Patent Grant
8250817
Not Applicable.
Not Applicable
Not Applicable.
1. Field of the Invention
This invention relates generally to guyed construction techniques, and, more particularly, to techniques for anchoring and for reinforcing the anchoring of guyed and additionally guyed towers.
2. Description of Related Art
Towers are widely used in many industries, including television transmission, radio communication, cell phone communication, wind turbines, and power transmission, to name a few.
Some towers, known as “guyed towers” or “additionally guyed towers,” rely on guy wires to maintain or assist in maintaining the towers in a vertical orientation. Generally speaking, these towers include a vertical main body, or “mast,” that stands on one end atop a base, which is generally concrete. Guy wires attach to the mast along its length, extend down and away from the mast, and attach securely to the ground using anchors. Most guyed towers are triangular in cross-section, and a minimum of three guy anchors are typically provided and are spaced apart by approximately 120-degrees to provide a stable base for holding the mast vertically. Often, guyed towers require three, six, or more guy anchors with multiple guy wires originating from different vertical levels of the tower attached to each guy anchor.
The term “guyed towers” describes towers whose masts have no independent means of support. They rely entirely upon guy wires to hold them upright. By contrast, the term “additionally guyed towers” describes towers that are essentially free standing, although they require guy wires to provide reinforcement and stability.
The typical guy anchor assembly 100 may also include turnbuckles 112. One turnbuckle 112 is generally provided for each guy wire 110. The role of the turnbuckles 112 is to fine-tune the tightness of each guy wire 110.
To prevent damage due to lightning strikes, the guy wires 110 are each electrically connected via a conductive cable 120 to a ground spike 122. The ground spike 122 is typically made of copper. The cable 120 and ground spike 122 form a low impedance path to ground. This arrangement is designed to conduct high current surges away from the shaft 116, thereby preventing damage to the shaft which could otherwise compromise the mechanical stability of the tower.
As is known, the shafts 116 of the guy anchors typically corrode over time. Guy shaft corrosion primarily affects the area of the shaft exposed to soil, i.e., underground but outside the region encased in the dead-man 118. Corrosion may be galvanic in nature, with the steel guy shaft forming a battery cell with the more noble copper ground spike 122. Corrosion may also be electrolytic in nature, or may be caused by other factors.
Over several years, corrosion may lead to a significant loss of material from the anchor shaft 116, which, under the tensile forces transmitted through the guy wires, can result in a separation of the guy anchor shaft from the dead-man and a consequent catastrophic collapse of the tower.
The cost of replacing a collapsed 120 meter wireless guyed tower is estimated to be approximately $400,000. In addition, tower collapse poses a great risk to human life and property in the vicinity of the tower.
Owners and operators of guyed towers have developed aggressive remedial measures to prevent guy anchor failure. These include the following:
The above-identified remedial measures to prevent guy anchor failure are time consuming and expensive. We have recognized that they are also merely temporary solutions to the corrosion problem. Over time, corrosion of the anchor shafts will worsen or recur, and additional remedial measures will typically be required.
What is needed, therefore, is a measure for preventing or forestalling guy anchor failure that is less expensive and labor-intensive than currently employed measures and provides a longer-lived solution.
According to one embodiment, a reinforcing system is disclosed for a guy anchor of a guyed tower or additionally guyed tower. The guy anchor includes an anchor head and an anchor shaft extending from the anchor head into the ground. The reinforcing system includes a solid structure around a portion of the anchor shaft, a supplemental anchor shaft attached to the anchor head and extending into the solid structure, and a retaining structure attached to or integral with the supplemental anchor shaft within the solid structure. The solid structure has a top surface disposed above grade level. It has a front wall portion facing the tower and extending below the top surface into the ground, and a back wall portion extending below the top surface into the ground. The solid structure further includes a middle portion between the front wall portion and the back wall portion and extending into the ground. The front wall portion and back wall portion extend more deeply into the ground than the middle portion.
According to another embodiment, a reinforcing system is disclosed for a guy anchor that supports a structure. The guy anchor has an anchor head and an anchor shaft extending from the anchor head into the ground. The reinforcing system includes a solid structure disposed around the anchor shaft. The solid structure has a base and at least one wall extending down from the base having a surface that faces the structure being supported. The reinforcing system further includes a supplemental anchor shaft, attached to the anchor head and extending into the solid structure, and a retaining structure, attached to or integral with the supplemental anchor shaft and encased within the solid structure.
According to yet another embodiment, a tower includes a mast and a plurality of guy anchors. The guy anchors are positioned at locations around the mast. Each guy anchor has an anchor head and an anchor shaft extending from the anchor head into the ground. The tower further includes a plurality of guy wires attached between the mast and the plurality of guy anchors. At least one of the plurality of guy anchors is reinforced with a reinforcement that includes a solid structure disposed around the respective anchor shaft. The solid structure has a base and at least one wall extending down from the base having a surface that faces the mast. The reinforcement further includes a supplemental anchor shaft, attached to the anchor head and extending into the solid structure, and a retaining structure, attached to or integral with the supplemental anchor shaft and encased within the solid structure.
According to still another embodiment, a method of reinforcing a guy anchor is presented. The guy anchor has an anchor head and an anchor shaft extending from the anchor head into the ground. The method includes excavating a region around the guy anchor to form an excavated region, attaching a supplemental anchor shaft to the anchor head with the supplemental anchor shaft extending into the excavated region, introducing a curable material into the excavated region, and causing or allowing the curable material to cure into a solid structure.
According to a still further embodiment, a system for anchoring guy wires to support a structure includes an anchor head for attaching to one or more guy wires, an anchor shaft extending from the anchor head, a retaining structure attached to or integral with the anchor shaft at a distal end of the anchor shaft, and a solid structure. The solid structure encases the retaining structure. The solid structure has a base and at least one wall extending down from the base. Each wall has a surface in contact with soil that faces the structure being supported.
As used throughout this document, words such as “comprising,” “including,” and “having” are intended to set forth certain items, steps, elements, or aspects of something in an open-ended fashion. Although certain embodiments are disclosed herein, it is understood that these are provided by way of example only and that the invention is not limited to these particular embodiments.
The techniques for reinforcing guy anchors as disclosed herein protect against corrosive failure of anchor shafts by providing a redundant support in the form of a supplemental anchor shaft encased in a solid structure. The supplemental anchor shaft does not generally come into contact with soil and is thus not exposed to the same corrosive environmental factors that affect the original anchor shaft. Preferably, the supplemental anchor shaft and solid structure are strong enough to completely replace the original anchor shaft and dead-man as the source of guy wire fixation. It is possible therefore for the original anchor shaft to corrode and completely disintegrate and the guy anchor to remain intact. Since the supplemental anchor is retained within the solid structure and generally has no direct and sustained contact with soil, it is relatively impervious to corrosion and is expected to provide a long service life as compared with conventional anchor shafts.
The solid structure 210 as shown has the shape of an inverted letter “U.” It includes a base 210a, which generally has the shape of a rectangular prism, and a pair of walls or wall portions 210b and 210c extending down from the base. The solid structure 210 has a top surface 210f, a front wall surface 210g, and a back wall surface 210h. By convention, the “front” of the solid structure 210 faces in the direction of the tower. Both the front wall surface 210g and the back wall surface 210h face in the direction of the tower.
The upper elongated member 310 is preferably longer than the lower elongated member 312. The difference in length allows the base 210 of the solid structure to be relatively shallow without exposing the elongated members 310/312 or distal structures 314 and 316 to soil.
It can be seen that the top surface 210f of the solid structure 210 is located slightly above grade level 320, preferably by about 5-8 cm (2-3 inches). With the top surface 210f above grade level, neither the elongated members 310/312 nor the distal structures 314/316 are exposed to soil. Thus, they are rendered relatively impervious to the degree of corrosion that affects anchor shafts buried in soil. Preferably, the top surface 210f is formed at a slight angle, with a slope facing the tower, to allow drainage and therefore prevent water from pooling around the guy anchor.
The size of the solid structure 210 may be varied based on site requirements, with larger solid structures used for supporting larger towers or where greater tensile forces are present. The example shown is typical for a guy anchor placed at 38 m (125 feet) from a tower mast that stands 114 m (375 feet) tall, wherein worst case expected forces are approximately 89 kN (20 Kips) lateral and 89 kN (20 Kips) uplift and ample safety margins are provided. Given this example and the general information provided herein, the skilled practitioner can readily produce a myriad of other examples of different sizes, shapes, and proportions, to suit site requirements.
In the example shown, the solid structure 210 is approximately 2.4 m (8 feet) long and 3.0 m (10 feet) wide. The depth of the base 210a is approximately 46 cm (1.5 feet), with the walls 210b and 210c being approximately 61 cm (2 feet) deeper than the base. In general, and although this is not required, the walls 210b and 210c in most cases preferably extend into the ground at least twice as deeply as the base 210a of the solid structure.
In the example shown, the cross-sectional dimensions of the angle bars used for the elongated members 310 and 312 and the distal structures 314 and 316 are typically 5 cm×5 cm×1 cm (2″×2″×⅜″). The angle bars forming the distal structures 314 and 316 are typically approximately 1 m long (3 feet). All angle bars are preferably grade A36 steel, or better, and have a yield strength of at least 345 MPa (50 KSI). Nuts and bolts are typically 1.6 cm (⅝ inch), A325.
The angle bars used to form the elongated members 310 and 312 are preferably shipped to the installation sites in lengths of approximately 107 cm to 122 cm (3.5 to 4 feet). They are preferably cut to size, drilled, and bolted to the anchor head on site. The anchor head 114 itself is preferably drilled on site to allow attachment of the elongated members 310 and 312. Any field-cut edges or field-drilled holes are preferably galvanized with two coats of zinc rich galvanizing compound.
The concrete used to form the solid structure 210 preferably has a maximum compressive strength of at least 18 kPa (2500 PSI) at 28 days. All reinforced concrete construction and materials are preferably in accordance with ACI Standards 318. The minimum concrete cover over the rebar is preferably 7.6 cm (3 inches). All rebar is preferably Grade 60, and all reinforcing material is preferably in accordance with ASTM A615-85.
Ideally, the three forces 820, 822, and 824 all intersect at a single point 826. This balanced design ensures that the solid structure 210 will not rotate under load, i.e., that neither its front wall 210b nor its back wall 210c will lift out of the ground and the structure will remain stable. Precise intersection of the three forces is preferred; however, only approximate intersection is needed for adequate operation, as small offsets are generally well tolerated. However, in cases where the three forces do not substantially intersect, a rigorous analysis should be conducted to ensure that the solid structure 210 will remain stable under load.
Generally, the solid structure 210 is placed relative to the guy anchor so that more of the mass of the solid structure lies behind the guy anchor than in front of it. This configuration naturally follows from the preferred condition that the 3 main forces intersect. In addition, different soil conditions typically involve different placements of the solid structure 210 with respect to the guy anchor. For example, placing the solid structure 210 in sandy soil tends to make the lateral force 824 act at a lower vertical level than it would ordinarily act in more solid soil. To ensure that the three forces 820, 822, and 824 substantially intersect at the same point when the solid structure is placed in sandy soil, the solid structure 210 should typically be placed farther back relative to the anchor head 114. Failing to do this will introduce a moment that tends to lift the back of the solid structure 210. Conversely, in very solid soil, the lateral force 824 generally acts at a higher vertical level, and positioning the solid structure 210 farther forward relative to the guy anchor is generally required to avoid a moment that tends to lift the front of the solid structure 210.
The shape of the solid structure 210 may be varied to better suit various site requirements. For example,
The reinforcing system as disclosed herein provides a safer, less costly, and more permanent solution to corroding guy anchors than the conventional solution of completely replacing the corroded guy anchor. Since the solid structure is installed close to the surface, it eliminates large scale excavations and the need for highly skilled and costly tower crews. Indeed, the guy anchor reinforcement as set forth herein can generally be performed by a relatively inexpensive concrete crew.
The reinforcing system as disclosed herein eliminates the need to relocate the existing guy wires to new anchor heads, since the existing anchor head is used. Problems with tower rotation and antenna repositioning are therefore avoided.
The reinforcing system virtually eliminates expensive and sometimes hazardous full excavations of existing anchor shafts, which are conventionally used to inspect the guy anchors to determine the extent of corrosion. It is often less costly simply to install the reinforcing system disclosed herein than to perform the excavation needed to inspect for corrosion.
The reinforcing system as disclosed herein is a complete and potentially maintenance-free solution. As the new steel used to secure the existing anchor head is either above grade or encased in concrete, a tower site fitted with this solution may never experience anchor shaft corrosion within its expected service life.
Having described certain embodiments, numerous alternative embodiments or variations can be made. For example, as shown and described, the solid structure 210/1010/1110/1210 is symmetrical. However, this is merely an example. Alternatively, it may be asymmetrical. For example, the front wall may be larger (e.g., thicker, deeper, or wider) than the back wall, or vice-versa. Indeed, it may be beneficial to make one wall larger than the other in order to move the center of mass of the solid structure forward or back. Allowing asymmetry therefore provides an additional degree of freedom for aligning the 3 main forces acting upon the solid structure.
As shown and described, the walls of the solid structure are planar. However, this is merely an example. Alternatively, they may have a concave shape or some other shape.
The solid structure is shown and described as a single block. However, this is not strictly required. Alternatively, a plurality of smaller segments can be made and fastened and/or interlocked together. For example, the base of the solid structure can be made separately from the walls.
Preferably, the solid structure is made of reinforced concrete and reinforced concrete is believed to provide the best results. However, this is not strictly required. Other curable materials, including various polymers and cement, may be used, depending on design requirements and the performance of those materials.
As shown and described, the reinforcing system is used as a remedial measure to support an existing guy anchor where there is a concern that the anchor shaft may fail. However, it may also be used for primary anchor installations. The usual anchor shaft and dead-man can be omitted, and the guy anchor can be held in place with the primary guy anchor and the solid structure. With this arrangement, a relatively short anchor shaft is used. The retaining structure is attached to the distal end of the anchor shaft and is encased within the solid structure. This technique protects against anchor shaft corrosion and does not require deep excavations as are normally needed when installing a dead-man.
A variety of anchoring arrangements may be used for the supplemental anchor shaft 220. For example, different numbers of cross pieces may be provided for the distal structures 314 and 316. The elongated members and distal structures may be formed together as integral units and then cut to length on site. Although angle bars are preferred for the elongated members 310/312 and distal structures 314/316, any available shape could be used. For instance, on very large towers, these structures may be made from channels, flat plates, bars, or steel cables. In addition, the number of elongated members 310/312 or the number of distal structures 314/316 may be varied.
Although the guy anchor reinforcing techniques disclosed herein are shown and described for use with towers, it is understood that they may also be used with other types of structures that are supported with guy wires.
Those skilled in the art will therefore understand that various changes in form and detail may be made to the embodiments disclosed herein without departing from the scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/361,900, filed Jul. 6, 2010 and of U.S. Provisional Application No. 61/363,620, filed Jul. 12, 2010, which are incorporated herein by reference in their entireties.
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