Patent Application
20090272049
Not applicable.
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.
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.
The invention may be better understood by referring to the accompanying drawings, in which:
The figures illustrate one embodiment of a tank that uses the invention. The tank 10 illustrated in
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
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
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
The illustrated dome 40 is covered by a steel tank liner 64, best seen in
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
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.
