US2920476A

US2920476A - Prestressed reinforced concrete mast

Info

Publication number: US2920476A
Application number: US555439A
Authority: US
Inventors: Robert J D Finfrock
Original assignee: Individual
Current assignee: Individual
Priority date: 1955-12-27
Filing date: 1955-12-27
Publication date: 1960-01-12
Anticipated expiration: 1977-01-12

Description

Jan. 12, 1960 R. J. D. FINFROCK PRESTRESSED REINFORCED CONCRETE MAST Filed Dec. 27, 1955 Q5? 2 WA 2), VAINVENTOR 16 j 6 mase7zzafm fem,

v BY P L 72 7 ATTORNEY United! States Patet PRESTRESSED REINFORCED CONCRETE MAST Robert J. D.'Finfrock, Orlando, Fla.

Application December 27, 1955, Serial No. 555,439

3 Claims. (Cl. 72-85) The present invention relates to a mast formed of concrete and designed for supporting electrical conductors serving numerous purposes such as an electrical power transmission line or the like and the invention more specifically pertains to a mast wherein a minimum of concrete is so disposed as to withstand forces in compression at one side of the neutral axis and having prestressed tendons embedded in portions of the concrete to handle the tensile stress developed at the opposite side of the neutral axis.

The prior art includes poles formed of concrete reinforced with rods or the like which are not prestressed but such structural elements have not been satisfactory. The principal deterrent to use of poles formed in accordance with the teachings of the prior art is that they have been so heavy that they are diflicult to handle particularly when the length is such as to satisfy present requirements of utility companies. It is accordingly an object of this invention to provide a mast formed of concrete having tendons therein stresesd in tension with the concrete so disposed and the tendons so located as to take advantage of the pronounced compression load resisting characteristics of the concrete and to make use of the pronounced tensile load carrying ability of steel or like tendons so as to obtain maximum benefit of these characteristics and to dispose the tensile members at maximum distances from neutral axes of the mast and at the sametime to reduce the bulk of the concrete. 1

Another object of the invention is to provide a reinforced concrete mast for supporting power lines or the like wherein the cross section of the pole is so shaped as.

to have a large perimeter surface to thereby increase con.- tact of the ground with the mast structure to provide for improved anchorage of the pole in the earth.

A still further object of the invention is to provide a concrete mast wherein the cables are prestressed in tension and disposed in flanges located remotely of the geometrical center of the mast to thereby provide large moment arms in relation to the neutral axis so that the mast will be capable of handling laterally applied loads with a minimum of reinforcement and concrete.

Another object of the invention is to provide a mast formed of concrete and reinforcing elements which are prestressed in tension and so located within a particular cross section that the pole is capable of withstanding loads transversely of the electrical line and handling loads applied longitudinally of the line.

Other objects and features of the invention will be appreciated and become apparent to those skilled in the masonry art pertaining to cantilever type structural elements and in the art pertaining to the electrical line suspension systems as the'present disclosure proceeds and upon consideration of the accompanying drawing and the following detailed description wherein an exemplary embodiment of the invention is disclosed.

In the drawing: I

Fig. 1- is'a 'side elevational view of a mast structure for supporting a power line wherein each of the upright members exhibits the invention.

Fig. 2 is an enlarged transverse sectional view of one of the upright members taken on the line 22 of Fig. 1 with the bottom. webs omitted.

Fig. 3 is an enlarged transverse sectional view taken on the line 33 of Fig. 1.

The present invention is directed to a mast formed of plied near the top thereof and other masts exhibiting the invention of lesser or greater height will handle an equal load with the same factor of safety.

Referring to the drawing there is shown in Fig. 1 two masts 10 of identical construction which are often used in pairs as illustrated in association with a cross bar 11 for supporting a plurality of electrical conductors by means of insulator assemblies 12. When two masts are employed angularly related members such as shown at 14 may be used and the cross bar 11 is usually connected to the poles by means of braces 16. The invention is directed to the structure of a mast 10 and the characteristics of one upright member is best shown in Figs. 2 and 3.

A mast embodying the invention includes a central web 18 which has a maximum width at the lower end of the upright member. The web 18 has a thickness at the lower end of the mast which is substantially equal to the thickness adjacent the upper end of the pole. The width of the web 18 decreases in proceeding upwardly from the lower end of the pole as will be apparent from a consideration of Figs. 2 and 3. The thickness of the web 18 however remains substantially uniform throughout the length of the pole. v

A web 21 is cast integral with one edge of the web 18 and the side web 21 is arranged substantially transversely of the web 18. The side web 21 has a thickness which remains substantially constant throughout the length of the mast. The width of the side web 21 decreases in progressing upwardly along the length of the mast. An outwardly extending flange 26 and an outwardly extendting flange 27 is formed integral with opposite ends of the side web 21. The cross sectional dimensions of the

flanges

26 and 27 adjacent the top of the mast are substantially the same as corresponding dimensions of the flanges at the bottom end of the mast. The flange portions 26 and 27 while having substantially uniform cross sections throughout the length of the mast are progrcssively spaced closer to each other in proceeding from the bottom to the top of the mast.

A web 31 is provided at the opposite edge of the central web 18 and the side web 31 is arranged generally transversely of the web 18 and is cast integral therewith. The width of the side web 31 corresponds to that of the side web 21. The width of the web 31 progressively decreases in proceeding upwardly from the lower end of the pole so that the end adjacent the top of the mast has a dimension like that shown in Fig. 3. The thickness of the side web 31 remains substantially the same throughout the length of the mast. A flange 32 is cast integral with one end of the side web 31 and a flange 33 is formed integral with the other end of the side web 31. The flanges 32 and 33 have the same transverse dimensions throughout the length of the pole as will be apparent from a consideration of Figs. 2 and 3. It will beobserved that large open areas 30 are provided between the

flanges

26 and 27 and between the flanges 32 and 33.

The rate of decrease in the width of the central web 18 may vary and in one embodiment of a mast exhibit-.

ing the invention it has been found that the ratio of reduction of width of this web in proceeding upwardly in order to provide for proper strength characteristics along the mast is at the rate of .021. The rate of reduction in the width of the side webs 21 and 31 may vary and in one embodiment it has been found that a reduction in width at a ratio of .0116 has been found to be satisfactory to provide the proper strength of the mast along its length.

The outwardly extending flange 26 has a plurality of prestressed tension members or tendons which may take the form of steel or other cables 41. A plurality of prestressed tension members 42 are also provided in the outwardly extending flange 27. It will be observed that these tendons 41 are aligned with each other along the major dimension of each flange 26 and the tension members 42 are similarly arranged in the flange 27. These tendons are each stressed lengthwise prior to the casting of the concrete forming the mast and when the tensile members are of steel they are each subjected to a prestressing of between 100,000 and 175,000 pounds per square inch. After setting of the concrete there is some loss of prestressing in the tendons but suflicient tension is nevertheless maintained in the cables to avoid the subjection of the concrete in the associated portion or portions of the mast to tension stresses when loads are applied laterally of the mast 10.

The flange 32 is provided with a plurality of prestressed tension members or tendons which may also take the form of steel or other cables 43. Similar tendons 4d are embedded in the flange portion 33. These tendons are stressed lengthwise prior to the casting of the concrete forming the mast and when the tensile members 43 and 44 are formed of steel each is subjected to a prestressing of between 100,000 and 175,000 pounds per square inch. The tendons 43 are aligned with each other lengthwise of the flange 32 and the tensile members 44 are similarly arranged in the flange 33. The prestressing of the tensile members 43 and 44 is such that during the application of forces to the pole transversely of the mast the concrete of the flanges 32 and 33 and in adjacent portions of the mast is not subjected to tensile stresses.

It will be observed that the outwardly extending flanges are widely spaced in the lower portion of the mast and are joined to each other by a skeleton type structure which includes the side webs 21 and 31 joined by the center Web 18. These webs have a small thickness in relation to their width and the primary load handling portions of the mast are four corner or flange portions. Such a structure reduces the overall weight of the mast to provide a reinforced concrete mast capable of being erected by conventional equipment and at the same time utilizes the best characteristic features of the tendons and utilizes the ability of concrete to absorb forces in compression.

The center web 18 and the side webs 21 and 31 are of a thickness which is sufficient to accommodate transverse tie members arranged at spaced intervals along the pole and one of such stirrups is shown at 51 in Fig. 2 and another at 52 in Fig. 3. Another stirrup representing one of a number arranged at spaced intervals along the mast is shown at 56 in Fig. 2 and another is shown at 57 in Fig. 3. The side web 31 is provided with stirrups at spaced intervals along the length of the pole and one is shown at 58 in Fig. 2 and another at 59 in Fig. 3.

Additional longitudinally extending tendons 61 and 62 are provided and embedded in the concrete forming the mast. These tensile members may be formed of suitable material and in one embodiment take the form of steel cables. The tensile member 61 extends throughout the section of the center web 18 with the side web 21. The

tensile member 62 is arranged at the other edge of the center web 18 and is similarly located. When the tendons 61 and 62 are steel cables they are each tensioned prior to casting of the concrete and are stressed in tension between 100,000 and 175,000 pounds per square inch. The stirrups 51 and 52 are desirably shaped so that the ends thereof embrace the tendons 61 and 62.

Additional tendons

63 and 64 may be employed located in the side webs 21 and 31 and in portions thereof inwardly from the outwardly extending flanges. When the

tendons

63 and 64 are incorporated they are each prestressed prior to casting of the concrete by subjecting them to loads in tension between 100,000 and 175,000 pounds per square inch.

The cross sectional characteristics of the mast adjacent the lower end thereof as shown in Fig. 2 has an unusually large surface area measured along the perimeter of the pole. Thus when the lower end is planted in the ground the level of which is indicated at 71 the earth contacts the pole over a large surface area. It is the practice to embed at least ten percent of the pole so that all of the exterior surfaces of the pole structure frictionally contacts the earth to more firmly anchor the mast. The flanges 27 and 33 may be joined by a horizontal web 72 which is also formed integral with the side webs 21 and 31 and the central web 18. A similar bottom web may be provided at the other side of the mast structure extending between the outwardly directed

flanges

26 and 32 and integral with the side webs 21 and 31 and the central web 18. Such horizontally disposed webs provide a base footing for the mast and promote further good anchoring of the pole in the ground.

The side webs 21 and 31 while being arranged in planes generally transverse of the central web 18 are not entirely within individual planes. The slight outward bowing of the side webs provides a desirable feature facilitating the removal of the forms after the concrete has set and this arrangement results in the disposition of the flanges further from the neutral axis of the mast.

While the invention has been described with reference to a concrete mast having a particular cross sectional shape and provided with the tendons located in certain portions of the concrete it will be appreciated that changes may be made in the structural details and positions of the tensile members as well and the materials. Such modifications and others may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A mast for supporting an electrical conductor in a position above the terrain comprising, a central web of solid concrete decreased in width in proceeding upwardly along the mast and having a substantially uniform thickness throughout the length of the mast, a side web of solid concrete with its intermediate portion integral with one edge of the central web and disposed in a plane generally transversely of said central web, said side web decreasing in width in proceeding upwardly along the mast and having substantially a uniform thickness throughout the length of the mast, another side web of solid concrete with its intermediate portion integral with the other edge of said central web and disposed in a plane generally transversely of the central web, said second side web decreasing in width in proceeding upwardly along the mast and having a substantially uniform thickness throughout the length of the mast, a flange of solid concrete integral with and extending outwardly from the outer face of each side web adjacent the free edge thereof, prestressed tendons within each flange extending throughout the length of the mast, each of said flanges being of substantially uniform cross section throughout the length of the mast, and each flange converging towards each other flange in proceeding upwardly along the mast.

portion integral with one edge of the central web and disposed in a plane generally transversely of said central web, said side web decreasing in Width in proceeding upwardly along the mast and having substantially a uniform thickness throughout the length of the mast, another side Web of solid concrete with its intermediate portion integral with the other edge of said central web and disposed in a plane generally transversely of the central web, said second side Web decreasing in width in proceeding upwardly along the mast and having a substantially uniform thickness throughout the length of the mast, an outwardly extending flange of solid concrete integral with an outer free edge of each side web, prestressed tendons within each flange extending throughout the length of the mast, each of said flanges being of substantially uniform cross section throughout the length of the mast, and webs of solid concrete at a base of said mast formed integral with the central web and said side webs and being disposed in a plane substantially at right angles to the longitudinal axis of the mast with the last-mentioned webs forming a base footing for the mast.

3. A mast for supporting a transmission line in an elevated position above the terrain comprising, a central web of solid concrete decreasing in width in proceeding upwardly along the mast at a rate of approximately .021 and having substantially a uniform thickness throughout the length of the mast, a side web of solid concrete having its intermediate portion integral with one edge of said '6 central web and disposed in a plane generally transversely of the central web, said side web having a substantially uniform thickness throughout the length of the mast with its width decreasing in proceeding upwardly along the mast at a ratio of .0116, a second side web of solid concrete having its intermediate portion integral with the other edge of the central web and being disposed in a plane generally transversely of said central web, said second side web having substantially a uniform thickness throughout the length of the mast with its width decreasing in proceeding upwardly along the mast at a ratio of .0116, a flange of solid concrete along and integral with an outer face of the free edge of each side web, prestressed steel cables within each flange extending throughout the length thereof with the tension of said cables prior to casting of the concrete being between one hundred thousand and one hundred seventy-five thousand pounds per square inch, and each of said flanges being substantially of uniform cross section throughout the length of the mast.

References Cited in the file of this patent UNITED STATES PATENTS 1,071,045 Graa Aug. 26, 1913 FOREIGN PATENTS 518,279 France May 21, 1921 804,429 France Aug. 3, 1936 449,668 Great Britain July 1, 1936 OTHER REFERENCES The Engineering nal, October 1953, pages 1235 -anr l1 2 86. i