 „
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