Static structures (e.g. – buildings) – Relatively yieldable preformed separator
Reexamination Certificate
2000-09-11
2002-09-17
Stephan, Beth A. (Department: 3635)
Static structures (e.g., buildings)
Relatively yieldable preformed separator
C052S251000, C052S252000, C052S259000, C052S434000, C052S402000, C052S459000, C052S321000, C052S322000, C052S332000, C052S335000
Reexamination Certificate
active
06449914
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to concrete panels for use in making concrete decks or floors for spanning between structural supports; and more particularly to resilient grout seals for precast concrete panels and beams used in constructing reinforced concrete decks for bridges supported by structural beams, and methods for fabricating concrete panels, decks, and support beams having grout seals.
2. Brief Description of the Prior Art
The construction of reinforced concrete decks and floors (e.g. on bridges and in buildings) has always been the most labor intensive and most costly component of the superstructure involved, and has been the component that controls the overall rate of progress of the construction. The need for temporary support of the reinforcing steel and freshly poured concrete until the concrete has attained sufficient strength to support itself is a major factor in the cost of such construction. The length of time such support must remain in place to allow the concrete to attain sufficient strength is the major factor in controlling the rate of progress of the structure.
The original method to provide the temporary support was to use a basic wood form made up of boards or plywood sheeting nailed to wood joist members, carried on wood timbers or steel beams, which in turn were supported on posts or columns from the ground or lower completed floor. This method is still used today with the development of a variety of complex high capacity column scaffolding systems and beam members that are adjustable for both span length and camber. Other developments in the use of the basic wood form include hanger systems that provide for hanging the form from the beam members of the permanent structure, thereby eliminating the need of posts or columns from below. Another development involved trussed framing systems that provided for the support of large areas of form on a very few bearing supports, and for the removal and re-setting of such large areas as a single unit.
The cost of using basic wood forms would be prohibitive if they were used just once, but they are normally not consumed or destroyed in a single use and are in fact in normal practice re-used several times before wear and tear makes them unfit for further re-use. The greater the number of re-uses of the forms, the more economical they become. Economics therefore dictates that the effort on any given project is to provide the minimum quantity of form that will permit reasonable progress to be achieved on the project, thereby gaining the greatest number of re-uses, even though availability of a greater quantity of forms would provide for a faster rate of progress.
The setting of wood forms preparatory to the placement of reinforcing steel and concrete is a labor intensive task by itself, but removing wood forms after the concrete has attained sufficient strength, usually requiring extensive scaffolding, requires a greater amount of costly labor and equipment. Moving to the location of its next use and the clean up and preparation for re-use of the form adds more labor and equipment cost.
The high labor and equipment costs, and the limitation of progress inherent in the use of wood forms, has encouraged development of alternative methods of providing support for deck and floor construction. The development of methods using materials that are durable, yet economical enough to be used once and then left in place, are gaining in favor. Some methods provide temporary support only and after the concrete has gained its strength are simply left in place. Light gage galvanized corrugated sheet steel panels supported directly by the permanent structure beams id the most popular of these methods.
Some methods provide temporary support but in addition become an integral permanent working part of the structure when the concrete gains its strength. Heavy gage corrugated sheet steel panels, supported directly by the permanent structure beams, with loop shear connectors connected (e.g. by welding) to the panels and then embedded in the concrete to make the panels and the cured concrete work as a composite unit is one example of this method. The most recent development in this area is the precast pre-stressed concrete panel supported directly by the permanent structure beams, and again the panels and the cast-in-place concrete work as a composite unit. The panels replace the wood forms and serve both as a form and as an integral part of the structure. A desired amount of concrete is poured onto the already-formed and already-hardened panel.
In becoming a permanent composite component of the structure, the panels replace structural materials that would otherwise have to be provided in the design of the structure. In the case of the sheet steel panels, part of the reinforcing steel is replaced by the panel. In the case of the pre-stressed panel, a substantial part of the reinforcing steel and of the concrete is replaced by the panel.
In exposed structures such as bridges, the concrete panels are popular with engineers and architects because they blend in with the appearance of the structure and provide the most natural look. Another important reason is that they are not subject to corrosion that might diminish the appearance at some later date, or even become a hazard by falling from the structure as sheet steel might do.
The currently popular design of pre-stressed concrete panels leaves serious and costly problems in the construction technique. To accomplish the composite relationship between the panel and the cast-in-place concrete, the first requirement is that the panel have a continuous rigid bearing contact with the top of the supporting beam along its ends. Since neither the top of the beam or the bottom of the panel can be depended upon to be perfectly flat, an intervening material, normally concrete or cement grout, that can be installed in a plastic state so it will conform to both surfaces and then harden in that shape is required. General practice (see
FIG. 1
) is to place a narrow strip of fiberboard along the edges of the top flange of the supporting beam, to set the concrete panel thereon so the panel overhangs the fiberboard strip over the beam, and then to either force the intervening material in its plastic state under the overhanging part of the panel, or wait until the cast-in-place concrete is poured and at that time force the concrete mix being used to flow under the overhanging part of the panel. The fiberboard is of sufficient thickness to allow for the intervening material to be forced under the overhanging part of the panel, and it prevents the plastic material from flowing over the edge of the beam.
To provide for the deflection of the beams and the design cambers that are required to provide the desired finished grade, the designer and/or the constructor is left with three undesirable options in the use of this method. The thickness of the fiberboard material (or other filler or sealing material) can be varied to compensate for deflection and camber which allows the thickness of the slab to remain constant; the thickness of the slab can be varied to provide the desired top surface grade while the bottom surface follows the deflection and camber of the beam; or the top surface of the beam can be re-graded to provide for deflection and camber with a cast-in-place concrete overlay prior to the placement of the fiberboard strips.
If the thickness of the fiberboard strip is varied, (see
FIG. 1
) measurement and placement of the strips according to a pre-calculated layout must be done by workmen working on top of the bare beams before the panels can be placed. This is slow and dangerous work, and completed work can easily be knocked or blown off of the beam, and at best the amount of variation that can be accomplished is very limited because excessive thickness of the fiberboard becomes unstable.
Methods of using concrete bricks under the panels along with galvanized sheet steel angles (see
FIG. 3
) to close the opening between the panel and the top
Bernard Ken
Horstketter Eugene A.
Smith Nat
Chavez Patrick J.
Horstketter Eugene A.
Roddy Kenneth A.
Stephan Beth A.
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