Static structures (e.g. – buildings) – With component having discrete prestressing means – Slab or panel construction
Reexamination Certificate
1999-08-20
2003-07-08
Mai, Lanna (Department: 3637)
Static structures (e.g., buildings)
With component having discrete prestressing means
Slab or panel construction
C052S223140, C052S584100, C014S073000, C014S073100, C014S077100, C404S056000
Reexamination Certificate
active
06588160
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to pre-cast concrete and steel composite structural members, such as used in modular bridge structures, and more particularly, to modular composite structural members which use a pre-compression assembly for the joint during construction, refurbishing and/or widening.
2. Description of the Prior Art
Large structures, such as bridges are well known and are obviously time-consuming to build or widen and even more time-consuming to rehabilitate. Typically, a bridge structure will have longitudinally extending girders with a concrete deck surface. The concrete deck is made composite with the girders by pouring the concrete in place around shear connectors connected to the girders. The structure may be formed upside down and then inverted to place it in its final operating position. This latter specialized technique is disclosed in U.S. Pat. Nos. 4,493,177, 4,646,493, 4,700,516, 5,144,710, 5,301,483, 5,305,575 and 5,553,439, copies of which are incorporated herein by reference.
To form such composite members of the type having an upper concrete surface and a metal support underneath, a mold typically is utilized. First, the steel supports, such as girders or beams, are placed beneath a mold assembly having two or more mold pieces disposed around and supported by the supports. Next, the concrete is poured into the mold such that the concrete fills the mold and extends over the girders or beams. When the concrete is hardened, the mold pieces are disassembled from around the supports such that the concrete rests on the supports. In most instances, these types of structural members are formed in place. This is usually advantageous so the concrete deck surface can better fit into the finished structure. The concrete deck portion is attached to the beams by shear connectors which are molded into the concrete, or which extend into openings in the concrete, which are then grouted in place. This technique works satisfactorily in many cases, particularly in original bridge construction where the area of construction is readily accessible.
When separate prefabricated composite units are used, the sections are positioned adjacent to one another, and the metal support members in those sections, such as girders or beams, are then positioned on the piers or abutments. This technique is particularly useful when it is not feasible to form the entire structure in place or when the use of prefabricated members can save construction time on site. It also works well in bridge widening projects where prefabricated members are installed next to the existing structure.
Certain construction constraints, such as those in which a bridge structure is being repaired or otherwise refurbished or rehabilitated, make many prior art methods of construction more expensive and result in associated problems, such as traffic delays. In repair or refurbishing, typically the old concrete deck, or at least a part of it, is removed, and another deck must be put in its place. If the replacement deck must be poured in place, molds must be set up, the concrete poured, and then the concrete allowed time to cure before a bridge structure can be reopened to traffic. In high-density traffic areas, this creates considerable traffic tie-up problems, which result in significant lost time and inconvenience to commuters and other travelers.
The use of prefabricated composite units which can be set in place, such as those described above, greatly reduces the repair time involved. That is, the old structure may be removed, and the new structure simply set in place on the piers or abutments and attached to them. Because of the prefabrication, the time necessary to construct molds, pour concrete and allow the concrete to cure all can occur prior to the placement of the composite units. Thus, the“down time” to repair the bridge structure is greatly reduced, which lowers costs and pleases motorists. However, this technique creates longitudinal and transverse joints that need to be filled and which become potential pathways for water and salt-laden water to fall objectionably on other parts of the structure.
The present invention all but eliminates this objectionable leakage without adding construction time to a constrained time window, such as occurs in overnight construction, because the modular units can carry traffic before they are permanently clamped together. In the present invention, prefabricated composite units are still positioned adjacent to one another, but are also pulled and clamped together by a pre-compression assembly which holds all of the units together in place. The structure can make use of match-casting the abutting faces so the usual ¾ to ½ inch wide gap is narrowed. The joint may be filled with an adhesive applied to the abutting faces of the joint before they are pulled together. Whether used with match-cast, abutting faces or a conventional, hardened, grout-filled joint, pre-compressing the joint has the advantage of creating an extremely water-tight joint and, at the same time, supplementing the tensile resistance of the joint adhesive with pre-compressive stresses. In the event that tensile stresses are produced in the joint that exceed the pre-compression combined with the tensile strength of the joint adhesive, the size of the formed crack is limited to less than about 0.001 inches by the pre-stressed steel immediately beneath the joint.
One conventional approach to pre-compressing bridge structures is to install conduit in the deck portions thereof which is accomplished by positioning the conduit and pouring the moldable material around it. Steel cables are installed in these conduits after the bridge structure is erected and compression applied to the structure in a transverse direction by post-tensioning the steel cables. This process has several problems, one of which is the difficulty of aligning the conduits during the erection of the bridge structure. Further, there is a potential for damaging both the cable and its protective coating when the cable is pulled through misaligned conduits. Additionally, any such damage and consequent future deterioration is not visible which can lead to unexpected and sudden failure. In the present invention, any future deterioration of the pre-compression components is readily visible and much more easily corrected than with hidden and buried cable.
SUMMARY OF THE INVENTION
The present invention is a composite structural member, such as used in bridge construction. The member generally comprises a plurality of composite units, each unit itself comprising a plurality of longitudinally extending girders or floor beams disposed on bridge supports and a deck portion made of a moldable material and attached to the beams. The member further comprises pre-compression means for clamping adjacent units together such that a gap between the facing deck portions thereof is substantially closed and a joint formed therebetween is pre-compressed. The joint may be filled with a hardened high-strength grout.
In one preferred embodiment, one of the first and second transversely facing sides of at least one of the deck portions of the units defines a groove therein, and the other of the first and second transversely facing sides of at least one of the deck portions has a tongue portion thereon adapted for extending into the groove of an adjacent, facing deck portion such that upper surfaces of the adjacent deck portions are held substantially aligned and positioned coplanar. An adhesive may be disposed in the gap between the deck portions and in the groove.
Facing beams of adjacent units define holes therein which are substantially aligned, and the pre-compression means comprises a threaded member disposed through the holes on the facing beams and fastener means threadingly attached to the threaded member when tightened on the threaded member. In one embodiment, the threaded member is a bolt extending through one of the holes in one of the facing beams and one of the holes in the other of
Dorsey Dennis L.
Mai Lanna
McAfee & Taft
LandOfFree
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