Patent Application
20080101864
1. Technical Field
This application relates generally to a pre-engineered, factory manufactured deadman useful for anchoring an underground storage tank (UST), particularly a long deadman about 30 feet or more in length with superior ultimate flexural strength capacity, and a method for shipping the same by truck with the UST.
2. Background of the Technology
Underground storage tanks (USTs) are commonly used for the storage of liquids, including gasoline, other petroleum products, and wastewater. These tanks are generally cylindrical in shape, with either curved (e.g., hemispherical) or flat ends. Underground storage tanks may be made of many materials, including steel and fiber reinforced plastic (referred to herein as FRP and fiberglass). Such tanks may be single- or multi-walled. Such tanks often include ribs, which may be internal or external.
USTs are installed in a wide variety of locations and under a wide variety of conditions. In some locations, the water table is high enough that some or all of the UST is below the water table. In these situations, an upward buoyant force will act on the tank. If the buoyant force exceeds the downward forces acting on the tank, the tank will “float” up out of the ground (referred to herein as flotation). The buoyant force on a UST increases as the tank is emptied, since the weight of the fluid within the tank no longer operates against the buoyant force.
Deadmen are commonly used as anchors to prevent flotation of the tank. Deadmen are typically constructed of reinforced concrete and installed in pairs, with one deadman on each side of and in the plane of the bottom of the tank. Typically, deadmen are rectangular in shape, are about 12 inches wide and 8 to 12 inches high, and have lengths that approximately match that of the corresponding tank. A detailed discussion of deadmen and their use in anchoring underground storage tanks can be found in U.S. Pat. No. 6,467,344, entitled “Underground Storage Tank Buoyancy and Buoyancy Safety Factor Calculation Method and Apparatus,” and U.S. Pat. No. 6,786,689, entitled “Low Profile Deadman and Method for Shipping the Same with a Tank,” which are commonly owned by the assignee of the present application and incorporated by reference herein.
Tanks are commonly connected to deadmen using straps. It is customary to provide a plurality of straps with one end of each strap connected to a deadman on one side of the tank, the other end of each strap connected to a deadman on the other side of the tank. The straps pass over the tank such that the straps, in combination with the deadmen and backfill over the deadmen, prevent the tank from floating upward. Each end of a strap typically has a hook or “D” ring that is used to engage a loop, lug, anchor or eyebolt on the deadman. A detailed discussion of straps for use with deadmen can be found in U.S. Pat. No. 7,028,967, entitled “Tank Retaining System,” which is commonly owned by the assignee of the present application and is incorporated by reference herein. As discussed in that patent, each strap may comprise a pair of straps that are commected together by a tensioning device such as a turnbuckle, come-along, or other device. As used herein, a strap should be understood to refer to a single, continuous strap as well as a strap that is formed from two or more sections that are joined together either directly or indirectly through a tensioning or other device.
The USTs required by customers are getting longer and longer. Current practice involves placing multiple deadmen end-to-end on each side of these long USTs. This practice, particularly in flooded installation sites, is very labor intensive and prone to error. There is a need to overcome these limitations, while preserving the ability to transport the deadmen with the USTs by truck.
The invention provides a steel reinforced concrete deadman with superior strength for anchoring underground storage tanks (USTs). Reinforcing steel bars about 0.88 inches in diameter provide an advantageously high ultimate flexural strength capacity for a concrete deadman. Among the advantages offered by high flexural strength is the ability to use a longer deadman about 30 feet or more in length, which simplifies installation of the UST system.
Accordingly, in a first aspect of the invention, a concrete deadman comprises four longitudinal reinforcing steel bars. The longitudinally reinforcing bars may be both “negative steel” and “positive steel,” i.e., the reinforcing bars may take the tension for both negative and positive bending moments. The bars have a nominal diameter of at least about 0.88 inches and a load weight of at least about 2.04 lb/ft. The concrete deadman, in conjunction with backfill, is capable of preventing floatation of an UST that is attached to the deadman. The negative moment strength of the deadman may exceed 400 kip-in. The deadman may have a length of at least about 30 feet. The deadman may comprise an upper surface, a lower surface, and an elongated slot, where the elongated slot extends over a portion of the length of the deadman and extends from the upper surface to the lower surface of the deadman, where the elongated slot accommodates an anchor point, which can be moved to various positions along the slot. The deadman alternately can be fabricated with an integral loop. To facilitate transportation in conjunction with a UST, the deadman may have a low profile, where at least one edge is chamfered. In a second aspect of the invention, a method of installing an UST comprises attaching a UST to a concrete deadman according to the first aspect of the invention.
In a third aspect of the invention, a shipping assembly comprises a flatbed trailer having a width of approximately ninety six inches that holds an underground storage tank on the flatbed trailer. In one embodiment, the UST has a generally cylindrical body with a diameter of approximately ten feet. Deadmen at least about 30 feet in length are positioned on both sides of the UST, where each of the deadmen has at least one chamfered edge, the chamfered edge being in a position facing the tank.
a) and
The present invention provides a concrete deadman comprising reinforcing steel bars, i.e., rebar, with a diameter and placement that achieves a high ultimate flexural strength capacity (both positive and negative) in the deadman. The increased flexural strength allows a greater load capacity for the deadman, while minimizing the potential for cracks, which expose the steel to corrosion. The increased flexural strength also allows the use of a longer deadman, resulting in various economies.
The ultimate flexural strength capacity of a concrete deadman primarily depends on the diameter and placement of longitudinal reinforcement, typically in the form of steel bars, i.e., rebar. A “high diameter rebar” has a nominal diameter of about 0.88 inches or higher, which corresponds to a weight of at least about 2.04 lb/ft. The negative moment strength, which relates to the tension the deadman can withstand when a force is applied to its top surface, may be at least about 400 kip-in (1 kip=444.8 N) when using at least two high diameter rebar as a longitudinal support. By comparison, a deadman that uses side-by-side reinforcing bars of smaller nominal diameter, e.g., 0.625 inches, in place of each high diameter rebar has a negative moment strength of only about 340-360 kip-in. Rebar with a diameter of about 0.625 inches has a weight capacity of about 1.04 lb/ft. This advantage of high diameter rebar can be achieved even when the longitudinal support is provided by two high diameter reinforcing bars in combination with two lower diameter reinforcing bars. Rebar, regardless of the diameter, preferably is placed at least 1.5 inches from a surface of the deadman, in accordance with American Concrete Institute (ACI) standards, so that the concrete will not crack and expose the rebar to corrosion when weight is applied to the deadman. Further, reinforced concrete made according to ACI standards may have a compressive strength of about 4000±400 psi. Rebar with a minimum yield strength of about 420 MPa (60,900 psi), i.e., 60 grade rebar, is typically used for longitudinal reinforcement.
Rebar is classified by diameter according to several standards, one of which is shown in TABLE 1. See CRSI Manual of Standard Practice, 27th ed., Concrete Reinforcing Steel Institute, Schaumburg, Ill. (2001). The rebar diameter listed in TABLE 1 is a “nominal diameter” because it does not account for deformations deliberately rolled onto the rebar, which help the concrete grip the rebar. A “high diameter rebar,” using this particular size standard, is a number 7 rebar or higher.
The increased ultimate flexural strength capacity of a deadman comprising high diameter reinforcing bars offers a number of advantages. For example, it is expected that high flexural strength corresponds to a high loading capacity for the deadman. The load placed on a deadman varies with the buoyant force acting on the UST, which in turn depends on the height of the local water table and the amount of fluid contained in the UST. See U.S. Pat. No. 6,467,344 for a more complete discussion. The load on a deadman typically is distributed over several points where the UST is anchored by straps, for example, to a fastening loop on the deadman. An “anchor point” refers herein to any device that facilitates connection of the strap to the deadman, e.g. a fastening loop, lug, anchor or eyebolt. Examples of straps and fastening loops are found in U.S. Pat. No. 7,028,967 and U.S. Pat. No. 6,786,689, incorporated herein by reference. In a preferred embodiment, the deadman comprises a longitudinal slot into which an anchor point may be placed. The anchor point may be moved to various positions along the longitudinal slot, simplifying alignment of the anchor point with the anchoring strap. This embodiment is described in more detail in U.S. Pat. No. 6,786,689.
For an 8 foot diameter tank anchored at 6 positions to a deadman, the load at each position may reach up to 6000 lb. An excessive load on the deadman may result in excessive flexural cracks. A flexural crack of about 2 mm width is considered to be an “excessive” flexural crack that is detrimental to the performance of a deadman located at a site with a variable depth water table. Accordingly, a deadman according to the present invention preferably accommodates a load of at least about 3000 lb per strap position, more preferably about 5000 lb per strap position, and even more preferably about 6000 lb per strap position, without developing flexural cracks of about 2 mm or higher.
A “long deadman” according to the present invention is at least about 30 feet in length. For example, the long deadman may be about 40 feet or more in length. Since the length of the deadman typically is roughly the same as the length of the corresponding UST, the use of a long deadman advantageously simplifies the installation of larger UST systems. The use of a long deadman having conventional resistance to flexural cracks, however, is complicated by the greater strains placed on a deadman during installation and transportation caused by its greater length. For example, installation typically requires that deadmen be hoisted into position, which puts flexural strains on the deadmen. The greater resistance of the present deadman to flexural cracks means that its length can be increased without developing excessive flexural cracks during the hoisting. Further, a deadman transported to an installation site is preferably placed on the smallest trailer bed possible, e.g. a stretch deck trailer, for economic reasons. The length of a conventional deadman must be chosen to limit the overhang of the deadman over the trailer bed, so that the weight of the overhanging portion of the deadman does not lead to excessive flexural cracks. The high flexural strength of the present long deadman facilitates transportation to the installation site, since the long deadman may overhang the trailer bed without developing flexure cracks of about 2 mm or greater. Because the long deadman may overhang the trailer bed, smaller trailers can be used to transport it, and the expense of transportation will decrease.
It is preferable for economic purposes to transport the deadmen and UST in a single operation. Preferably, a UST is transported with a deadman placed at each side of the UST on the trailer bed. In one particularly preferred embodiment, the deadmen transported in this configuration are low profile deadmen, described in U.S. Pat. No. 6,786,689. The low profile of such a deadman advantageously provides sufficient room on a single trailer bed of average width to accommodate a deadman on either side of a large diameter UST. The low profile may be achieved, for example, by chamfering one or both of the top edges of the deadman, as described in U.S. Pat. No. 6,786,689.
Accordingly, in one embodiment of the invention, a shipping assembly comprises a flatbed trailer having a width of approximately ninety six inches that holds an underground storage tank on the flatbed trailer. In one embodiment, the UST is a large diameter UST with a generally cylindrical body and a diameter of approximately ten feet. A deadman at least about 30 feet in length is positioned on either side of the UST, where each deadman has at least one chamfered edge, the chamfered edge being in a position facing the tank. The long deadmen may overhang the trailer bed.
When constructing the shipping assembly, “2″×4″” wood stops typically 16″ in length are placed vertically in the rub rails of the tractor trailer. The wood stops help prevent side-to-side movement of the deadmen when the deadmen are loaded onto the trailer. Stops are placed near the front and rear of each long deadman. If the tractor trailer deck is metal, each deadman additionally is loaded onto two ¼″ wood spacers to prevent the deadman from sliding. The deadmen are loaded onto the trailer bed so that each deadman is near the edge of the bed, abutting the wood stops and covering part of the wood spacers. Once the deadmen are loaded, they are further secured by placing at least two “2″×4″” wood blocks between the deadmen, where the blocks are placed perpendicular to the deadmen and fit tightly between the deadmen. The wide side of the blocks is placed flat against the trailer bed, and the blocks are secured by fastening them to the trailer bed with nails, for example. Blocks are placed near the front and back of each deadmen.
A foam cushion between the deadmen is used to support the UST. After the deadmen are placed on the trailer, the foam is placed lengthwise down the center of the trailer bed between the deadmen. The foam is cut widthwise where blocks bisect the foam cushion, so that foam does not cover the top of the blocks. In one embodiment, the foam is about two feet wide and about 1″-1½″ thick. Regular building foam can be used for most types of USTs, but high density foam is required for double- or triple-walled USTs that contain a monitoring liquid in the annulus between the walls. Before the UST is placed on the foam cushion, straps further secure the deadmen. The straps are placed across both the deadmen and attached to the rub rails on each side of the trailer bed. Enough slack should be left in the straps so that they will be taut when the UST is placed over the straps. The UST is finally placed on the center line of the trailer bed, on top of the straps and foam cushion. Additional straps are then placed around the top of the UST to secure it to the trailer bed. In the embodiments where the deadmen comprise fastening loops, the fastening loops are separately secured to the trailer bed by a third set of straps. Additional blocking is fastened onto the blocking at the rear of the trailer bed, so that this blocking is two or three boards thick. This prevents the deadmen from jumping over the rear block because of vibrations during transportation.
The long deadman of the present invention is a particularly advantageous alternative when installing a UST with dimensions that otherwise would require end-to-end installation of multiple deadmen. Using a conventional method of installation, a UST typically is anchored by deadmen placed on each side of the UST, as described, for example, in U.S. Pat. No. 6,467,344, assigned to Xerxes Corporation. If the UST were sufficiently long, two conventionally sized deadmen would need to installed end-to-end to prevent floatation of the UST (in combination with the backfill). The present invention provides instead the placement of a single long deadman on each side of a long UST, which simplifies installation. The long deadman is particularly useful where the hole is partially or fully flooded, as is often the case in some areas of Florida, for example.
A preferred deadman according to the invention is depicted in
The deadman 100 depicted in
The present deadman may comprise a substantially flat upper surface and a substantially flat lower surface parallel to the upper surface, where the lower surface is wider than the upper surface. In one embodiment, the deadman 100 has a height of approximately 8¾″ and a width of approximately 18″. In this embodiment, the width of the top surface is approximately 7″, and chamfered edge 90 begins at a height of approximately 5¾″ from the bottom of the deadman 100. In another embodiment, the width of the deadman is 14″, which matches the width of a popular deadman currently sold by the assignee of the application, Xerxes Corporation. That embodiment is also low profile, with a height approximately equal to 9″. Although the deadman depicted in
The elongated longitudinal slot 10 extending over a portion of the length of the deadman may extend from the upper surface to the lower surface of the deadman. The elongated slot may comprise an upper portion 12 and a wide lower portion 14, which accommodates a fastening loop. In one embodiment, the fastening loop comprises a curved portion connected to a bottom plate, where the bottom plate is sized to fit into the lower portion 14, and where the upper portion 12 is sized to allow the curved portion of the fastening loop to pass through and extend beyond the upper surface of the deadman. With reference to
The discussion of the present invention above refers to preferred embodiments of deadmen and methods of installing and transporting such deadmen with a UST. Specific details, such as specific materials and dimensions, provide a thorough understanding of the present invention, but the preferred embodiments discussed herein should not be understood to limit the invention.
Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. While the foregoing specification teaches the principles of the present invention, with examples provided for the purpose of illustration, it will be appreciated by one skilled in the art from reading this disclosure that various changes in form and detail can be made without departing from the true scope of the invention.
