Abstract:
A precast concrete bridge system containing one or more sections wherein each section includes a horizontally disposed, load-bearing span that is integrally cast with a pair of vertical side walls. Each wall contains lightweight cores encapsulated in the concrete to create a series of longitudinally extended beams in each wall so that the beams in one wall are coaxially aligned with the beams in an adjacent wall. The cores constitute between 16-35 % of the total section volume.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to a precast concrete bridge system that is made up of a plurality of sections, and specifically to a concrete bridge system for maximizing a waterway opening while at the same time minimizing the weight of the structure without sacrificing strength. 
     BACKGROUND OF THE INVENTION 
     As described in U.S. Pat. No. 4,564,313, precast structures for use in bridge systems are presently in use which permit safe passage of motor vehicles and the like over waterways, such as culverts, creeks and the like. The bridge is precast in sections wherein each section includes a horizontal deck wall that spans between a pair of vertically disposed legs or side wall supports that are integrally cast with the deck. The sections are placed in a side-by-side relationship upon suitable footings and the completed decking is then paved to complete the structure. The size of each section making up the entire concrete bridge structure is generally limited by the weight of the section that can be safely and legally transported from the casting site to the installation site. As a result of this size limitation, the length of the span that can be achieved by the finished structure is correspondingly limited. 
     A similar precast bridge is disclosed in U.S. Pat. No. 4,993,872. The precast sections, in this case, contain an arched deck wall having a radius of curvature of between twenty five and forty feet. The arch increases the difficulties involved in lifting, hauling and erecting the sections and results in a loss of waterway openings in the final structure. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to reduce the weight of precast concrete bridge sections without reducing the load carrying capacity of the sections. 
     A further object of the present invention is to reduce the difficulties associated with lifting, transporting, and erecting precast bridge sections. 
     A still further object of the present invention is to provide light weight precast bridge sections that can be more easily transported from the casting site to the erection site. 
     Another object of the present invention is to reduce the cost of precast bridge sections. 
     Yet another object of the present invention is to provide bridge sections containing voids in the top deck wall and side walls to reduce the dead load weight of the sections while not adversely effecting the load carrying capacity of the sections. 
     These and other and further objects of the present invention are attained by a concrete bridge system that contains a series of precast sections. Each section includes a planar horizontally disposed deck wall that is integrally joined to a pair of spaced apart vertically disposed legs or side walls. The deck wall and the side walls each contain a plurality of interior cores cast therein that follow the geometry of the containing wall. The cores constitute between 16 to 35 percent of the volume of each wall and are placed so that the load carrying capacity of the structure is not adversely effected. Reinforcing rods are placed between the voids and the opposed outer surfaces of each wall to further enhance the strength and load carrying capacity of the structure. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     For a further understanding of these and objects of the invention, reference will be made to the following detailed description of the invention which is to be read in connection with the accompanying drawing, wherein: 
     FIG. 1 is a partial perspective view of a bridge system embodying the teachings of the present invention; 
     FIG. 2 is a side view of the bridge system shown in FIG. 1 with the wings removed; 
     FIG. 3 is a side elevation of a bridge section used in the present system; 
     FIG. 4 is an end view of the bridge section shown in FIG. 3; 
     FIG. 5 is an enlarged partial side view in section of a bridge section; and 
     FIG. 6 is a section taken along lines  6 — 6  in FIG. 5 showing the location of the reinforcing bars and the void contained in the side walls of each bridge section. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning now to FIGS. 1 and 2, there is shown a concrete bridge system, generally referenced  10 , that embodies the teachings of the present invention. The system is made up of individual precast sections  12 . Each section includes a flat horizontally disposed deck wall  13  that is integrally precast with an opposed pair of spaced apart side walls  14  and  15 . At the time of erection, to create a channel  10  shaped structure, the side walls of each section are set upon footings  18  situated on either bank of a stream, river, culvert, walkway or the like that the bridge system is designed to span. In this embodiment of the invention, the bridge is shown spanning a relatively wide river  19 . Typically, a roadway  20  for vehicular or pedestrian traffic is laid over the combined deck walls of the system. The roadway is typically made up of a bottom layer of soil  21  and a top layer of asphalt or concrete  22 . The entrance and exit to the bridge system may be equipped with precast wings  25  for holding back soil in these regions and, in waterway applications as depicted herein, for conducting water into and out of the bridge tunnel. 
     As best illustrated in FIG. 2, the outer surfaces of the sidewalls of each section are backfilled with soil or stone fill  26  which helps to support the sections in assembly and to provide the system with additional strength for supporting vertical loads that are placed on the system by vehicular traffic or the like crossing the bridge. As further illustrated in FIG. 2, the deck wall and sidewalls of each section are provided with a plurality of voids  30  and  31 , respectively, which are precast in the walls at the time of manufacture. As will be explained in greater detail below, the cores are generally rectangular in shape and follow the contour of each containing wall. The cores are formed by mounting lightweight foam blocks  32  and  33  (see FIGS. 5 and 6) into the mold forms at the time of casting and pouring the concrete about the blocks to encapsulate the blocks within the walls. The foam material may be polystyrene or any other similar material capable of forming a desired internal core and preventing the concrete from filling the core volume. 
     Turning now to FIGS. 3 and 4, there is illustrated a bridge section  12  that contains five parallely aligned rectangular cores  40 — 40  within the opposed side walls. Five rectangular voids  50 — 50  are similarly cast into the deck wall of the section. Although five cores are employed in the present embodiment of the invention, it should become evident from the disclosure below that the number and shape of the cores can be varied depending upon the length and the width and the thickness of the sections without departing from the teachings of the present invention. 
     FIGS. 5 and 6 further illustrate the construction of section  12 . The sidewalls  14  and  15  are cast integrally with the deck wall  13  to form right angle corners with the deck walls. A gusset  52  is cast into the interior corners between the walls. The gusset forms a 45° angle with each of the interior wall surfaces making up each of the corners. Each gusset preferably extends along the width of the section, however, the gusset may be of lesser length or cast in segments along the length of the corners without departing from the teachings of the invention. As best illustrated in FIG. 5, the opposed ends  54  of the cores established in the deck wall terminate at about the point that the inclined wall  55  of each gusset joins the deck wall. Similarly, the top surfaces  57  of the cores contained in the side walls of each section terminate at the. point that the inclined wall of the gusset joins the side wall. Accordingly, the region formed at the corners is completely filled with concrete and reinforced by the gussets to provide high load carrying capacity at the corners. 
     FIG. 6 is a sectional view taken through either the deck wall  13  or either of the side walls  14  and  15 , each section being a mirror image of the other because the overall width across the walls is the same and the location of the voids across the width of the walls is identical. Each parallely aligned core is placed apart from its neighbor a distance (d). The surface  60  of each end core is similarly spaced from the opposed outer surfaces  61  and  62  of the containing wall a distance (c). Preferably, the spacing (c) is about equal to the spacing (d). The outside surfaces  64  and the inside surfaces  65  of the parallely aligned cores are in coplanar alignment and run parallel with the outside surface  67  and the inside surface  68  of each containing wall, respectively. The spacing between the last core in the alignment and the inner or outer wall surface (e) is about one-half that of the spacing (d) separating the cores. As noted above, the cores are suspended in the pouring form and concrete is poured about the voids to completely encapsulate each core creating a Styrofoam block within the precast structure. 
     As illustrated in FIG. 5, the bottom surfaces  69  of the cores in each side wall alignment contained within the two side walls terminate a height (h) above the distal end face  59  of each side wall. Accordingly, this lower region, as well as the upper region of each side wall, is completely filled with concrete and thus forms top and bottom headers to which the concrete beams  80  running upwardly along the cores are integrally joined at the time of casting. As can be seen, the beams act as support columns in the final structure. As clearly illustrated in FIG. 4, the concrete beams in the side walls are placed in coplanar alignment with the beams  14  of the bridge span to uniformly distribute the load along the beams and translate induced loads efficiently to the footings. 
     Similarly, the opposed end sections relating to the deck wall are completely filled with concrete to again create end headers in the deck wall to which the horizontal beams running along the cores are also integrally joined. In this case, the elongated beams act as joists in the deck wall. The concrete columns and joist act in the same manner as similar structural elements found in wooden or steel structures to provide the required strength while considerably reducing the weight of the structure. 
     Reinforcing bars  70  are contained in each of the walls with the bars extending across the length and width of the containing wall. The bars are laid down to form a square pattern grid  71  and are tied together in a manner that is well known in the art. The grids are positioned in assembly on either side of the core alignment adjacent to the inside and outside wall surfaces  67  and  68  as shown in FIGS. 5 and 6. The grids in the sidewalls are cojoined with those in the deck wall in each corner region  75 . 
     While the present invention has been particularly shown and described with reference to the preferred mode as illustrated in the drawing, it will be understood by one skilled in the art that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.