FIELD OF THE INVENTION
The present invention generally relates to lifting anchors for precast concrete structures, and more particularly to lifting anchors and assemblies for reinforced and/or prestressed concrete beams, girders, slabs, columns, panels, and the like.
BACKGROUND OF THE INVENTION
Precast concrete structures are often used in building constructions, and lifting anchors are commonly embedded or cast in the precast concrete structures to facilitate handling, since these structures can be difficult to hoist and position due to their weight, bulkiness, and susceptibility to damage, such as cracking, chipping, and other breakage. With respect to prestressed concrete structures, precompressed tensile zones of the structure can make the structure more susceptible to damage during handling and installation, such as when lifting anchors are ineffectively designed and/or located to cause interference with the prestressed strands embedded in the structure.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a lifting anchor that is configured to be embedded in a precast concrete structure, such as a single-tee beam or double-tee slab or the like, that has pretensioned or prestressed strands forming a compressed zone or zones in the concrete structure. The lifting anchor includes a single strand or piece of metal bar stock that is bent to have a pair of elongated, parallel legs and a central section that integrally interconnects the legs and is used as the attachment point for connecting lifting chains or cables or the like. A lower end section of each of the legs includes undulations, such as waves, that are configured to engage the compressed zone in the concrete structure in a manner that provides a stable and secure lifting point and minimizes interference with the prestressed strands. The lifting anchor may be positioned to straddle opposing sides of the prestressed strands or to be disposed between spaced apart prestressed strands, thus allowing the lifting anchor to accommodate differently shaped and configured precast concrete structures in a manner that prevents interference with the prestressed strands.
According to one aspect of the present invention, a lifting anchor is configured to be embedded in a precast concrete structure. The lifting anchor includes a single strand of metal bar stock that is bent to have a pair of elongated legs and a central section that integrally interconnects the pair of elongated legs. A lower end section of each of the pair of elongated legs includes undulations that are configured to engage in a compressed zone of a concrete structure resulting from prestressed strands cast in the concrete structure and configured to minimize interference with the prestressed strands.
According to another aspect of the present invention, an apparatus includes a precast concrete structure that has a surface-forming panel portion, a panel-reinforcing rib portion, and prestressed strands disposed within the rib portion. A plurality of lifting anchors are positioned within the rib portion, where the plurality of lifting anchors each include a single strand of metal bar stock that has a pair of parallel legs and a leg-connecting section. A lower end section of each of the pair of parallel legs includes undulations shaped to engage in a compressed zone in the rib portion proximate the prestressed strands.
According to yet another aspect of the present invention, a method is provided for forming a concrete structure. The method includes providing a plurality of lifting anchors that each have a single strand of metal bar stock that includes a pair of parallel legs and a leg-connecting section, where a lower end section of the legs includes undulations bent into the single strand. Concrete is cast to form a precast concrete structure that includes a surface-forming panel portion, a panel-reinforcing rib portion, and prestressed strands that extend along a length of the rib portion. Prior to hardening of the precast concrete structure, the plurality of lifting anchors are disposed within the rib portion with the undulations positioned to engage a compressed concrete zone in the precast concrete structure and to minimize interference with prestressed strands in the concrete structure.
These and other objects, advantages, purposes, and features of the present invention will become apparent upon review of the following specification in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a precast concrete structure having a lifting anchor with legs disposed between spaced apart arrangements of prestressed strands extending in the precast concrete structure to position waves formed at ends of the legs at a compressive zone formed by the prestressed strands, in accordance with the present invention;
FIG. 2 is a cross-sectional view of a precast concrete structure having an additional embodiment of a lifting anchor with legs disposed on opposing sides of prestressed strands extending in the precast concrete structure to position waves formed at ends of the legs at a compressive zone formed by the prestressed strands, in accordance with the present invention;
FIG. 3 is a side elevational view of the lifting anchor shown in FIG. 1;
FIG. 4 is an additional side elevational view of the lifting anchor shown in FIG. 3;
FIG. 5 is a perspective view of the lifting anchor shown in FIG. 3;
FIG. 6 is another perspective view of the lifting anchor shown in FIG. 3;
FIG. 7 is a top plan view of the lifting anchor shown in FIG. 3;
FIG. 8 is a side elevational view of the lifting anchor shown in FIG. 2;
FIG. 9 is an additional side elevational view of the lifting anchor shown in FIG. 8;
FIG. 10 is a perspective view of the lifting anchor shown in FIG. 8;
FIG. 11 is another perspective view of the lifting anchor shown in FIG. 8;
FIG. 12 is a top plan view of the lifting anchor shown in FIG. 8;
FIG. 13 is an upper perspective view of an additional embodiment of a lifting anchor having an attached void former;
FIG. 14 is a side elevational view of the lifting anchor shown in FIG. 13;
FIG. 15 is an additional side elevational view of the lifting anchor shown in FIG. 13;
FIG. 16 is a top plan view of the lifting anchor shown in FIG. 13; and
FIG. 17 is a bottom plan view of the lifting anchor shown in FIG. 13.
DETAILED DESCRIPTION OF EMBODIMENTS
Referring now to the drawings and the illustrative embodiments depicted therein, a lifting anchor 10 (FIGS. 1 and 3-7), 110 (FIGS. 2 and 8-12), 210 (FIGS. 13-17) is configured to be cast or embedded in a precast concrete structure 40, 140, such as a single-tee beam (FIGS. 1 and 2) or double-tee slab or the like. The precast concrete structure 40, 140 has pretensioned or prestressed strands 42, 142 that form a compressed zone or zones in the concrete structure 40, 140, which compress the concrete structure longitudinally along and in a direction generally parallel to the prestressed strands. The lifting anchor 10, 110 is embedded in the precast concrete structure 40, 140 at or near the compressed zone or zones to provide a secure anchor or attachment point for a lift chain or cable or the like, while also minimizing interference with the prestressed strands 42, 142. Further, the lifting anchor 10, 110 may be configured to be positioned to either be disposed between spaced apart prestressed strands 42 (FIG. 1) or to straddle opposing sides of closely arranged prestressed strands 142 (FIG. 2), thus allowing the lifting anchor to accommodate differently shaped and configured precast concrete structures and pretensioning arrangements, within the functional requirements of particular structures.
As shown in FIGS. 1 and 2, the concrete structures 40, 140 are similarly shaped and include a surface-forming panel portion 44, 144 and a panel-reinforcing rib portion 46, 146, where the prestressed strands 42, 142 are disposed within and extend, parallel to each other, along a length of the rib portion 46, 146. The panel portion 44, 144 is configured to be generally horizontally oriented, such as to form a base or support surface of a road, building, or parking structure or the like. The rib portion 46, 146 extends along a lower section of the panel portion 44, 144 to provide support and reinforcement to the panel portion 44, 144, thus increasing the load capacity of such a structure 40, 140.
As also illustrated in FIGS. 1 and 2, the prestressed strands 42, 142 extend generally horizontally through the concrete structure 40, 140 and are each disposed or spaced in two vertical arrangements or columns, with three strands spaced apart in a generally vertical stacked arrangement. Thus, the prestressed strands 42, 142 in each concrete structure 40, 140 form a compressed zone that generally surrounds the prestressed strands 42, 142 in a lower section of the rib portion 46, 146. As generally understood, the strands 42, 142 provide additional strength to the structure 40, 140 by promoting compressive forces over tensile forces and provide stress distribution along the concrete structures 40, 140 to help prevent flexural cracking and to counteract tension due to expected gravity loads, such as self-weight, superimposed dead loads, live loads, and the like. It is understood that the concrete structure in accordance with the present invention may be cast in various alternative shapes and pretensioning arrangements, such as with more or few strands and/or differently arranged strands.
With further reference to FIGS. 1 and 2, the lifting anchor 10, 110 or strand lifter is embedded in the precast concrete structure 40, 140 to facilitate lifting and handling of the structure 40, 140. The illustrated lifting anchor 10, 110 is made from a single strand or piece of metal bar stock that is bent or otherwise formed to have a pair of elongated, parallel legs 12, 112 and a central, leg-connecting section 14, 114 that integrally interconnects the legs 12, 112 and is used as an attachment point for connecting lifting chains or cables or the like. The single strand of metal bar stock that forms the illustrated lifting anchor 10, 110 has a generally square cross-sectional shape. However, it is contemplated that the lifting anchor in additional embodiments can be made from a single strand of bar stock of desired cross-sectional thickness and shape, such as round or rectangular or the like. The central section 14, 114 includes an inverted V shape that is configured to be positioned as the uppermost portion of the lifting anchor 10, 110 to be exposed by a void or cavity 48, 148 or otherwise not embedded in the concrete structure 40, 140. Thus, the legs 12, 112 are generally vertically arranged or disposed in the concrete structure to be generally perpendicular to the horizontally extending prestressed strands 42, 142. A lower end section 12a, 112a of each of the legs 12, 112 includes undulations 16, 116 that are configured to engage the compressed zone in the rib portion 46, 146 of the concrete structure 40, 140 in a manner that provides a stable and secure connection with the concrete structure 40, 140 and minimizes interference with the prestressed strands 42, 142.
The lifting anchor 10 can be positioned to extend between spaced apart prestressed strands 42, such as shown in FIG. 1, and the lifting anchor 110 can be positioned to straddle opposing sides of the prestressed strands 142, such as shown in FIG. 2. Multiple lifting anchors may be arranged along the concrete structure to provide multiple lifting points for the particular structure. It is conceivable that the lifting anchor in other embodiments may be arranged in different orientations, such as by lifting anchors engaging a single structure in alternating orientations along a length of the structure or by the lifting anchor accommodating differently shaped and configured precast concrete structures.
With reference to the lifting anchor 10 shown in FIGS. 1 and 3-7, the prestressed strands 42 are arranged with the two vertical arrangements or columns spaced apart laterally a sufficient distance to accommodate the legs 12 between the vertical arrangements of strands 42. The central, leg-connecting section 14 and upper sections 12b of the legs 12 extend generally in a common plane that extends longitudinally along the concrete structure 10 in substantial parallel alignment to the prestressed strands 42. The undulations 16 at the lower end sections 12a of the legs 12 are each provided as a wave shape that extends generally within the common plane defined by the legs 12. Further, the undulations protrude laterally outward from a plane P1 (FIG. 3) defined by a linear extension of each of the upper sections 12b of the legs 12. Thus, the planes P1 defined separately by each of the legs 12 are generally perpendicular to the common plane extending between the legs 12, such that the undulations 16 in the planes P1 disperse the loads applied by using the lifting anchor 10 to the concrete structure vertically along the undulations 16. As such, the undulations 16 protrude away from the planes P1 generally in the direction of the compressive forces in the concrete structure that are applied by the prestressed strands 42, thereby minimizing interference with the prestressed strands 42.
The wave shape of the undulations 16 shown in FIGS. 1 and 3-7 include an amplitude defined between crests 16a, 16b (FIG. 3) of the wave, where the interior crests 16b are generally aligned with the plane P1 defined at each of the legs 12 and the exterior crests 16a extend from the plane P1 a sufficient distance to provide a strong, secure, and minimally intrusive anchor point. Further, the illustrated undulations 16 at the lower end sections 12a of the elongated legs are substantially mirror images of each other, and both lower end sections 12a of the legs 12 of the lifting anchor 10 are formed to provide waves that protrude laterally outwardly from each of the legs 12. Again, as illustrated in FIG. 1, the entire lifting anchor 10 extends generally within a common plane that is substantially parallel to the longitudinal direction of the strands 42, positioning the undulations 16 to extend longitudinally within the concrete structure 40. It is also contemplated that the undulations in additional embodiments of the lifting anchor may be differently shaped, such as with non-mirrored shapes and more or fewer wavelengths, such as a single wavelength or three wavelengths, among other conceivable shapes.
In an additional embodiment, as shown in FIGS. 2 and 8-12, the prestressed strands 142 are arranged with the two vertical arrangements or columns spaced closed together at a sufficient distance to allow the legs 112 to straddle opposing sides of the vertical arrangements of the prestressed strands 142. As such, the central, leg-connecting section 114 is shaped to separate the pair of parallel legs 112 away from each other at a spaced distance configured to dispose the legs 112 on opposing sides of the prestressed strands 142. Thus, the common plane P2 (FIG. 9) that is defined by the central, leg-connecting section 114 and the upper sections 112b of both of the legs 112 extends substantially perpendicular to the prestressed strands 142.
With reference to FIGS. 2 and 8-12, the lifting anchor 110 is formed from bending a single strand of generally square cross-sectional shaped bar stock to provide a central section 114 and a pair of elongated, parallel legs 112 that integrally extend from the central section 114. As shown in FIG. 9, the central upper sections 112b of the legs 112 define a common plane P2, where the undulations 116 at the lower end sections 112a of the legs 112 extend only from one side of the common plane P2. The undulations 116 at the lower end sections 112a of legs 112 are bent to a wave shape generally equally on both side of legs 112. As illustrated in FIGS. 2 and 9, the plane P2 extends generally perpendicularly to the strands 142, such that and the waves extend in generally parallel alignment with the opposing vertical arrangements of strands 142. The undulations 116 shown in FIGS. 9-12 are bent to a wave shape with wavelengths that extend two portions 16a, 16b (shown as crests of the wave) from each of the legs 112, with one side of the crests 16a generally aligned with the common plane P2. Thus, as shown in FIG. 2, the undulations 116 protrude generally in the direction of the compressive forces in the concrete structure 140 that are applied by the prestressed strands 142, thereby dispersing the loads applied by using the lifting anchor 110 to the concrete structure 140 vertically along the undulations 116 and minimizing interference with the prestressed strands 142.
As shown in FIGS. 13-17, an additional embodiment of a lifting anchor 210 is provided that has a generally round or circular cross-sectional shape, and further the central, leg-connecting section 214 and upper sections 212b of the legs 212 extend generally in a common plane P3 (FIG. 14) that may extend substantially parallel or perpendicular to prestressed strands extending within a concrete structure. The undulations 216 at the lower end sections 212a of the legs 212 are each provided as a wave shape that disperses the loads applied by using the lifting anchor 210 to the concrete structure vertically along the undulations 216 so as to prevent the load from being concentrated on a single strand and thereby minimizing interference with the prestressed strands. The wave shape of the undulations 216 are shown to include at least two wavelengths, where the wave shape of the undulations 216 have an amplitude defined between crests 216a, 216b (FIG. 3) of the wave, which may be configured to be is less than a lateral spacing between two vertical arrangements or columns of the prestressed strands cast in a concrete structure. It is contemplated that the undulations may include more or fewer wavelengths, such as a single wavelength or three wavelengths, among other conceivable shapes.
As shown in FIG. 14, the undulations 216 at the lower end sections 212a of the elongated legs 212 extend generally equally from both sides of the common plane P3, as defined by the central section 214 and upper sections 212b of the legs 212. Thus, both lower end sections 212a of the legs 212 of the lifting anchor 210 are formed to provide waves that protrude from both sides of the common plane P3. When the plane P3 is arranged to extend generally parallel to the strands in a precast structure, the waves extend toward and perpendicular to the longitudinal direction of the strands. The undulations 216 shown in FIGS. 13-17 are bent or formed or cast to a wave shape with at least two wavelengths that extend two portions 216a, 216b (shown as crests of the wave) of each of the legs 212 from both sides of the common plane P3.
As further shown in FIGS. 13-17, the lifting anchor 210 has a recess-forming member or void former 218 engaged with the central section 214 of the lifting anchor 210 to conceal the central section 214 of the lifting anchor 210. When the concrete structure cures and hardens (from wet/fluid concrete in the concrete form), the void former 218 is removed to provide a cavity, such as shown as the cavities 48, 148 in FIGS. 1 and 2 at the upper surface of the concrete structure 40, 140, to exposes the central section 214 of the anchor member 212. The illustrated void former 218 includes openings that receive the outwardly-angled portions of the central section 214 to prevent intrusion of fluid concrete during the casting process. The void former 218 and lifting anchor 210 are configured to be disposed in the cast concrete, so that the central section 214 does not protrude above an outer flat surface of the concrete structure. Recess-forming members or void formers are generally known, such as provided in U.S. Design Pat. No. D559,499, which is hereby incorporated herein by reference in its entirety.
For purposes of this disclosure, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in FIG. 1. However, it is to be understood that the invention may assume various alternative orientations, except where expressly specified to the contrary. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in this specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.
Changes and modifications in the specifically described embodiments may be carried out without departing from the principles of the present invention, which is intended to be limited only by the scope of the appended claims as interpreted according to the principles of patent law. The disclosure has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present disclosure are possible in light of the above teachings, and the disclosure may be practiced otherwise than as specifically described.
Patent Application
20170247892
