GENERAL SPECIFICATIONS FOR ELEVATED STEEL TANKS ON TOWERS, AND 



FOR STAND-PIPES.* 



PART I. DESIGN OF ELEVATED STEEL TANKS ON TOWERS. 



Definition. i. An elevated tank is a vessel placed on a tower in order to furnish a certain 

 required prrssun- head. The lank is filled through a riser or inlet pipe. 



2. Klev.ited tanks are mostly used in connection with pumping stations, or are connected 

 directly to Artesian wells, in order to store water under pressure. 



3. As practically all tanks are cylindrical, this specification will only have reference to those 

 of that shape. 



Loads. 4. The dead load shall consist of the weight of the structural and ornamental steel- 

 work, platforms, roof construction, piping, etc. 



5. The live load shall be the contents of the tank, the movable load on the platforms and 

 roof, and the wind pressure. 



6. The live load on the platforms and roof shall be assumed at 30 Ib. per sq. ft., or a 2OO-lb. 

 concentrated load applied at any point. 



7. The wind pressure shall be assumed at 30 Ib. per sq. ft., acting in any direction. The 

 surfaces of cylindrical tanks exposed to the wind shall be calculated at two-thirds of the diameter 

 multiplied by the height. Similar assumptions may also be made for spherical and conical surfaces 

 by using the correct heights. 



8. The live load on platforms and roof shall not be considered as acting together with the 

 wind pressure. 



Unit Stresses. 9. All parts of the structure shall be proportioned so that the sum of the dead 

 and live loads shall not cause the stresses to exceed those given in Table I. 



TABLE I. 



Tension in tank plates 12,000 Ib. per sq. in. of net area. 



Tension in other part of structure 16,000 Ib. per sq. in. of net area. 



Compression 16,000 Ib. per sq. in. reduced. 



Shear on shop rivets and pins 12,000 Ib. per sq. in. 



Shear on field rivets (tank rivets) and bolts 9,000 Ib. per sq. in. 



Shear in plates 10,000 Ib. per sq. in. of gross area. 



Bearing pressure on shop rivets and pins 24,000 Ib. per sq. in. 



Bearing pressure on field rivets (tank rivets) 18,000 Ib. per sq. in. 



Fiber strain in pins 24,000 Ib. per sq. in. 



10. For compression members, the permissible unit stress of 16,000 Ib. shall be reduced by the 

 formula: 



p = 16,000 70 l/r, 



, where p = permissible working stress in compression, in Ib. per sq. in.: 



/ = length of member, from center to center of connections, in inches; 

 r least radius of gyration of section, in inches. 



The ratio, l/r, shall never exceed 120 for main members and 180 for struts and roof construc- 

 tion members. 



11. Stresses due to wind may be neglected if they are less than 25 per cent of the combined 

 dead and live loads. 



12. Unit stresses in bracing and other members taking wind stresses may be increased to 

 20,000 Ib. per sq. in., except as shown in Section n. 



13. The pressures given in Table II will be permissible on bearing plates. 



TABLE II. 



Brickwork with cement mortar 200 Ib. per sq. in. 



Portland cement concrete 350 Ib. per sq. in. 



First-class sandstone 400 Ib. per sq. in. 



First-class limestone 500 Ib. per sq. in. 



First-class granite 600 Ib. per sq. in. 



* Condensed from Specifications by C. W. Birch-Nord, Assoc. M. Am. Soc. C. E., Trans. 

 Am. Soc. C. E., Vol. 64, pp. 548 to 563. The preliminary statement and the specifications for the 

 foundations have been omitted. These specifications have been adopted by the American Bridge 

 Company. 



379 



