Patent Application
20170319907
This invention relates generally to the repair and maintenance of utility towers, radio and cell phone towers, telephone poles, utility poles and the like and, in particular, to methods and apparatus for the safe ascending and descending of such towers and poles by linemen, repairmen and others.
It is well-known in the art to attach a series of step-bolts to utility towers, utility pylons, radio towers, cell phone towers, telephone poles, utility poles and the like (hereinafter collectively referred to as a “support tower” or simply “tower”) to provide a foot purchase and/or hand grip for a lineman, repairman or other authorized individual to use to ascend the tower. A conventional step-bolt, however, is typically nothing more than a cylindrical bolt between ⅝″ and ¾″ in diameter, with an enlarged head approximately 2″ in diameter, similar to the head of a carriage bolt, which acts as a stop to prevent the lineman's foot from slipping off the end of the step-bolt.
Historically, lineman and communications tower workers would ascend a utility tower by free climbing without any safety strap or harness, since this is the fastest way to ascend and descend the tower. However, in the aftermath of an epidemic of cell phone tower deaths (13 deaths in 2013 and 11 deaths in 2014), OSHA and the communications industry have begun to focus on methods of improving the safety of communications tower workers. Similar efforts to improve worker safety are underway in the power transmission industry. One method that has been implemented to improve worker safety is to provide the worker with a wearable safety harness, which can be attached to the tower step-bolts using a lanyard with a carabiner attached to the end. Unfortunately, most common carabiners are designed primarily to attach to a D-ring or overhead cable, rather than to a cantilevered step-bolt. Therefore, a typical carabiner that has a gap between the nose and gate sufficient to accommodate a ¾″ bolt will also have a basket that is larger than the 2-inch diameter head of a standard step-bolt. Finally, a standard step-bolt, while adequate to support the weight of a 95th percentile male when climbing, will yield and bend downward under the shock load of a falling worker, especially if the carabiner has moved to the extreme free end of the step-bolt, where the moment arm for the shock load is greatest. These two defects could result in a carabiner slipping off the end of the step-bolt with potentially disastrous consequences.
It is also cumbersome to use a conventional carabiner since the gate must be manipulated by hand (typically by holding the carabiner with one hand and pulling and twisting the gate with the other hand) each time the carabiner is moved. Accordingly, many linemen and communications workers prefer a purpose-built carabiner and safety lanyard such as the “Step Safe Lanyard 2002” sold by Total Access (UK) Ltd, Eccleshall UK. The Step Safe lanyard has a gate and lock that can both be manipulated with a single hand. It also has a basket (throat) that is sized to closely-match the diameter of a step-bolt (i.e. ⅝″ and ¾″ in diameter) and therefore should not slip off the end of the step-bolt, even if the step-bolt yields and bends downward. The Safe Step lanyard does not, however, have any way of preventing the carabiner from moving to the free end of the step-bolt where the bending moment arm is greatest.
What is needed therefore, is the combination of a purpose-built carabiner, and a step-bolt configured to prevent the carabiner from sliding to the outer end of the step-bolt. Preventing the carabiner from sliding outward results in reduced bending loads on the step-bolt during a fall arrest, eliminating the possibility that the step-bolt will bend downward (or fail completely).
The present invention solves the foregoing problem by providing a tower equipped with a plurality of step-bolts, and a method of using the step-bolts to safely ascend or descend a tower using a carabiner attached to a safety lanyard. According to an illustrative embodiment, each of the step-bolts comprises a threaded portion that attaches to pre-existing holes in the tower and a shaft portion that extends outward from the tower. The shaft portion of each of the step-bolts includes an undercut section that is sized to match (with minimal clearance) the throat of the carabiner, while the remainder of the shaft portion is larger in diameter than the throat of the carabiner. In one embodiment, the undercut section is centered about the midpoint of the shaft portion of the step-bolt, which prevents the carabiner from sliding out toward the end of the step-bolt when attached. In another embodiment, the undercut section is offset inward from the midpoint of the shaft portion to further reduce the bending moment arm of the carabiner on the step-bolt during a fall arrest. According to an illustrative method, a support tower is provided with the step-bolts as described above. The user ascends and descends the tower by attaching the carabiner to the undercut region of one step-bolt while stepping on another of the step-bolts. In another embodiment, a tower is provided with bolts having an undercut region as described above, but which are too short to step on. These short step-bolts (referred to hereinafter as carabiner bolts) are used solely for the purpose of attaching the carabiner. Other step-bolts, including conventional step-bolts, are used to support the user's weight in the normal course of ascending and descending the tower in conjunction with the carabiner bolts.
The step-bolts and carabiner bolts may include a base flange between the threads and the shaft. Use of a base flange significantly reduces the bending stress at the junction between the shaft and the tower wall. A tip flange may also be included to help prevent the user's foot from slipping off the end of the step-bolt. Optionally, the base flange is blended smoothly into the shaft and the shaft is blended smoothly into the undercut section in order to reduce stress concentrations.
The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements and, in which:
The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the detailed description and in the drawing figures, specific illustrative examples are shown and herein described in detail. It should be understood, however, that the drawing figures and detailed description are not intended to limit the invention to the particular form disclosed, but are merely illustrative and intended to teach one of ordinary skill how to make and/or use the invention claimed herein and for setting forth the best mode for carrying out the invention.
With reference to the drawing figures,
With additional reference to
Body 12 further includes a shaft portion 18 extending away from threaded portion 16. A base flange 20 approximately 0.175 inches thick and having an outside diameter of 1½ inches separates shaft portion 18, from threaded portion 16. Base flange 16 provides a large bearing surface between step-bolt 10 and support tower 8 to reduce the potential bending stresses on step-bolt 10 in a fall-arrest situation. Shaft portion 18 includes an enlarged section 22 and an undercut region 24, the purpose of which will be explained in further detail hereinafter. Undercut region 24 is offset toward base flange 20 relative to the full length of shaft portion 18. The free end 26 of step-bolt 10 terminates at a tip flange 28 approximately ¼ inch thick by 1½ inches in diameter. Tip flange 28 provides a conventional stop to prevent a user's foot from sliding off the free end 26 of step-bolt 10.
With additional reference to
Although in the illustrative embodiment, dimension “T” is slightly more than ¾ inches, in practice, the diameter of undercut region 22 should be 0.005 to 0.200 inches, preferably 0.010 to 0.100 inches and most preferably about 0.050 less than the actual dimension “T” of the corresponding carabiner, irrespective of the nominal throat dimension of the carabiner. Similarly, although in the illustrative embodiment the diameter of enlarged section 22 is 1 inch, in practice enlarged section can be any diameter that is larger than dimension “T” by a sufficient amount (e.g. 0.050″-0.100″) to prevent carabiner 30 from moving outside of undercut region 24.
With particular reference to
As can be determined from the foregoing, a major consideration in the design of a step-bolt is reducing the bending stress in the step-bolt during a fall arrest. Consequently, the inventor of the present invention determined that it would be important to reduce stress concentrations Kt especially in the portions of the step-bolt that would be supporting the user in a fall. With reference to
Although certain illustrative embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the invention. For example, although in the illustrative embodiment, the support tower is a power transmission tower, the support tower can be any utility pole, radio tower, or other vertical structure that can be climbed by a utility worker or other user. Similarly, although the illustrative embodiment discloses a bolt that is machined from a solid billet of material, the invention is not limited to a unitary bolt, but could be made from multiple pieces, such as a threaded rod that is threaded, pressed or otherwise attached to the elongate shaft portion. Additionally, although in the illustrative embodiment undercut region 24 is offset toward base flange 20 relative to the full length of shaft portion 18, undercut region 20 could be centered relative to the full length of shaft portion 18, or even offset toward the free end 26 of shaft portion 18. Accordingly, it is intended that the invention should be limited only to the extent required by the appended claims and the rules and principles of applicable law.
As used herein, references to direction such as “up” or “down” as well as recited materials or methods of attachment are intended to be exemplary and are not considered as limiting the invention and, unless otherwise specifically defined, the terms “generally,” “substantially,” or “approximately” when used with mathematical concepts or measurements mean within ±10 degrees of angle or within 10 percent of the measurement, whichever is greater. As used herein, a step of “providing” a structural element recited in a method claim means and includes obtaining, fabricating, purchasing, acquiring or otherwise gaining access to the structural element for performing the steps of the method. As used herein, the claim terms are to be given their broadest reasonable meaning unless a clear disavowal of that meaning appears in the record in substantially the following form (“As used herein the term ______ is defined to mean ______”)
This application claims priority of U.S. Provisional Patent Application 62/331,950 filed on May 4, 2016.
| Number | Date | Country | |
|---|---|---|---|
| 62331950 | May 2016 | US |
