Patent Application
20220412090
Reinforced concrete is very frequently employed in large-scale construction projects, such as roads, bridges, large buildings and containers for hazardous materials. Reinforcing bars, or “rebars”, set within the concrete are used to compensate for inherent weaknesses of concrete in tension. Typically, the rebars have a similar coefficient of thermal expansion as the surrounding concrete, to avoid or mitigate any internal thermal stresses.
Typically, rebars are formed from untreated carbon steel, which is vulnerable to corrosion from a variety of sources include salts such as sodium chloride (e.g., which itself may derive from a maritime environment or the use of deicing salts). Thus, steel rebars may require surface treatment prior to installation, adding unneeded complexity. Further, their general use may be limited or even proscribed in some specific applications (e.g., in hospitals with Magnetic Resonance Imaging (MRI) facilities). For these and other reasons, the use of non-metallic materials in rebars, such as a fiber reinforced polymer (FRP) in rebars has gained traction.
Generally, FRP and other non-metallic rebars present significant advantages for builders and constructors when compared to steel rebars. However, there still remain challenges in the course of their everyday, practical use. For instance, a cumbersome process is frequently encountered when joining FRP or other non-metallic rebars end-to-end, whether in a context of pre-cast (or modular) concrete panels, or cast-in-place concrete at a work site. Conventional arrangements present problems such as rebar cage congestion, corrosion, and over-reliance on transferring tensile forces through the concrete rather than through the rebars themselves. As such, there is a need for a quick and reliable manner of joining together FRP (or other non-metallic) rebars.
This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.
In one aspect, embodiments disclosed herein relate to a mechanical coupling for two rebars. The coupling includes a first extremity disposed on a first of the two rebars, and a second extremity disposed on a second of the two rebars. Each of the first and second extremities are machined to effect an interlocking, form-fit connection between the two rebars, wherein the form-fit connection prevents separation of the extremities and inhibits axial displacement of the two rebars with respect to each other. The coupling further includes a covering disposed about the two extremities when the extremities are interconnected via the interlocking, form-fit connection.
In one aspect, embodiments disclosed herein relate to a method which includes: obtaining two rebars; and machining an extremity on each of the two rebars to effect an interlocking, form-fit connection between the two rebars, wherein the form-fit connection prevents separation of the extremities and inhibits axial displacement of the two rebars with respect to each other. The method further includes: interconnecting the rebar extremities via the interlocking, form-fit connection; and thereafter disposing a covering about the rebar extremities.
In one aspect, embodiments disclosed herein relate to a mechanical coupling for two FRP rebars. The coupling includes a first extremity disposed on a first of the two FRP rebars, and a second extremity disposed on a second of the two FRP rebars. Each of the first and second extremities are machined to effect an interlocking, form-fit connection between the two FRP rebars, wherein the form-fit connection prevents separation of the extremities and inhibits axial displacement of the two FRP rebars with respect to each other. The coupling further includes a non-metallic sleeve disposed about the two extremities when the extremities are interconnected via the interlocking, form-fit connection, wherein the sleeve is formed from a material which is stronger than a material forming each of the first and second rebars. Additionally, the coupling includes one or more clamping elements which clamp the sleeve about the first and second extremities. When clamped, the sleeve absorbs the majority of a tensile load applied to the first and second rebars.
Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.
Specific embodiments of the disclosed technology will now be described in detail with reference to the accompanying figures. Like elements in the various figures are denoted by like reference numerals for consistency.
In the following detailed description of embodiments of the disclosure, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to one of ordinary skill in the art that the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the description.
Throughout the application, ordinal numbers (e.g., first, second, third, etc.) may be used as an adjective for an element (i.e., any noun in the application). The use of ordinal numbers is not to imply or create any particular ordering of the elements nor to limit any element to being only a single element unless expressly disclosed, such as using the terms “before”, “after”, “single”, and other such terminology. Rather, the use of ordinal numbers is to distinguish between the elements. By way of an example, a first element is distinct from a second element, and the first element may encompass more than one element and succeed (or precede) the second element in an ordering of elements.
Broadly described and contemplated herein, in accordance with one or more embodiments, are systems and methods for effecting a mechanical coupling of two FRP (or other non-metallic) rebars. Loads are predominantly transferred via a mechanical coupling, and not via surrounding concrete.
In accordance with one or more embodiments, the mechanical coupling is provided in part via a simple machining of the extremities of rebars. The machining permits and effects an interlocking, form-fit connection directly between two rebars, wherein the connection prevents separation of the extremities and inhibits axial displacement of the rebars with respect to each other. When interconnected, the rebar extremities may be covered (e.g., surrounded) by a covering disposed thereabout (e.g., about a region of interconnection of the two rebars). The covering may be embodied by a light, high-strength tubular sleeve, and the assembly (including the interlocking rebar extremities) may be clamped via one or more cable ties or other fasteners. A quickly established, simple construction of a mechanical coupling is thereby provided. Further, the mechanical coupling offers a “synergistic” combination of a strong, clamped connection which facilitates the transfer of tensile/axial loads mainly via the covering, and a physical, form-fit interlocking connection of the rebar extremities themselves, serving a function of inhibiting axial displacement of the extremities relative to one another.
Rebars are generally formed from a metallic material and are often crudely interconnected at best. Typically, two rebar extremities are mutually positioned via “lap splicing”, or the mere side-by-side positioning of the extremities, whether directly adjacent (involving physical contact) or not, and whether directly interconnected (e.g., via one or more surrounding loops or bands) or not. In such arrangements, tensile loads are transferred via the surrounding concrete, which greatly complicates the related structural design. For instance, a specific concrete grade would usually need to be chosen, and the extra rebar length needed (for side-by-side lap splicing) will make the structure heavier and increase congestion as the ratio of rebar weight to concrete weight becomes too high.
In accordance with one or more embodiments, using a mechanical coupling of the rebars results in a significant increase in structural integrity as the coupler assembly, including a tubular sleeve portion and clamps or fasteners, ends up absorbing a great majority of associated tensile loads, in a strictly axial direction. In comparison with lap splicing for conventional metallic rebars, the length of interconnection may also be reduced by a significant factor.
In accordance with one or more embodiments, the fasteners may be embodied by at least two clamping clips or cable ties which each constrict about the tubular sleeve. For their part, the rebar extremities may be machined on-site (e.g., at a building or highway construction site), or could be machined then included in a modular concrete component (e.g., a concrete slab or beam). Such machining may impart three-dimensional, mutually engaging “male-female” structural patterns to the extremities, which upon interconnection, permit the two rebars to remain coaxial with respect to one another.
Generally, in accordance with one or more embodiments, the machined (e.g., male/female) interconnection of the rebar extremities serves a physical “anti-slip” function, while absorbing a small portion of a tensile load applied to the rebars. At the same time, the coupler assembly (including the tubular sleeve and fasteners) serves a role of absorbing the great majority of a tensile load.
Turning now to the figures, to facilitate easier reference when describing
As such, in accordance with one or more embodiments, the first and second extremities 226, 228 are machined to effect an interlocking, form-fit connection between the two rebars 222, 224. The form-fit connection prevents separation of the extremities and inhibits axial displacement of the rebars with respect to each other. The extremities 226 and 228 may be brought into connection with each other (see 230) essentially from a side-to-side or radial orientation, or any other orientation that is not necessarily strictly axial.
In accordance with one or more embodiments, the FRP material which may be employed for rebars 222, 224, may be a glass fiber-reinforced material. However, other types of fiber reinforcement may be employed for the FRP material, such as reinforcement via basalt fibers, aramid fibers, carbon fibers or even polymer fibers (e.g., PET [Polyethylene Terephthalate], UHMWPE [Ultra-High Molecular Weight Polyethylene] and polypropylene, among other possibilities). Depending on the material used, dimensions and properties for ancillary components such as a covering/sleeve and clamping elements (see, e.g., 234 and 236 in
In accordance with one or more embodiments, the covering 234 may be embodied by a tubular sleeve, itself formed from material (e.g., non-metallic) which is stronger than that of the rebars 222, 224 themselves. Covering 234 may be generally cylindrical in shape, with an annular cross-section dimensioned to surround the region of interconnection 232 (shown in
In accordance with one or more embodiments, the covering 234 may be formed from a light, strong composite material, e.g., an FRP material, e.g., reinforced with high modulus fibers such as carbon, aramid or even Ultra-High Molecular Weight Polyethylene (UHMWPE) fibers. The clamping elements 236 may be embodied by two or more clamping clips or loops which, e.g., may be primarily nonmetallic with steel wire reinforcement. In this respect, the clamping clips or loops permit a tightening of the covering 234 with respect to the two rebars 222, 224 via applying the radially inwardly constricting force as mentioned. The constricting force thus mechanically connects the rebar extremities 226, 228 (see
In accordance with one or more embodiments, in order to help ensure a durable tightening force which avoids creep and relaxation, continuous reinforcement may be used within the clamping elements 236 such as continuous glass, carbon, or steel fibers. If steel reinforcement is chosen, the steel wires may be fully embedded (e.g., over-molded) in a resin matrix so as to prevent corrosion. (If there are concerns about electromagnetic compatibility in a facility where it may be a concern, it is not expected that the very low amount of steel wire would appreciably cause any issues.)
In accordance with one or more embodiments, and with continued reference to
The disclosure now turns to working examples of a mechanical coupling in accordance with one or more embodiments, as described and illustrated with respect to
In a similar vein,
In accordance with one or more embodiments, alternatives to a sine-wave profile (internal or external) could be provided for rebar extremities 326, 328. However, a sine-wave profile can be advantageous as it minimizes the inclusion of edges, and thus the development of stress concentrations susceptible that may potentially decrease the strength of the interconnection between rebars 322, 324 (e.g., in comparison with a square-wave profile on each rebar extremity 326, 328). Further, a sine-wave profile provides a significant degree of contact (between rebar extremities 326, 328) in a normal (radial) direction with respect to the longitudinal axis of the rebars 322, 324, in addition to contact along the axial direction. Thus, the significant degree of contact in both directions (radial and axial) helps significantly both in preventing separation of the rebar extremities 326, 328 and in inhibiting axial displacement of the two rebars 322, 324 with respect to each other.
In accordance with one or more embodiments, in order to help balance the relative strength of the two extremities 326, 328 with respect to each other, each extremity 326, 328 may have a cross-sectional area, constituted by solid material, that is approximately half of that of a cross-sectional area of the main body portion of a rebar.
In accordance with one or more embodiments, first rebar 422 includes a machined extremity 426 characterized primarily by a projection (or male portion) 438 extending longitudinally away from main body portion 427 of the first rebar 422. As with the example of
Additionally, in accordance with one or more embodiments, second rebar 424 includes a machined extremity 428 characterized primarily by a recess (or female portion) 440. As with the example of
In accordance with one or more embodiments, per the working example of
In accordance with one or more embodiments, the first and second rebars 522, 524 may be formed from an FRP material, while the sleeve 534 may be formed from an FRP material which is stronger than that of each of the rebars 522, 524. As such, in order to help ensure radial and axial strength and stiffness, the sleeve 534 can exhibit a high modulus and strength in the axial direction of the fiber (of its FRP material). Therefore, the sleeve 534 may be embodied by a unidirectional fiber-reinforced structure. In this connection, the low transverse stiffness of the material would permit constricting the sleeve 534 about the extremities of the rebars 522, 524 without appreciably inviting a risk of forming cracks in the sleeve. Further, the thickness of the sleeve 534 is a parameter that can be tailored in order to adjust the amount of required load to transfer from one of the rebars 522, 524 to the other. If the required load to transfer is sufficiently high as to warrant a thickness of sleeve 534 that itself necessitates an appreciably high tightening force (via clamping elements 536), then one or more several axial cuts at each end of the sleeve 534 could provide some circumferential flexibility and decrease the required torque to tighten the sleeve 534 around the rebars 522, 524.
It can be appreciated from the foregoing that, in accordance with one or more embodiments, methods of mechanically coupling two rebars are broadly contemplated, as illustrated in the flowchart of
As can be appreciated from the foregoing by a person of ordinary skill, in accordance with one or more embodiments, there is broadly contemplated herein a mechanical connection where two rebars are interconnected with no increase in cross-sectional area along a region of interconnection, while being joined with a double mechanical system including an interlocking design and a tightening mechanism. The interlocking design includes complementary male and female machined portions at the extremity of each rebar.
Further, it can be appreciated that, in accordance with one or more embodiments, there is a “synergistic” effect provided via a strong tightening mechanism and effective anti-slip (interlocking) mechanism. Particularly, the mere physical interlocking of rebar extremities may not be solely sufficient for transferring tensile/axial loads applied to the rebars, while such interlocking as contemplated herein indeed is highly effective in inhibiting relative axial displacement of the rebars and even preventing separation of the rebar extremities. A covering or sleeve, as broadly contemplated herein, then is applied to absorb the great majority of tensile/axial loads applied to the rebars (e.g., between about 70% and about 90% of such loads). At the same time, though, with relative axial slip of the rebars prevented via the interlocking connection, the tightening force applied by the covering/sleeve and clamping elements remains completely (or virtually completely) radial in orientation.
Generally, it can be appreciated from the foregoing that among the advantages afforded by one or more embodiments as broadly contemplated herein, there is a minimization of any tensile and shear load that may be transferred through surrounding concrete, as normally would be the case with conventional interconnection techniques such as lap splicing. Instead, such loads are transferred largely through the mechanical connection involving the rebar extremities, the covering and the clamping elements. Such a connection also averts the use of use of any grout, which decreases the weight of the connection. Moreover, the use of a ready-made covering/sleeve (e.g., formed from FRP) can help decrease overall assembly time without sacrificing any mechanical properties, compared to any structural adhesives that may be used in certain patching technologies.
Additionally, in accordance with one or more embodiments, it should be appreciated that with the co-axial arrangement of two rebars as afforded by the interlocking connection and covering/clamping broadly contemplated herein, an effect of physical “congestion” is greatly reduced in comparison with a lap splicing arrangement. Thus, in comparison with lap splicing, concrete being poured will flow much more easily for cast-in-place purposes.
Among other advantages afforded in accordance with one or more embodiments, as broadly contemplated herein, a mechanical connection can impart a strength that is significantly higher than that afforded by the rebars themselves (e.g., about 115% of the rebar strength itself), thus keeping regions outside of the connection below a maximum strain value of the rebar material.
Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. § 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words ‘means for’ together with an associated function.
