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.
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.
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.
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.
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:
Referring now to the drawings, wherein like reference numerals and characters denote like or corresponding parts throughout the several views,
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 10a 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 12a 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 12b in the vicinity of the counterweight 17.
The energy absorbing assemblies 28 and 29 are adjusted with the leafs 10a and 10b 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
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 48b which threadedly engage threads 34b on the inner surface of the housing cylindrical wall 34. The threads 34b extend upwardly from an annular bottom shoulder 36a 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 48a of the annular spring carrier 48, and a guide bushing 46. The lower end portion of guide pin 42 depends into a recess 36b circumscribed by shoulder 36a for mounting a washer 50 and a retainer ring 52 in an annular groove 42a to secure Bellville spring washers 44 axially between the cap shoe 38 and the adjustable spring carrier 48. As best seen in
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 (
The stabilizer assemblies are adjusted in situ while bridge leafs 10a and 10b 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 34b and 48b 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
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
In a further embodiment illustrated in
One energy-absorber cushion shoe assembly 29, as described above, is disposed between a tail end portion 92a 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 92a for engaging an upper surface portion 92b thereof. As described above, the assembly 29 is adjusted in situ to insure firm contact of its cap shoe with girder tail end portion 92a.
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
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.