Method to Compress Prefabricated Deck Units By Tensioning Supporting Girders |
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申请号 | US12963233 | 申请日 | 2010-12-08 | 公开(公告)号 | US20110138549A1 | 公开(公告)日 | 2011-06-16 |
申请人 | Yidong He; | 发明人 | Yidong He; | ||||
摘要 | A structural system comprised of prefabricated deck units spaced along longitudinal load-carrying members, which produce longitudinal axial compression in deck units by tensioning the longitudinal load-carrying members without the use of standard post-tensioning details. During construction, prefabricated deck units are erected on top of and supported by the longitudinal load-carrying members via leveling devices, which also permit relative motion between the longitudinal load-carrying members and the prefabricated deck units. Jacking apparatuses are used to introduce deck compression by jacking against the longitudinal load-carrying members. This system can be used for new structures and for deck replacement of existing structures. | ||||||
权利要求 | I claim: |
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说明书全文 | This application claims the benefit of U.S. Provisional Application No. 61/285,507, filed Dec. 10, 2009 by the present inventor. Not Applicable Not Applicable 1. Field of Invention This invention relates to the design and construction of structures, specifically to structures with prefabricated deck units. 2. Prior Art Full-depth precast concrete deck has gained popularity as an accelerated construction method. Use of full-depth precast concrete deck allows for the deck concrete and reinforcement to be placed in a controlled environment, improving the quality of the deck. Since the units are prefabricated, they can be delivered to a site and erected quickly. Structures using full-depth precast concrete deck typically consist of a plurality of longitudinally spaced concrete deck units supported by longitudinal load-carrying members. This member or members is usually a single girder or multiple girders. This member or members can be comprised of various materials including steel, concrete, wood or fiber-reinforced plastic. To improve deck durability, it is important to have a pre-compression force across deck joints to minimize the propensity of the deck to crack under loading. Currently, such pre-compression force is supplied via standard post-tensioning systems, which utilize post-tensioning tendons or bars within ducts. US Federal Highway Administration technical report (#FHWA-IF-09-010) provides a comprehensive summary of current engineering practice using precast deck units, showing that all current precast deck systems with longitudinal compression utilize post-tensioning systems in the deck. Other patent references, such as U.S. Pat. No. 7,475,446, U.S. Pat. No. 7,461,427, and U.S. Pat. No. 5,457,839, illustrate various methods of using post-tensioning system to provide deck compression. However, using standard post-tensioning details carries with it the disadvantage of requiring additional cost and time to construct. This invention provides a more economical solution. The pre-compression force across deck joint is produced not by post-tensioning tendons but by tensioning the supporting girders themselves. Accordingly, several objects and advantages of the present invention are to provide a structural system that: a. facilitates rapid construction of a structure consisting of prefabricated deck units, wherein increasingly tight construction schedules and/or site constraints can be accommodated; b. provides pre-compression across joints between deck units to improve deck durability by tensioning the bridge girder; c. typically increases the overall load resistance of the structure by tensioning the girder, whereby significantly reducing the amount of material required in the girders; d. eliminates the need for standard post-tensioning details, whereby reducing the cost and time of construction. Further objects and advantages will become apparent from a consideration of the ensuing description and drawings. In accordance with the present invention a structural construction system comprises prefabricated deck units spaced along longitudinal load-carrying members. Axial compression of these prefabricated deck units is produced by various means to react against the longitudinal load-carrying members.
A preferred embodiment of the bridge construction system of the present invention is illustrated in However, those features comprising the structural construction system mentioned in the preferred embodiment and the substructure and span arrangement mentioned above can have various embodiments not mentioned in the preferred embodiment, as discussed in detail hereinafter and as will become apparent from a consideration of the ensuing description and drawings. Steel girders 11 are placed on and supported by abutments 12 and pier 13. Steel girders 11 are of fabricated plate girders, but may be of any suitable structural shape, such as tub girders, rolled beams, trusses, etc. On top of girders 11, a plurality of leveling devices is placed that also allows for relative longitudinal motion between girders 11 and the precast concrete deck units 18. In the preferred embodiment, the leveling devices are comprised of shims, however leveling bolts or other devices that can provide support for the deck and allow for relative longitudinal motion between girders 11 and the precast concrete deck units 18 can be used. As will be evident from the description hereinafter, this allowance for relative motion will allow for the precast concrete deck units to be compressed by reacting to the tensioning of girders 11. Shims may be of steel, plastic, elastomeric materials, teflon-based or teflon-impregnated materials, etc. A plurality of voids 28, similar to those used in conventional precast deck placement, are provided in deck units 18 above girders 11 to allow for mechanical connection of deck units 18 to girders 11 while shear connectors voids 28 are grouted. Haunches 30 will also be grouted at the same time as the shear connector voids 28. Shear connectors shall be detailed to allow relative motion between precast concrete deck units 18 and girders 11 during the precast concrete deck unit erection process, as hereinafter described. In the preferred embodiment, shear connectors are shear studs 26 welded to the girders 11. Joints 20 between adjacent precast concrete deck units can be of the match-cast type, with or without epoxy, or cast-in-place using concrete, grout or other suitable jointing materials. In the preferred embodiment, match-cast epoxy joints are used. In the preferred embodiment, jacking frames 31 are connected to the girder at both ends of the bridge, as shown in In the preferred embodiment, the girder connection at the pier location is simply supported for dead load and continuous for live load. This is achieved by making the girder bottom flange connection at pier after all dead loads are applied to the structure. Alternate embodiments for the present invention are described hereinafter:
The preferred embodiment in the context of the example bridge is illustrated hereinafter. Abutments 12 and pier 13 are constructed. Girders 11 are erected. The top flange connections at the median pier location between girder units are made. The bottom flange connection of girders at the median pier location is not be installed at this time. The girder top elevation is then surveyed and the shim thickness at each supporting point calculated so as to provide the correct setting elevations for deck units. Shims are placed on top of the girders. Jacking frames 31 are attached to the girder ends. Precast deck units 18 are erected, placing one unit adjacent to the previously erected one and applying epoxy to the adjacent faces of the two units. Means is employed to provide a certain amount of compression over the epoxy joint (typically at 40 psi, similar to segmental bridge construction) to ensure the joint is properly set. This process is repeated until all deck units 18 are installed. After all deck units are installed, jacks 32 are placed at the jacking frame 31 locations. Jacks are of types with lock nuts so that the jacking effect can be maintained for an extended period of time without relying on the associated hydraulic or pneumatic system. The jacking operations consist of the following steps:
After jacking operation, shear connector voids 28 and haunches of the deck connection units 30 are grouted. After grout reaches the design strength, jacks are released and removed. A secondary concrete pour will then be conducted to fill in the closure pour housing the jacks. The girder bottom flange connection at the median pier is then made at this time so that the girder connection at pier location can function as continuous under live load. The operational description above is particular to the preferred embodiment of the present invention in the context of the two-span bridge heretofore defined. Alternate materials, member shapes, connection types at the median piers, means of jacking, etc. can be used in employing the structural construction system of the present invention. The operational sequences described above are for methods using jacking frames similar to these shown in The present invention provides a structural system that eliminates many of the drawbacks found in current precast deck construction associated with standard longitudinal post-tensioning. Notably, it offers an alternate to provide pre-compression across joints of precast deck units without employment of post-tensioning tendons or bars and associated ducts. This significantly reduces the cost and time of construction required. Beyond simply providing a system that eliminates the drawbacks in current precast deck construction, the present invention can potentially increase the load carrying capacity of longitudinal load-carrying members by employing appropriate connection details at the median pier, and correct construction steps. In the preferred embodiment, the jacking introduces a negative moment at the midspan of the girders, which offsets part of the girder moment under service load. In conclusion, the present invention provides a structural construction system utilizing prefabricated deck units that is durable, easy to construct and cost-effective. The present invention can accommodate a variety of structural configurations and can be rapidly constructed. Although the description above contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. For example, as illustrated and described herein, the present invention can accommodate a variety of jacking methods and details, a variety of girder connection methods, and a variety of shapes and materials for longitudinal load-carrying members. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given. |