US2899820A - Prestressed joint between bottoms - Google Patents

Description

J. F. HEADRICK PRESTRESSED JOINT BETWEEN BOTTOMS AND SHELLS OF LARGE TANKS Filed Sept. 15, 1954 INVENTOR.

JOHN HEADRICK BY A T TORNEVS Aug. 18, 1959 United States Patent pansrnnssnn ronsr BETWEEN BOTTOMS AND,

' snares or LARGE TANKS John F. Hendrick, Berger, Tern, assignor to Phillips Petroleum Company, a corporation of Delaware Application September 13, 1954 Serial No. 455,428

Claims. ((11. 7213).

This invention relates to the construction of large storage tanks and to a prestressed joint between the bottom and the shell of such a tank. A specific aspect of the invention pertains to a process or method for prestressing such a joint.

It is conventional to construct concrete bottoms in both old and new steel storage tanks.

Considerable difficulty with leaks in large steel storage tanks for the storage of petroleum products, such as oil, and other liquids, has been experienced because of the stress applied by the liquid to the shell of the tank which separates the shell from the concrete bottom of the tank. Conventional steel tank bottoms corrode inside and outside and must eventually be replaced. Cement or concrete has been used for this purpose, but the joint between the concrete and the steel shell opens up when the tank is filled, thereby permitting corrosive liquids to come into contact with the bottom and eventually find its way out of the tank. Conventional concrete water tanks use a sliding joint between the bottom and the shell but these frequently leak also. The leaks cause progressive damage to the concrete and ultimately the interior of the joint must be caulked.

The objects of the invention are several and include, to provide an improved tank construction which may be embodied in either a new tank or in an old tank which has a deteriorated bottom; to provide aprestressed joint between the bottom and shell of a tank; to provide a method of constructing such a prestressed joint; and to provide a liquid tight joint between a tank shell and a cement or concrete bottom which will withstand liquid pressure without opening up. ()ther objects of the invention will become apparent from a consideration of the accompanying disclosure. I i

In accordance with the invention, a concrete slab or bottom is formed in a tank with a flexible sealing member or means bonded to the vertical edge of the bottom and extending into contact with the shell of the tank along the upper edge of the sealing member. This sealing means is liquid tight so that when the tank is filled with water or other suitable liquid, the shell of the tank is expanded under the hydraulic pressure, thereby providing an open space between the edge of the slab or sealing means bonded thereto and the shell of the tank. While the shell is thus expanded, a flowable cement, such as grout, is forced into the open space through openings in the shell adjacent the open space so as to completely fill the space. After the cast cement has set and hardened, the shell adjacent the bottom is held in a permanently stressed condition by the rigid solid annulus of cast cement material so that the tank will hold any storage liquid without expanding in the area of the joint, thereby avoiding an opening in the joint which will result in leakage and/ or deterioration of the tank.

In a preferred embodiment of the invention, the slab or bottom is formed in the tank to provide .an initial open space intermediate the sealing means and the shell "ice of. the tank so as to provide a larger space for grout than is provided by expansion alone.

Also, it is preferred that the liquid filling the tank during the grouting operation have a higher specific grayity than the stored liquid, whereby the initial stress the shell is never entirely removed. 7

A more complete understanding of the invention may be had from a consideration of the accompanying drawing of which Figure 1 is a sectional elevation of a preferred embodiment of the invention; Figure 2 is a detailed sectional elevation of a bottom corner of a tank showing a srnilar embodiment of the invention; and Figure 3 is a detailed sectional elevation of a bottom corner of a tank having a cement bottom and shell. All of the figures are schematic.

Refe 'lug to Figure 1, a steel tank 10 comprises a steel shell 11 joined to a steel bottorn 12 by means of steel angle 13, and rivets 14. The, shell and steel bottom may be: fabricated from steel sheet in sections by either riveting or welding. The tank has a roof 15 attached to the shell by meansof brackets 16 or other suitable fixtures. A concrete bottom or slab 17 covers the bottom of the tank to within a short distance of the shell and has bonded -edge a flexible iron or steel sheet 18 so as to provide an open space 19 intermediate sheet 18 and shell 11. Helical concrete, nails, spaced at short intervals around the iperipheryfof the bottom and driven through small holesin flexible sheet 18 before pouring of the cement bottorn, serve to hold the sheet in close bond with the cement after setting. Coarse mesh Wire screen 22 in the center area of the slab to impart strength to the same. Connectors 23 and 24 in openings in the shell provide rneans for forcing grout or other suitable hardening cement into the open space 19 while the shell is expanded by hydraulic pressure.

Referring to Figure 2, corresponding parts of this figure, as well as of Figure 3, bear numerals corresponding to those, oi Figure 1. It can be seen that the construction in Figure 2 is similar to that of Figure l, the essen tial difference being in the weld 28 utilized to attach the shell 11 to bottom 12. Another diflerence lies in the bottom cutout 29 which leaves only an annular section of the steel bottom on which the cement slab is poured. I some p ic t ns the ce te s c n 29 of the tank bott m m be sa ag d o e n m c r as ns- Figure 3 shows new tank construction in which .a poured bottom slab '22 having an ofiset section 31 as a support or foundation for shell 11 is provided. Wire re afa e n n ar e o t d o th shell i til zed to resist cracking of the shell during expansion and to give added strength to the shell. While these heavy wires are shown embedded in the concrete, it is also feasible to construct the concrete shell in vertical sections and hold the sec tions in fluid tight relation to each other by means of a .Inultiplicity of steel rods or hands around the outside of the shell. Turnbuckles or other tightening means may be utilized to apply tension on the outside of the shell. The sealing means between bottom 22 and shell 11 in this :type of construction comprises two separate metal sheets 18 and 13a, 18 having its upper edge embedded in :lht "Concrete of shell 11 and extending downwardly toward the bottom of the tank and 18a having its lower edge embedded in the tank bottom and extending upwardly along the step-down edge of the bottom and thence into contact with sheet 18 to which it is welded by weld 26.

In constructing the perstressed joint of the invention according to the modification shown in Figures 1 and 2, iron .or steel sheet 18 is positioned in the tank with its upper edge adjacent the shell and its lower edge spaced from the shell by any suitable means, such as bybniall spacers (not shown) which function to hold the sheet in place to resist pressure of the cement while it is fluid. In this manner, with spacers of the desired thickness intermediate shell 11 and flexible sheet 18, the latter is utilized as the form for the edge of the bottom. It is also feasible to construct removable forms intermediate shell 11 and sheet 18 which can be removed before the upper edge of sheet 18 is welded to the shell. If spacers are utilized, they should avoid blocking of the flow of grout from section to section of space 19. A suitable arrangement is to place one vertical spacer intermediate each pair of connectors 23 and 24 around the base of the shell. It is not necessary to remove the spacers before filling space 19 with cement.

Elements 21 are firmly fixed in place before the sheet is inserted in the tank. This can be done by drilling holes smaller than the helical nails and driving the nails into the holes to bring the heads up solid. Weld 26 may be formed either before or after pouring the bottom but must be made prior to filling the tank with water or other liquid. The cement is then poured and allowed to harden and the tank is filled with water to apply maximum stress on the shell 18 and to elfect as much expansion thereof as will ever occur during utilization of the tank for storage of liquid. In some instances, it may be desirable to stress the tank with a liquid heavier than water, such as an aqueous solution of soluble material. When the tank is in this stressed condition and the shell is under maximum expansion, grout or other suitable hardening cement is forced into space 19 under pressure through connectors 23 until the same flows out through openings 24 to indicate that the space is filled. The grout pressure should not substantially exceed the hydrostatic pressure on sealing means 18 because of the possibility of breaking the seal along weld 26 and impairing the joint. After the grout is set and properly hardened, water in the tank can be removed and the tank is ready for use in storing any suitable liquid, such as petroleum products of all types.

Flexible sheet 18 is extended upwardly a small but substantial distance above the top surface of the slab or bottom and the space between this sheet and the shell at the edge of the slab is maintained small so as to provide sufllcient flexibility in the sealing means upon expansion of the shell. Other arrangements of the sealing means which permit relatively small movement of the portion of the sealing means intermediate the shell and the concrete bottom are feasible and within the scope of the invention, in fact, any arrangement which provides a liquid tight seal between the sealing means 18 and both shell 11 and bottom 17 may be used and are within the purview of the invention.

In construction of the tank shown in Figure 3, bottom 22 is poured first with sheet 18a and nails 21 fixed in the position shown attached to the forms utilized in forming up the tank bottom. After bottom 17 is properly set, the forms are removed and forms for shell 11 are constructed with flexible sheet 18 properly in place inside the forms or extending through a crack in the forms. It is also feasible to attach element 18 to the concrete by suitable nails and caulking material after removal of the forms. The projection of 18a above the bottom may be temporarily bent out of position to allow room for the forms and after pouring of the concrete of shell 11, 18 may be brought into contact with 18a and the weld completed. In instances where shell 11 is constructed of vertical sections, these sections containing element 18 are merely positioned on the offset portion 31 of slab 17 in proper position and compression rods or bands traversing the outside of the shell are tightened so as to form a seal between the vertical sections of cement. Caulking material may be used between the joints of the vertical sections to effect a seal. The joints in 18 and the joint with 18a are then welded so as to form a liquid tight seal between shell 11 and bottom 17. This permits the filling of the tank with a liquid so as to prestress the joint after which grout is forced into the space 19, as described in connection with Figures 1 and 2.

Sealing member 18 is preferably made of relatively thin sheet metal, such as 20-28 gauge black iron. Any other metal may be used which can be successfully welded or soldered to provide a liquid tight union between the metal shell and the sheet. It is also feasible to utilize impervious heavy fabric, such as rubber impregnated woven or cord material, as the flexible sealing member between the bottom of the tank and the shell. In such instances, the fabric may be bonded to the cement bottom by extending the lower edge under the cement or into the cement in the manner shown in Figure 3 ( element 18 or 18a) and the upper edge of the flexible fabric may be sealed to the shell by means of caulking compound. In the conventional large storage tanks, the pressure at the juncture of the bottom and the shell of the tank is usually in the range of 2025 p.s.i.g. It is desirable to prestress the joint to a pressure of at least 20 p.s.i.g. and preferably to a greater pressure than will ever be exerted by a storage liquid in the tank.

Storage tanks are often found with the peripheral portion in sunken position after a long period of service and the method and structure of the invention is equally applicable to tanks found in this condition without raising the sunken portion of the tank.

Certain modifications of the invention will become apparent to those skilled in the art and the illustrative details disclosed are not to be construed as imposing unnecessary limitations on the invention.

I claim:

1. A tank having a generally cylindrical shell and a concrete bottom and -a prestressed sealed joint therebetween comprising an annular flexible sealing member of flexible sheet material between the side of the bottom and the inside wall of said shell, which sealing member is attached along its top to said shell at a short distance above the upper surface of said bottom, and a separate cast hardened cement element under compression completely filling a space formed between said flexible sealing means and said wall of said shell, which hardened cement element under compression is exerting an expanding force on said shell.

2. A tank having a shell and a concrete bottom and a prestressed sealed joint therebetween comprising a flexible sealing means between the side of the bottom and the inside wall of said shell and a separate cast hardened cement element under compression completely filling a space formed between said flexible sealing means and said wall of said shell, which hardened cement element under compression is exerting an expanding force on said shell, wherein said shell is a steel cylinder and said flexible sealing means comprises an annular metal sheet attached at its top edge to said shell at a relatively short distance above the upper surface of said bottom.

3. A tank having a shell and a concrete bottom and a prestressed sealed joint therebetween comprising a flexible sealing means between the side of the bottom and the inside wall of said shell and a separate cast hardened cement element under compression completely filling a space formed between said flexible sealing means and said wall of said shell, which hardened cement element under compression is exerting an expanding force on said shell, wherein said shell is a concrete cylinder and said sealing means comprises a pair of flexible metal sheets, a first sheet having its upper edge imbedded in said shell and extending downwardly toward said bottom, a second sheet having its lower edge imbedded in said bottom and extending upwardly to form a sealed joint with said first sheet.

4. A metal tank ha /ing an upright expansible cylindrical metal wall; a rigid concrete bottom within said tank extending to within a short distance from said wall forming a narrow annular space between the lower inside Surface of the tank wall and the outer peripheral wall of the said bottom; a separate rigid solid annulus of cast cement material under compression in said space and filling said annular space, thus holding said metal wall adjacent said annulus in expanded condition so that when said tank is filled with liquid said metal wall retains tight contact with said annulus.

5. The tank of claim 4 wherein said annulus extends above said bottom.

1,138,394 Mueser May 4, 1915 6 Chappell July 3, 1934 McNeil Mar. 31, 1936 Walker Jan. 9, 1940 Logeman Nov. 3, 1942 Smith et al. Nov. 9, 1943 Pomykala Aug. 14, 1945 Maceratta May 13, 1952 FOREIGN PATENTS France May 27, 1953

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