1. Field of the Invention
This invention relates to a mechanical anchorage device and to a method for connecting the device out in the field to the upstanding end of a rebar which may be embedded within and project from a section of concrete. The anchorage device forms a wide head on the rebar which will be covered with concrete to create one or more bearing surfaces and thereby enable the rebar to better withstand forces applied thereto through the concrete.
2. Background Art
Steel reinforcement bars (i.e., rebars) are well known to be embedded within a reinforced concrete structure (e.g., a wall, panel, or the like) so that the structure will be less likely to shift or suffer damage caused by physical forces, such as those generated during an earthquake. In some cases, the rebars can become prematurely separated from their concrete structure as a consequence of tensile loads applied to the rebar.
In order to stabilize and better hold the rebars in place within the concrete structure so as to more reliably withstand tensile loads, a relatively wide head is often formed to establish a wide bearing surface at the end of each rebar. The headed end is then covered over with additional concrete. However, it is sometimes difficult to form a wide head out in the field on a rebar that is already installed and embedded in a concrete structure with one end projecting from the structure to be subjected to a heading process. While it may be simpler to head the rebar prior to its installation in the field, the precise length of the rebar that will project from the concrete structure is often difficult to predict. That is to say, the end of the rebar may need to be cut and shortened in the field resulting in the preformed head being cut off the end. In other cases, the end of each rebar is bent over to form a hook so as to increase the bearing area thereof. Alternatively, a plate has been welded to the end of the rebar. In any case, special equipment and/or tools may have to be transported into the field for post-installation treatment of the top ends of the rebars to better resist tensile loads. The requirement for special equipment and tools slows the construction project and increases cost.
Accordingly, it would be desirable to be able to quickly and reliably connect a mechanical anchor to and increase the bearing surface at the upstanding end of a rebar that projects from a concrete structure out in the field without the cost or inconvenience of having to use such special equipment and tools and without stressing or loading the rebar during the connection of the anchor.
In general terms, this invention relates to a mechanical anchor and to a method for connecting the anchor to the upstanding end of a steel reinforcement bar (i.e., a rebar) that projects from a concrete structure. Once it is connected, the rebar anchor will be embedded within concrete so as to create a large bearing surface by which to enable the rebar to better withstand tensile forces such as those which are generated during an earthquake and applied to the rebar through the concrete.
According to a preferred embodiment, the rebar anchor includes a cylindrical barrel to surround the upstanding end of the rebar. A tapered bore runs longitudinally through the barrel within which to receive the end of the rebar. A disk-shaped resistance lid extends across the top of the barrel over the end of the rebar. The diameter of the lid may be greater than the diameter of the barrel to create a bearing surface below the lid. Located inside the tapered bore through the barrel is a tapered segmented jaw that is split into a plurality of wedges. The angle of the wedges matches the angle of the tapered bore. The wedges of the jaw are laid end-to-end and seated against the tapered bore. The wedges of the jaw are configured to surround and grip the rebar. To this end, the wedges are provided with teeth or sharp threads adapted to bite into and prevent a displacement of the rebar relative to the barrel of the rebar anchor. A helically-wound spring is positioned at the top of the tapered bore of the barrel to lie between the lid and the relatively wide top end of the tapered segmented jaw of the rebar anchor.
As an important feature, a threaded bolt is moved through a correspondingly threaded bolt hole formed in the lid so as to apply an axial pushing force against the end of the rebar surrounded by the barrel. Accordingly, the rebar is pushed downwardly through the tapered bore and outwardly relative to the barrel to cause the segmented jaw to slide therealong so that the correspondingly angled wedges of the jaw close tightly around and are locked against the rebar, regardless of the diameter of the rebar. Thus, the rebar anchor is quickly and positively connected in surrounding engagement with the rebar out in the field to create a wide head thereon without requiring the use of special tools or machinery. When the rebar anchor is covered with concrete, the bottom of the cylindrical barrel creates an additional bearing surface by which to hold the rebar in place embedded in the concrete so as to be advantageously adapted to withstand tensile loads applied thereto. However, the rebar anchor of this invention does not add tension to or load the rebar to which it is connected.
Details of the mechanical rebar anchor 3 and a preferred embodiment by which the rebar anchor is connected to a rebar are now explained while referring concurrently to
A disk-shaped resistance lid 12 is connected over the upstanding end of rebar 1. The lid 12 is preferably welded to or rotated into surrounding mating engagement across the top of the barrel 5 of rebar anchor 3 so that the upstanding end of the rebar 1 moves upwardly towards the inside of the lid 12 when the barrel 5 is attached. The lid 12 has a peripheral lip 14 extending downwardly therefrom. In the case where the lid 12 will be rotated into such surrounding mating engagement with the barrel 5, the inside edge of the lip 14 of lid 12 is provided with a set of threads 16 running therearound. The top of the barrel 5 is provided with a complementary set of threads 18 running therearound. The threaded top of barrel 5 may be recessed with respect to the cylindrical outside wall 7 thereof at which the threaded lip 14 will be received when the lid 12 is rotated around the top of barrel 5 and the sets of threads 16 and 18 are mated to one another. As best shown in
Located within the bore 10 running through the barrel 5 of rebar anchor 3 is a tapered, segmented jaw 24. As is best shown in
A (e.g., steel or rubber) O-ring 30 is received by a peripheral groove formed in the wide (i.e., thickest) top ends of the wedges 26 of the jaw 24 so as to hold the wedges 26 together. Laying on top of the O-ring 30 and surrounding the rebar 1 is a disk-shaped spring support 32. A helically-wound spring 34 is located above the jaw 24 at the top of the bore 10 of the barrel 5 of rebar anchor 3. The spring 34 is sized to surround the upstanding end of rebar 1 and positioned to lie between the inside of lid 12 and the spring support 32.
As an important feature of the rebar anchor 3 disclosed herein, a threaded bolt hole 38 is formed through the lid 12. A correspondingly threaded fastener (e.g., a bolt 40) is rotated through the bolt hole 38 and into contact with the top end of the rebar 1 which is surrounded within the bore 10 of barrel 5 by the spring 34. The bolt 40 is axially advanced through the bolt hole 38 towards and into contact with the rebar 1 by means of a torque wrench or the like.
The bolt 40 applies a downward pushing force directly against the top of the rebar 1 to force the rebar downwardly through the bore 10 and slightly outward from the barrel 5 of the rebar anchor 3. The helically-wound spring 34 is compressed by the lid 12 to exert a pushing force against the spring support 32 and thereby urge the wedges 26 of the tapered and segmented jaw 24 to slide downwardly along the tapered inside wall 9 of the bore 10 of the barrel 5. As it moves through the tapered bore 10, the segmented jaw 24 will automatically close around the rebar 1. More particularly, the angled wedges 26 of jaw 24 are forced radially inward towards rebar 1 by the matching tapered bore 10 so that the teeth 28 of wedges 26 bite into and are locked against the rebar. Accordingly, the rebar anchor 3 is quickly and positively connected to the top of the rebar 1 with minimal slippage to create a relatively wide head thereon after the rebar is already installed out in the field and without requiring the use of special tools or heading machines. The axial pushing force applied by the bolt 40 takes up any slack within the barrel 5 and thereby enables the rebar anchor 3 to be snugly held in surrounding engagement with the top of rebar 1. In other words, the combination bolt 40 and resistance lid 12 cooperate to eliminate internal movement (i.e., slippage) in both tension and compression to enable the post-installed anchor 3 to replicate a pre-installed rebar having an integral head that is formed by forging or welding.
Once the rebar anchor 3 is connected to the rebar 1 to form a head at the upstanding end thereof, the anchor is covered by concrete. The relatively wide bottom of the barrel 5 of anchor 3 creates a primary bearing surface (designated 42 in
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