Reinforcement bar support
The proposed support is preferably constructed from high-compression concrete and may be custom-dimensioned according to project requirements. The support may have one or more bearing pads at one or more heights which may include one or more anchoring arms. The support may include a bore sized to accommodate a range of rebar sizes. A length of pre-cut angled rebar may be may be cast in place or may be secured within the bore by epoxy or other means at the time of manufacture or in the field. To maximize stability and overcome low soil-bearing capacity, the bottom surface area of the support is preferably larger than the bearing pad surface area. At least two opposing sides of the support include at a shear-key to anchor the support within the finished slab.
The present invention relates to improved technology in the field of reinforcement bar support structures used in concrete construction, and more particularly to an economical, precast, high-compression concrete support structure which has a size and overall configuration that is application-specific, which has a footprint that overcomes low soil-bearing capacity where the support is used directly adjacent grade, which eliminates the need for continuous runners on metal decking, which stably supports reinforcement material prior to placement of wet concrete during slab formation, which facilitates convenient tie wire attachment of reinforcement material with a minimum of effort, and which interlocks with the finished concrete slab.
BACKGROUND OF THE INVENTIONVarious structures are currently available for supporting reinforcement bar (rebar) prior to pouring concrete to form a slab. The support is needed to raise the rebar to a sufficient height to embed it properly within the resulting slab. One widely used conventional support structure is a “wire chair,” which typically consists of two or more metal legs, usually steel. Wire chairs may include only a few legs or may include multiple sets of legs with one or more bolsters extending between them. Bolstered wire chairs are generally more expensive than smaller chairs, but their narrow footprint makes them one of the only options currently available for use on corrugated metal decking such as that which typically underlays second or greater story slabs.
Because most wire chair legs are small diameter, they are prone to sink into subgrade when used directly adjacent grade, especially where expansive soil conditions exist, for example in low-lying areas. Although some wire chairs include feet or dowels which extend parallel to ground, the feet are usually so small that this added protection against sinkage is negligible. Sinking can cause the wire chairs to protrude from the resulting slab and wick moisture into the slab and to the rebar, which may lead to rust and/or structural weaknesses. As a result, most wire chairs require plates affixed to the legs to enlarge the footprint area. The cost of wire chairs increases based on size and quantity of additional foot plates necessary to avert sinkage. Even where the cost of plate-enhanced wire chairs may be feasible, the increased footprint area they may provide may still be insufficient to appreciably prevent sinkage. The spindly structure of wire chairs also makes them especially prone to inadvertent lateral displacement.
Another concern with wire chairs is their propensity to form rust. This may be especially problematic in finished overhead slabs where any rust that forms may be visible and may also come into contact with humidity or rainwater and cause damaging runoff (for example, to vehicles parked in cement parking garage structures). Consequently, wire chairs for use in overhead slabs generally require the added expense of plastic tips, epoxy, or some other protective coating to try to prevent rust with varying degrees of success.
Finally, the price of even the most simple conventionally available wire chairs can be quite high, which can significantly impact total cost of construction where large numbers of wire chairs are needed. In commercial building projects, it is not unusual to need as many as 30,000 wire chairs. Cost is greater where coated chairs are necessary. The cost may increase even further where bolstered chairs are needed for metal decking. Finally, in thicker concrete slabs with more than one layer of reinforcement, the number of chairs needed may easily double.
The high cost of wire chairs may lead builders to use shorter, less expensive chairs that fall shy of the 3-inch minimum height required by national building code. Cutting chair height could compromise the structural integrity of the finished slab since the height of the chairs directly affects placement of reinforcement within the slab.
Other conventional rebar supports include dobies, often available only in pallet quantities. In plainest form, a dobie is a 6-sided square or rectangular block around which tie wire must be wrapped to when securing supported rebar. Wire wrapping the circumference of the dobie requires displacing the dobie, which may be problematic where initial placement is important. Further, circumferential wrapping requires significant time and labor, more so in sizeable construction projects. Plain dobies also include no features for keeping rebar in position, which may increase time and labor required if repositioning is necessary prior to wiring the rebar in place. Limited availability may also negatively impact costs where odd or ongoing quantities are needed. Finally, because the plain dobie is smooth-sided, it does not integrate with the finished slab. Consequently, a sizeable cold joint is created, which may cause the dobie to shift or settle and could lead to structural weaknesses in the finished slab.
A second type of conventionally available dobie is essentially identical to the plain dobie except that it includes a set of tie wires with which to secure supported rebar. The tie wires are typically 16-gauge annealed wire, which easily forms rust with exposure to the elements and subsequently becomes brittle and prone to breakage. This is especially a concern where the dobie will not be used immediately and may be exposed to moisture in the interim between acquisition and usage, almost always the case in construction projects. Despite the high potential for breakage of tie wires, the wire dobie may be up to 70% more costly than the plain dobie. Further, where breakage occurs, time and labor is likely to be lost on circumferential wrapping just as with the plain dobie.
A third type of conventionally available dobie is a combination dobie. The combination dobie has an elongate rectangular shape that allows for use at one of two heights depending on whether it is positioned on a short side or a long side. Combination dobies include a channel for keeping supported rebar in position prior to wiring, usually along one long side and one short side. During use, at least three sides of the combination dobie will remain unintegrated with the finished slab, making it subject to the same cold joint problems described above. Moreover, time and labor is likely to be lost on circumferential wrapping just as with the plain dobie.
A fourth conventionally available dobie is a dowel dobie, similar to the combination dobie except that one of the two channels is replaced by a hole. The channel may be used to support a reinforcing mat at a lower height, or the hole may be fitted with rebar to elevate a reinforcing mat. Because a single channel (or alternatively the hole) will not sufficiently anchor the dowel dobie within the finished slab, settling and slab integrity are still concerns.
Another conventional structure for supporting rebar, yet one which is not generally approved by structural engineers or inspectors, is concrete brick, usually constructed from lower-strength (typically 1500 psi) concrete. National building standards require at least 3 inches between a reinforcing layer and grade, necessitating a minimum 3-inch support. Despite the fact that concrete bricks may not satisfy code, contractors often resort to using them because they may be cheap and, positioned with their largest surface area side adjacent soil, they may overcome low soil-bearing capacities better than currently available alternatives.
What is therefore needed is a structural support which is constructed of high-compression concrete, can stably support reinforcement materials during concrete slab formation, is designed to overcome low soil-bearing capacities, eliminates the need for bolstered chairs on metal decking, minimizes the possibility of rust in the finished slab, facilitates convenient tie wire attachment with minimum effort, securely integrates with the finished slab to minimize the possibility of settling and shifting, is pre-cast to satisfy code and construction specifications, yet is economical.
SUMMARY OF THE INVENTIONThe support of present invention is affordable, effective, and superior to conventionally available alternatives. The proposed support may be pre-cast to specification. The support is preferably constructed of high-compression concrete, typically exceeding 2,500 psi. The overall shape of the support may be, but is not limited to, any shaped base leading up to an upper surface and may be frusto-pyramidal with as little as three sides, to an infinite number of sides (of any shape) to approach a frusto-conical shape, as well as any other shape which lends itself to the present invention. The height of the support may vary based on the height of the slab, the relative height needed for the rebar reinforcing layer, or code requirements. The support may be cast with multi-level bearing pads where a single slab will include more than reinforcing layer. The width and length of the support may be varied according to structural engineering and code requirements of a given construction project.
The support may include one or more anchoring arms which may be sized according to the size of reinforcement material to be supported. The anchoring arms are preferably constructed from steel, including, but not limited to, plain, hot dipped galvanized, or stainless. Reinforcement material may be conveniently wired to one or both anchoring arms without displacing the support. The anchoring arms may be cast in place during manufacturing, and may preferably be situated a sufficient distance from the edges of the bearing pad surface to prevent the finished slab from cracking over the anchoring arms.
The support may include a blind bore which may be sized to accommodate a range of rebar sizes. Pre-cut angled rebar may be fixed in the bore at manufacture or in the field for supporting a reinforcing mat or post-tension cable at an elevated height. The rebar may be secured in the bore by epoxy or other effective means or may even be cast in place.
The base of the support is preferably larger than the bearing pad surface area to maximize stability, to overcome low soil-bearing capacity, and to broaden the variety of applications in which the support can be used effectively. The sides of the support are preferably sloped, with slope dependent upon both the height of the support and the dimensions of the bearing pad surface and base. Because the support is preferably constructed entirely of concrete with no metal projections which may form rust, the potential for exposed rust in a finished slab is virtually eliminated. The support may also be used successfully on corrugated metal decking as the base may be easily sized to span adjacent ridges or fit within the troughs between ridges.
The support may preferably include one or more shear-keys to help anchor the support in the finished slab. The shear-keys may be any of a variety of shapes, including, but not limited to, cylindrical, square, trapezoidal, pyramidal, angular, or other.
The invention, its configuration, construction, and operation will be best further described in the following detailed description, taken in conjunction with the accompanying drawings in which:
The description and operation of the invention will be best initiated with reference to
Support 51 may have a bearing pad surface 65 and a base surface indicated by hooked arrow 67. The area of base 67 may preferably be larger than that of bearing pad surface 65 to increase stability of support 51 and facilitate ease of use in a variety of applications. The larger area of base 67 is ideal where soil-bearing capacity is lessened by wet conditions such as those in low-lying areas or where underground water is a concern. Additionally, because base 67 may be customized to a given size, support 51 is optimal for use on metal decking, where corrugations make the use of conventional supports difficult because they may tilt if the base size is only slightly larger than a corrugation trough.
Bearing pad surface 65 may include a first anchoring arm 69 and possibly a second anchoring arm 71. Anchoring arms 69 and 71 may preferably be constructed from bent rods of any cross sectional shape which may preferably range from 3/32 to ⅜ inch in diameter, depending on the size of rebar to be supported and engineering specifications. Anchoring arms 69 and 71 may preferably be fabricated from steel, which may be, but is not limited to, plain, hot dipped galvanized, mill galvanized, or stainless. Anchoring arms 69 and 71 may preferably be cast in place in support 51 and positioned ¼ to ¾ inch from edges of bearing pad surface 65 to prevent the finished slab from cracking over anchoring arms 69 and 71.
First side 55 may include a first shear key 75 and third side 61 may include a second shear key 77. A third or fourth shear key may also be present. The overall shape of support 51 and opposing shear keys 75 and 77 help to anchor support 51 in place, potentially minimizing shifting and settling and the consequent potential for developed structural deficiencies in the finished slab.
Although support 51 is illustrated in
Also illustrated in
Based on the possible measurements for H1, W1, W2, L1 and L2, angle α may range from about 97° (at maximum H1 of 12 inches, minimum W1 and L1 of 1 inch, and minimum W2 and L2 of 4 inches) to about 170° (at minimum H1 of ¾ inch, maximum W1 and L1 of 4 inches, and maximum W2 and L2 of 12 inches). Similarly, angle β may range from about 10° to about 83°. Because support 51 is symmetrical, the possible ranges of angles δ and ε will be similar to those described for angles α and β.
Height H2 of anchoring arm 69 relative to bearing pad surface 65 may preferably be about ⅜ to about 1 inch. Depth D2 of anchoring arm 69 in support 51 may preferably be about ½ to about 2.5 inches.
D3 indicates the depth of bore 87 in support 85. To effectively support rebar 91, bore 87 may preferably be at least 2 inches deep. Further, for optimal structural integrity of support 85, there may be at least one inch between bottom of bore 87 and base 67. Consequently, H1 for support 85 may preferably be at least 3 inches to accommodate bore 87.
Diameter D4 of bore 87 and opening 89 may be sized to accommodate rebar from about ⅜ inch (#3 bar) to about 1 inch (#8 bar). Though
Height H3 may be determined by where the reinforcing mat is to be located within the finished slab. If necessary, height H4 may also be varied by vertically adjusting rebar 91 prior to securing it in bore 87.
Support 99 may include a blind rebar support bore 123 extending partially through support 99 and opening onto bearing pad surface 119 at opening 125. In addition to support bore 123, support 99 may include an anchoring arm 127 subject to specifications similar to those described for anchoring arms 69 and 71 of
Angle α in
Measurements H2, H3, H4, D2, D3 and D4 are all subject to specifications similar to those described for similar features in the previous figures. Anchoring arm 127 is subject to specifications similar to those described for anchoring arms 69 and 71 of
First side 151 may include a cylindrically-shaped first shear key 165 and third side 155 may include a cylindrically-shaped second shear key 167 adjacent lower bearing pad surface 149. An angled third shear key 171 may be defined by fifth side 161. Shear keys 165, 167, and 171 are not constrained by the shapes shown, but may be any shape which helps to anchor support 143 in a finished slab.
Support 143 may include a blind bore 173 opening onto upper bearing pad surface 147 at opening 175 and an anchoring arm 177 on lower bearing pad surface 149. The specifications for bore 173 and anchoring arm 177 are similar to those described for similar features of support 99 in
Width W1 of upper bearing pad surface 147 may range from about 1 to about 10 inches, and length L1 may range from about 1 to about 8 inches. Width W2 of base 163 may range from about 6 to about 12 inches and length L2 of base 163 may range from about 4 to about 10 inches. Width W3 of lower bearing pad surface 149 may range from about 1 to about 10 inches, and width L3 may range from about 1 to about 8 inches.
Angle α may range from about 101° (at maximum H1 of 12 inches, and minimum W1 and L1 of 1 inches, W2 of 6 inches, and L2 of 4 inches) to about 144° (at minimum H1 of ¾ inch and maximum W1 of 10 inches, L1 of 8 inches, W2 of 12 inches, and L2 of 10 inches). Angle β may range from about 79° to about 36°.
Although lower bearing pad surface 149 is shown with L3 equal to L2, L3 may be narrower than L2, for example if lower bearing pad surface 149 was tapered or if second and fourth sides 153 and 159 were indented along lower bearing pad surface 149. Conversely, L3 may be greater than L2 if second and fourth sides 153 and 159 were widened along lower bearing pad surface 149. Furthermore, although second and fourth sides 153 and 159 are shown as having a continuous slope from first side 151 to fifth side 161, their slope could conceivably change between upper bearing pad surface 147 and lower bearing pad surface 149. For example, second and fourth sides 153 and 159 may be angled farther inward toward lower bearing pad surface 149 or farther outward away from lower bearing pad surface 149.
For structural soundness, the angular shape of third shear key 171 may preferably be employed only where H5 is less than about 1.5 inches. The features of anchoring arm 177 are similar to the features of anchoring arms described in previous figures, including nailhead 179 and tip 181.
A description of the process used to form various embodiments of the support of the present invention is best initiated with reference to support 99, although the process may be used to form any of supports 51, 85, 99, or 143 in the previous
Continuing to use support 99 as an example, to achieve the proper height between anchoring arm 127 and bearing pad surface 119, groove 247 may preferably be from about ½ to about ¾ inch deep, the depth being sufficient to support the “nail” without an interference fit. Groove 247 may extend completely across bearing pad insert 231 to allow for custom length or placement of an anchoring arm. Groove 247 may preferably be from about ¼ to about ⅛ inch in diameter. Similarly, through bore 245 may preferably have a diameter from about ½ to about 1 inch to accommodate various rebar sizes.
Bearing pad insert 231 is shown with anchoring arm 127 inverted in support groove 247 and a dowel 251 inserted in through bore 245 to form rebar support bore 123. Dowel 251 may vary in height depending upon the desired depth of a given bore. A liner 253 may be seen adjacent side walls 221 and 227 and may preferably extend along all side walls of compartment 217. Liner 253 may preferably be constructed from material which will facilitate easy removal of a finished support from compartment 217, such as plastic, vinyl, or metal, for example. Further, liner 253 may be coated with a release agent prior to pouring support 99 to make the resulting support 99 easier to remove from form 215.
A first shear key insert 255 may preferably be installed adjacent or attached to liner 253 along first short side wall 221 and a second shear key insert 257 may preferably be installed adjacent or attached liner 253 along second short side wall 227. Shear key inserts 255 and 257 are illustrated as cylindrically-shaped but may be any shape, including trapezoidal, square, angled, or pyramidal, for example. Other shear key inserts may be added as necessary.
After approximately 4 to 6 hours, support 99 may be removed from compartment 217 by inverting form 215 and gently tapping to break any bonds between form 215 and concrete 263. Once support 99 is free of form 215, form 215 may be lifted away, leaving liner 253 in place to protect support 99 from vibration and movement as it continues to cure. Optimally, support 99 should be cured at least 24 hours before removing it from liner 253. During the curing process, base 121 may be engraved with information which may include, but is not limited to, specifications of the support useful for forensic purposes.
Rebar 131 may preferably be cut to a pre-specified length according to project requirements. It may be preferable for the load-bearing end of rebar 131, which may ultimately be inserted into support bore 123, to be cut as nearly as possible to 90° relative to vertical portion 135 to prevent loading and punching. Rebar 131 may be secured in bore 131 at the time of manufacture or later in the field. Further, although a considerably more complicated endeavor, rebar 131 may be cast in place in support 99 during manufacture.
A description of the process used to form various embodiments of the support of the present invention is best continued with reference to support 143, although the process may be used to form any of supports 51, 85, 99, or 143 in the previous
Although the invention has been derived with reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. Therefore, included within the patent warranted hereon are all such changes and modifications as may reasonably and properly be included within the scope of this contribution to the art.
Claims
1. A support structure comprising:
- a body having a bottom surface and a top surface, and wherein the body has at least one inclusion between the top surface and the bottom surface for vertically anchoring the support structure in a finished concrete slab.
2. The support structure recited in claim 1 wherein the area of the bottom surface is greater than the area of the top surface.
3. The support structure recited in claim 2 wherein the shape of the support structure is at least one of frusto-pyramidal and frusto-conical.
4. The support structure recited in claim 2 and further comprising an anchoring structure.
5. The support structure recited in claim 4 wherein the anchoring structure a has a first end, a second end, and a midsection extending between the first and second ends.
6. The anchoring structure recited in claim 5 wherein the midsection includes at least one bend.
7. The anchoring structure recited in claim 5 wherein at least one of the first and second ends of the anchoring structure has a circumference which is greater than the circumference of the midsection.
8. The support structure recited in claim 4 wherein the anchoring structure is a bore extending into the support structure.
9. The anchoring structure recited in claim 8 and further comprising a support member having a first end, a second end, wherein the support structure includes at least one bend and wherein the first end of the support member is supported within the bore.
10. The support structure recited in claim 4 wherein the length of the bottom surface exceeds the width of the bottom surface.
11. The support structure recited in claim 10 wherein the top surface of the support structure comprises at least a first section at a first height relative to the bottom surface, and a second section at a second height relative to the bottom surface, and wherein the height of the first section exceeds the height of the second section.
12. A process for manufacturing a support structure comprising the steps of:
- providing a form having a floor and a side wall, and having a height, length, and width which correspond to a set of desired support dimensions;
- placing a first bearing pad insert, having at least one of a support groove and a through bore, onto the floor of the form;
- performing at least one of inserting a dowel into a through bore on the bearing pad insert, the size of the dowel corresponding with the dimensions of the support bore to be formed in the support structure, and inserting an inverted anchoring arm into a support groove on the bearing pad insert;
- placing a first shear key insert within the form;
- pouring a concrete mixture into the form and allowing the concrete mixture to set; and
- after allowing the support structure to cure completely, removing the support structure from the form.
13. The process recited in claim 12, and further comprising the step of lining the form with a non-stick liner prior to installing the shear key insert.
14. The process recited in claim 12, and further comprising the step of coating the liner with a releasing agent prior to pouring the concrete mixture.
15. The process recited in claim 12, and further comprising the step of applying a sealant between the bearing pad insert and the form prior to pouring the concrete mixture.
16. The process recited in claim 12 and wherein the pouring a concrete mixture into the form step includes the steps of pouring a succession of concrete layers and smoothing each layer before the subsequent layer is poured.
17. The process recited in claim 12 and further comprising the step of selecting a second bearing pad insert which includes at least one of a support groove and a through bore and placing the second bearing pad insert into the form on top of a step insert provided adjacent the side wall.
18. The process recited in claim 12, and further comprising the steps of:
- providing a high-strength reinforcing member which has been right-angle cut to a specified length and has been angled to form a first end and a second end;
- applying a cement to the first end of the reinforcing member; and
- inserting the first end of the reinforcing member into the support bore to fix the reinforcing member into the support structure.
19. A process for using a support structure comprising the steps of:
- determining the site designated for concrete slab placement;
- placing a support structure having a body with a top surface and a bottom surface, the top surface including at least one of an anchoring arm and an elevated support member, atop at least one of grade and decking; and
- pouring concrete to a level over the support structure to form a concrete slab.
20. The process recited in claim 19 and further comprising the steps of securing at least one of a component of a reinforcing mat or a component of a post-tension cable to at least one of the anchoring arm and elevated support member.
Type: Application
Filed: Jul 31, 2008
Publication Date: Feb 4, 2010
Inventor: Kiel E. Strahin (Stock bridge, GA)
Application Number: 12/221,227
International Classification: E04C 5/12 (20060101);