This invention relates to a chair for supporting rebar during a concrete pour.
Concrete is poured in many different situations for many different purposes. In many concrete pours, metal reinforcements known as rebar are used to increase the strength of the cured concrete. By itself, concrete is impressively strong in compression but surprisingly weak in tension. Including metal rebar in concrete increases tensile strength substantially thereby allowing concrete to be used in many situations.
The most common concrete pour is a foundation for residential homes, apartments and commercial buildings. Concrete is poured into a perimeter trench and one or more interior intersecting trenches and onto a horizontal rebar grid overlapping the trenches. In the horizontal section, lengths of rebar are laid in intersecting perpendicular rows that are typically tied together. Rebar is supported off the underlying ground surface by what the industry calls chairs. The purpose of chairs is to support the rebar at an elevation that falls inside the thickness of the concrete and is not too close to the top or bottom. In the perimeter and interior trenches, chairs are also used to elevate an assembly of vertical rebar from the bottom of the trench. The pour may be made onto the underlying ground surface or may be made onto a plastic sheet suitable for this purpose.
A second type common concrete pour is for a tilt wall where concrete is poured onto a horizontal mold resting on the underlying concrete foundation of a building. After the concrete cures, the mold is removed and the wall tilted to a vertical position and secured to the foundation. Suitable joists or beams connect the vertical walls and provide a support for the building roof. One peculiarity of tilt wall type pours is that chairs leave marks on the underside of the wall and thus leave a mark on either the inside or the outside of the cured or finished wall.
Although the most commonly used rebar chair is a piece of brick, the prior art is replete with many different styles and types of more sophisticated chairs. Typical disclosures are found in U.S. Pat. Nos. 3,387,423; 4,060,954; 4,498,270; 4,831,803; 5,014,485; 6,089,522; 6,732,484 and 8,099,925; United States Printed Patent Applications 2010/0146889 and 2012/0011799 and U.S. Design Pat. Nos. D354,218; D548,055; D548,056 and D706,608.
The chair of this invention is provided to support rebar in a variety of situations involving a horizontal foundation or ground pour or a tilt wall pour and is thus a more universal device. In one embodiment, a chair provides configurations for a foundation pour where the rebar can be supported at three different elevations and provides configurations for a tilt wall pour where the rebar can also be supported at three different elevations.
In one embodiment, the chair is preferably a rectangular box like shape having a long dimension, a width dimension and a height dimension, all of which may be different to provide different heights for the plane of rebar supported by the chair. Interior braces prevent the box from distorting due to the load of concrete. In some embodiments, chairs may be stacked to increase the rebar height over what is available from use of only one chair. In some embodiments, feet or rails are provided to be positioned down in tilt wall pours and up in ground pours. The feet or rails, when down, desirably leave a very small mark on the cured wall.
The chair 10 is of generally rectangular shape providing a length dimension which is its longest dimension, a height dimension and a width dimension, all of which are of different distance or linear extent to provide different rebar elevations from an underlying surface. Because the height and width dimensions depend on which side is up, this terminology is used as an example for descriptive purposes. Because the chair 10 may be used in any orientation, the terms top and bottom are arbitrary as are upwardly and downwardly.
Referring to
One or more braces or struts 22, 24 extend between opposite walls and act to prevent or minimize distorting of the walls 14, 16, 18, 20 reacting against wet concrete poured into the chair 10. The walls 14, 16 may preferably include coplanar sections 26, 26 interrupted by a V-shaped section or notch 30, 32 of sufficient depth to hold and support a reinforcing element or rebar 34 when the appropriate end wall is horizontal. The side walls 18, 20 may preferably include coplanar sections 36, 38 interrupted by a V-shaped section or notch 40, 42 of sufficient depth to hold and support rebar 34 when the rim 12 is oriented appropriately. The braces 22, 24 may intersect at the apex of the notch V to more effectively transmit loads between the walls 14, 16, 18, 20 and the braces 22, 24.
As more fully apparent hereinafter, the walls 14, 16, 18, 20 are basically flat providing a large surface area in contact with the underlying surface thereby promoting stability in a foundation pour mode.
The angle 44 of the notches 30, 32, 40, 42 is subject to wide variation and may be different but the angles 44 may typically all be the same and may be between 80-170° or more preferably between 120-160°, as discussed more fully hereinafter in conjunction with
The top 46 and the bottom 48 of the chair 10 may preferably be open as shown by a comparison of
The end and side walls 14, 16, 18, 20 are connected by corner structures 50 which are illustrated as being columnar or circular in cross-section although many other suitable shapes exist. One advantage of the corner structures 50 is to reinforce the joint between the end walls 12, 14 and the side walls 16, 18. Concrete flowing through the chair 10 is dynamic and unpredictable, meaning that forces can be applied to spread the joint or flatten it. One advantage of the corner structures 50 is to act as gussets to strengthen or stabilize the corner joints.
The corner structures 50 may each include a socket 52 on the top each corner and a pin, peg or foot 54 projecting from the bottom of each corner. The feet 54 may be tapered slightly to fit easily in the sockets 52 so the chairs 10 can be stacked to increase the height of rebar 34 in the stacked configuration. The height of the rebar 34 may accordingly be multiples of the height dimension of the chair 10.
The feet 54 have another important advantage in the tilt wall pour configuration in which the feet 54 are down against a slick plastic sheet on the underlying surface. When concrete is poured into the wall mold, the feet 54 support the rebar 34 from the sheet but there is an area under the feet 54 where no concrete can reach. This leaves a mark on the tilt wall which must be covered later, as with stucco, plaster, filler or the like. The feet 54 taper to a smooth generally hemispherical point 56 to minimize the mark of the chair 10 on the cured tilt wall.
The chair 10 also includes a first set of spaced rails or feet 58 extending away from only one of the side walls 18, 20 and a second set of spaced rails or feet 60 extending away from only one of the end walls 14, 16. In the illustrated embodiment, the rails 58 are on the side wall 18 and the rails 60 are on the end wall 14. The rails 58, 60 have one of the same advantages as the feet 54, i.e. in a tilt wall pour, the mark of the chair 10 on the cured wall is minimized. The rails 58, 60 may accordingly be a more-or-less continuous support terminating in a more-or-less hemispherical smooth edge 62, 64. When the chairs 10 are placed in a tilt wall mold on a slick plastic sheet with the rails 58 down, rebar 34 may be placed in the notch 42. When concrete is poured and cured, the only mark on the cured tilt wall is left by a trace of the edges 62. This mark on the tilt wall may be covered, as with stucco, plaster, filler or the like and is much smaller than if the entire side wall or end wall were supported on the underlying surface. This clearly makes the cosmetic clean up simpler, easier and less time consuming thereby reducing costs. The feet 58, 60 are conveniently attached to the side wall 18 and end wall 14. In the alternative, the feet 60 may simply span the distance between the adjacent side walls 18, 20, leaving an end of the rim 12 open but this eliminates use of this side as a rebar support.
An advantage of the feet 58, 60 is leaving a very small mark on the cured wall in a tilt wall type pour. The size of this mark may be compared to the area of the flat spots on the wall opposite the feet or on the area of the opposite wall. The mark may be no more than 40% of the size of the flat part of the opposite wall, may preferably be less than 12% of the size of the flat part of the opposite wall and may ideally be less than 6%. It will be apparent this reduces the cost of cosmetically repairing a cured wall in a tilt pour.
If the side walls 18, 20 or end walls 14, 16 were adjacent the underlying mold surface, a mark would be left on the cured wall of the size of the flat sections 36, 38, 26, 28. In one size prototype, measuring 2½″ wide×3″ high×4″ long, the flat sections 36, 38 on the side walls are approximately 7 square inches and the flat sections on the end walls are about 5 square inches. In this prototype, the rails 58 are about 4″ long and have a bearing surface against the mold of about 0.04″, meaning the mark left by the prototype is about 4″×2 rails×0.04″−0.32 square inches. Thus, the size of the mark on the cured tilt wall is about 0.32/7 or about 5% of the area of the flat sections 36 of the side wall 18. In the case of the end walls 16, the bearing area of the feet 60 is about 3″×2×0.04″ or about 0.24 square inches. Thus, the size of the mark on the cured tilt wall is about 0.24/5 or about 5% of the area of the flat sections 28 of the end wall 16 or less when compared to the area of the end wall 16.
The size of the mark compared to the area of the flat spots is affected by the width of the notch in the wall and is thus more variable than the area of the adjoining wall. The size of the mark may be below 35% of the area of the adjoining wall and may preferably be below 10% and may ideally be below 5%. In the case of one embodiment measuring 2½ inches high, 3 inches wide and 4″ long, the feet on the side wall 18 have a mark of 0.32 square inches which is 0.32/12 which is about 3% and the feet on the end wall 14 leave a mark of about 0.24 square inches which is 0.24/7.5 also about 3%.
The side walls 18, 20 include opposite edges 66, 68 which incline to provide a notch 70, 72 for supporting a rebar 34 when the feet 54 are up or down. The angle 74 of the notches 70, 72 may be of the same order of magnitude as the angle 44. The end walls 14, 16 also include opposite edges 76, 78 which incline to provide a notch 80, 82 for supporting rebar 34 when the feet 60 point up or down. The angle 84 of the notches 80, 82 may be of the same order of magnitude as the angles 44, 74.
In a tilt wall pour, there are several rebar heights available by use of the chairs 10. With the feet 54 down as shown in
In a foundation pour mode, there are several rebar heights available by use of the chair 10. With the side wall 20 down, the height of the rebar 34 will be basically the width D of a side wall 16 as may be envisioned from
Although the exact dimensions of the height, width and length of the chair 10 is subject to wide variation, one suitable embodiment is 2½ inches high plus the feet 54 measuring three eighths inch, 3″ wide and 4″ long. In this version, the following rebar heights are achieved:
These distances assume the size of the rebar exactly offsets the depth of the notch. In other situations, an adjustment needs to be made for the size of the rebar and the inclination of the notch, all as discussed in conjunction with
The chair 10 is of a configuration that can be manufactured by injection molding of conventional polymers and is thus susceptible of low cost production.
It will be apparent that the embodiment of
In some embodiments, the width and height of the rim 12 are reasonably close together and do not provide substantially different elevations of the rebar plane. In these situations, an acceptable device may be made with only two different elevations as shown by a chair 106 in
Although this invention has been disclosed and described in its preferred forms with a certain degree of particularity, it is understood that the present disclosure of the preferred forms is only by way of example and that numerous changes in the details of operation and in the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention.
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Number | Date | Country | |
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20200291596 A1 | Sep 2020 | US |
Number | Date | Country | |
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62819520 | Mar 2019 | US |