US2690273A

US2690273A - Elevated storage tank

Info

Publication number: US2690273A
Application number: US86615A
Authority: US
Inventors: Arne Christian
Original assignee: Chicago Bridge and Iron Co
Current assignee: Chicago Bridge and Iron Co
Priority date: 1949-04-11
Filing date: 1949-04-11
Publication date: 1954-09-28
Anticipated expiration: 1971-09-28

Description

28, 1954 Q ARNE ELEVATED STORAGE TANK Filed April l l, 1949 Patented Sept. 28, 1954 ELEVATED STORAGE TANK Christian Arne, Chicago, Ill., assignor to Chicago Bridge & Iron Company, a corporation of Illinois Application April -11, 1949, Serial No. 86,615

2 Claims.

This invention relates to column construction and more particularly to an air filled structural member having increased compressive strength.

In the construction of elevated structures supporting members are used which are under compressive forces. The normal practice has been to design the supporting members so. as to have sufficient strength safely to support the structure. When this principle is applied to an elevated structure supported by steel columns the thickness of the steel in each column is so calculated as to produce such a supporting member. Obviously, as the weight of the structure to be supported increases, the amount of steel used to support the structure also increases. It is clear that any saving in the amount of steel necessary to support an elevated structur reduces the cost, not only because of the smaller quantity of steel used but because of the fact that lighter columns are easier to manufacture, assemble, and weld.

I have found that by filling a hollow supporting member with compressed fluid, for example with compressed air, that I can increase substantially the compressive load which such a column can withstand.

The invention will be described in conjunction with the accompanying drawings in which:

Fig. 1 is a sectional view through a column embodying the invention;

Fig. 2 is a sectional view through a supporting column embodying the invention and made up of a plurality of sections;

Fig. 3 is a vertical section through an elevated water tank supported by a column constructed in accordance with the invention.

Referring now to the drawings I show in Fig. 1 a column 10 having a cylindrical sidewall ll resting upon a base plate 12 which in turn rests upon a foundation is. The upper end of the column is closed by a plate [4 and each of the plates 12 and Hi is welded to the column, as shown.

If the radius of the column is R and the thickness of the shell i l is t and if the allowable compression stress in the column is C, the load W the column can carry equals 21rRtC.

If the ends of the column are closed and the allowable circumferential tensile stress is 'I, the column can withstand an internal fluid pressure of P and The cross-sectional area of the column is, of course, 1B and, therefore, the fluid pressure P increases the carrying capacity of the column by w, and

2 It is clear from the last equation that the increase in the carrying capacity 10 is independent of the column length and of W. It, therefore, follows that:

While with certain columns the allowable compression C may be more than the allowable tension T, it is the general rule that T is at least equal to C and is usually greater. Thus, for example, if the allowable tension T is 15,000 lbs. per sq. inch and the allowable compression C is also 15,000 lbs. per sq. inch,

and, therefore, w=.5W. Thus, the carrying capacity of the column is increased by 50%.

Failure in diagonal shear is quite unlikely since structural plates are known to have a tensile strength of about 60,000 11. s. i. and a shear strength of 40,000 p. s. i. Thus considering a 1 inch square of the column wall, inches thick with C p. s. i. compressive stress and T p. s. i. tensile stress acting on the square, the shearing stress on a diagonal section is If C=T p. s. 1., then shearing stress on the diagonal is equal to T. Working stresses for C and T are known to be 15,000 p. s. i. which is far below the 40,000 p. s. i. shear strength.

It will also be clear to those skilled in the art that the fluid to be placed under pressure in a tubular supporting column need not be a gas but may be a liquid. For example, tubular compression members may be filled with water under pressure and immersed in water. Such supporting members may be, for example, sub-surface supports for a bridge and being located under the surface Of the water are not subject to bend ing from the weight of the water contained therein.

Naturally, with an increase in the carrying capacity of the column the thickness of the steel required safely to support any load may be reduced. v

The column may be charged with fluid under pressure, such as compressed air, by means of a pump or otherwise through a valve. device which is sealed up after the proper pressure has been reached. 'The pressure within the column can also be attained by placing therein a volatile liquid having a vapor pressure which will result in the desired pressure at the prevailing temperatures. A column constructed in accordance with this invention should be inspected for pressure about as often as it is painted.

Compressed air inside of the column tends to keep the column round and takes the place of stifiening rings and obviously with greater stifiness it is reasonable to allow greater compressive stress in the steel column. Thus, the value of C may be increased.

Referring now to the column shown in Fig. 2, it can be seen that it is made up of a first tubular section if: and a second tubular section IS. The lower end of the section 15 is sealed to a plate I! which rests upon a foundation 18 while the upper end of section I6 is sealed by another plate I9 welded thereto. Each of the sections 15 and I6 is sealed adjacent the end opposite the plates by diaphragms 20 and 2| respectively. It will be noted that that portion of each section between the plates H or 19 and the diaphragm 2B or 2| is constructed of metal thinner than the metal employed between the diaphragm and the adjoining ends of the section. It is contemplated that the closed portion of each section, that is, the portion between the end plate and the diaphragm will be filled with a compressed gas to create therein a circumferential tension which at the highest temperatures to be expected in the area where the column is to be used are substantially equal to the allowable circumferential tension stress. Inasmuch as that portion of each section adjacent their abutting ends is not reinforced by compressed air those sections are made thicker and may be welded to each other by welding in the groove 22.

Fig. 2 demonstrates clearly the savings effected by the use of my invention in any particular column construction. Were it not for the fact that each section is filled (and thus reinforced) with compressed air between the plates and the diaphragms, the whole of each of such sections would have to be constructed of steel as thick as is required at the abutting ends of those sections as shown in the drawings.

Referring now to Fig. 3, I show a specific structure, namely an elevated water tank, embodying the column construction of the invention. In that figure a substantially spherical tank 311 is supported on a closed cylindrical column 3 l. The lower edge of the column is welded or otherwise sealed to a base plate 32 which rests upon a foundation 33 while the upper edge of the column 3| is welded to the tank 30. A riser 34 extends downwardly from the tank through the column and thence outwardly through the foundation, the riser being sealed to the base plate 32 as by the weld 35. A hollow pipe 38 is secured to the bottom of the tank 30 and extends upwardly therethrou'gh, the pipe opening at its upper end to the interior of the tank 30 above the liquid level therein and opening at its lower end to the interior of the column 3 I.

When the tank 30 is first filled with water the air therein is compressed and forced through the pipe 36- into the interior of the column 3| to increase the air pressure therein and. thus to add to the permissible compressive stress on the column. Should the volume of the column be such, relative to the volume of the tank, that th filling of the tank does not sufiiciently increase the pressure within the column, additional air under pressure may be admitted through the fitting 31.

As water is withdrawn from the tank and liquid level falls therein, air within the column 3| will enter the space above the fallin liquid level and thus reduce the pressure in the column. However, as the weight of the tank 30 decreases when water is withdrawn therefrom it is clear that the load to which the column is subjected is also reduced. On the other hand, when the tank is being refilled and its weight is increasing the compression of the air within the column 31 also increases.

An additional feature of the elevated tank shown in Fig. 3 is that the water pressure at the bottom of the riser is equal to the hydrostatic head of the water above the outlet plus the pressure of air existing in the space above the liquid level in the tank. Thus, the compressed air within the column 3| serves not only to strengthen and reinforce that column but also to increase the water pressure at the outlet.

By the use of the word columns in the specification and claims I do not restrict myself, nor are the invention and the principles thereof re stricted to vertical, cylindrical, or metallic columns. It is clear that the invention is equally applicable to a strut and truss bridge, or to an arch, or to any other supporting member subjected to compression stresses.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

Iclaim:

1. An elevated liquid storage tank supported by a single hollow column filled with gas under superatmospheric pressure and a pipe connecting the interior of-the column with the interior of the tank above the level of the liquid.

2. An elevated liquid storage tank comprising, a storage portion, a hollow metal column supporting the storage portion at a fixed elevation above a base, said column alone being incapable of supporting the storage portion when full, said hollow column being filled with gas under pressure to raise its supporting strength and a connection providing communication between the interior of the column and the interior of the tank above the level of the liquid.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date D. 122,600 Horton Sept. 17, 1940 64,783 Merrill May 14, 1867 511,472 Sumovski Dec. 26, 1893 1,057,414 Drake et al Apr. 1, 1913 1,482,541 Braisted Feb, 5, 1924 1,665,827 Tillmann Apr. 10, 1928 1,753,259 Badger Apr. 8, 1930 1,915,303 Forsyth June 27, 1933 1,958,421 Daniels May 15, 16 4 2,062,574 Heinze Dec. 1, 1936 2,264,668 Horton Dec. 2, 1941 2,315,453 Pitman Mar. 30, 1943 2,341,100 Horton Feb. 8, 1944 2,391,120 Berthelmann Dec. 18, 1945 FOREIGN PATENTS Number Country Date 454,200 France Apr. 23, 1913 74,541 France Apr. 2, 1924