Wind resilient mast arm mounting assembly

An attachment assembly and a method of mounting a traffic control device to a mast arm are provided. The assembly includes a first attachment device having a first surface and a second surface opposite the first surface and a second attachment device having a first surface and a second surface. The second attachment device is operably connectable to the first attachment device so that the first surface of the first attachment device and the second surface of the second attachment device face each other and are spaced apart from each other. The attachment assembly also includes a cable operably connected the second attachment device and connectable to the mast arm so that the first surface of the second attachment device faces the mast arm and a portion of the cable is positionable between the first surface of the first attachment device and the second surface of the second attachment device.

FIELD OF THE INVENTION

The present invention relates generally to the field of traffic control devices and in particular to mast arm support structures and traffic control devices each susceptible to dynamic wind loads that may damage the connection between the horizontal and vertical mast arm support structure and between the traffic control device and the mast arm and to flexible mounting assemblies for mounting traffic control devices to mast arms,

BACKGROUND

Roadway intersections, when warranted, require signalization to maintain safety and efficient movement of vehicular traffic. Traffic control devices (signals, signs, cameras, etc.) are generally supported on roadside posts, suspended from span wires or rigidly mounted on steel mast arms cantilevered over the roadway from a vertical pole that is designed as a rigid structure.

The current designs for supporting traffic signal structures use a rigid connection including drilled and tapped cast aluminum connections to connect the traffic signal to the mast arm. Common prior art cable securements rely on single in-plane surface plate to cable pressures and non-consistent, unpredictable use of acute cable angles.

What is needed in the art is an attachment device and an attachment assembly for connecting a traffic control device to a mast arm that provides a flexible connection for connecting the traffic control device to the mast arm. In some aspects, using cables to secure the traffic control device to the mast arm, an assembly including multiplane surface-cable pressures and that provides for consistent use of acute cable angles is needed.

BRIEF SUMMARY

It is an object of the present invention to provide a device and a method having features that resolve or improve on rigid connection devices connecting traffic control devices to mast arms.

In one aspect, an attachment assembly for mounting a traffic control device to a mast arm is provided. The assembly includes a first attachment device having a first surface and a second surface opposite the first surface and a second attachment device having a first surface and a second surface opposite the first surface. The second attachment device is operably connectable to the first attachment device so that the first surface of the first attachment device and the second surface of the second attachment device face each other and are spaced apart from each other. The assembly also includes a cable operably connected to the second attachment device and connectable to the mast arm so that the first surface of the second attachment device faces the mast arm and a portion of the cable is positionable between the first surface of the first attachment device and the second surface of the second attachment device.

In another aspect, a method of mounting a traffic control device to a mast arm is provided. The method includes connecting an end portion of a cable to a second attachment device, forming a loop from a portion of the cable and positioning the second attachment device on the mast arm. The method further includes positioning the loop over the mast arm and hooking the loop around connectors connected to the second attachment device. The method also includes positioning the cable between the second attachment device and a first attachment device and tightening the cable to secure the second attachment device to the mast arm.

Advantages of the present disclosure will become more apparent to those skilled in the art from the following description of embodiments that have been shown and described by way of illustration. The invention is capable of other and different embodiments, and its details are capable of modification in various respects. Accordingly, the drawings and description are to be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION

The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and functioning of the various elements of this invention are better understood by the following detailed description. However, the embodiments of this invention are not limited to the embodiments illustrated in the drawings. It should be understood that the drawings are not to scale, and in certain instances details have been omitted which are not necessary for an understanding of the present invention, such as conventional fabrication and assembly.

In some aspects, the present invention is directed to the improvement of common mast arm rigid traffic control device mounting assemblies that provide a rigid connection between a traffic control device and a mast arm. The present invention addresses the known structural deficiencies of the prior art by providing a flexible mast arm saddle and/or flexible swivel type connection device that is approximately 3-5 times stronger, and not susceptible to cracking due to either wind loading and/or installer failure to torque properly. In addition, the present invention provides a much stronger shear-type connection using through bolting to connect the traffic control device to the mast arm.

Rigidity is the property of a structure that it does not bend or flex under an applied force. The opposite of rigidity is flexibility. In structural rigidity theory, structures are formed by collections of objects that are themselves rigid bodies. A structure is rigid if it cannot flex; that is, if there is no continuous motion of the structure that preserves the shape of its rigid components and the pattern of their connections then the structure becomes susceptible to forces placed upon the structure such as wind induced accelerations.

It is a basic engineering design principle that, if possible, a structure must have features that allow for flexibility, while still maintaining its structural loading requirements such as gravitational and wind induced accelerations. The present invention utilizes the “Flexible Moment Connection”, semi-rigid approach. The basic principles of the FMC approach are to treat the beams (saddle & swivel) as simply connected under gravity loads but as moment connected under lateral (wind) loads. The FMC can be basically described as three types of connections: One that exhibits a small amount of rotation with a large amount of moment is noted as a rigid connection (prior art). A second connection that exhibits a large amount of rotation with a small amount of moment is noted as simple. The third connection is noted as a semi-rigid connection and provides some moment restraint while permitting some rotation (present invention). Semi-rigid connections can fall anywhere between simple and rigid. In general, connections capable of resisting at least 90 percent of the beam fixed-end moment are referred to as rigid. Those that offer enough ductility to accommodate beam end rotation while resisting no more than 20 percent of the fixed-end moment are referred to as simple. Any connection that is capable of resisting a moment between these limits while permitting some rotation must be treated as semi-rigid or flexible.

When a lateral load (wind) is applied to a mast arm structure, the windward connection of both the mast arm saddle, the swivel plate and the traffic signal will load in a flexural response in the present invention, therefore resulting in a significant increased wind resistance over the prior arts common rigid saddle, swivel plate, and traffic signal support tubes that have very limited, if any, resiliency. It is better for any structure to have less stress due to elasticity than having to absorb any amount of wind force or wind induced kinetic energy.

Cantilevered mast arms are susceptible to four types of wind loading that may induce vibrations that can lead to fatigue failures such as vortex shedding, galloping, natural, wind gust and truck-induced wind gust failures.

In another aspect, the present invention avoids galvanic corrosion risk, especially in wet, salty coastal areas with the aluminum and stainless steel in contact with one another, typical to all prior art aluminum castings that are secured with stainless steel fasteners and more importantly stainless steel cables used to secure the entire traffic control device to the mast arm support. In order for galvanic corrosion to occur, three elements are required: 1) Two metals with different corrosion potentials; 2) Direct metal-to-metal electrical contact; and 3) A conductive electrolyte solution (e.g., moisture) must connect the two metals on a regular basis. The electrolyte solution creates a “conductive path” such as when there is regular immersion, condensation, rain, fog exposure or other sources of moisture that dampen and connect the two metals.

In some embodiments, the attachment assembly of the present invention provides a wind resilient and hurricane resistant traffic signal mounting device by providing a much stronger connection to a cantilevered mast arm.

In some embodiments, the attachment assembly of the present invention is directed to improving the survival of mast arm signalization during high wind events by resisting and minimizing the structural failures (cracked castings) known to occur in current—typical rigid cast aluminum traffic signal mounting bracket assemblies.

In some embodiments, the attachment assembly of the present invention provides additional strength (bending moments) by relocating the tube tensioning connections longitudinally further apart therefore providing an improved fulcrum spacing. In some embodiments, the attachment assembly of the present invention provides compatibility to any current signal head support tube with bracket arms commonly used to hang the traffic control device.

FIG. 1represents a right side perspective of an embodiment of an attachment assembly10for connecting a traffic control device to a mast arm42of a traffic signal support structure. The attachment assembly10includes a mast arm saddle or plate12and a swivel plate14. The mast arm saddle12and the swivel plate14may be provided so that when the assembly10is connected to the mast arm42, one or both of the mast arm saddle12and the swivel plate14are flexible. A cable16operably connects the mast arm saddle12to the mast arm42. A plurality of connectors connects the attachment assembly10together as described in more detail below.

In some embodiments, both the mast arm saddle12and the swivel plate14may be fabricated out of metal, for example, a weather resistant stainless steel plate in a thickness ranging from ⅛″ to 5/16 pending upon design criteria based upon different wind zones. Other materials such as flexible engineered plastics may also be desirable in some applications. In some embodiments, combinations of materials may be used. The mast arm saddle12and the swivel plate14may be fabricated using computer controlled (CNC), laser or water jet cutting. Other methods known to one skilled in the art may also be used to fabricate the mast arm saddle12and the swivel plate14, including, but not limited to stamp and punch pressing. In some embodiments, the mast arm saddle12may be first cut out as a flat plate with a plurality of apertures. The apertures may include one or more adjustment slots23and a plurality of apertures25for receiving fasteners therethrough for connecting the mast arm saddle12to the swivel plate14(further explained below). The cable16may also be threaded through some of the apertures. The mast arm saddle12may also include an opening26that is sized and shaped to receive wires for electrical connections for the traffic control device.

After cutting the mast arm saddle12from the flat plate, one or more mast arm engagement flanges40may be cold bent approximately 90° downward from a first surface13of the saddle12. In some embodiments, the engagement flanges40may be positioned at opposite ends19of the saddle12. Ends41of the engagement flanges40may each include a curved portion that is adapted to contact a curved portion of the mast arm42when the mast arm saddle12is positioned on the mast arm42, for example, when the mast arm42is curved. The ends41of the engagement flanges40may be configured to have any shape that conforms to the shape of the mast arm42. In some embodiments, the ends41may be angular or straight. As shown inFIG. 4, the ends41of the engagement flanges40contact the mast arm42and the first surface13of the mast arm saddle12faces the mast arm42. The first surface13of the mast arm saddle12is spaced apart from the mast arm42such that a gap65exists between the mast arm saddle12and the mast arm42to accommodate flexing of the mast arm saddle12. In some embodiments, the engagement flange40may be positioned other than at the opposite ends19of the mast arm saddle12. By way of non-limiting example, one or more engagement flanges40may be positioned away from the ends19of the mast arm saddle12at a central position or offset from the center. Additionally, in some embodiments, an acute angle connection flange38may be cold bent approximately 10° to 20° upward from a second surface15of the saddle12pending final design criteria as shown inFIGS. 1,3A and3B.

FIGS. 3A and 3Bare isometric views showing the mast arm saddle12for reference without any attachments. BothFIGS. 3A and 3Bgenerally illustrate the saddle12post cutting and bending. Eased-rounded edges46are shown and may be provided to prevent any fraying or shear points of the cable16. In some embodiments, the mast arm saddle may include a “turned down” longitudinal flange (not shown) to utilize a thinner saddle material. The longitudinal turned down flange is free from contact with the mast arm.

The swivel plate14may be similarly fabricated (laser cut) from a flat plate. The swivel plate14may include one or more arcuate slots24for receiving fasteners therethrough for connecting the mast arm saddle12to the swivel plate14. The swivel plate14may also include an opening26that is sized and shaped to receive wires for electrical connections for the traffic control device. The opening26in the mast arm saddle12and the opening26in the swivel plate14may be aligned to facilitate passage of the electrical connections therethrough.

The swivel plate14is shown for reference attached to saddle12inFIG. 1without the traffic signal tube as depicted and more fully described inFIG. 2. As shown inFIG. 1, the swivel plate14may include four arcuate slots24that receive bolts32and inverted flange nuts30(phantom). Vertical and in some installations horizontal mounting is possible by utilizing slots24to adjust the swivel plate14in order to achieve the required plumbness (vertical applications) or level (horizontal applications), HG,6is a plan view showing the swivel plate14without any attachments. In the embodiment shown in Ha6, an expansion area14amay be included in some embodiments for additional flexibility of the swivel plate14. The wire access opening26and the arcuate slots24are also shown. Fastening apertures25may be used for securing the swivel plate14to a signal securing tube44using utility U-bolts20(shown in Ha2) or flexible signal brackets17(shown inFIGS. 7 and 8).

FIG. 5is a cross sectional view taken along 5 ofFIG. 1. For reference, a portion of the mast arm saddle12and swivel plate14is shown with an exemplary connection. By way of non-limiting example, an inverted flange nut30may be installed over washer33secured to the mast arm saddle12. In some embodiments, washers, bushings, coupling nuts or other fasteners may also be used. The purpose of inverting the flange nut30is dual functioning; first to allow the mast arm saddle12and the swivel plate14to move relative to one another by the separation of the second surface15of the mast arm saddle12from a first surface53of the swivel plate14, creating a displacement gap55. The term “displacement” as used herein is defined as the distance of a flexible body from its equilibrium. In some embodiments, it may be preferable to increase a length of a gap55ato provide additional displacement and/or clearance of the cable16. In contrast to the typical prior art connections where the saddle and plate faces are typically closely positioned adjacent to each other for rigidity with no space therebetween, the flange nut30and washer33positioned between the mast arm saddle12and the swivel plate14create the displacement gap55at each moment connection area that allow one or both the mast arm saddle12and swivel plate14to flex independent from each other. The second function is to capture the cable16temporarily while pre-tensioning as described with reference to installation of the attachment assembly10. The final securement of the swivel plate14will prevent release of a cable loop19.

FIGS. 2 and 7illustrate the mast arm saddle12shown connected to the mast arm42with the curved surface41of the engagement flange40positioned against the mast arm42.FIG. 2illustrates a conventional signal support tube44connected to flexible the swivel plate14without the traffic control device for clarity.FIG. 2depicts a portional side view of the attachment assembly10showing the displacement gap55between the mast arm saddle12and the swivel plate14.FIG. 2also illustrates a gap65between the swivel plate and the support tube44. For reference, the signal support tube44is sometimes channeled and in most instances gusseted for added strength—both common and typical to mast arm traffic signal mounting hardware. The tube44generally includes a bottom bracket and a top bracket with a traffic control device between the two brackets (seeFIG. 11). In some embodiments, it may be preferable to replace the rigid tube and cast aluminum brackets with flexible rectangular stainless steel signal bracket.

Final electrical connections are made utilizing conductors52into terminal housing50through waterproof grommet51to connection block (not shown) located in terminal housing50. Embodiments of the attachment assembly10are also adaptable to be used with common tube, brackets, traffic control device and a means to provide wire access.

The embodiments, for example as shown inFIGS. 2 and 11, take into account the mass of the bracket(s), tube44and traffic control device as it relates to gravitational and wind loading in respect to acceleration and deceleration forces upon the saddle plate12and swivel plate14. The flexibility and the resiliency of the attachment assembly10are a function of the mass of the traffic control device, the length of the swivel plate and/or the signal bracket, the thickness of the swivel plate and/or the signal bracket, the width of the mast arm saddle and the thickness of the mast arm saddle. The amount of flexibility is determined by the material thickness and the amount of lateral clearance in the gap65between the second face57of the swivel plate14and the tube44. The gap65is created by either a saddle18against the support tube44and/or stand off nuts36and is directly proportional to the overall length of the swivel plate14. The tube44is secured to swivel plate14utilizing U-bolts20around the tube44, through the saddle18and connected with appropriate fasteners.

An exemplary method for installing the attachment assembly10is described. One skilled in the art will recognize that other methods may also be used, including, but not limited to, metal bands or bent to fit bolts. Prior to installation on the mast arm42, a swedge bolt28connected to the cable16is inserted into the adjustment slot23of the angle connection flange38of the mast arm saddle12and is temporarily attached utilizing washer33and nut34. The connection flange38of the mast arm saddle12has an upward acute plane to lessen cable stress from different diameter mast arms. It is important at this stage to just start nut34preferably less than full nut thread length so as to be able, upon tensioning, achieve the greater amount of tensioning range. The free end of the cable16is inserted through a cable clamp22connected to the mast arm saddle12, then threaded upward through the slot23over the second surface15of the saddle12to the slot23athen through the slot23adownward continuing along the first surface13of the mast arm saddle12and outward and through a clamp22a. At this stage the cable16now has a loop19which is temporarily secured to the attachment assembly10. Prior to securing to the attachment assembly10utilizing inverted flange nuts30as shown inFIG. 1, the saddle12is placed temporarily on top of mast arm42utilizing the engagement flanges40. The loop19is brought up over the mast arm42and hooked around inverted flange nuts30, see alsoFIG. 5. Slack in the cable16may then be removed by hand pulling of the cable end16ato pre-tension the cable16. As shown inFIG. 7, the cable16extends a length A along the second surface15of the mast arm saddle12, a length B along the first surface13of the mast arm saddle12and through slots23and23ain the mast arm saddle12having a length C.

FIG. 8illustrates a cross sectional view taken along line ofFIG. 7and showing the mast arm saddle12positioned on top of the mast arm42. A small gap101may be provided between the cable16and the second surface15where the cable16extends the length A between the slots23and23aand the cable clamp22ais temporarily tightened. The cable clamps22,22amay include a standard cable saddle depending upon the wind loading at a particular location.

FIG. 9illustrates a tool102that may be used to apply pre-tension between the mast arm saddle12and the mast arm42. The tool102includes a handle103and a lever plate105. In some embodiments, the lever plate105is integrally formed with the handle103. The lever plate105has a first end104having a chisel shape to facilitate placement of the end104between the cable16and the second surface15of the mast arm saddle12. The lever plate105includes a second end106that may include a rounded shape that allows for less stress on the cable16.

FIG. 10illustrates use of the tool102with the mast arm assembly10. As shown, the lever plate105of the tool102may be inserted into the gap101and rotated until cable slack is removed from the cable16and a firm tension is applied. While maintaining the tension, cable clamp22is tightened. The tool102is removed and clamp22ais loosened. Extra slack is removed by pulling on cable end16aand then secured by retightening clamp22a. The mast arm saddle12is rotated on the mast arm42to the desired vertical plane relative to the roadway below. In some instances, depending on the shape of the mast arm42, i.e., a12sided polygon, it may be difficult to rotate the mast arm saddle12. By loosening the clamp22, only the tensioning forces between the tool-leverage and the hand tensioning of the cable slack described above remain and should minimize any difficulty in rotating the mast arm saddle12. The swedge bolt28for the cable16is tightened to cinch the mast arm saddle12to the mast arm42.

In some embodiments, the traffic control device63is connected to the support tube44using the appropriate fasteners. Then the tube44is connected to the swivel plate14for example using u-bolts20connected to saddles18as shown inFIG. 11. The swivel plate14with the traffic control device63connected thereto is connected to the mast arm saddle12and the slots24of the swivel plate14are used to adjust the traffic control device to be level or plumb.

While the embodiments here in have been described with reference to use with a mast arm system, the embodiments may also be used with lighting poles and other structures, such as street lighting and high mast interstate lighting systems. The embodiments described herein may also be used with signs.

The above Figures and disclosure are intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in the art. All such variations and alternatives are intended to be encompassed within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the attached claims.