Abstract:
A slip base support system for tubular posts. The post supporting a highway sign or other highway roadside device is held in a casting that has a triangular, multi-directional base plate. The base plate mates with a similar shaped ground plate, and the two plates are held together with bolts oriented in notches in the apexes of each triangle. Upon impact by a vehicle, the post and support casting break away from the ground plate by ejecting one or more of the bolts laterally from the notches. The post is held within the casting after impact by an internal locking pin, which is retained within the post by grommets, thus minimizing the projectile missiles after impact. To facilitate breakaway, two sheets of galvanized steel having a low coefficient of friction are positioned between the base plate and ground plate. After impact, nearly all parts of the system, including the post, casting, ground plate and bolts, are able to be re-used.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    Not applicable. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002] Not applicable. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    1. Field of Invention  
           [0004]    This invention relates to a slip base support for tubular posts. Specifically, the invention describes a slip base unit having a casting which includes a triangular, multi-directional base plate and an integral coupler which secures a support post using an internal locking pin.  
           [0005]    2. Related Art  
           [0006]    Roadside signs can pose a serious safety hazard to motorists. Signs located next to roads pose potential collision points of impact for vehicles. Effective breakaway devices for roadside signs and light pole supports are necessary to achieve the highest levels of highway safety. Therefore, the U.S. Department of Transportation&#39;s Federal Highway Administration (FHWA) policy requires that all roadside sign and light pole supports used on the National Highway System meet the performance criteria contained in the National Cooperative Highway Research Program (NCHRP) Report 350,  Recommended Procedures for the Safety Performance Evaluation of Highway Features  (Report 350). Similarly, State transportation agencies have similar performance criteria for roadside sign and light pole supports. Report 350 was prepared based on research sponsored by the American Association of State Highway and Transportation Officials (AASHTO) in cooperation with the FHWA, and outlines the required criteria for breakaway or yielding supports for signs and luminaries. The three primary appraisal factors for evaluating crash test performance are 1) structural adequacy, 2) occupant risk, and 3) after-collision vehicle trajectory.  
           [0007]    Structural adequacy relates to the support&#39;s ability to break away or yield after impact in a predictable manner. The support structure must be able to break away cleanly without undue deformation or any shattering.  
           [0008]    Occupant risk relates to the degree of hazard to which occupants in the impacting vehicle would be subjected. Occupant risk is evaluated by the degree of i) detached elements from the support, ii) vehicle rollover, iii) occupant impact velocities, iv) occupant ridedown accelerations, and v) change in vehicle velocity.  
           [0009]    Detached elements, fragments or other debris from the sign support structure should not penetrate or show potential for penetrating the occupant compartment of the vehicle, or present an undue hazard to other traffic, pedestrians, or personnel in a work zone. Deformation of, or intrusions into, the occupant compartment that could cause serious injuries should not be permitted. Thus, fragments and components, including connectors, of the sign support system may become dangerous flying projectiles. Units that have unrestrained components, including fasteners and subcomponents, pose a higher number of potential missiles.  
           [0010]    Vehicle rollover should not be caused by impact with the sign structure. Systems that have posts that shatter upon impact, creating tire puncture hazards and flipping poles under the vehicle, may pose a rollover hazard.  
           [0011]    Occupant impact velocity is the speed at which an unrestrained passenger strikes some part of the vehicle interior such as the instrument panel, window, or door after the vehicle impacts a fixed or moveable object. The maximum allowable occupant impact velocity is 16.40 f.p.s. (5 m/s), with 9.84 f.p.s. (3 m/s) being the preferable maximum. Like occupant ridedown acceleration and change in vehicle velocity, this factor is primarily influenced by the amount of lateral force required to disengage the sign post from its base mounting structure.  
           [0012]    Occupant ridedown acceleration is the highest lateral and longitudinal component of resultant vehicular acceleration averaged over any 10-ms interval for the collision pulse subsequent to occupant impact. Occupant ridedown acceleration is a function of the initial change in velocity (acceleration) of the occupant relative to the vehicle immediately after the vehicle impacts a fixed or moveable object. The maximum allowable ridedown acceleration is 20 g&#39;s, with 15 g&#39;s being the preferred maximum allowable ridedown acceleration.  
           [0013]    Change in vehicle velocity is based on the change in velocity of an 1800# (816.5 kg) vehicle immediately after striking a breakaway support at speeds of 20 mph to 60 mph (32 kmph to 97 kmph). The maximum allowable change in velocity is 16 fps (4.87 mps), but preferably does not exceed 10 fps (3.05 mps).  
           [0014]    After-collision vehicle trajectory is a measure of the potential of the post-impact trajectory of the vehicle to cause a subsequent multi-vehicle accident. After collision it is preferable that the vehicle&#39;s trajectory not intrude into adjacent traffic lanes. This factor is influenced primarily by the ease with which the sign post breaks away from its base mounting.  
           [0015]    To address these and similar safety parameters for crash sign supports, numerous designs have been introduced. Most prior art describes signs that collapse upon impact, but do not “break away”. For example, Hugron (U.S. Pat. No. 5,160,111-Nov. 3, 1992) describes a collapsible signal post having an insert tube connecting a base post and a sign post. The replaceable tubular insert has a helical cut, which allows the top post to bend upon impact. Deficiencies in this design include the non-reusable nature of the tubular insert, due to designed deformation upon impact, making the system expensive to repair/replace. Daggs et al. (U.S. Pat. No. 4,565,466-Jan. 21, 1986) discloses a spring loaded return jointed sign post pedestal. The sign post mates with a fluted bell, which prevents rotation. Deficiencies include the inability to replace the sign post without replacing the attached base post, since the strength of the spring must be such that field reattachment of the sign and base posts is not practical. Miller (U.S. Pat. No. 2,141,067-Dec. 20, 1938) utilizes a spring loaded lightweight post. However, this design lacks the ability to support a large sign, due to strength limitations of the spring and its connections.  
           [0016]    A commonly used breakaway system is described by Nehls (U.S. Pat. No. 4,926,592-May 22, 1990). The device has four main components: a ground engaging mounting post, a pedestal mounting member, a support post mounting member, and a support post for the sign. The ground engaging mounting post is buried in the ground, typically embedded in concrete. The pedestal mounting member, with a triangular plate at one end and a shaft at the other, slides its shaft within the ground engaging mounting post, where it is bolted. The support post mounting member also has a triangular plate at one end, and a vertical standard, typically elongated C-channels that form an open sided square cross-section. The triangular plate of the support post mounting member bolts to the triangular plate of the pedestal mounting member, such that there is a bottom plate (connected to the ground support) and a top plate (for connection to the sign post). The support post holding the sign is slid within the C-channels of the support post mounting member, and the post and channels are bolted together. It essential that the C-channels be bolted tightly against the sign post, which has multiple pre-drilled holes for bolt alignment. The triangular plates have notches in their apexes, through which cam bolts are fastened, securing the top plate to the bottom plate. The cam bolts each have a pair of cam rollers around the shaft of the bolt. The first roller is rollable across the interior of a notch of the support post triangular plate/flange, and the second cam is rollable across the interior of a notch if the pedestal mounting triangular plate/flange. When a vehicle strikes the sign post, the top plate slides off the bottom plate, and the cam bolts are ejected laterally out of the notches as the cams rotate. A friction reducing gasket, preferably made of TEFLON, is between the two triangular plates to facilitate the sliding movement of the top plate off the bottom plate. Deficiencies in the Nehls design include the bolting system of the sign post to the post mounting member, the securement of the C-channels to the triangular plate, the friction reducing gasket.  
           [0017]    One disadvantage of the Nehls &#39;592 system relates to the bolting system of the sign post. The system is designed to be used on posts having multiple holes, which facilitate telescoping. Exposed bolts firmly attach the sign post to the C-channels to a tightness level sufficient to eliminate any yield or take up that could occur upon impact, which would add to the breakaway force of the coupling. This connection system poses three problems. First, the exposed bolts are subject to rusting and/or locking up due to environmental exposure. Thus, replacing the sign post within the C-channels is difficult if not infeasible. Second, when the sign post is impacted by a vehicle, the exposed nuts, bolts and washers are free to fly forward, creating projective missile hazards. Third, if mounted transversely to the point of vehicle impact, the bolts form a pivot point about which the sign support may rotate, pressing against the base of the C-channels causing the C-channel welds to the triangular base to fail.  
           [0018]    The C-channels are so shaped to afford water drainage away from the sign post. Thus, there must be an open side for the C-shape. Casting such a device is not technologically and economically feasible, thus the C-channels must be welded to the triangular plate. This poses a weak connection, and a source of failure upon vehicular impact. When the weld breaks, the triangular plate and C-channel pieces add to the protective missile debris with the bolts, nuts and washers.  
           [0019]    The effectiveness of the friction reducing plate of the Nehls &#39;592 patent is also limited. Because of the opening in the middle of the TEFLON friction reducing gasket, there is a strong likelihood that upon impact there will be direct metal-to-metal contact between the top triangular plate and the bottom triangular plate. This is typical where the triangular plate rotates upward in the front of the plate due to rotational torque about the sign post upon vehicular impact, causing the back portion of the top plate to drag across the unprotected portion of the bottom plate. Likewise, a crack in the side of the TEFLON gasket can allow the gasket to degrade from water seepage, dramatically reducing its friction reducing capability.  
           [0020]    To reduce the amount of force required to break away the coupling, Nehls &#39;592 requires the use of roller cams around the coupling connector bolts. These cams roll, typically in opposite directions, across the notch surfaces in the upper and lower flanges of the coupler. The present invention does not typically use such cams, and still outperforms the Nehls &#39;592 design, as shown in Table 1: 
                                 TABLE 1                       Vehicle Velocity Change                                    Vehicle velocity at impact   ˜20 mph   ˜60 mph           Nehls ′592 system   10.4 f.p.s.    6.0 f.p.s.           Present invention   2.46 f.p.s.   2.64 f.p.s.                      
 
           [0021]    Source: USDOT-FHA May 1, 1991 correspondence to Unistrut Corporation; Texas Transportation Institute NCHRP Report 350 Evaluation of the Northwest Sign Company Slip Sign Support for Square Posts, April 2000.  
           [0022]    Under similar test conditions, the present invention breaks away with much less force than found in the prior art described by Nehls &#39;592, resulting in less vehicle velocity change after impact, thus resulting in less internal momentum change on occupants.  
           [0023]    It would therefore be a useful improvement of the prior art for a sign support slipbase system to smoothly disengage from a ground support upon impact from a vehicle, with a minimum of projective missiles ejected from the disengaged system.  
         BRIEF SUMMARY OF THE INVENTION  
         [0024]    Accordingly, the objectives of this invention are to provide, inter alia, a new and improved breakaway post slipbase that:  
           [0025]    easily breaks away from a ground stub base upon impact from a vehicle;  
           [0026]    confines connection hardware after impact;  
           [0027]    is resistant to harsh environments;  
           [0028]    affords reuse of the post; and  
           [0029]    is cost efficient.  
           [0030]    These objectives are addressed by the structure and use of the inventive breakaway post slipbase. A base stub is embedded in the ground, typically within a concrete footing, which is buried such that the base stub extends approximately 3″ above the ground, terminating at a triangular ground stub base flange. A slip base casting receives a post, typically a thin walled square tubing, such as a sign post. The slip base casting also has a triangular flange, which bolts to the ground base stub flange with flange bolts that pass though corresponding notches in each of the apexes of both triangles. A bolt keeper plate, which is a triangular shaped sheet of thin metal, restricts and aligns the bolts within the notches, maximizing contact area with the flanges, and preventing bolt “creep” over time from vibration and other forces caused by wind and the environment against the supported sign or device. The bolt keeper plate also provides a solid slick surface for a slip plate to slide across during breakaway. This slip plate is secured to the slip base casting by a locking pin, which is inside the slip base casting. The locking pin also has a primary function, which is to secure the sign post to the slip base casting. The locking pin preferably has retaining grommets, to keep the pin in place after impact, thus holding together as one unit the post, slip plate and slip base casting, preventing the pin from becoming a projectile. The design affords smooth breakaway of the coupling between the base stub and slip base casting, such that typically the post, casting, locking pin, grommets and even flange bolts can be reused after breakaway.  
           [0031]    Other objects of the invention will become apparent from time to time throughout the specification hereinafter disclosed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0032]    [0032]FIG. 1-A depicts a view of the post slipbase system installed in the ground.  
         [0033]    [0033]FIG. 1-B depicts an alternate embodiment of the post slipbase system installed on a surface mount plate.  
         [0034]    [0034]FIG. 2 depicts a detailed exploded view of the slipbase system.  
         [0035]    [0035]FIG. 3 depicts a cross section of the slip base casting with a post secured using a locking pin.  
         [0036]    [0036]FIG. 4 depicts a bottom view of the slip base casting without the post or locking pin. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0037]    The present invention is described in post slipbase system  10 .  
         [0038]    As seen in FIG. 1-A, post slipbase system  10  includes tubular post  45 , which slides and locks into slip base casting  60 , which is bolted to ground stub base  35 , which is embedded in the ground. While post slipbase system  10  is depicted in FIG. 1-A as a single stand-alone unit having a single vertical tubular post  45 , it is understood that post slipbase system  10  may be used in multiple units to support wide signs, barricades, warning devices and similar roadway devices. Further, tubular post  45  may have a “Y”, trident or other shape extending from a single base pole.  
         [0039]    Ground stub base  35  comprises base stub  25  and base stub flange  30 , which is connected, typically via welding, to one end of base stub  25 . Base stub  25  is embedded in the ground, preferably at least 33″ deep and preferably adheringly set in concrete footing  20 , which is flush with the ground. Alternatively, stub base  25  may be attached, typically by bolts and nuts, to an outer sleeve (not shown) which is embedded in the ground, with or without a concrete surrounding support base. Base stub flange  30  is preferably positioned such that base stub flange top surface is 3″ above ground level. The shape of base stub flange top surface  36  is shown in FIG. 2. It is generally triangular shaped, with notches in each apex of the triangle to receive flange bolts  27 .  
         [0040]    Alternatively, slip base flange  40  may be bolted to surface mount assembly  31 . Surface mount assembly  31  includes base stub flange  30 , which is normal to and connected to (typically via fillet welding) surface mount stub  29 , which is normal to and connected to (typically via fillet welding) surface mount plate  33 . Surface mount plate  33  is secured to concrete topping  22  such that the lower surface of surface mount plate  33  is contiguous to the top surface of concrete topping  22 . Concrete topping  22  may be a sidewalk, roadway or other surface. The surface is preferably concrete to adequately secure the connection, although asphalt and other surfaces may be used if adequate connectors are used to connect surface mount plate  33  to the surface. If concrete topping  22  is pre-existing (set), the preferred method of connecting surface mount plate  33  to concrete topping  22  is by drilling holes into concrete topping  22 , and then driving wedge anchor bolts  34  into the drilled holes such that wedge anchor bolts  34  are aligned to pass upwards through plate holes  24  of surface mount plate  33 . Nuts  37  (not shown in FIG. 1-B) attach to wedge anchor bolts  34  to secure surface mount assembly  31  to the surface of concrete topping  22 .  
         [0041]    Details of the preferred embodiment of post slipbase system  10  are shown in exploded view in FIG. 2. Base stub flange  30 , including base stub flange top surface  36  and stub base flange undersurface  39 , is normal to the axis of base stub  25 . Superposed on base stub flange top surface  36  is bolt keeper plate  65 . Bolt keeper plate  65  has the same general triangular dimensions as base stub flange top surface  36 , except notches  32  are replaced with keeper plate bolt holes  66 . In the preferred embodiment, bolt keeper plate  65  is constructed of  30  gauge galvanized steel, or similar material with a low coefficient of friction and high tensile strength. Bolt keeper plate  65  thus covers base stub flange top surface  36 , with keeper plate bolt holes  66  affording passage of flange bolts  27 .  
         [0042]    Superposed and generally centered on bolt keeper plate  65  is slip plate  50 . Slip plate  50  is preferably constructed of  30  gauge galvanized steel, or similar material having a low coefficient of friction and high tensile strength. Slip plate  50  is secured against slip base flange bottom surface  42 , and is held in place by locking pin  55  through securement tab hole  52 . As described below, locking pin  55  is held within tubular post  45  through post sidewall holes  90 . The perimeter shape and dimensions of slip base flange bottom surface  42  are the same triangular shape with apex notches  32  as found on base stub flange top surface  36 .  
         [0043]    As seen in FIGS. 3 and 4, slip base casting  60  includes upper post support  61 ; cavity  80 , which extends the entire vertical length of the interior of slip base casting  60 ; and at least one pin channel  56 , which extends from slip base flange bottom surface upward in the interior of slip base casting  60 , terminating in the lower section of the interior. The diameter of cavity  80  is slightly larger than the outer diameter of post  45 , particularly the first end of post  45  than is inserted into cavity  80 . The cross section of cavity  80  is generally the same shape as the cross section of post  45 , such that the first end of post  45  mates smoothly when slid into cavity  80 . In the preferred embodiment, the cross section of post  45  and cavity  80  is a square. Alternatively, this cross section may be any circular, oval or polyhedral shape.  
         [0044]    Channel width  57  is slightly larger than the diameter of locking pin  55  and channel length  58  is slightly longer than the length of locking pin  55 , affording the ends of locking pin  55  the ability to slide transversely into pin channel  56  when oriented within tubular post  45 . Locking pin  55  is secured transversely to tubular post  45  by grommets  62  circumferential positioned about locking pin  55 . A first grommet  62  is oriented adjacent one side of the interior surface of tubular post  45 , and a second grommet  62  is oriented adjacent the interior surface of slip plate securement tab  51 , such that slip plate securement tab  51  is pressing against an opposite side of the interior surface of tubular post  45 . In the preferred embodiment, post sidewall holes  90  are located on opposing sides of tubular post  45 , and at a distance from post end  46  such that the distance from the top edges of post sidewall holes  90  to post end  46  is just slightly more (preferably {fraction (1/16)}″) than channel depth  59 . Thus, when slip base casting  60  slides down over tubular post  45 , the ends of locking pin  55  are pressed against the top ends of pin channels  56 . As seen in FIG. 3, locking pin  55  secures slip plate securement tab  51  between grommet  62  and the interior wall of tubular post  45 , grommets  62  keep locking pin  55  secured to tubular post  45 , and locking pin  55  against the top ends of pin channels  56  prevents upward movement of tubular post  45 . In the preferred embodiment, tubular post  45  is a square post  70 , each exterior side of the square being approximately 2½″.  
         [0045]    As seen in FIG. 4, slip base casting  60  preferably has four pin channels  56 , each subsequent pin channel  56  offset by 90°, such that there are two pairs of pin channels  56 , each pair having two pin channels  56  aligned in the same plane, and the second pair of pin channels  56  being aligned perpendicular to the first pair. This orientation allows post  45  to be rotated 90° before final assembly, affording the installer the option of facing the sign attached to post  45  in any of four directions (by rotating post  45  and by mounting the sign on one side or the other of rotating post  45 ). Alternatively, slip base casting  60  may have as few as one pin channel  56 , if only one end of locking pin  55  is used to secure post  45  to slip base casting  60 .  
         [0046]    As its name implies, slip base casting  60  is preferably constructed by metal casting techniques. Alternatively, slip base casting  60  may be manufactured by any metalworking technique known in the art, including welding together components to arrive at the final product depicted as slip base casting  60 .  
         [0047]    The slip base flange  40  of slip base casting  60  bolts to base stub flange  30 . Flange bolts  27  bolt to nuts  37 , with washers  38  circumferential to the shaft of flange bolts  27  and adjacent the bolt head of flange bolts  27  and nuts  37 . Thus washers  38  are adjacent stub base flange under surface  39  and slip base flange top surface  41  when flange bolts  27  are tightened down on nuts  37 . To prevent flange bolts  27  from “creeping” out of notches  32 , each bolt passes through keeper plate bolt hole  66  of bolt keeper plate  65 , which is between slip base flange  40  and base stub flange  30 . Thus, each flange bolt  27  is oriented within a notch  32  of slip base flange  30 , a keeper plate bolt hole  66  of bolt keeper plate  65 , and a corresponding notch  32  of base stub flange  30 . When flange bolts  27  are tightened down, base stub flange top surface  36  presses against bolt keeper plate bottom surface  67 , and bolt keeper plate top surface  64  presses against slip plate bottom surface  53 , and slip plate top surface  49  presses against slip base flange bottom surface  42 . In the preferred embodiment, flange bolts  27  are standard bolts, defined as not having cam rollers such as those described in the Nehls U.S. Pat. No. 4,926,592.  
         [0048]    Post end  46  rests against slip plate top surface  49 , and tubular post  45  is held within cavity  80  of slip base casting  60  by locking pin  55  being snug against the top end of pin channels  56 .  
       Operation  
       [0049]    The preferred installation of post slipbase system  10  is as follows. First, a 12″ or 14″ diameter hole 33″ deep is drilled for concrete footing  20 . Soft soil may require a larger diameter hole. The hole is filled with concrete, and base stub  25  is pressed into the hole so that base stub flange top surface  36  is a maximum of 3″ above the ground. Base stub flange  30  is aligned so that a flat edge of base stub flange  30  is facing on-coming traffic. Base stub flange top surface  36  should be level and, if used together with additional post slipbase systems  10 , should typically be at the same elevation as the other base stub flange top surfaces  36 . Slip base casting  60  is slid up around tubular post  45  so that post end  46  and post sidewall holes  90  are accessible. Slip plate securement tab  51  is inserted inside tubular post  45 . Locking pin  55  is slid through a first post sidewall hole  90 , and both grommets  62  are pushed around locking pin  55 . Locking pin  55  is then pushed through securement tab hole  52  and then through a second post sidewall hole  90  such that equal lengths of locking pin  55  are protruding outside tubular post  45 . Grommets  62  are then slid outward against the interior walls of tubular post  45 , securing locking pin  55  in position. Slip base casting  60  is then slid down with locking pin  55  sliding up pin channels  56 , leaving about {fraction (1/16)}″ of tubular post  45  protruding below slip base flange bottom surface  42 . Upper post support  61  provides lateral support to tubular post  45 . The sign or other object to be supported by tubular post  45  may optionally be attached at this point.  
         [0050]    Flange bolts  27 , each having a washer  38 , are positioned upward through notches  32  of base stub flange  30 , and then through keeper plate bolt holes  66  of bolt keeper plate  65 . Slip base casting  60 , now attached to tubular post  45  and slip plate  50  by locking pin  55 , is placed on top of base stub flange  30  such that slip base flange bottom surface  42  and slip plate bottom surface  53  mate against bolt keeper plate top surface  64 , and flange bolts  27  extend up through notches  32  of slip base flange  40 . Washers  38  are placed over each flange bolt  27 , and nuts  37  secured to each flange bolt  27 . Each flange bolt  27  should be tightened to 40 to 80 foot pounds of torque.  
         [0051]    When post slipbase system  10  is struck by a vehicle, slip plate  50  slides across bolt keeper plate  65 , and one or more flange bolts  27  are ejected out of notches  32  of base stub flange  30  and slip base flange  40 , tearing out a small amount of metal around the edge of keeper plate bolt hole  66 . Post  45 , slip plate  50  and slip base casting  60  remain connected after vehicle impact by locking pin  55 . Locking pin  55  remains integral with post  45 , slip plate  50  and slip base casting  60  due to the retention afforded by grommets  62 . Thus the number of small projectile missiles after vehicular impact is minimal, increasing the safety of the system.  
         [0052]    Depending on the speed of the vehicle, after vehicular impact tubular post  45  typically will fly over the vehicle (at high speeds) or will fall to the side of the impacting vehicle (at low speeds). In both cases, all parts are typically undamaged after vehicular impact with post slipbase system  10  except for bolt keeper plate  65 , which will have at least one edge next to a keeper plate bolt hole  66  tom out as at least one flange bolt  27  ejects out of a notch  32 . Typically, even flange bolts  27  are able to be re-used after impact. Thus post slipbase system  10  provides a very economical breakaway sign system causing minimal damage both to post slipbase system  10  as well as the striking vehicle.  
         [0053]    The foregoing disclosure and description of the invention is illustrative and explanatory thereof. Various changes in the details of the illustrated construction may be made within the scope of the appended claims without departing from the spirit of the invention. The present invention should only be limited by the following claims and their legal equivalents.