This Non-Provisional Patent Application is related to the U.S. Provisional Patent Application No. 62/748,775, entitled “Shear Transfer Ring,” filed on 22 Oct. 2018, the disclosure of which is hereby expressly incorporated by reference in its entirety.
This application relates generally to repair and reinforcement of piles and columns. More specifically, this application relates to a method for replacement or creation and transfer of the required shear force between a damaged metallic pile and the concrete that is poured around the pile for reinforcement.
The drawings, when considered in connection with the following description, are presented for the purpose of facilitating an understanding of the subject matter sought to be protected.
While the present disclosure is described with reference to several illustrative embodiments described herein, it should be clear that the present disclosure should not be limited to such embodiments. Therefore, the description of the embodiments provided herein is illustrative of the present disclosure and should not limit the scope of the disclosure as claimed. In addition, while the following description references steel piles, concrete reinforcement and steel Shear Transfer Rings and Clamps, it will be appreciated that the disclosure may include other curable and other reinforcement materials and piles made of materials other than steel to which the disclosed methods also apply. Furthermore, these methods may be utilized to repair and reinforce beams, pipes, columns and the like.
This disclosure is related to the general field of construction and in particular to the repair of columns and piles under compressive and flexural forces, some of which columns may even be submerged in water. Many such structures are damaged by corrosion after several years of service and requires strengthening. In addition, there are many columns that have to be strengthened to carry larger and heavier loads. A common method of strengthening such piles and columns is to encase them in a shell of concrete. Typical repairs require placing a formwork (or jacket), commonly made of fiberglass, around the pile and filling the annular space between the formwork and the pile with concrete. In some cases additional reinforcing bars can be placed in the annular space between the column and the formwork. Some of these formworks may even be left in place as a stay-in-place-form.
In design of structures, there are many instances where concrete and steel are designed to work in what is known as a “composite” structure to resist the external loads. This requires the stresses in concrete to be transferred to steel and vice versa. For decades, the common practice for such shear transfer has been the use of “shear connectors” or “shear studs”. These shear studs are typically made of a cylindrical steel shaft like a bolt and are about 2-8 inches long. The number of these single studs, their size (diameter and length) and their spacing are designed by the engineers. The calculations are partially based on the magnitude of the loads being transferred.
In the traditional method one end of the studs is welded to the surface of the steel structure and in most projects numerous such single studs are required. Manufacturers supply these shear studs in a variety of sizes. The load transfer mechanism is primarily through bearing of concrete on the projected surface of the bolt, which can be calculated. Thus, it is advantageous to have a large projected area so more loads can be transferred per each connector/stud. The other limiting values are the shear strength of the steel bolt and the strength of the weld that connects the base of the shear connector to the steel. So, in general, the stronger the weld and the steel, the more load the stud can transfer.
In
In the traditional method, there are other design parameters that engineers consider as well, for example, the spacing between adjacent studs. In general, if the studs are too closely spaced, there is a loss of strength; i.e., the contribution of three closely-spaced cluster of studs becomes less than the sum of the strength of each of the three studs if they were installed with a larger spacing between them. These shear connectors or studs are used in all kinds of structural elements, such as columns, walls, beams, sheet piles, pipe, etc. and they can transfer loads that are produced from dead load, live load, earthquake, wind, temperature, shrinkage, fluid pressure and the like.
In some projects, for example, the engineers are tasked with the design of shear studs to transfer the loads from a cylindrical steel pile to concrete. Such steel piles, which are manufactured from steel tubes (pipes) with or without filling the inside with concrete, are often used in construction of supports for ports and piers. With aging, the steel tube corrodes and requires to be repaired. In some cases, the loading on the pile is increased and a strengthening beyond the original capacity is required so the pile can resist the new loads safely. Such applications require casting a tube of concrete (1-4 inches thick) around the host steel pile. Examples of these reinforcements are disclosed in detail in some of the inventor's patents and patent applications such as U.S. Pat. Nos. 8,650,831; 9,376,782; and 9,890,546.
As mentioned above, because the steel surface of the piles slips relative to the adjacent concrete, the transfer of the load between the concrete and steel in such repairs requires the use of shear studs or shear connectors. However, there are several problems associated with the use of welded shear studs as listed below:
To overcome the above shortcomings of the traditional methods, a new technique that utilizes a Shear Transfer Ring (STR) is disclosed below which replaces the individually welded shear connectors or shear studs. The method presented here is particularly well suited for cylindrical or oval-shaped structures such as piles, columns and pipes, although it can be applied to structures of any cross-sectional shape such as H and I cross-section. The physics principal (friction forces) that the disclosed method is based on is totally different from the physics principal (shear forces) employed in the method using shear connectors or shear studs.
Among the factors that will be discussed in the following paragraphs, two of the more important variables that determine the contribution of the STR are the following:
In the traditional method, the transfer of loads from the studs to the steel structure is achieved through shear forces attained by the weld. In the disclosed STR system, these forces are transferred by means of friction. As it is known to those in this field, friction force is calculated as:
F=μN, where
F=Friction Force
N=Normal force, and
μ=Coefficient of Friction between the two surfaces coming in contact
F=μN=μ(4T)=4μT
In this expression, it can be shown that F is the sum of all friction forces 326 around the pile 310 (i.e. 360 degrees all around the pile). Therefore, the maximum force that each STR 312 can transfer by means of friction 326 to the skin 311 of the pile 310 is equal to 4 μT. Therefore, it is clear that by increasing the tension force “T”, one can bypass the damaged area of the pile 310 and transfer a larger load to the lower portion of the pile 310. Thus, it is best to build the STR with a high strength material (e.g. steel) and tighten the STR with a large tension force in the fastener 314.
It is also evident that a higher coefficient of friction is more desirable. Thus a rusted skin surface 311 of pile 310 offers more friction and a higher friction force compared to a cleaned “white metal” finished surface.
The Projected Bearing Area
The second variable in the disclosed system is the area 318 of the STR 312 that projects outward and away from the surface 311 of pile 310. As shown in
The STR can be made with a variety of products, such as steel angles, chains, high-strength cables (such as those used in post-tensioning), links that are in the shape of an arc of a circle and their ends are pinned together, etc. The STR described above can also be constructed in a variety of shapes and with numerous products while in all cases the mechanism of load transfer remains the same, namely bearing on the protruding projected area and friction that is achieved by tightly wrapping and tensioning the STR around the host pile.
In various embodiments, the tensioning force in the tensioning device can be monitored to remain at desired level. This can be done, for example by using a torque wrench to accurately tighten the bolt 508 to the desired level. Another option is to use a Tension Control Bolt. These bolts have a piece at the end of the shank that breaks off when the predetermined tension force in the bolt is reached. This guarantees the tension force in the bolt is as it was calculated in the design.
In the above embodiments various example configurations and materials for an STR have been described with different advantages. For example, a cable is very flexible and can be easily conform to the shape of the pile. It is also easier to cut a cable STR to the required length in the field from a long roll of chain. The option in
In some embodiments the STR may be glued to the pile in addition to or instead of tightening it around the pile. In other embodiments the surface of the STR or of the clamps that are in contact with the surface of the pile may be roughened by different methods to increase the friction between the surface of the STR or of the clamps and the surface of the pile. In various embodiments the part of surface of the pile that is in contact with the surface of the STR or of the clamps may be coarsened.
In some embodiments the frictions between the STR(s) and the pile, at the location of wrapping(s), is calculated such that on each side of the damaged area the total friction is a desired fraction of or is equal to or is a desired multiple of the total load on the pile.
In some embodiments in which the entire lower part of a pile is damaged, the STR(s) may be wrapped around the pile above the damaged area and encase the pile in reinforcement material that encloses the STR(s) and continues all the way to the foundation on which the pile is erected or all the way to another stationary platform that can support the loads imposed on the pile. Such method transfers the forces exerted on the damaged pile to the foundation of the pile or the stationary platform through the encasement material and bypasses the damaged part of the pile. The tension in the STR(s) is/are calculated to provide a desired friction force between the pile and the STR(s) such that the (total) friction force is a desired fraction of or a desired multiple of or equal to the forces exerted on the pile.
Design Example
The simplified example provided here is intended to demonstrate some of the key steps in designing a STR in accordance to the disclosed technique. Given the following information about a cylindrical steel pile being repaired calculate the amount of force that can be transferred through a STR that is constructed with the following cable wrapped around the pile:
D=pile diameter=24 inches
Concrete shell thickness=2 inches
Compressive strength of concrete=f′c=4,000 psi
Cable used=7-wire high-strength strand with fpu=270 ksi (commonly used in post-tensioning)
Cable Diameter=0.5 inch
Cable cross section area=0.153 in.2
The capacity of the STR based on Tension Force and Projected Bearing Area will be calculated and the lower number will control the design.
a) Tension Force
Assume cable can be stressed to 70% of its ultimate strength of 0.7×270 ksi=189 ksi. T=0.153×189=28.9 kips=the force in the bolt pulling the ends of the cable towards each other
Assume μ=0.4 for steel to steel contact.
F=4×0.4×28.9 kips=46.2 kips
b) Projected Bearing Area
Due to the round shape of the cable, conservatively assume that the projected profile of the cable is:
0.8×0.5 in.=0.4 in. wide.
Perimeter or total length of the cable=24 in.×3.14=75 in.
Projected Bearing Area=75×0.4=30 in.2
Bearing Force=(0.55×4,000 psi)×30 in.2=66,000 pounds=66 kips
In this case, the capacity of the STR is 46.2 kips which is the smaller of the two numbers. Thus, if we wish to transfer a force of 130 kips from the concrete to the pile, we need 130 kips÷(46.2 kips/STR)=2.81 STR or rounded to the next whole number, three (3) STR units.
In the above example, losses in the prestressing cable as it wraps around the pile have been ignored. Also, as engineers know, there are other calculations that must be performed to make sure the steel pile does not fail because of the tensioning force. If this happens, a smaller tensioning force can be used which could dictate more STR units. Another alternative is to use a flat bar similar to
While the foregoing discussion and example have focused on axial compressive loads being applied to a pile, those skilled in the art realize that the same system of load transfer can be achieved when the host structure is subjected to other loads and stresses that induce, tension, flexure, or shear in the host structure.
Changes can be made to the claimed invention in light of the above Detailed Description. While the above description details certain embodiments of the invention and describes the best mode contemplated, no matter how detailed the above appears in text, the claimed invention can be practiced in many ways. Details of the system may vary considerably in its implementation details, while still being encompassed by the claimed invention disclosed herein.
Particular terminology used when describing certain features or aspects of the invention should not be taken to imply that the terminology is being redefined herein to be restricted to any specific characteristics, features, or aspects of the invention with which that terminology is associated. In general, the terms used in the following claims should not be construed to limit the claimed invention to the specific embodiments disclosed in the specification, unless the above Detailed Description section explicitly defines such terms. Accordingly, the actual scope of the claimed invention encompasses not only the disclosed embodiments, but also all equivalent ways of practicing or implementing the claimed invention.
It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to “at least one of A, B, and C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B,” and also the phrase “A and/or B” will be understood to include the possibilities of “A” or “B” or “A and B.”
The above specification, examples, and data provide a complete description of the manufacture and use of the composition of the invention. Since many embodiments of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. It is further understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
While the present disclosure has been described in connection with what is considered the most practical and preferred embodiment, it is understood that this disclosure is not limited to the disclosed embodiments, but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.
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