Bridges – Bridge construction method
Reexamination Certificate
2002-10-03
2004-09-28
Hartmann, Gary S. (Department: 3671)
Bridges
Bridge construction method
C405S149000
Reexamination Certificate
active
06795992
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
This invention relates to the construction of new railroad or roadway bridges and more particularly, to a method for, where two roadways or two railroad tracks or one railroad track and one roadway already exist and intersect, constructing an underpass below one of the intersecting ways to allow the second of the ways to pass there below with minimal interruption of traffic along each of the roadways. The method is also for widening an existing underpass. For the purposes of this application, the description hereinafter will focus on constructing a new railroad bridge along an active railroad track that intersects an active roadway to allow for passage of the roadway under the railroad.
One way to increase profits in the railroad industry is to increase the average rate at which trains transport product between various locations. While there are many different factors that affect average train speed, one of the more important speed determining factors includes cross traffic intersections. To this end, in order to minimize the possibility of accidents and reduce noise, many communities limit train speed through cross traffic intersections where vehicles such as cars and trucks pass across the tracks. Because train tracks have historically been laid so as to pass through small villages and towns or, in the alternative, villages and towns have sprung up along the paths defined by railroad routes, there are a large number of cross traffic intersections such that their combined affect is to appreciably reduce average train speed.
At first blush it would not appear as though slowing down a few trains at cross traffic intersections would appreciably affect average train speed. However, upon a more detailed study of train traffic patterns, it becomes apparent that an appreciable ripple effect occurs whenever even a single train is slowed. This ripple effect results from the fact that trains can only pass through a reduced speed zone such as a cross traffic intersection one at a time and often routes through reduced speed zones are the only suitable routes for trains to pass over when moving from one location to another. The result is that trains often become “stacked up” in a sort of holding pattern where trains have to, in effect, wait their turn to pass through the reduced speed zones. Thus, even trains that are traveling outside a reduced speed zone may have to slow appreciably to time their arrival at and passing through the reduced speed zones.
One way to increase average train speed has been to replace cross traffic intersections with underpasses where one of the roadway or the train track is routed underneath the other so that traffic on the track passes by traffic on the road unobstructed and vice versa. The construction industry generally has developed several different methods for constructing underpasses under existing tracks and/or roadways.
According to one method, a construction company or municipality purchases temporary rights to use land adjacent an existing trackroadway intersection and builds “run-arounds” or “shoo-flies” on the adjacent land to route both train and vehicular traffic around the intersection. Thereafter, while traffic is still traveling along the intersecting routes, the construction company lays out a temporary road and a temporary train track along the shoo-fly routes. After the track and roadway are completed, the construction company reroutes the train and vehicular traffic along the shoo-fly's thereby rendering the original intersection unused. Next the construction company excavates under the intersection, constructs foundations for a bridge on either side of the space over which the bridge is to extend, constructs abutments on top of the foundations and on either side of the space over which the bridge is to extend, installs girders that extend generally between the top ends of, and that are supported by the top ends of, the abutments, constructs one of the track or the roadway on the top of the girders and the other of the track and roadway below the girders, reroutes the train and vehicular traffic to the bridge and underpass and then must dismantle the temporary shoo-fly routes and place the land occupied thereby in its original condition.
Clearly the process of constructing shoo-flies is time consuming and very costly in the short term. In some cases underpass construction processes like the one described above take several weeks and even months to complete. Process costs are exacerbated where, as is often the case, shoo-flies have to begin and terminate several miles from an original intersection to ensure that the turns required to form the shoo-fly are not too sharp. Costs are further exacerbated when one considers the effects on railroad traffic from constructing a shoofly about an intersection. To this end, often, train speed has to be reduced along shoo-fly track segments as the turns required to accommodate the fly can cause dangerous operating conditions. Thus, during underpass construction the very problem that is to be eliminated, slowed train traffic, is exacerbated.
One way to reduce costs associated with constructing an underpass is to design the underpass/bridge construction so that the design thereof is relatively cost effective. To this end, generally, costs can be minimized by designing an underpass/bridge that minimizes the “surface height differential” between a top overpass surface of a track or roadway and the surface of an underpass below the track or roadway. This is because construction costs are at least in part related to the amount of excavating required to construct an underpass and the height of abutments required to maintain a bridge over the underpass. Thus, where the surface height differential is minimized, either required excavation can be minimized, abutment structure height can be minimized or some optimal combination of reduced excavation and minimized abutments can be chosen to reduce overall costs. Of course, in any bridge design, the lowest most portion of the bridge has to be high enough above the underpass surface to enable vehicles passing there along to clear the bridge structure.
One other consideration when designing a traffic bearing bridge is safety. To this end, in the railroad industry, wherever possible, it is desirable to have all bridge components reside outside harms way and, more specifically, below the rail road tracks supported thereby. For instance, all bridge girder components should ideally reside below track level so that any equipment attached to a train or even a derailed train will not impact the bridge components and cause or exacerbate damage.
In some cases it is impossible for a construction company or a municipality to acquire the right to temporarily use property adjacent an existing intersection for constructing shoo-flies. The industry has developed several different solutions for constructing underpasses where shoo-flies are not possible. One such solution that does not require a shoo-fly is described in U.S. Pat. No. 3,843,988 (hereinafter “the '988 patent”) which issued on Oct. 29, 1974 and which is entitled “Method for Excavating an Underpass Beneath an Existing Roadway”.
The '988 patent recognizes that whenever a railroad track already exists and an underpass has to be formed to either route the track or an intersecting roadway below the other of the track and roadway, because of train rerouting difficulties and stacking problems, the least expensive option is almost always to minimize train traffic disruption by constructing the underpass to pass below the track. In addition, the '988 patent recognizes that, generally, at least a portion of an underpass and associated bridge structure can be constructed prior to disrupting train traffic thereby reducing underpass construction costs overall.
To minimize track down time, the '988 patent teaches that, where an underpass is to be c
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