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CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application and claims benefit under 35 U.S.C. §120 to U.S. patent application Ser. No. 12/112,574, filed on Apr. 30, 2008, now U.S. Pat. No. 8,261,510, Incorporated by reference in its intirety herein. 
    
    
     BACKGROUND OF THE INVENTION 
     A new innovation has been developed relating generally to elevated water storage tanks such as those used by municipalities. The capacity of such water storage tanks can range from about one hundred thousand U.S. gallons to several million gallons, and conventionally such tanks are built entirely of steel, or with a steel reservoir on top of a concrete pedestal. 
     In structures that use a concrete pedestal (“composite elevated tanks”), high risk work tasks and expensive formwork have historically been required to build a concrete dome on top of the tower, to support the water reservoir. 
     BRIEF SUMMARY 
     The applicants have developed new method of building a concrete dome in a composite elevated tank. Like most such tanks, the new tank has a tank shell positioned above a tower section, and the top of the tower section includes a ringbeam that supports the dome and the tank shell. 
     Historically, the structural dome on a composite elevated tank is constructed using a cast-in-place method of construction. A series of pie-shaped forms is erected on top of the tower section (typically from fifty to two hundred feet above the ground) to form a spherical segment. Reinforcing steel is placed on the formwork, and then concrete is poured using either a pump or a concrete bucket or trolley. The top of the concrete is then screeded with a circular screed to create a spherical surface. Once the concrete is cured, the formwork on the underside of the dome is stripped and lowered to the ground using a derrick or crane. 
     A novel method can be used to build the new tank. In that method, wedge-shaped concrete floor segments are cast near grade (or even off-site) and individually lifted to the ring beam. The segments can be curved in either length or breadth (or both) but, in some circumstances, might also be linear in either or both dimensions. The segments are placed side-by-side over the internal opening in the ringbeam, with the outer end of each segment on a supporting face on the ring beam. The inner end of the segment is positioned higher than the than the outer end and, when needed, can be supported by a temporary support. When they are all placed, the floor segments create the shape of the dome. The dome can be linear in both horizontal cross-section and in profile (like a pyramid), curved in profile but not in horizontal cross-section (like an umbrella), curved in horizontal cross-section but not in profile (like a cone), or curved in both horizontal cross-section and in profile (like a spherical section). 
     This method eliminates the need for preparing and raising complicated and expensive formwork to build the dome. In addition, less labor is required at the top of the tower, reducing the risk of injury. The concrete segments can be cast directly against steel liner plates, providing further advantages of an integral or composite segment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be better understood by referring to the accompanying drawings, in which: 
         FIG. 1  is a side view of one embodiment of a composite elevated tank that uses the invention. 
         FIG. 2  is an enlarged fragmentary cross-sectional view of the top of the tank seen in  FIG. 1 . 
         FIG. 3  is an enlarged cross-sectional view of the ringbeam, dome, and access tube of the tank. 
         FIG. 4  is a top view of one of the panels of the dome, in a raised position. 
         FIG. 5  is a side view of the panel seen in  FIG. 4 . 
         FIG. 6  is a top view of the panels in the dome. 
         FIG. 7  is a fragmentary top view showing the edges of the panels adjacent the access tube. 
         FIG. 8  is a side view of the dome, showing a tank liner in place. 
         FIG. 9  is a top view of the liner. 
     
    
    
     DETAILED DESCRIPTION 
     The figures illustrate one embodiment of a tank that uses the invention. The tank  10  illustrated in  FIG. 1  has a tower section  12 , tank shell  14 , and an intermediate section  16 . Each of these parts will be described in more detail below. The description of the parts of the tank will be followed by a discussion of the tank&#39;s construction. 
     The Tower Section 
     The illustrated tower section  12  is approximately 100 feet tall and made of  13  cast-in place concrete rings. The tower section is approximately 36 feet in diameter, and has cylindrical walls that are approximately 10 inches thick. The size and configuration of the tower section can be varied to meet the particular needs of a job. 
     The Outer Tank Shell 
     The tank shell  14  is positioned above the tower section  12 . The tank shell that is illustrated here is made of steel and has a frustoconical bottom section  20 , a cylindrical section  22  above it, and a domed roof  24 . All these sections of the tank shell are made primarily of steel. The cylindrical section is made of multiple courses of steel shell plates. Overall, the tank shell is approximately 70 feet in diameter and 40 feet tall from a top capacity level  25  to a bottom capacity level  26 , providing a capacity of approximately one million U.S. gallons. In other situations, the arrangement or dimensions of the tank shell could vary, and could provide a capacity ranging from one hundred thousand U.S. gallons to several million gallons. 
     The Intermediate Section 
     The intermediate section  16  of the illustrated tank  10  includes a ringbeam  30 , best seen in  FIGS. 2 and 3 , at the top of the tower section  12 . The ringbeam surrounds an internal area that, in this example, accommodates a four-foot diameter access tube  32  ( FIG. 3 ) that extends from within the tank volume into an interior of the tower section. The illustrated ringbeam is made of concrete and has internal steel reinforcement  33 , as shown in  FIG. 3 . 
     The ringbeam is configured with a ring-shaped, upwardly-facing supporting face  34  that resists downward forces. In this example, the supporting face is a horizontal surface adjacent to the innermost upper edge of the ringbeam  30 . Here, the supporting face is approximately 11 inches wide. In other situations, the supporting face could be inclined or segmented, and could be as little as 4″ wide. 
     The intermediate section  16  of the tank  10  also includes a dome  40  that sits on the supporting face  34  of the ringbeam  30 . The dome is made of laterally adjacent concrete dome segments  42  that are best seen in  FIGS. 4-6 . When placed, these segments essentially cover the internal area within the central opening of the ringbeam. In this example, the access tube  32  passes through that internal area, so the dome has an opening to accommodate the access tube. 
     Each of the dome segments  42  illustrated here is made of concrete and has an outer end  44 , an inner end  46 , a pair of lateral sides  48 , and a vaulted top surface  50 . Internal steel reinforcement  52  is included in the illustrated dome segments for tensile strength. For ease of fabrication, it will generally be preferred for all or most of the segments to be the same size. The illustrated segments are approximately 1 foot wide at the inner end, approximately 8 feet wide at the outer end, and measure approximately 14 feet from the inner end to the outer end. For strength, the inner end is thicker than the outer end. The size may vary, however. 
     The lateral sides  48  of the segment  42  define a segment angle α that can be measured when the segment is laid flat, with both the inner end and the outer end resting on a horizontal surface. In the illustrated example, there are twelve dome segments and the segment angle of each segment is approximately 28°. In other situations, the segment angle and number of segments will generally be between six segments with segment angles of approximately 56° and thirty segments with segment angles of approximately 11°. In other situations, segment angles outside this range could also be useful. In all these cases, however, the sum of the segment angles of each of the dome segments used in a dome will be less than 360° when the angle is measured with the segments lying flat, and positioning the segments in a flat circular arrangement will leave wider gaps near the outer ends of the segments than near the inner ends. 
     When installed, the inner ends  46  of the segments  42  are raised above the outer ends  44 , shortening the horizontal distance between the inner and outer ends and increasing the apparent angle, when viewed from above, between the lateral sides  48 . This raising of the inner ends of the segments enables the segments to fit together, with parts of the lateral sides of each segment lying close to or directly against the lateral sides of each adjacent segment, as seen in  FIG. 6 . Once assembled in this way, the segments combine to provide a vaulted upper surface on the dome  40  that extends from the supporting face  34  on the ringbeam  30  to the access tube  32 . With the outer ends of the segments supported against outward displacement (in this case by a 1½-foot tall, 1-foot wide reinforced concrete upper wall  62  on the ringbeam, best seen in  FIG. 3 ), the floor can withstand construction loads. Cement grout or a comparable compression-resistant spacing material can then be used to fill the gaps between the segments. Once grouted, the dome is self-supporting and can withstand all design loads. 
     The illustrated dome  40  is covered by a steel tank liner  64 , best seen in  FIGS. 8 and 9 , which is welded to the tank shell. The illustrated liner includes an outer, planar section  66  and an inner, vaulted section  68 . 
     In some circumstances, the liner  64  can be formed from liner segments that are integrally cast with the dome segments  42 . Integrally forming the liner segments with the dome segments can be accomplished by casting the concrete against the liner, using embeds or studs. When the dome  40  is assembled, the liner segments on adjacent dome segments can be connected by welded sealing strips. This process provides a tight fit between the concrete dome segments and the liner, eliminates the need for erecting the liner separately, and reduces the amount of dangerous work at high elevations. 
     Construction of the Tower 
     Conventional construction techniques are well understood by those skilled in the art, and can be used in many stages of the construction of the illustrated tank  10 . 
     After the tower section  12  is constructed, the ringbeam  30  is added to the top of the tower section. 
     The wedge-shaped dome segments  42  can be cast on site or fabricated off site. They are lifted to the ring beam and placed side-by-side over the internal opening in the ringbeam  30 . The segments are installed with the outer ends  44  of the segments on the supporting face  34  on the ringbeam and the inner ends  46  of the segments higher than the outer end. A temporary support  69  can be used to temporarily support the inner end of the segments. 
     After placement, the joints  41  between adjacent dome segments  42  are filled with grout  43  as shown in  FIGS. 6 and 7 . In this example, the sides of the adjoining segments are spaced between ¾″ and 1½ inches apart. It is preferred that spacing be relatively close, to reduce concerns about the ability of the grout to withstand shrinkage and load cycling. To help withstand shear loads between the segments, it may also be useful to provide shear keys on the lateral faces of segments. Once the last segment is installed and grouted, the temporary support  69  can be removed. In some cases, it may be practical to remove it after all construction is complete. 
     In the illustrated example, an optional concrete pourback  70  may be added at the outer ends of the dome  40 . This pourback provides a smooth transition from the top of the upper wall  62  on the ringbeam  30  to the vaulted surface of the dome, and does not require either formwork or internal reinforcement. 
     In this example, the steel liner  64  is then applied onto the vaulted surface of the dome  40  and the top of the pourback  70  and the upper wall  62 . The liner is connected to the steel tank shell  14 , forming the liquid reservoir. 
     This description of various embodiments of the invention has been provided for illustrative purposes. Revisions or modifications may be apparent to those of ordinary skill in the art without departing from the invention. The full scope of the invention is set forth in the following claims.

Summary:
A liquid storage tank has a tower section. A tank shell above the tower section encompasses a tank volume that has a capacity of at least 100,000 U.S. gallons. A reinforced ringbeam at the top of the tower section surrounds an internal area that withstands the downward force of the liquid. The ringbeam has at least one supporting face that resists downward forces. A dome sits on the supporting face and essentially covers the internal area. The dome is made of a series of laterally adjacent dome where each dome segment has an inner end that is positioned above an outer end.