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FIELD OF THE INVENTION 
     This invention relates generally to railroad bridges and more particularly to a system and method for positioning a pile cap underneath an existing elevated bridge assembly to upgrade the bridge assembly to support a rail assembly. 
     BACKGROUND OF THE INVENTION 
     Many existing wooden railroad bridges were built 70 or 80 years ago and are now in the process of being repaired because of deterioration or upgraded to handle the freight loads and speeds of modern trains. Most of the existing wooden railroad bridges are supported by wooden piles topped by wooden pile caps. The repair and upgrade of the bridges includes installing new steel beam piles and topping the new piles with pre-cast, concrete pile caps. Ultimately, the old, wooden piles and caps are removed, and new pre-cast, concrete spans, which are supported by the new caps and piles, are used to support the rail assembly. 
     A typical concrete pile cap is 17 feet long by three feet wide by three feet deep, and weighs 30,000 pounds. Currently, concrete pile caps are cast with lifting loops at each end so that the pile cap may be lowered straight down from the rail assembly onto the steel piles. This, however, requires that at least portions of all the stingers be removed and that both rails be cut and removed from the rail assembly. Train traffic is interrupted since the rail assembly is separated, and traffic cannot resume until the pile cap is placed on the steel piles and the rail assembly is restored. 
     It is preferred that upgrading the exiting wooden bridges is done with a minimum interruption of the train traffic. Windows of opportunity for performing the construction are seldom longer than six hours and frequently are as short as forty-five minutes. Current systems and methods in the art do not allow for minimum interruption. 
     The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above. 
     SUMMARY OF THE INVENTION 
     A system and method for positioning a pile cap underneath an existing bridge assembly is disclosed. A portion of the rail assembly is removed to define an access area. At least three new piles are installed through the access area. The piles include a center pile and two opposing outer piles. Each pile has a proximal end and a distal end. The distal ends of each pile are driven into a support surface so that each pile generally extends from the support surface to the existing elevated rail assembly. The proximal ends of each pile are removed to define a gap between the piles and the existing elevated rail assembly. A new pile cap is then inserted into the gap. To insert the pile cap, a lifting device and a crane are used. The lifting device is used to incrementally insert the pile cap into the gap. The pile cap is supported on the piles and is used to support a new span for supporting the rail assembly. 
     The foregoing summary is not intended to summarize each potential embodiment, or every aspect of the invention disclosed herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing summary, a preferred embodiment, and other aspects of the present invention will be best understood with reference to a detailed description of specific embodiments of the invention, which follows, when read in conjunction with the accompanying drawings, in which: 
     FIG. 1 illustrates a perspective view of an existing bridge assembly having wooden piles and wooden pile caps; 
     FIG. 2A illustrates the bridge assembly being partially upgraded according to the present invention; 
     FIG. 2B illustrates a side view of the partially upgraded bridge assembly of FIG. 2A; 
     FIG. 3 illustrates a perspective view of the existing bridge assembly of FIG. 1 with a portion of the wooden ballast retainers and cross-ties removed according to the present invention; 
     FIG. 4 illustrates the bridge assembly with ballast boards removed according to the present invention; 
     FIG. 5 illustrates the bridge assembly with outboard non-load-bearing stringers removed according to the present invention. 
     FIG. 6 illustrates a new, center pile positioned through the assembly according to the present invention; 
     FIG. 7 illustrates the center pile, a first outer pile, and a second outer pile positioned through the assembly according to the present invention; 
     FIG. 8 illustrates a front view of proximal ends removed from the new piles to define a gap according to the present invention; 
     FIG. 9 illustrates a crane and a freight car positioned over the prepared portion of the assembly according to the present invention; 
     FIG. 10 illustrates a support bar being connected to a new pile cap according to the present invention; 
     FIG. 11 illustrates the crane lifting the pile cap out of the freight car according to the present invention; 
     FIG. 12 illustrates the crane lowering the pile cap adjacent the assembly according to the present invention; 
     FIG. 13 illustrates the crane rotating the pile cap to be perpendicular to the assembly according to the present invention; 
     FIGS. 14A-B illustrate the crane utilizing a first pair of lifting rods to position the pile cap to rest on two, new piles according to the present invention; 
     FIGS. 15A-B illustrate the crane positioning the pile cap further into the rail assembly utilizing a second pair of lifting rods with one of the lifting rods being located between the rails; 
     FIGS. 16A-B illustrate the crane positioning the pile cap further into the rail assembly utilizing a third pair of lifting rods with one of the lifting rods being located between the rails; 
     FIG. 17 illustrates the crane positioning the pile cap further into the rail assembly utilizing a fourth pair of lifting rods with one of the lifting rods being located between the rails; 
     FIGS. 18A-B illustrate the crane positioning the pile cap into a final position utilizing a fifth pair of lifting rods located outside of both rails; 
     FIG. 19 illustrates the crane placing the support bar into the freight car according to the present invention; 
     FIG. 20 illustrates an embodiment of a support bar in cross-section having lifting rods according to the present invention; 
     FIG. 21 illustrates an embodiment of a lifting rod according to the present invention; 
     FIG. 22A illustrates a perspective view of an embodiment of a pile cap according to the present invention; 
     FIG. 22B is a cross sectional view of FIG. 22A taken from line A—A; and 
     FIG. 23 illustrates a rope used to raise and lower a lifting rod according to the present invention. 
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 illustrates a portion of an existing bridge assembly  100  typically used to span a low elevational area, such as a valley, canyon, riverbed, or creek bed. The bridge assembly  100  includes an elevated rail assembly  102  supported by wooden pile caps  106  on wooden piles  104 . The wooden piles  104  extend into a support surface or ground surface  108 . 
     The rail assembly  102  includes first and second, parallel rails  114  and  16  used by railroad cars and engines. The rails  114  and  116  are supported on a plurality of cross-ties  118  along the length of the rails  114  and  116 . The cross-ties  118  are supported on crushed stone ballast (not shown) and a plurality of ballast boards  122 , which also extend along the length of rails  114  and  116 . The ballast boards  122  are fastened together by a plurality of side ballast retainers  120  located at each end of the ballast boards  122 . 
     The ballast boards  122  are supported on a plurality of outboard non-load-bearing stringers  124  and a plurality of load-bearing stringers  126   a - 126   e . The non-load-bearing stingers  124  are located underneath and at the ends of the ballast boards  122 . The plurality of load-bearing stringers  126   a - 126   e  is supported on the wooden pile caps  106 . The stingers on bridge assemblies can have a number of configurations. In one configuration, for example, the load-bearing stringers  126   a - 126   e  extend between adjacent, wooden caps  106  and are spaced approximately 18 inches apart in relation to each other with  126   a  being an inboard stringer and  126   e  being an outboard stringer. 
     Referring to FIGS. 2A-B, the existing, wooden bridge assembly  100  is illustrated partially upgraded according to the present invention. FIG. 2A illustrates a perspective view of the bridge assembly  100  showing only selected components, and FIG. 2B illustrates a side view of the bridge assembly  100  of FIG.  2 A. Upgrading the existing, wooden bridge assembly  100  to handle the freight loads and speeds of modern trains involves replacing the existing wooden piles  104  with new piles  110 , which are preferably made of steel, and replacing the existing wooden pile caps  106  with new pile caps  112 , preferably made of pre-cast concrete. In addition, upgrading the wooden bridge assembly  100  involves replacing the exiting stingers  124  and  126  and ballast boards  122  with new spans  50 , which are preferably pre-cast and made of concrete. 
     It is to be understood that FIGS. 2A-B do not necessarily represent how the bridge assembly  100  would appear during the process of upgrading the assembly according to the present invention. Rather, the partially upgraded bridge assembly  100  is presented to contrast the existing wooden structures (piles  104 , caps  106 , ballast boards, stingers  126 , etc.) with the new structures (piles  110 , caps  112 , and spans  50 ) that are used to replace them. 
     Two sections  101   a  and  101   b  of the assembly  100  are shown for illustrative purposes. The first section  101   a  shows the exiting assembly  100  in an incomplete form. In the first section  101   a , the rails  114  and  116  are shown supported on existing cross-ties  118 , as best described above. For clarity, neither the crushed ballast nor the plurality of ballast boards is shown. For illustrative purposes, a part of the first section  101   a  is shown without the cross-ties, crushed ballast, and ballast boards so that the plurality of stringers  126  can be seen supported on the existing wooden caps  106  and piles  104 . 
     In accordance with upgrading the bridge assembly  100 , a new, concrete pile cap  112   a  is shown positioned underneath the stingers  126  between existing wooden pile caps  106   b  and  106   c . This new, concrete pile cap  112   a  is supported on a plurality of new piles  110   a . Preferably, the new piles  110   a  are steel H beams having a width of approximately 14 inches. The new piles  110   a  extend from the support surface  108  to the pile cap  112   a . In the process of upgrading the bridge assembly  100  described in detail below, distal ends of the piles  110   a  are stabilized with the support surface or driven into the ground  108 . Opposite, proximal ends of the piles  110   a  are eventually cut off to make room for the new pile cap  112   a  to be positioned below the exiting stingers  126 . 
     To elucidate the system and method described in more detail below, the second section  101   b  of the assembly illustrates the desired result of the present invention. For illustrative purposes, the second section  101   b  is shown in an incomplete form. New piles and caps, such as piles  110   b-c  and caps  112   b-c , are installed between every other wooden cap  106  and piles  104 . In contrast to the conventional wooden piles  104  and caps  106  that are positioned every 15-feet along the assembly  100 , the new piles  110   b-c  and caps  110   b-c  are positioned approximately every 30-feet along the assembly  100 . After installing the new piles  110   b-c  and caps  112   b-c  under the existing stingers, the old, wooden components are removed. In particular, the old caps are removed, and the old, piles are removed or truncated, such as piles  105 . Ultimately, the newly installed caps  112   b-c  and piles  110   b-c  support pre-cast, concrete spans  50   a  and  50   b . The concrete spans  50   a-b  hold the ballast (not shown), cross-ties  118 , and rails  114  and  116  of the rail assembly  102  and replace the old stingers and ballast boards. 
     The new pile caps  112  are approximately 34-inches in height, while the old wooden pile caps  106  are about 14-inches. As best shown in the side view of FIG. 2B, the top surface of the new pile caps  112  are set about three or four feet lower than the old wooden pile caps  106 . This allows for the approximately three feet depth of the pre-cast, concrete bridge spans  50  that will eventually be positioned on the new pile caps  112 , such as the span  50   b  supported on caps  112   b  and  112   c  and piles  110   b  and  110   c  in the second section  101   b . In addition, the position of the concrete piles  112  can include about another foot in depth to accommodate for ballast (not shown). The 30-inch deep span  50   b  replaces the 17-inch wood stingers  126  and the 3-inch wooden ballast boards (not shown). 
     With the benefit of the overview of the system and method according to the present invention described above, particular steps for positioning new piles and caps underneath an existing elevated bridge assembly to upgrade the assembly will now be discussed in more detail with reference to FIGS. 3-24. Referring to FIGS. 3 through 5, initial steps for creating an access area  128  in the assembly  100  according to the present invention are discussed and illustrated. Creation of the access area  128  allows new piles (not shown) to be installed through the rail assembly  102  and allows new pile caps (not shown) to be positioned on top of the new piles. In FIGS. 3-5 and in FIGS. 6-19 described below, the exiting wooden piles used to support the wooden caps  106  are not shown for simplicity. 
     FIG. 3 illustrates a first step in creating the access area. A plurality of cross-ties  118  is removed from underneath the rails  114  and  116 . Side ballast retainers  120  adjacent the removed cross-ties are also removed from the both sides of the rail assembly  102 . Although not shown, a three-foot section of crushed stone ballast is removed from the rail assembly  102  as well. 
     As illustrated in FIG. 4, ballast boards  122  are removed from underneath the rails  114  and  116  where the cross-ties  118  were previously removed. At this point, the stringers  126   a - 126   e  are exposed to view from the top of the rail assembly  102 . As illustrated in FIG. 5, outboard, non-load-bearing stringers  124  are removed on both sides of the rail assembly  102 . At this point, only the stringers  126   a - 126   e  span across the access area  128 . A center stringer may also be removed if necessary. 
     As illustrated in FIG. 6, a center pile  130  is positioned between the rails  114  and  116 , between a central pair of stringers  126 , and through the access area  128 . Alternatively, depending on the spacing of the stringers  126 , a portion of one of the stringer may be cut away to make room for the center pile  130 . A distal end  130   d  of the pile  130  is then stabilized to a support surface  108 . For example, the distal end  130   d  is driven into the ground  108  “to refusal” so that the center pile  130  extends generally from the ground  108  to the existing elevated rail assembly  102 . Alternatively, the distal end  130   d  can be stabilized to another support or structure by methods known in the art. In the present embodiment, the pile  130  is preferably a steel H beam having a width of approximately 14 inches, but it will be appreciated that other support members or structures known in the art can be used. 
     As illustrated in FIG. 7, a first outer pile  132  and an opposing second outer pile  134  are then positioned through the access area  128 . Distal ends  132   d  and  134   d  of each of the outer piles are driven into the ground  108 . Each of the outer piles  132  and  134  generally extend from the ground surface  108  to the existing elevated rail assembly  102 . Preferably, the two outer piles  132  and  134  extend from the ground surface  108  at convergent angles relative to the center pile  130 . 
     Proximal ends  130   p ,  132   p , and  134   p  of each pile are horizontally cut off to define a generally uniform gap  136  between piles  130 ,  132 ,  134  and the rail assembly  102 , as illustrated in FIG.  8 . The ends  130   p ,  132   p , and  134   p  are cut with level tops to a precise height for welding to steel plates on the bottom of a new, pre-cast concrete pile cap (not shown). The proximal ends are cut immediately after the piles are driven into the ground surface  108  so that rail assembly  102  can continue to be used for rail traffic. In the present embodiment, the steel piles  130 ,  132 , and  134  can be cut using a gas/oxygen flame at exactly the height where the cut end will be welded to the new caps. As noted above, it is understood that other members or structures can be used for the new piles. Thus, the step of horizontally cutting proximal ends of the piles may be unnecessary when the piles are not driven into the ground as described above, but are stabilized by other methods or structures. 
     At this point, the ballast, a substantial majority of cross-ties  118 , and the rails  114  and  116  are still in place, and there are no obstacles to normal train traffic. The cross-ties that were removed to allow for driving the new piles can be replaced, and other cross-ties  118  approximately 30-feet away can be removed for driving the next set of piles. 
     Once the piles  110  are ready, a new, pile cap  112  of pre-cast concrete can be delivered by railroad car on the existing rail assembly  102 , as illustrated in FIG. 9. A locomotive crane  138  is moved approximately over the access area  128 . Coupled to the crane  138  is a freight car  144  housing the new pile cap  112 . The crane  138  and freight car  144  are stopped in a position where the coupling (not shown) between the car  144  and crane  138  does not block the access area  128  from the top. The hand brake is set on the freight car  144 , and the coupling is opened. 
     As shown in FIG. 10, the crane  138  is moved away from the car  144  to clear the coupling from the access area  128 . The crane  138  has a boom  142  and a retractable cable  146 . To lift and move the new pile cap  112 , a lifting device is used. The lifting device includes an intermediate member or support bar  148  and a plurality of interconnecting members or lifting rods  150 - 160 . Relevant details of the lifting device are provided below with reference to FIGS. 20,  21 , and  23 . 
     The cable  146  is connected to a center rod  152 , which extends from the support bar  148  along with a first end lifting rod  150 . The first end lifting rod  150  and the center lifting rod  152  define a first pair of lifting rods, which are both releasably connected to lifting points on the concrete pile cap  112 . Relevant details of the pile cap  112  are provided below with reference to FIGS. 22A-B. 
     The lifting rods  150 ,  152  each have an extended position and a retracted position on the support bar  148 . In FIG. 10, the first end-lifting rod  150  and the center-lifting rod  152  are shown in the extended position releasably connected to lifting points on the pile cap  112 . A second end lifting rod  154 , a first mid-portion lifting rod  156 , a second mid-portion lifting rod  158 , and a third mid-portion lifting rod  160  are shown in the retracted position on the support bar  148 . 
     As will be further described below, each lifting rod corresponds to a lifting point or threaded hole in the pile cap  112  being approximately determined by the spacing of the stingers  126 . The lifting rods each weigh approximately 90-lbs. and must be raised approximately eight feet when retracted on the support bar  148 . To aid in the lifting of the rods, a double-sheave block is suspended from the crane arm to support two, one-inch diameter ropes. The ropes have eye splices at one end, which are slipped over the tops of the two active lifting rods. In a preferred embodiment shown in FIG. 23, a rope  137  is threaded through a sheave  139 . The rope  137  has an eye splice  141  at the working end. It is slipped over the top of one of the lifting rods, for example  150 . A pin  164  is placed through the top end of the lifting rod  150  so that the rope  137  may be used to raise and lower the lifting rod  150 . 
     As shown in FIG. 11, the crane  138  lifts the pile cap  112  out of the freight car  144 . The weight of the pile cap  112  is transferred through the center-lifting rod  152 , while the first end lifting rod  150  helps to stabilize the pile cap  112 . The pile cap  112  is lifted high enough to clear the side of the freight car  144  and is swung to the side of the rail assembly  102 . The crane  138  preferably rotates approximately 20 degrees or less. The pile cap  112  is positioned parallel to the rails to decrease the required rotation of the crane and the resulting moment arm thereon. 
     As shown in FIG. 12, the crane  138  lowers the pile cap  112  adjacent the access area  128  to approximately a few inches, such as three inches, above the pile cap&#39;s intended final elevation. The crane  138  is then moved away from the access area  128  backward until the crane&#39;s lifting arc is directly over the center pile  130 . The pile cap  112  is then rotated by a rope (not shown) attached to the first end lifting rod  150  until the pile cap  112  is generally perpendicular to the rail assembly  102 , as shown in FIG.  13 . 
     In this preferred embodiment, the locomotive crane  138  is used to lift and move the new concrete pile cap  112 . It understood that attention must be made to the maximum moment arm on the crane  138 , which can tend to overturn the crane as it holds the approximately 30,000-lb. pile cap  112  adjacent the rail assembly  102 . While lowering the cap  112  adjacent the access area  128 , the new cap  112  is preferably slightly rotated to clear the existing wooden pile cap  106  at one end and to clear the edge of the bridge assembly at the other end. In this way, the maximum overturning moment arm can be limited to approximately 100-inches measured from the center of the rails  114  and  116  to the lifting cable  146 . 
     If such a locomotive train is not used to move the pile cap adjacent the access area  128 , then particular attention must be further paid to the maximum overturning moment arm. For example, in another embodiment, a crane can be carried in a freight car delivering the new pile caps. With a crane in a freight car, the limiting point of the overturning moment arm is a side bearing on top of a truck bolster of the freight car, which is only about 20 inches from an axial centerline of the rails  114  and  116 . This imposes a severe limit on the load and or/moment arm that can be handled without danger of overturning the crane and freight car. Accordingly, if other cranes, mechanisms, or methods are used in the art to lift and move the concrete pile caps, particular attention must be paid to the overturning moment. It will be appreciated by one of ordinary skill in the art, however, that a number of cranes, methods, and mechanisms are known in the art for providing an increased maximum moment arm to resist overturning. 
     As shown in FIGS. 14A-B, the crane  138  positions one end of the pile cap  112  partially into the access area  128  and gap  136  from the side of the rail assembly until the center lifting rod  152  is adjacent to or in contact with the outboard stringer  126   a . At this position, an additional lifting point on the pile cap  112  that is approximately 60 inches from the center is visible through the access area  128 . As shown in FIG. 14B, the cable of the crane  146  can include a hook or other connector  147  connected to one end of the center lifting rod  152 . 
     As shown in FIGS. 15A-B, the crane  138  lowers the pile cap  112  onto at least two piles, such as the center pile  130  and the first outer pile  132 . The weight of the pile cap  112  is thereby taken off the lifting rods. The first mid-portion lifting rod  156  is extended from the support bar  148  and is releasably connected to the lifting position of the pile cap  112  visible through the access area  128 . The center lifting rod  152  is disconnected from the pile cap  112  and is retracted up into the support bar  148 , as best shown in the end view of FIG.  15 B. Thus, at least two lifting rods are preferably connected to the pile cap  112  when alternating the interconnection of the rods with the pile cap. The center lifting rod  152  and the first mid-portion lifting rod  156  define a second pair of lifting rods extending from the support bar  148 . The first end lifting rod  150  stabilizes the pile cap  112 , while the center lifting rod  152  is retracted from support bar  148  and the first mid-portion lifting pipe  156  is releasably connected to the pile cap  112 . 
     The crane  138  then lifts the pile cap  112  off the center pile  130  and the first outer pile  132 . The crane  138  further positions the pile cap  112  into gap  136  by moving the center of the pile cap  112  approximately 18-inches closer to the center of the rail assembly  102 . At this position, an additional lifting point on the pile cap  112  that is approximately 42 inches from the center is visible through the access area  128 . The pile cap  112  is then lowered to rest on at least two of the piles, such as center pile  130  and first outer pile  132 . 
     The second mid-portion lifting rod  158  is extended from the support bar  148  and is releasably connected to the pile cap  112 , as best shown in the end view of FIG.  16 B. The first mid-portion lifting rod  156  is then disconnected from the pile cap  112  and retracted from the support bar  148 . The second mid-portion lifting rod  158  and the first end lifting rod  150  define a third pair of lifting rods extending from the support bar  148 . The crane  138  then lifts the pile cap  112  off the center pile  130  and the first outer pile  132 . 
     The crane  138  further positions the pile cap into the gap  136  an additional 18 inches toward the center until the second mid-portion lifting rod  158  is adjacent to or in contact with stringer  126   c . At this point, an additional lifting point on the pile cap  24  inches from the center of the cap is visible through the access area  128 . The pile cap  112  is then lowered to rest upon two piles, such as center pile  130  and first outer pile  132 . 
     As illustrated in FIG. 17, the third mid-portion lifting rod  160  is extended from the support bar  148  and is releasably connected to the pile cap  112 . The second mid-portion lifting rod  158  is disconnected from the pile cap  112  and retracted from the support bar  148 . The third mid-portion lifting rod  160  and the first end-lifting rod  150  define a fourth pair of lifting rods. 
     The crane  138  then lifts the pile cap  112  off the center pile  130  and outer pile  132 . The crane  138  further positions the pile cap  112  into the gap  136  an additional 18-inches until the third mid-portion lifting rod  160  is adjacent to or in contact with the next stringer  126   d . At this point, an outboard lifting point in the pile cap  112  is visible beyond the outboard stringer  126   e . The pile cap is then lowered to rest upon piles  130 ,  132 , and  134 . 
     As illustrated in FIGS. 18A-B, the second end lifting rod  154  is then extended from the support bar  148  and is releasably connected to the pile cap  112 . The second end-lifting rod  154  and the first end-lifting rod  150  define a fifth pair of lifting rods. Then, the third mid-portion lifting rod  160  is disconnected from the pile cap  112  and retracted from the support bar  148 . The crane  138  then lifts the pile cap  112  off piles  130 ,  132 , and  134 . The crane  138  further positions the pile cap  112  into the gap  136  so that the pile cap  112  is centered directly under the rail assembly  102 . The pile cap  112  is then lowered onto piles  130 ,  132 , and  134  so that the weight of the pile cap  112  is taken off the fifth pair of lifting rods  150  and  154 . 
     The pile cap  112  includes three steel plates (not shown) that are cast and anchored into a bottom surface of the pile cap  112 . These steel plates correspond to the spacing of the piles  130 ,  132 , and  134 . The pile cap  112  is welded at the juncture of the steel plates and the piles  130 ,  132 , and  134 . The first end lifting rod  150  and the second end lifting rod  154  are then disconnected from the pile cap  112  and retracted from the support bar  148 . The crane  138  then lifts the support bar  148  and the lifting rods back into the freight car  144 , as illustrated in FIG.  19 . 
     With the new cap  112  and piles  130 ,  132 , and  134  installed, the above system and method according to the present invention can be repeated at further locations along the bridge assembly. As discussed above, new caps and piles are positioned between every other wooden cap and piles or about every 30-feet along the bridge assembly. Once the new caps and piles are installed below the exiting bridge assembly, the old, wooden caps, piles, and ballast can be removed. 
     In practice of the present invention, it is understood that all the steps discussed above need to be preformed at one location at one time on the bridge assembly  100 . Instead, it is preferred that at least some of the steps be performed along the length of the assembly  100  before further steps are performed. For example, creating the access area, driving the new piles, cutting the new piles, and positioning the new caps on the piles can be performed at one location and then further locations along the assembly before the wooden caps and piles are replaced with new, concrete spans. As evidenced herein, the system and method according to the present invention advantageously maintains a substantial portion of the load-bearing components of the rail and bridge assembly and allows the exiting rails and bridge assembly to be used while performing the steps in this manner. 
     FIG. 20 illustrates an embodiment of a lifting device according the present invention. The lifting device includes an intermediate member or support bar  148  and a plurality of interconnecting members or lifting rods  150 - 160 . The support bar  148  is illustrated in cross-section to show an internal hollow defined therein. The support bar  148  defines a plurality of first or top apertures  161   a  from a top of the bar to the internal hollow. The support bar  148  defines a plurality of equally located, second or bottom apertures  161   b  from a bottom of the bar to the internal hollow. The bottom apertures  161   b  have a greater dimension than the top apertures  161   a.    
     The lifting rods  150 - 160  are disposed in the plurality of apertures  161   a-b  in the support bar  148 . The apertures  161   a-b  are approximately spaced to cooperate with the spacing of the stringers of the rail assembly and with the spacing of the lifting points on the new pile cap. For example, the first mid-portion lifting rod  156  is preferably spaced approximately 60 inches from the center-lifting rod  152 . Also, the second mid-portion lifting rod  158  is preferably spaced approximately 42 inches from the center lifting rod  152 , and the third mid-portion lifting rod  160  is preferably spaced approximately 24 inches from the center lifting rod  152 . This spacing accommodates the typical spacing of stringers in a rail assembly, although it is understood that other arrangements of spacing may also be applicable to the present invention. In an alternative embodiment, three additional lifting rods (not shown) can be located between the center lifting rod  152  and the first end lifting rod  150 . The spacing of the three, additional lifting rods can be similar to the first, second, and third mid-portion lifting rods from the center. 
     The first end lifting rod  150  and the second end lifting rod  154  are shown in the extended position in relation to the support bar  148 . The center lifting rod  152 , the first mid-portion lifting rod  156 , the second mid-portion lifting rod  158 , and the third mid-portion lifting rod  160  are all shown in the retracted position. Removable pins  164  are used to hold the rods in the retracted position. Preferably, all of the lifting rods can be retracted so that a threaded end can be housed in the internal hollow of the support bar, which protects the threads from damage when not in use. 
     The center-lifting rod  152  is movably disposed in central apertures of the support bar  148  between extended and retracted positions. The center-lifting rod  152  has a lower end capable of releasably connecting to the cap at one of the lifting points when in the extended position (not shown). The lower end is also capable of engaging the inner hollow of the support bar  148  adjacent the upper aperture  161   a  when in the retracted position as shown in FIG.  20 . The center-lifting rod  152  also has an upper end capable of connecting to the cable. In one embodiment, the center-lifting rod  152  includes a swivel and shackle  162  so that the cable of the crane can be attached to the center-lifting rod  152 . The upper end is also capable of engaging the outer surface of the support bar  148  adjacent the upper aperture  161   a  when in the extended position (not shown). 
     The plurality of other lifting rods  150 ,  154 ,  156 ,  158 , and  160  are also movably disposed in the apertures  161   a-b  of the support beam between extended and retracted positions. These rods have a lower end capable of releasably connecting to the cap at one of the lifting points when in the extended position. These rods also have an upper end capable of engaging outside surface of the support beam adjacent the upper aperture  161   a  when in the extended position, such as rods  150  and  154  are shown in FIG.  20 . 
     FIG. 21 illustrates an embodiment of a lifting rod according to the present invention. Shown by way of example is a first end lifting rod  150  with an upper collar  166  at an upper end of the lifting rod and a large diameter area  168  at a lower end of the lifting rod. The upper collar  166 , which may be welded to the rod, is a stop to keep the lifting rod  150  from sliding out of the support bar when the pile cap is being lifted. Adjacent to the large diameter area  168  is a male member or tapered threaded section  170  for releasably connecting to the cap. The lifting rod  150  further includes an aperture  172  for a pin, such as the pin  164  in FIG. 20, to hold the rod  150  in the retracted position in the support bar. The lifting rod also includes another aperture  173  receiving the pin to retract and extend the rod in the support bar. The male member  170  on the rod  150  can be threaded to a lifting point on the pile cap by a hydraulic motor on the crane under the remote operation of the operator. 
     FIGS. 22A-B illustrate an embodiment of a pile cap  112  according to the present invention. The pile cap  112  includes a plurality of lifting points or threaded holes  174 ,  176 ,  178 ,  180 ,  182 , and  184  used for the lifting rods. The lifting points are positioned along a longitudinal axis of the pile cap  112 . In particular, the pile cap  112  includes a first outboard-threaded hole  174  and a center threaded hole  176  at the center of the pile cap  112 . Opposite the outboard-threaded hole  174  is a second outboard-threaded hole  178 . Spaced apart between the center threaded hole  176  and the outboard-threaded hole  178  is a first threaded hole  180 , a second threaded hole  182 , and a third threaded hole  184 . The threaded holes on the pile cap  112  are spaced to match the spacing of the lifting rods spaced across the support bar  148 . 
     The releasable connection between the threaded holes and the lifting rods is made by mating the threads of the lifting rods with the appropriate threaded hole of the pile cap  112 . The load bearing surface  186  is adapted to support new pre-cast concrete bridge spans, which in turn support the existing elevated rail assembly. The pile cap  112  can further include three additional threaded holes located between the center-threaded hole  176  and the inboard-threaded hole  174  so that the pile cap  112  is symmetrical about the center. 
     Past attempts of providing the lifting points or threaded holes in the pile cap  112  involved welding threaded steel nuts to reinforcing steel that was then cast in the material of the cap. It has been found that the heavy load of the pile cap striped the threads of the welded nuts. Thus, as best shown in FIG. 22B, the threaded holes  174 ,  176 ,  178 ,  180 ,  182 , and  184  according to the present invention are preferably formed from cut lengths of oil well drilling pipe  190 . The pipes  190  are attached to reinforcing steel  188  and then cast into the concrete when the cap  112  is formed. The oil well drilling pipe  190  is internally threaded and is flush with the load bearing surface  186  of the cap  112 . The flush ends of the pipe  190  will not interfere with the new, pre-cast concrete spans to be supported on the load bearing surface  186 . 
     The threaded holes  174 ,  176 ,  178 ,  180 ,  182 , and  184  are tapered to provide automatic alignment with the threaded section of the lifting rods, such as section  170  in FIG.  21 . The threads are very coarse so that only a few turns of the lifting rod is required to make the releasable connection. As is known in the art, the threads of the oil well drilling pipe  190  are designed to support thousands of feet of interconnected drill pipe, which can impose loads of 100,000-lbs. or more on couplings of the upper pipes. This is many times the weight of the pile cap  112  to be lifted. As discussed above, at least two lifting rods are releasably connected to the lifting points on the cap  112 . Thus, the internal threads of two pipes  190  are adequately capable of sustaining the approximately 30,000-lbs. load of the pile cap  12  when coupled to at least two lifting rods. 
     Preferably, the pile cap  112  has a reinforcement bar  188  extending through the threaded oil well drilling pipes  190 . Prior to the pile cap  112  being cast with concrete, holes are drilled in the oil well drilling pipes  190  for interconnecting the reinforcement bar  188  with the pipes  190 . The reinforcement bar  188  is preferably steel re-bar and is preferably disposed through the holes in the pipes  190  and not welded to them. The reinforcement bar  188  helps to retain the pipes  190  in the pile cap  112  when lifted. As at the tops of the pipes, the lower ends of the pipes  190  are flush with the bottom of the pile cap  112 . In addition, the bottom ends of the pipes  190  are open, and the pipes  190  are able to drain rain water. 
     While the invention has been described with reference to the preferred embodiments, obvious modifications and alterations are possible by those skilled in the related art. Therefore, it is intended that the invention include all such modifications and alterations to the full extent that they come within the scope of the following claims or the equivalents thereof.

Summary:
A system and method for inserting pre-cast concrete pile caps under wooden railroad bridges without removing essential load bearing rails, cross-ties, and stringers is disclosed. The system and method minimizes the time that the track is closed to normal rail traffic. The system and method uses recycled oil well drill pipes that are cast into pile caps so that female-threaded ends are flushed with an upper surface of the pile caps. Lifting rods have male threaded ends that are used with a multi-point lifting device that allows the pile cap to be slipped under the existing bridge in a number of small incremental steps utilizing the spaces between wooden bridge stringers.