DESCRIPTION OF PREFERRED EMBODIMENTS

[0007] This invention is an innovative system of short- and medium-spans for bridges and other structures. The new system can apply to hundreds of bridges constructed every year. In this system, the superstructure is built mainly from materials that are not vulnerable to corrosion. Additional advantages are reduced self-weight of the structure and enhanced durability. The light weight should reduce load on the supports and allow for longer spans, resulting in reduction in the size of substructure and in the number of supporting piers in multi-span bridges and, hence, reduction in the initial cost. The improved durability should reduce the maintenance cost and extend the life span of the structure.

[0008] FIGS. 1, 2 and 3 show two versions of a corrosion-free bridge system according to a preferred embodiment of the present invention. The invention consists of precast prestressed concrete truss girders (generally indicated by the reference numeral 10) and a concrete deck slab 30. Each girder 10 has top and bottom concrete bulbs (i.e. flanges) 12, 14 connected by precast vertical and diagonal truss members 16, 18. In addition to concrete, the materials used are fibre-reinforced polymers (FRP) and corrosion-resistant steel. The term corrosion-resistant steel or metal means a product that has delayed corrosion properties.

[0009] The materials used in the present invention will now be descibed in some greater detail. Referring first to the bridge deck 30, particular attention is given to the bridge deck as it represents an important component that considerably affects the overall cost and quality of the structure.

[0010] The bridge deck can be made of a cast-in-situ reinforced concrete slab 30a (as illustrated in FIG. 2) or of an assembly of precast concrete panels 30b tied together by longitudinal with or without transverse prestressing tendons 32, 33 (FIG. 3).

[0011] Reinforcement of a cast-in-situ deck slab 30a (FIG. 2) can be glass, carbon or other FRP bars 34. Alternatively, the FRP bars can be used in both the transverse and longitudinal directions for the top reinforcement, whereas the bottom reinforcement can be composed of corrosion-resistant steel bars 36 in the transverse direction and FRP bars in the longitudinal direction.

[0012] Post-tensioning of precast deck slab panels 30b (FIG. 3) can be done by FRP or corrosion-resistant steel tendons 32, 33.

[0013] Corrosion-resistant steel double-head studs 38 (i.e. steel bars with heads for anchorage) will be used to connect the deck slab to the girders. When precast deck panels 30b are used, pockets are left in the panels at the location of the studs to be filled with grout subsequent to post-tensioning.

[0014] Specific attention will now be given to the various features of the bridge girders 10.

[0015] The concrete bulbs 12, 14 are pretensioned with FRP or corrosion-resistant steel tendons 16. The bulbs are provided with corrosion-resistant steel stirrups 18 and with longitudinal non-prestressed FRP or corrosion-resistant steel bars 20 at the corners of the stirrup.

[0016] The vertical and diagonal truss members 16, 18, for resisting shear forces are made of FRP or corrosion-resistant steel tubes filled with high-strength concrete. The truss members can alternatively be made of precast concrete elements, thus eliminating the need for hollow tubes. In this case, corrosion-resistant steel stirrups or spirals may be provided. A preferred outer diameter of the verticals 16, which are mainly in compression, is approximately 150 mm, although other sizes may be suitable as well. The diagonals 18, which are mainly in tension, have an outer diameter of approximately 90 mm, although other sizes may also be suitable depending on the application. Both the verticals and the diagonals are produced prior to the bulbs 12, 14. FRP or corrosion-resistant steel dowels 22 protrude from the ends of the verticals to connect them to the bulbs. Double-head studs 24 connect the diagonals to the bulbs. Alternatively, the diagonals can be pretensioned with FRP flexible tendons or corrosion-resistant steel tendons. The pretensioning should provide the diagonals with a reserve tensile capacity in case the FRP tubes are damaged by fire. The tendons protrude from the ends of the diagonals and are bent to serve as dowels connecting the diagonals to the bulbs. For ease in production, it is preferable that the bulbs be cast in a rotated position, while the verticals and diagonals lie on a horizontal surface. In case of damage by fire, the FRP tubes can be easily replaced by wrapping the concrete diagonals and verticals by FRP sheets or jackets.

[0017] After casting the concrete slab 30a or placing the deck panels 30b, the precast truss girders 10 are post-tensioned by external FRP or corrosion-resistant steel tendons to balance the slab weight, to provide continuity between the different spans, and to resist subsequent loads on the bridge. The external tendons are harped (i.e. held down) to the bottom bulb 14 at two points within the span and held up to the top bulb 12 at one or two points near the intermediate supports in continuous bridges. No deviators will be required at the harping points. The horizontal parts of the tendons between the harping points pass through ducts placed inside the bottom bulb, for a single-span bridge, or inside both the top and bottom bulbs in a continuous bridge. The ducts may be left ungrouted for easy replacement of the tendons, or may be grouted to achieve bond between the horizontal parts of the tendons and the concrete bulb(s).

[0018] The above description is intended in an illustrative rather than a restrictive sense and variations to the specific configurations described may be apparent to skilled persons in adapting the present invention to specific applications. Such variations are intended to form part of the present invention insofar as they are within the spirit and scope of the claims below. For instance, the system of the present invention may be applied to curved bridges and may be easily adapted to space trusses and segmental construction for use in bridges and other structures.