You are an expert at summarizing long articles. Proceed to summarize the following text:

You are an expert at summarizing long articles. Proceed to summarize the following text: 
[0001]    This application claims priority of U.S. Provisional Patent Application 62/331,950 filed on May 4, 2016. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    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. 
         [0003]    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&#39;s foot from slipping off the end of the step-bolt. 
         [0004]    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. 
         [0005]    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. 
         [0006]    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). 
       SUMMARY OF THE INVENTION 
       [0007]    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&#39;s weight in the normal course of ascending and descending the tower in conjunction with the carabiner bolts. 
         [0008]    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&#39;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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]    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: 
           [0010]      FIG. 1  is a perspective view of a pair of utility transmission towers having step-bolts incorporating features of the present invention; 
           [0011]      FIG. 2  is a side view of a step-bolt incorporating features of the present invention; 
           [0012]      FIG. 3  is a perspective view of a carabiner prior to being attached to the step-bolt of  FIG. 2 ; 
           [0013]      FIG. 4  is a perspective view of a carabiner after being attached to the step-bolt of  FIG. 2 ; 
           [0014]      FIG. 5  is a cross sectional view of a carabiner attached to the step-bolt of  FIG. 2 ; 
           [0015]      FIG. 6  is a perspective view of a lineman ascending a tower in accordance with a method incorporating features of the present invention; and 
           [0016]      FIG. 7A-7D  are cross-sectional views of alternative embodiments of a step-bolt incorporating features of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    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. 
         [0018]    With reference to the drawing figures,  FIG. 1  is an illustration of a pair of support towers  8  of the type typically used by power companies for transmission of electric power. In accordance with the invention, support towers  8  include a plurality of step-bolts  10 , which are threaded into threaded apertures in support towers  8 . Step-bolts  10  are spaced apart along the length of the tower to provide a foot purchase and/or hand grip for a lineman, repairman or other authorized individual to use to ascend and descend the tower. 
         [0019]    With additional reference to  FIG. 2 , each of step-bolts  10  comprises a solid substantially cylindrical elongate body  12 , preferably machined, cast, rolled or otherwise formed from a solid round bar of steel, aluminum, titanium or other suitable material. One end  14  of body  12  comprises an attachment means, which in the illustrative embodiment comprises a threaded portion  16 , typically with ⅝″ or ¾″ male UNC threads to match the existing apertures in support tower  8 . Step-bolt  10  may be secured to tower  8  by threading into a threaded aperture formed in tower  8  or may be secured by a corresponding nut, where it is possible to access the back side of the aperture with a wrench. Thread size and the method of attachment should not, however, be considered a limitation of the invention. Other means of attachment, including for example, insertion of an enlarged head portion of end  14  into a vertical keyhole slot, forming female threads in end  14 , and press/shrink interference fit are all considered attachment means within the scope of the invention. 
         [0020]    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  1 ½ inches in diameter. Tip flange  28  provides a conventional stop to prevent a user&#39;s foot from sliding off the free end  26  of step-bolt  10 . 
         [0021]    With additional reference to  FIGS. 3-7 , a carabiner  30  is provided, along with a shock absorbing lanyard  32  and safety harness  34 . The carabiner may be of any design, but preferably is the type that can be manipulated by a single hand, such as the “Step Safe Lanyard 2002” sold by Total Access (UK) Ltd, Eccleshall UK. Carabiner  30  includes a gate  36 , a lock  36  and a basket  40  having a throat  42 . In the illustrative embodiment, with gate  36  closed, throat  42  has a dimension “T” of slightly more than 3/4 inches as is necessary to attach it to a standard ¾ inch step-bolt. Undercut region  24  of step-bolt  10 , therefore, is machined to approximately the same diameter as a standard 3/4 inch step-bolt for compatibility with carabiner  30 . Enlarged section  22  is machined to approximately 1 inch in diameter. This enables enlarged section  22  to provides a surface that prevents carabiner  30  from moving outside of undercut region  24 . 
         [0022]    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 . 
         [0023]    With particular reference to  FIG. 6 , in accordance with a method incorporating features of the present invention, a lineman, communications worker or other user  50  ascends tower  8  by attaching a carabiner  30  to one of the step-bolts  10  as hereinbefore described. The undercut region  24  in combination with the enlarged section  22  retain carabiner  30  in the undercut region adjacent to the base flange  20  of step-bolt  10 . This ensures that in the event of a fall, the bending stresses on step-bolt  10  will be minimized. Once the carabiner  30  is attached to a step-bolt, the user  50  can ascend the tower by stepping onto a different one of the step-bolts  10  and then attaching carabiner  30   a  to yet another step-bolt. This process is repeated until the user  50  has ascended the tower to the desired location and repeated in reverse as the user  50  descends the tower. In an alternative embodiment, carabiner bolts  10   a  are provided for attaching carabiner  30  to tower  8 . Carabiner bolts are made intentionally too short for user  50  to step on, but are used in conjunction with step-bolts  10 , or conventional step-bolts, to provide an attachment point for carabiner  30 , while step-bolts  10 , or conventional step-bolts are used for foot and/or hand purchase during ascent and descent. 
         [0024]    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 K t  especially in the portions of the step-bolt that would be supporting the user in a fall. With reference to  FIG. 7A , step-bolt  10   b  includes a fillet having a radius R 1  which forms a 90-degree arc between undercut section  24   b  and enlarged region  22   b  and a fillet having a radius R 2 , which forms a 90-degree arc between enlarged region  22   b  and base flange  20   b . These radii are relatively small and, therefore, have a relatively high stress concentration factor K t . With reference to  FIG. 7B , step-bolt  10   c  includes a fillet having a radius R 3  between undercut section  24   b  and enlarged region  22   c  and a fillet having a radius R 4 , between enlarged region  22   c  and base flange  20   c . R 3  and R 4  do not form 90 degree arcs and therefore are larger than R 1  and R 2 . The increase in radius results in a decrease in the stress concentration factor K t . With reference to  FIG. 7C , step-bolt  10   d  includes a fillet having a blended radius R 5  and R 6  between undercut section  24   d  and enlarged region  22   d  and a fillet having a blended radius R 7  and R 8 , between enlarged region  22   d  and base flange  20   d . R 6  is larger than R 5  and R 8  is larger than R 7 . The compound curve resulting from the blended radii further decreases the stress concentration factor K t  relative to a fillet having a constant radius. Finally, with reference to  FIG. 7D , step-bolt  10   e  includes a fillet between undercut section  24   e  and enlarged region  22   e . The fillet has an elliptical profile, so that the radius R 9  is continuously decreasing moving axially inward from undercut section  24   e  toward enlarged section  22   e . Step-bolt  10   e  further includes a fillet between enlarged region  22   e  and base flange  20   e . The fillet has an elliptical profile, so that the radius R 10  is continuously decreasing moving axially inward from enlarged section  22   e  to base flange  20   e . This results in still further decrease in the stress concentration factor K t . A fillet may also optionally be provided between undercut region  24  and enlarged region  22  at the free end as shown in  FIGS. 7A-7D , although a sharp transition at the free end of undercut region  24  may be more effective in preventing carabiner  30  from sliding outward along shaft  18 . 
         [0025]    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. 
         [0026]    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 ______”)

Summary:
A support tower is equipped with a plurality of step-bolts, each of which comprises (1) a threaded portion that is attached to a pre-existing hole in the tower and (2) 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 a corresponding carabiner, which is attached to a safety harness worn by the user. The remainder of the shaft portion of the step-bolt is larger in diameter than the throat of the carabiner so that the carabiner cannot slide out toward the free end of the step-bolt.