Patent Application
20060059841
Concrete is characterized by high compressive strength and notoriously poor tensile strength. In a typical reinforced concrete structure this deficiency in the tensile strength of the concrete is obviated by imbedding in the concrete at those points where tensile stress will be encountered, reinforcing bars, typically of steel. Where a section of a reinforced concrete structure terminates at another section, such as at a beam/wall or beam/column intersection, provision must also be made to insure that the ends of the rebars will not pull out of the wall or column when tensile stress is encountered. Conventionally, this was remedied by bending the end of the rebar and perhaps inserting another rebar beneath the bend perpendicularly to the length of the first rebar. Typically, a joint of this type is congested to begin with and this remedy compounded the congestion, resulting in higher concrete placement costs and possible concrete consolidation problems.
To avoid these problems it is known to provide an enlarged head at the rebar end, either through forging or by welding a plate on the rebar end, or providing a plate with a threaded opening, upsetting the end of the rebar to enlarge its diameter and then threading the enlarged end complementarily to the anchor plate threaded opening and screwing the plate onto the threaded rebar end.
Where the rebar ends are provided with a forged head, a very large forging press is required, a substantial portion of the rebar must be preheated for forging with a commensurate expenditure of time and energy, and multiple strikes of the press are required to create the headed end. Where the end plate is a separate part with a threaded opening receiving a threaded end of the rebar, the rebar end must first be upsized through a forging process before the threads are cut into the rebar end. This is necessary to achieve the ultimate strength of the rebar. If the rebar were threaded without upsizing the end, the thread would create a weak point that would reduce the overall tensile strength of the rebar.
As noted above, it is also known to weld an anchor plate to the end of a rebar, typically through an inertia welding process. This approach has the drawbacks of requiring a separate fabricated anchor plate and requiring the upsizing of the rebar end prior to welding, but more importantly, the welding process is subject to various process variables that contribute to quality considerations.
It will be seen, therefore, that a need exists for a rebar anchorage to reduce congestion at a joint intersection in a reinforced concrete structure, but without the disadvantages noted above with respect to conventional methods of providing an end anchorage for concrete reinforcing bars.
The present invention provides a method of manufacturing an end anchor of superior structural performance but with the expenditure of less energy required than in comparable prior art methods, resulting in cost savings and a unique end anchor product.
Specifically, in accordance with the present invention a separate anchor plate is provided, which may be round, square, rectangular or other configuration and through the plate an opening having irregular wall portions is formed. Conventional rebar having an effective outer diameter smaller than the size of the opening through the anchor plate is preheated at its end, the heated end inserted into the opening through the plate and then forged onto the plate by upsizing the rebar end and filling the hole through the plate with rebar material to form a mechanical interlock with the irregular wall portions of the opening through the anchor plate.
This method permits the use of smaller forging presses than would be required to forge the end of a rebar into an end anchor and requires less heat prior to forging and less strikes of the forging press to complete the assembly. Thus, an end anchor in accordance with the present invention may be produced in less time and with less energy than comparable processes for forming rebar end anchors.
As a result, the construction of an intersecting joint, such as the termination of a beam into a column or wall in a reinforced concrete structure is greatly facilitated, while conserving the energy and commensurate expense thereof usually associated with end anchors of this type. Therefore, in a typical intersection of this type, where reinforcing bars and associated ties create a congested condition, the necessity of contributing to that congestion by bending the end of the terminating rebar and providing cross rebar members within the bend is avoided but again, without the expense attended to conventional end anchors.
Additionally, the process of forging the rebar into the anchor plate provides the added benefit of upsizing the rebar at the connection. This provides a stronger section of rebar at the connection and ensures that the rebar, if subjected to ultimate tensile stress, will break at a location distant from the anchor plate connection. This is an important feature because there are standards that require failure to occur away from the connection. This makes it obvious that the rebar has failed and not the anchor plate-rebar connection.
These and other objects and advantages of the present invention will become apparent from the following description, the accompanying drawings and the appended claims.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the invention.
Thus, as seen in
In any case, it will be noted from
However, prior to placing the anchor end 40 of the rebar 37 into the opening 34, end 40 is first heated and then, after it is received in the opening, subjected to an axial force and thus forged into place in mechanical interlocking relationship with the irregular wall portions 36 of the anchor plate 32. In other words, the heated end 40 of the rebar 37 is upsized by forging, filling in the irregularities 36 in the opening 34 through the anchor plate 32 with material from the rebar to form a mechanical joint. As noted above, upsizing the rebar ensures that should it encounter ultimate tensile stress, it will break at a point remote from the joint with the anchor plate,
While the end anchor construction shown in
While in the embodiment of
Regardless of the specific configuration of the anchor plate it will be apparent that the present invention provides a method of fastening securely an anchor plate to an standard rebar by forming an irregularly shaped wall portion defining an opening through the anchor plate, heating an end of the rebar, inserting it into the opening in the anchor plate and then forging the heated end of the rebar to upsize it and fill the interstices provided by the irregular wall portions of the opening through the anchor plate, resulting in a secure mechanical interlock between the end of the rebar and the anchor plate. Thus, the advantages of utilizing an end anchor in place of merely bending the terminal portion of a rebar and inserting a crossing rebar are obtained, but without the expenditure of energy and expense associated with end anchors of this type. While the methods and structures formed thereby described herein constitute preferred embodiments of the invention it is to be understood that the invention is not limited to these precise forms of method and structure formed thereby and that changes may be made therein without departing from the scope of the invention as defined in the appended claims.
