Abstract:
An adjustable static stabilizer used to ameliorate shock loading. The static stabilizer has a housing forming a chamber and an upwardly-open cylindrical carrier moveably mounted in the chamber. A plurality of spring washers are mounted in the carrier, and a shoe cap extends transverse to the carrier for engaging the spring washers therein. A tie rod interconnects the shoe cap and the carrier for displacement of the shoe cap relative to the housing, and a threaded means is disposed between the housing and the carrier for rotatably mounting the carrier in the housing which is operable upon rotation of the shoe cap relative to the housing to enable the overall height of the stabilizer to be adjusted.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to bridges, and more particularly, the present invention relates to apparatus for reducing impact loads to movable bascule bridge leafs and associated support structures as the leafs close as well as for maintaining static stability of the leafs when fully closed. 
   BACKGROUND OF THE INVENTION 
   Bascule bridges need to possess the ability for the bridge operator to quickly and reliably change span orientation to alternately permit the passage of land and waterway traffic. Bascule bridges must be able to open and close on demand; yet, at the same time they should be as rigid in their closed position as a fixed span. The system intended to secure bridge leafs in the closed position is customarily known as a “Static Stabilizing System” and it normally includes components such as span locks, live load shoes, anchorages, machinery brakes and, in some instances, tail locks. Live load shoes and anchorages are the heart of the system because they transfer the traffic loads directly from the leaf to the pier. Both of these components are frequently subjected to shock loads both when the leaf is closing into its fully seated position and when the leaf is closed with heavy traffic crossing the span. Leaf pounding, or bounce, resulting from vehicle passage and from the leaf slamming down hard onto its seats with each closing, imparts shock loads to the movable leaf structure as well as to the pier and supporting structures. Repetitive shock loading causes abnormal wear of the live load shoes, anchorages and their respective seats. 
   Over years of bridge service, the excessive wear, coupled with normal thermal expansion and contraction, corrosion and deterioration, diminishes the ability of the components to act in concert with one another and function as a system. Many serious problems result, including distress and failures in machinery components, which are directly attributable to poorly adjusted and maintained static stabilizing components. For example, there is spalling and cracking of live load seat concrete support columns from frequent high shock loads due to slamming the leaf onto its seat during closing plus repetitive shock loads from vehicles passing across the span; fracture of pinion or rack teeth in the operating machinery caused by cyclic shock loads on both faces of a tooth while the leaf is closed; and, fracture of trunnion bearing bushings caused by extremely high loads and repetitive shocks due to poorly adjusted live load shoes, anchorages and span locks. 
   Frequent periodic bridge maintenance is required to assure that live load shoes are in firm contact with their seats and the anchorages are adjusted as intended. Adjustment usually requires complete removal of each live load shoe and anchorage in order to insert shims of proper thickness between them and their respective supporting structures. When the leaf is closed and the span locks are engaged, the live load shoes should not have any clearance with their seats. Correct anchorage adjustments depend on the particular design of the bascule leaf. Some do not require any clearance with their seats, and others require a slight, e.g. 0.020 to 0.050 inch clearance. Live load shoe and anchorage adjustment is tedious and difficult because the components are cumbersome, weighing hundreds of pounds, and because anchorages are often situated in inaccessible locations with respect to the bascule leaf. Adjustment is a time-consuming, labor-intensive process that requires the span be closed to all vehicular and waterway traffic, and this results in inconveniences to the traveling public. Failure to keep the static stabilizing system properly adjusted is an invitation to more serious trouble and damage, greater repair and replacement costs, and lengthier periods of inconvenience to users of the bascule bridge. 
   OBJECTS OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an improved bascule bridge static stabilizing system which minimizes the shock loads caused by slamming down of the leaf during closing and resulting from the passage of heavy vehicular traffic when the leaf is fully closed. 
   Another object is to provide apparatus useful with a bascule bridge leaf to assure positive stability and integrity for the leaf in the closed position. 
   Yet another object is to provide a bascule bridge static stabilization system in which the bascule leaf can be maintained and repaired with a minimum of interruption of bridge service to vehicular and waterway traffic and attendant inconvenience to the traveling public. 
   Still another object is to provide a bascule bridge leaf static stabilizing system which can be easily adjusted for correct clearance between contacting parts to ensure positive integrity and rigidity throughout the bridge leafs when in their closed position. 
   A further object of the invention is to provide a unique energy-absorbing assembly for use with a bascule bridge leaf to enable it to be readily adjusted in situ for proper contact between support members and the leaf without causing major disruption of bridge service to vehicular and waterway traffic. 
   A still further object is to provide for a bridge span, a live load energy-absorber which is easy to install or to remove for replacement or repair, and which can be manufactured and maintained efficiently. 
   SUMMARY OF THE INVENTION 
   These and other objects, features and advantages of the invention are accomplished by means of energy-absorbing static stabilizers juxtaposed with a bridge span and its associated supporting structure to cushion shock loading. Each stabilizer includes a stack of Bellville washer springs carried within a housing juxtaposed between a fixed structure and an end portion of the span. The spring stack is preferable vertically adjustable in the housing to enable a span leaf-engageable bearing cap to be adjusted in situ to effect proper clearance when used in association with bascule bridges. An embodiment that does not include the adjustability feature is also disclosed for use with fixed span bridges. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding and appreciation of the invention and its many attendant advantages, reference will be made to the following detailed description taken in conjunction with the accompanying drawings, in which: 
       FIGS. 1A ,  1 B and  1 C are schematic representations in elevation of three bascule bride embodiments according to the invention; 
       FIG. 2  is a plan view of an adjustable energy absorbing stabilizer assembly for use in effecting static stabilization of the bascule bridge embodiments of  FIGS. 1A ,  1 B and  1 C; 
       FIG. 3  is a view in cross section of the assembly of  FIG. 2  taken in a radial plane on Line  3 — 3  of  FIG. 2 ; 
       FIG. 4  is a view of a portion of the assembly of  FIG. 2  taken in a transverse plane on Line  4 — 4  of  FIG. 3 ; and 
       FIG. 5  is a view in cross section of the portion of the assembly of  FIG. 2  taken in a plane on Line  5 — 5  of  FIG. 4 . 
       FIG. 6  is a view in vertical cross-section of another embodiment which does not include in situ adjustability features. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, wherein like reference numerals and characters denote like or corresponding parts throughout the several views,  FIG. 1A  illustrates one embodiment of the invention incorporated in a trunnion bascule bridge  10  having a pair of opposed complementary span sections or leafs  10   a  and  10   b . Each leaf, such as the leaf  10   a , pivots about a trunnion  16  supported in a bearing (not shown) mounted on a fixed pier (not shown). The leafs  10   a  and  10   b  are similar in construction and include at least two girders  12  extending the full length of the movable span. Each girder has a forward leaf span portion  12   a  and a reward leaf tail portion  12   b . A road bed surface  15  for vehicular traffic is supported by the leaf girders  12  on its forward span extension over a waterway below the bridge. A counterweight  17  is attached to rearward leaf tail portions  12   b  of girders  12  so that the movable leaf  10   a  is essentially balanced about a horizontal pivot axis extending through the trunnion  16 . A motor driven pinion  18  meshes with a sector gear  20  affixed to girders  12  for rotating the leaf  10   a  from a substantially horizontal, or closed position endwise aligned with companion leaf  10   b  and spanning between opposed approach roadways  22  (shown in full) to an open upwardly-inclined position (shown in phantom). In this embodiment, a road break  24  is located forwardly of the trunnion  16  toward an outer end  12   a  of girder  12 . Preferably, an energy absorbing span lock system  18 , such as disclosed in U.S. Pat. No. 6,588,041, issued to Steward Machine Co., Inc. the owner of the present application, connects to outer ends of leafs  10   a  and  10   b  when they are aligned with in the bridge in its fully closed position. 
   According to this preferred embodiment, two energy-absorbing static stabizer assemblies  28  and  29 , are provided in juxtaposition with respect to the leaf trunnion  16  to statically secure bridge leaf  10   a  when closed and to absorb shocks while closing. One assembly  28 , commonly called a live load shoe, is mounted on a top surface of a fixed concrete pier  30  located below the bridge leaf  10  for releasable contact with a lower surface of girder  12  between trunnion  16  and the forward outer end  12   a  of girder  12 . The other assembly  29 , commonly called an anchorage, is mounted underneath approach roadway structure  22  for releasable contact with an upper surface of the rearward tail end portion of the girder  12   b  in the vicinity of the counterweight  17 . 
   The energy absorbing assemblies  28  and  29  are adjusted with the leafs  10   a  and  10   b  in their closed positions in relation to one another for cooperatively reducing repetitive, high shock loads to the supporting structures  30  and  22  resulting from constant, heavy vehicular traffic. To this end, as best seen in  FIGS. 2–5 , each energy absorbing assembly, such as assembly  28 , is of like construction to the other, but each may differ in size and resiliency according to design shock loads expected to be encountered. Each assembly, such as the assembly  28 , comprises a housing  32  having a cylindrical wall  34  closed at one end by a planar rectangular base  36  that is normal to a central vertical cylindrical axis A—A. The base  36  is adapted to be mounted by conventional means, such as lag bolts, (not shown) on either pier  30  or under approach roadway structure  22 . The housing  32  is enclosed at the end opposite the base  36  by a rectangular cap shoe  38  having a circular flange  40  depending into cylindrical wall  34  on vertical axis A—A. A protective skirt  41  depends from the cap periphery to encircle an annular gap  43  between the telescopically overlapping surfaces of housing wall  34  and cap shoe  38  for preventing foreign matter from entering the assembly  28 . An arcuate load bearing surface  38   a  is provided on the cap to engage girders  12  along a single line of contact L—L as well known in the art. 
   The cap shoe  38  is adjustable relative to the base  36 . To this end, a cup-shaped spring carriage  48  is mounted inside the cylindrical housing wall  34  for vertical adjustment relative thereto. The inner surface of spring carrier  48  is contiguous with a bushing  46 , and the outer surface has threads  48   b  which threadedly engage threads  34   b  on the inner surface of the housing cylindrical wall  34 . The threads  34   b  extend upwardly from an annular bottom shoulder  36   a  in base  36 . A cylindrical guide pin  42  is welded at W around its upper end to the underside of cap shoe  38 . The guide pin depends into carrier  47  through a stack of Bellville spring washers  44  coaxially confined between two spaced apart flat washers  45 , a shoulder  48   a  of the annular spring carrier  48 , and a guide bushing  46 . The lower end portion of guide pin  42  depends into a recess  36   b  circumscribed by shoulder  36   a  for mounting a washer  50  and a retainer ring  52  in an annular groove  42   a  to secure Bellville spring washers  44  axially between the cap shoe  38  and the adjustable spring carrier  48 . As best seen in  FIG. 4 , guide pin  42  terminates in a diametrical slot  54  for receiving with an axial clearance a diametrical elongate yoke  56  which is connected at opposite ends to carrier  48  by bolts  58  to assure correct orientation of arcuate surface  38   a  with aligning slots  64  in spring carrier  48 . 
   The stabilizer assembly  28  is lubricated prior to being placed in service, and can be lubricated while in service. For this purpose, at least one grease cap  38  ( FIG. 3 ) is mounted on housing wall  34  for communicating via one or more passages  31   a  through spring carrier  48  to enable additional heavy duty lubricants to be pumped into the housing periodically. A plurality of grease cups  31  and related passages may be provided at various locations in the periphery of the housing wall  34  to afford handy access for lubrication after installation. Any excess lubricant can overflow through the gap  43  between the cap shoe and housing wall. 
   The stabilizer assemblies are adjusted in situ while bridge leafs  10   a  and  10   b  are in the closed position with no vehicular traffic passing across the leafs. To this end, sockets  60  are provided in opposite sides of each shoe  38  approximately aligned with the line of contact L—L. An elongate bar (not shown) is inserted into a sockets for rotating the cap shoe  38  and spring carrier  48  in housing  34  until a desired clearance, as required by the particular application, is obtained with the leaf girder  12 . As the cap shoe  38  rotates, threads  34   b  and  48   b  slowly displace the spring carrier  48  relative to housing  32 . The spring carrier  48  is locked in selected 180° rotational increments by means of at least one, but preferably a pair of, alignment screws  62  threaded into housing wall  34  and laterally engageable in diametrically opposed vertical slots  64  in carrier  48 . Each 180° increment of rotation of shoe  38  displaces spring carrier  48  upwardly or downwardly an amount equal to one half of the thread pitch. A preferred thread pitch is fourteen (14) threads per inch. With no external loads present on cap shoe  38 , the Bellville washers are in a relaxed condition, but under either vehicular traffic loading, or slamming of the leafs upon closing, the Bellville spring washers  44  compress to absorb the shock loads. 
   By way of example, and not by way of limitation, one version of a static stabilizer designed to accommodate a maximum vertical load of about 132,000 pounds has an overall volumetric dimension of about one cubic foot. The maximum vertical travel of the cap shoe is limited to less than about 0.100 inch. For a maximum live load of 132,000 pounds, five Bellville springs are used in series each carrying a maximum live load component of about 26,400 pounds. Thus, the overall spring rate is in excess of about 1,000,000 pounds/inch of deflection. The pitch of the spring carrier threads is such as to provide a total height adjustment on the order of about ½ inch in about 1/32 inch increments for each 180° turn for each of the cap shoe about its vertical axis. In the event that a lower live load is anticipated, one or more spring washers could be replaced with one or more flat washers of the same thickness. As a result, the stabilizer design is able to be readily configured for a variety of design loads with minimal changes in either external or internal structure. This facilitates efficient manufacture and assembly. In addition, the static stabilizers can be mounted cap side up as illustrated at  28  in  FIG. 1A  or cap side down as illustrated at  29 . Preferably, the static stabilizers are mounted to stationary bridge structures as illustrated, but there may be applications in which mounting on moveable bridge components might be indicated. 
     FIG. 1B  illustrates another embodiment of a trunnion bascule bridge  70  having opposed leaf span girders  72  of like construction shown in solid lines locked in a fully closed position. Each leaf supports a road bed  73  spanning opposite approach roadway structures, such as roadway  74 . A span lock system  18 , as described supra, is shown in phantom connecting the leaf spans when in their fully closed positions. Each leaf span girder  72  includes a trunnion  76 , carried in a support bearing mounted on a fixed pier (not shown). Each leaf girder  72  is pivoted from a closed position to an open position by a motor driven pinion  78  meshing with a sector gear  80  fixed to each girder  72 . A road break  82  is provided between roadbed  73  and approach roadway structure  74  along the width of leaf girders  72  between trunnion  76  and the rearward leaf tail portion  72   a  extension of girder  72 . 
   In this embodiment, two energy absorbing assemblies, such as assembly  28 , described above, are installed at predetermined locations along the length of leaf girder  72  at locations similar to those described in  FIG. 1 . One assembly  28 , a live load shoe, is mounted by its base  36  on a fixed concrete support  84  and contacts a lower surface of leaf  72 ; the second assembly  29 , an anchorage, is mounted by its base  36  to a lower surface of the support structure for approach roadway  74  to engage an upper surface of leaf tail end portion  72   a ; and a third assembly  28 ′, another live load shoe, is mounted by its base  36  on a fixed concrete support  86  for engaging a lower surface of a retractable tail lock  88  of conventional construction. Each cushion shoe assembly  28  and  29  is adjusted as described above, and as required by the design, with the span in the closed position and the tail lock  88  disposed in its full line position in  FIG. 1B  to statically stabilize the span against shock loads as described above. 
   In a further embodiment illustrated in  FIG. 2C , a rolling lift bascule bridge  90  having opposed leafs of similar construction is shown in solid lines in a fully closed position supporting a road bed  94  and is shown in phantom lines in the open position. The leafs are locked in the closed position by a span lock system  18 , discussed, supra, with road breaks  97  located between road bed  94  and approach roadway structure  96 . The tail end  92   a  of each girder  92  has an arcuate sector  98  of constant radius measured from a horizontal axis of rotation A near an inner, or tail, end  92   a  thereof. A motor-driven pinion  100  fixed to leaf  92  at axis A causes sector  98  to roll on an elongate horizontal bearing plate  102  mounted on a concrete pier  106 . 
   One energy-absorber cushion shoe assembly  29 , as described above, is disposed between a tail end portion  92   a  of each girder  92  and a static structure adjacent the roadway approach to provide a desired tail-end static stabilization of the bridge leaf. To this end, assembly  29 , an anchorage, is mounted below a fixed structure  108  above leaf tail end portion  92   a  for engaging an upper surface portion  92   b  thereof. As described above, the assembly  29  is adjusted in situ to insure firm contact of its cap shoe with girder tail end portion  92   a.    
   In the preceding embodiments, adjustable static stabilizers are disclosed for use in association with various types of bascule bridges that require periodic adjustment due to the inherent nature of their moveable components. For fixed span bridges that may not require periodic adjustment, but which are subject to shock loading due to heavy-fast moving traffic, another embodiment is provided. As best seen in  FIG. 6 , the static stabilizer  128  illustrated is similar in many respects to the static stabilizer  28  in that it has a similar moveable cap shoe  138 , a somewhat similar housing  136 , and a stack of Bellville spring washers  144 . In this embodiment however, the spring washer stack  144  is not vertically adjustable in the housing  136 . Rather, the stack is are confined in a cylindrical chamber  136   a  between a housing bottom wall  136   b  and the underside of the shoe cap boss  142 . The shoe cap  138  is connected to the housing  136  in a manner similar to the stabilizer  28 , having a connecting rod portion  142   a  depending from the shoe cap boss and fastened in a similar manner at its lower end to a circular  136   c  flange adjacent to the base of the housing  136 . A closure plate  156  is slotted (not shown) for cooperating with a tang (not shown) on the bottom of the connecting rod portion  142   a  to anti-rotatively connect the shoe cap to the housing  136 . An O-ring  142  cooperates with a descending peripheral skirt  141  to protect the interior of the stabilizer from the ingress of foreign matter. Downward displacement of the shoe cap  138  compresses the spring washers in the stack  144  to absorb shock loads such as in the manner described heretofore. In this embodiment, the displacement is less than about 0.100 inches as indicated by the dimension d in  FIG. 6 . By way of example and not by way of limitation, in this embodiment, for a dead load design of 100,000 lbs., and a 212,000 lbs. load to full deflection “d”, eight (8) Bellville spring washers are contained in a housing having an overall height of about 16 inches and a base 24 inches square. 
   In view of the foregoing, it should be apparent that the disclosed embodiments provide statically stabilized bridges in which shock loads are reduced. As a result, damage to the piers and supporting structures, and consequent costly repairs and replacements are greatly reduced. In addition, when used on bascule bridges the static stabilizing systems are easy to adjust with a minimum of bridge downtime and cost and a minimum of interruption of service to both vehicular and waterway traffic. 
   Various modifications, alterations and changes may be made without departing from the spirit and scope of the invention as defined in the appended claims.