Mechanical coupler for reinforcing bars

Abstract

Described herein is a rebar coupler comprising a collapsible chamber, a solid compressible core located in the collapsible chamber, the solid compressible core resisting a collapsing motion of the collapsible chamber by opposing surfaces of the solid compressible core abutting opposing interior surfaces of the collapsible chamber as the collapsible chamber moves from a relative expanded position to a relative collapsed position. Under axial tension, the core undergoes controlled inelastic deformation — classic yielding for steel or stress-induced phase transformation for shape-memory-alloy (SMA) cores — while the surrounding sleeve remains elastic. When an SMA core is used, the coupler exhibits self-centering with negligible residual deformation, enabling rapid post-earthquake functionality. The modular core concept allows cost-tiered material selection — for example, steel, Cu-Al-Mn SMA, NiTi SMA, and others — while retaining common sleeve geometry and conventional fabrication practices, providing a tunable, replaceable fuse for seismic applications in reinforced-concrete construction, based on a validated force hierarchy that ensures the core yields before the rebar or sleeve.

Description

[0001] MECHANICAL COUPLER FOR REINFORCING BARS

[0002] BACKGROUND OF THE INVENTION

[0003] Field of the Invention

[0004] The present invention relates generally to construction with reinforcement bars (also known as rebars), and more particularly to a mechanical rebar coupler for splicing neighboring serially aligned reinforcement bars.

[0005] Description of the Related Art

[0006] Disruptive impact of seismic activity includes loss of life, injury, structural damage, and loss of functionality of a structure following the seismic activity, and is a well-recognized problem. Many solutions to mitigate risks of seismic activity have been implemented by improving, for example, design and construction techniques; land use controls, sensors, prediction and early-warning systems, coordinated emergency preparedness, and public education.

[0007] Regarding improved construction techniques, use of reinforcing bar couplers or mechanical splices in reinforced concrete construction is considered an improvement over lapped splices, with examples of improved parameters including tensile strength, ductility, permanent set slip, and cyclic loading fatigue performance. Load transfer for reinforcing bars linked by lap splicing is achieved through development of a cementitious bond. Effectiveness of lap links depends on type of bar and the strength and quality of concrete, and as bars are laid side by side, the load transfer is indirect, whereas rebar couplers and mechanical splices provide a direct in-line load transfer.

[0008] A key aspect of construction standards is the seismic design philosophy, which centers around dissipating seismic energy by allowing steel rebars to yield. However, this approach can lead to permanent deformations post-seismic activity, potentially rendering the structure irreparable. The risk of permanent deformations post-seismic activity can be mitigated by replacing steel bars with shape memory alloy (SMA) bars. Using SMA bars instead of steel bars can significantly reduce seismic residual deformations and structural damage and make repairs relatively easier following seismic activity. However, SMA bars are more expensive than steel rebars; for example they may be 30-fold more expensive. While a high cost of SMA bars is a valid concern, a strategic approach can mitigate this concern. Cost-effectiveness can be balanced with structural resilience by using SMA bars at critical locations and employing steel bars elsewhere. This approach attempts to maximize benefits of SMA bars without incurring excessive costs. The cost of using SMA bars can also be reduced by using SMA bars as a mechanical splice to couple steel rebars.

[0009] Regardless of whether SMA bars are used to replace steel rebars or are mechanically spiced to neighboring serially aligned steel rebars, one of the hurdles for using SMA bars is that SMA bars are not easily connected to rebars. Machining SMA bars is very expensive and they cannot be welded. The problem associated with connecting SMA bars to rebars was solved by threading the SMA bar to connect them using threaded couplers. The threading process is extremely expensive and will add a barrier to using the SMA bars. As a proof of concept, threaded SMA bars were utilized in the construction of the piers of a bridge in Seattle. Details about this bridge can be found in: Jiping GE, M. Saiid SAIIDI, Sebastian VARELA, “Computational studies on the seismic response of the State Route 99 bridge in Seattle with SMA / ECC plastic hinges”, Front. Struct. Civ. Eng., 2019, 13(1): 149 164 https: / / doi.org / 10.1007 / sl 1709-018-0482-6.

[0010] Despite improvements in construction techniques and efforts by governments and private businesses to mitigate disruptive impact of seismic activity, devastating consequences of seismic activity persist in current times. For example, Table 1 shows that a death toll from earthquakes is a long-recognized problem compiling recorded data from 1900 to 2016. Table 2 shows that large numbers of deaths from earthquakes continue to occur in a current time frame (for example greater than 200000 deaths in both 2004 and 2010). The counts in Table 1 and Table 2 are presented by Statista.com and are generally confirmed by statistics maintained by the United States Geological Survey, a USA government agency.

[0011] Table 1. Countries with the most earthquake fatalities 1900-2016 according to Statista.com (17 November 2016 report). Table 2. Global death toll due to earthquakes from 2000 to 2015 according to Statista.com (30 September 2016 report).

[0012] Reasons for persistent death and damage often include ineffective construction, for example due to absence of federally legislated and enforced building codes as occurred in the Haiti 2010 earthquake, or due to inaccurate assessment of seismic risk as a result of insufficient knowledge of an underlying fault line and its inherent seismic risk as occurred in the 2011 Christchurch earthquake.

[0013] Clearly, disruptive impacts from seismic activity persist at an unacceptable level despite advances in construction techniques and other aspects of seismic risk mitigation. Accordingly, there is a continuing need to provide alternative solutions to the construction industry to reduce disruptive impacts of seismic activity.

[0014] SUMMARY OF THE INVENTION

[0015] In an aspect there is provided, a rebar coupler comprising a collapsible chamber, a solid compressible core located in the collapsible chamber, the solid compressible core resisting a collapsing motion of the collapsible chamber by opposing surfaces of the solid compressible core abutting opposing interior surfaces of the collapsible chamber as the collapsible chamber moves from a relatively expanded position to a relatively collapsed position.

[0016] A combination of the collapsible chamber and the solid compressible core provides an opposing / restoring force vector when a tension vector is applied to the rebar coupler at a splice joint with a rebar. The compressible core is qualified as solid to distinguish the compressible core from liquid and gas, and the term solid is intended in a conventional sense to include any typical material properties of a solid, except where a specific material property or a specific quantified range of a material property is indicated.

[0017] In another aspect there is provided, a rebar coupler comprising: an elongate first frame and an elongate second frame; the first frame defining a first central longitudinal axis, the first frame comprising a first connector positioned a first distance from a first transverse plate oriented transverse to the first central longitudinal axis, the first connector configured for coupling / attachment of a first rebar; the second frame defining a second central longitudinal axis, the second frame comprising a second connector positioned a second distance from a second transverse plate oriented transverse to the second central longitudinal axis, the second connector configured for coupling / attachment of a second rebar, the first frame and the second frame slidably engaged to overlap the first distance and the second distance to define a third distance extending from the first transverse plate to the second transverse plate, the first frame and the second frame combining to form a chamber defining an interior space for holding / capturing a solid compressible core, the interior space defined by a longitudinal dimension equal to the third distance, the first longitudinal axis aligned to be substantially parallel to the second longitudinal axis.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 shows a perspective view of a first variant of a rebar coupler.

[0020] Figure 2 shows a first exploded view of the rebar coupler shown in Fig. 1 (solid compressible core not shown).

[0021] Figure 3 shows a second exploded view of the rebar coupler shown in Fig. 1 (solid compressible core shown).

[0022] Figure 4 shows a first side view of the rebar coupler shown in Fig. 1.

[0023] Figure 5 shows a second side view of the rebar coupler shown in Fig. 1.

[0024] Figure 6 shows a cross-section view of the rebar coupler taken along the cut line 6-6 shown in Fig. 4.

[0025] Figure 7 shows a schematic representation of the solid compressible core providing an opposing / restoring force vector when a tension vector is applied to the rebar coupler shown in Fig. 1 at a splice joint with a rebar.

[0026] Figure 8 shows the same side view of the rebar coupler shown in Fig. 4, except including attachment to first and second rebars.

[0027] Figure 9 shows the same side view of the rebar coupler shown in Fig. 5, except including attachment to first and second rebars.

[0028] Figure 10 shows a perspective view of a second variant of a rebar coupler. Figure 11 shows an exploded view of the rebar coupler shown in Fig. 10 (solid compressible core shown).

[0029] Figure 12 shows connector points of the rebar coupler shown in Fig. 10 in attachment to first and second rebars.

[0030] Figure 13 shows a conceptual schematic of the rebar coupler shown in Fig. 1 to accompany description provided in Table 3.

[0031] Figure 14 shows a conceptual schematic of the rebar coupler shown in Fig. 10 to accompany description provided in Table 4.

[0032] Figure 15 shows a photograph of a proof-of-concept rebar coupler tested in Experimental Example 2.

[0033] Figure 16 shows a plot of typical Stress-Strain behaviour of mild steel used to construct the rebar coupler in Experimental Example 2.

[0034] Figure 17(A-C) show schematic illustration and photographic evidence of test set-up in Experimental Example 2. Fig. 17A shows a schematic depiction of the test set-up. Fig. 17B shows a photograph of a test of a continuous 15M rebar. Fig. 17C shows a photograph of a test of the rebar coupler shown in Fig. 15 spliced to first and second rebars.

[0035] Figure 18 shows a plot of Load-Displacement curve results of testing in Experimental Example 2.

[0036] Figure 19 shows a plot of hysteresis envelope for Cases I-IV (SMA cores) in Experimental Example 3.

[0037] Figure 20 shows a plot of FE vs. Experiment Overlay: Load-Displacement Loop for Case V (Mild-Steel Core) with the C-COUP Test Trace (Experimental Example 3.5).

[0038] Figure 21 shows a plot of Core Stress-Strain Curve for the SMA core (Experimental Example 3.6).

[0039] Figure 22 shows Von-Mises Distribution in the Sleeve at Peak Load for Cases I-IV: peak stress in the legend represents the yield strength of the sleeve, i.e. stresses with a black hatch violate the assumed stress hierarchy, 0.8 F_y, frame.

[0040] Figure 23 shows a Von Mises Stress Contour (Violation Case I in Experimental Example 3.7.2).

[0041] Figure 24 shows a Plastic Strain Contour (Violation Case I).

[0042] Figure 25 shows a Stress-Strain of External Steel Rebars (Violation Case I).

[0043] Figure 26 shows a Stress-Strain of Core Material (Violation Case I). Figure 27 shows a Von Mises Stress Contour (Violation Case II in Experimental Example

[0044] 3.7.2).

[0045] Figure 28 shows a Plastic Strain Contour (Violation Case II).

[0046] Figure 29 shows a Stress-Strain of Frame Material (Violation Case II).

[0047] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0048] Referring to the drawings, various examples of a rebar coupler are described. A common feature of all examples of the rebar coupler is a collapsible chamber holding a resistance material. More specifically, the rebar coupler requires the collapsible chamber and a solid compressible core located in the collapsible chamber. In most examples, the collapsible chamber is typically elongate and typically centrally located within the rebar coupler, and first and second arms extend longitudinally beyond opposing ends of the collapsible chamber, the first arm provides a splice joint for a first rebar and the second arm provides a splice joint for a second rebar. The solid compressible core provides an opposing / restoring force vector by abutting against interior surfaces of the collapsible chamber when a tension vector is applied to the rebar coupler at a splice joint with a rebar. More specifically, the solid compressible core resists a collapsing motion of the collapsible chamber by opposing surfaces of the solid compressible core abutting opposing interior surfaces of the collapsible chamber as the collapsible chamber moves from a relative expanded position to a relative collapsed position. The collapsible chamber moves from the relative expanded position to the relative collapsed position due to a tension vector applied to the rebar coupler at a rebar splice joint, specifically an increase in the applied tension vector results in the movement from the relative expanded position to the relative collapsed position, so that comparing a first tension vector at the relative expanded position with a second tension vector causing movement to the relative collapsed position, the second tension vector is greater than the first tension vector. The direction of the first and second tension vectors is co-axial with the rebar(s). The tension vector is the force vector in the steel rebar. The coupler and the internal core should be co-axial to the reinforcing bar to transmit the tensile force between the coupled bars without inducing additional stresses in the concrete.

[0049] Figs. 1-9 show a first example of the rebar coupler 10. The rebar coupler 10 includes an elongate first frame 20 and an elongate second frame 30. The first frame 20 defines a first central longitudinal axis A20, the first frame comprising a first connector 22 positioned a first distance D20 from a first transverse plate 24 oriented transverse to the first central longitudinal axis A20, the first connector 22 configured for coupling / attachment to a first rebar 26. The second frame 30 defines a second central longitudinal axis A30, the second frame comprising a second connector 32 positioned a second distance D30 from a second transverse plate 34 oriented transverse to the second central longitudinal axis A30, the second connector 32 configured for coupling / attachment to a second rebar 36. The first frame 20 and the second frame 30 are slidably engaged to overlap the first distance D20 and the second distance D30 to define a third distance D40 extending from the first transverse plate 24 to the second transverse plate 34, the first frame and the second frame combining to form a collapsible chamber 40 defining an interior space for holding / capturing a solid compressible core 50, the interior space defined by an interior longitudinal dimension of the collapsible chamber 40 equal to the third distance D40, the first longitudinal axis A20 aligned to be substantially parallel to the second longitudinal axis A30. In some examples, the first and second frames are configured and aligned so that the first longitudinal axis A20 is co-axial with the second longitudinal axis A30.

[0050] Considering Figs. 1-9, components of the rebar coupler can be described in greater detail. For example, the first frame 20 and the second frame 30 both provide rectangular bodies that are slidably linked together. The rectangular bodies are elongate and each defines an interior space that cooperates to form a volume for holding the solid compressible core 50. For ease of reference in describing interconnection of frame components, the elongate rectangular bodies are composed of a pair of substantially parallel longer sides joined by a pair of substantially parallel shorter ends with the rebar connectors or splice joints located at or near one of the pair of shorter ends and the transverse plates located at or near the other of the pair of shorter ends.

[0051] The first frame 20 includes a first connector 22 formed as a female receptacle configured for attaching, coupling, securing, or fixing the first rebar 26 using any convenient fastening mechanism or technique including for example threaded engagement, transverse screws, transverse pins, transverse rivets, welding, combinations thereof, and the like. As an example, the first connector 22 formed as a female receptacle may be a first female port or a first female socket for securing or fixing the first rebar. As another example, the first female port or socket may be threaded on its interior surface for mated threaded engagement with a threaded end of the first rebar. The first frame 20 is formed as a rectangular body defining an elongate interior space, and the rectangular body connects the first connector 22 (eg., first female port or socket) to the first transverse plate 24, with the first female port or socket and the first transverse plate disposed at or proximal to opposing ends of the rectangular body. The first transverse plate 24 may be formed as a first block, cover, or cap for engaging or abutting a first end 52 of the solid compressible core 50. Components of the first frame 20 may be detachable including for example, the first connector 22 being detachable from the rectangular body, the transverse plate 24 being detachable from the rectangular body, or any other portion of the rectangular body being detachable. Reversible or semi -permanent detachment / attachment may be accomplished by any convenient mechanism including for example mated engagement, screws, pins, rivets, partial welding, adhesive, and the like.

[0052] The second frame 30 includes a second connector 32 formed as a female receptacle configured for attaching, coupling, securing, or fixing the second rebar 36 using any convenient fastening mechanism or technique including for example threaded engagement, transverse screws, transverse pins, transverse rivets, welding, combinations thereof, and the like. As an example, the second connector 32 formed as a female receptacle may be a second female port or a second female socket for securing or fixing the second rebar. As another example, the second female port or socket may be threaded on its interior surface for mated threaded engagement with a threaded end of the second rebar. The second frame 30 is formed as a rectangular body defining an elongate interior space, and the rectangular body connects the second connector 32 (eg., second female port or socket) to the second transverse plate 34, with the second female port or socket and the second transverse plate disposed at or proximal to opposing ends of the rectangular body. The second transverse plate 34 may be formed as a second block, cover, or cap for engaging or abutting a second end 53 of the solid compressible core 50. Components of the second frame 30 may be detachable including for example, the second connector 32 being detachable from the rectangular body, the transverse plate 34 being detachable from the rectangular body, or any other portion of the rectangular body being detachable. Reversible or semi -permanent detachment / attachment may be accomplished by any convenient mechanism including for example mated engagement, screws, pins, rivets, partial welding, adhesive, and the like. As an example of possible detachable portions of the second frame 30, the second transverse plate 34 is shown as being detachable from the second frame 30. The second transverse plate 34 is reversibly inserted into an aligned pair of apertures formed on opposing sides of the rectangular body of the second frame 32. The transverse plate is sized to be longer than the exterior transverse distance between the opposing sides so that when the second transverse plate 34 is inserted through the aligned pair of apertures a portion of the transverse plate extends beyond the exterior surface of the opposing sides forming an exterior overhang of the second transverse plate 34 on either side of the opposing sides. First and second bores formed in the overhangs of the second transverse plate receive first and second latching pins (34a, 34b) to reversibly (eg., interference fit of latching pins in corresponding bores) or semipermanently (eg., interference fit with spot welding of latching pins in corresponding bores) fix the transverse plate 34 within the pair of aligned apertures in the second frame 30. Latching pins are simply an illustrative example of securing the second transverse plate 34, and any other convenient technique such as rivets inserted in corresponding bores of the overhangs may be used.

[0053] The first frame 20 and the second frame 30 are positioned in their sliding linkage to provide a sequential longitudinal spatial ordering in forward or reverse of the first connector 22 (first receptacle / port / socket for coupling the first rebar) followed by the second transverse plate 34 (second block / cover / cap) followed by the second end 53 of the solid compressible core 50 followed by the first end 52 of the solid compressible core 50 followed by the first transverse plate 24 (first block / cover / cap) followed by the second connector 32 (second receptacle / port / socket for coupling the second rebar).

[0054] The first frame 20 and the second frame 30 are positioned in their sliding linkage to provide an overlapped section, the overlapped section bound longitudinally by the first transverse plate 24 (first block / cover / cap) and the second transverse plate 34 (second block / cover / cap) with the solid compressible core located between the first and second transverse plates (24, 34), the first transverse plate 24 (first block / cover / cap) and the second transverse plate 34 (second block / cover / cap) forming opposing longitudinal ends of the collapsible chamber 40 to hold the solid compressible core 50.

[0055] The first frame 20 and the second frame 30 are slidably engaged so that tension applied to one or both of the first connector 22 (first receptacle / port / socket) and the second connector 32 (second receptacle / port / socket) causes a decrease in longitudinal distance of the collapsible chamber as defined by the spacing between the first transverse plate 24 (first block / cover / cap) and the second transverse plate 34 (second block / cover / cap), and the solid compressible core resists the decrease in longitudinal distance. Alternatively stated in terms of distances marked in Fig. 6 and considering the schematic representation of vectors shown in Fig. 7, as tension from one or both of the first and second rebars is transferred to the rebar coupler the collapsible chamber decreases in its longitudinal distance D40 (the third distance), while both the first and second distances (D20, D30) remain constant. More specifically, the first distance D20 which characterizes a spacing between the first connector 22 and the first transverse plate 24 remains constant and the second distance D30 which characterizes a spacing between the second connector 32 and the second transverse plate 34 remains constant. As schematically illustrated in Fig. 7, the solid compressible core 50 provides an opposing / restoring force vector by abutting against interior surfaces of the collapsible chamber when a tension vector is applied to the rebar coupler at a splice joint with a rebar. More specifically, the solid compressible core resists a collapsing motion of the collapsible chamber by opposing surfaces of the solid compressible core abutting opposing interior surfaces (depicted by compression force vectors opposing or countering the tension force vectors applied to the first and second frames) of the collapsible chamber as the collapsible chamber moves from a relative expanded position to a relative collapsed position.

[0056] Figs. 10-12 show a second example of the rebar coupler 100. The rebar coupler 100 includes an elongate first frame 120 and an elongate second frame 130. The first frame 120 defines a first central longitudinal axis A 120, the first frame comprising a first connector 122 positioned a first distance DI 20 from a first transverse plate 124 oriented transverse to the first central longitudinal axis A120, the first connector 122 configured for coupling or attachment to a first rebar 126. The second frame 130 defines a second central longitudinal axis A l 30, the second frame comprising a second connector 132 positioned a second distance D130 from a second transverse plate 134 oriented transverse to the second central longitudinal axis A l 30, the second connector 132 configured for coupling or attachment to a second rebar 136. The first frame 120 and the second frame 130 are slidably engaged to overlap the first distance DI 20 and the second distance DI 30 to define a third distance D140 extending from the first transverse plate 124 to the second transverse plate 134, the first frame and the second frame combining to form a collapsible chamber 140 defining an interior space for holding or capturing a solid compressible core 150, the interior space defined by an interior longitudinal dimension of the collapsible chamber 140 equal to the third distance D140, the first longitudinal axis A 120 aligned to be substantially parallel to the second longitudinal axis A l 30. Often, the first and second frames are configured and aligned so that the first longitudinal axis A120 is co-axial with the second longitudinal axis A l 30. While a co-axial alignment is a typical configuration, an offset from co-axial alignment may be tolerated and accommodated.

[0057] Significant differences between the second example of the rebar coupler 100 and the first example of the rebar coupler 10 is that the rebar coupler does not have a detachable component (specifically, the second transverse plate 134 is not detachable from the second frame 130) and the first and second frames (120, 130) are formed as tubular cages rather than rectangular bodies. The two differences are related in that formation of the first and second frames as open-ended tubular cages permits sliding linkage of first and second frames (120, 130) from a first separated / unassembled position to a second engaged / assembled position without needing detachment of a component of either frame. By contrast, rebar coupler 10 is formed by sliding linkage of two closed rectangular frames and therefore requires detachment of a component (for example, the second transverse plate 34) of one of the first and second frames (20, 30) to permit sliding linkage of first and second frames (20, 30) from a first separated / unassembled position to a second engaged / assembled position. While an open-ended tubular cage design of the first and second frames (120, 130) permits linkage without detachment of a frame component, components of the frames may be made detachable as desired or additional components may be attached as desired to suit a particular manufacturing technique or particular implementation. For example, a female port / socket may be welded to at least one of the first and second connectors (122, 132) after the first and second frames are assembled in a sliding linkage to capture the solid compressible core 150.

[0058] Further comparison of rebar coupler 10 and rebar coupler 100 can be gleaned from review of Table 3 accompanied by Fig. 13 and Table 4 accompanied by Fig. 14.

[0059] Table 3. Summary of parts for rebar coupler 10. Table 4. Summary of parts for rebar coupler 100.

[0060] Considering the open-ended tubular cage shape of rebar coupler 100 in greater detail, both first and second frames are similarly constructed, with the first frame being a tubular cage bound by a closed end formed by the first transverse plate and a first longitudinal tubular body formed by a first plurality of gapped bars (the first plurality of gapped bars separated by a first plurality of longitudinal gaps for spacing neighboring gapped bars) extending longitudinally from the first transverse plate, the first plurality of gapped bars terminating with an open end for receiving and coupling a rebar at or near the open end. Similarly, the second frame is a tubular cage bound by a closed end formed by the second transverse plate and a second longitudinal tubular body formed by a second plurality of gapped bars (the second plurality of gapped bars separated by a second plurality of longitudinal gaps for spacing neighboring gapped bars) extending longitudinally from the second transverse plate, the second plurality of gapped bars terminating with an open end for receiving and coupling a rebar at or near the open end. The plurality of gapped bars in the first and second frames (120, 130) are dimensioned for mating engagement of the first and second frames for sliding linkage. More specifically, the first plurality of longitudinal gaps defined in the first longitudinal tubular body are sized with a circumferential dimension that matches the second plurality of gapped bars in the second longitudinal tubular body, and the second plurality of longitudinal gaps defined in the second longitudinal tubular body are sized with a circumferential dimension that matches the first plurality of gapped bars in the first longitudinal tubular body, so that in a sliding linkage the first plurality of the gapped bars in the first longitudinal tubular body are inserted in and fit in the second plurality of longitudinal gaps defined in the second longitudinal tubular body and the second plurality of the gapped bars in the second longitudinal tubular body are inserted in and fit in the first plurality of longitudinal gaps defined in the first longitudinal tubular body, thereby allowing the first plurality of gapped bars to translate relative to the second plurality of gapped bars when the first and second frames are in sliding linkage. Since matching is achieved by matching dimensions of the first plurality of gapped bars with the second plurality of gaps, and vice versa, dimension(s) of the first plurality of gapped bars need not be matched to dimension(s) of the second plurality of gapped bars, and may differ in circumference, tubular interior diameter, tubular exterior diameter, tubular length, and the like. Furthermore, individual differences in dimension(s) of the plurality of gapped bars may be accommodated as may be suited to a particular implementation.

[0061] The currently disclosed rebar coupler has been validated by experimental testing. Experimental testing results demonstrate ability of the disclosed device to effectively splice rebars and transfer tensile forces through a compressive load transfer mechanism. The following experimental examples are for illustration purposes only and are not intended to be a limiting description.

[0062] Experimental Exemplification: Experimental Example 1 (candidate material property profiles).

[0063] Example 1 presents the mechanical properties of candidate SMA core and steel sleeve (frame) materials, forming the technical foundation for simulation and design validation in accordance with global mechanical splice standards.

[0064] • Table 5 lists quantitative core properties, including transformation (plateau) stress, ultimate tensile strength, elastic modulus, and superelastic plateau strain range, aligned with ISO 15835- 1 (2018) and EAD 160129 (2020).

[0065] • Table 6 summarizes qualitative cyclic behaviour (strain hardening, energy dissipation, and residual deformation) referenced against the SMA performance categories defined in ISO 15835- 1 (2018) and the low-cycle seismic loading criteria of EAD 160129 (2020). • Table 7 compiles sleeve (frame) material data, including yield and ultimate strength, stiffness, weldability, and suitability for fabrication, ensuring compliance with the coupler material specifications required under EAD 160129 (2020).

[0066] These datasets form the material framework for subsequent finite element modelling and capacity-hierarchy validation, all justified under recognized international standards (ISO 15835 - 1, ASTM A1034, and EAD 160129).

[0067] Table 5. Quantitative Mechanical Properties of Candidate Core Materials (SMA & mild steel). Table 6. Qualitative Cyclic-Behaviour Descriptors for Core Materials.

[0068] Table 7. Candidate Sleeve Steels - Strength, Weldability, Application.

[0069] Experimental Exemplification: Experimental Example 2 (tension tests).

[0070] The coupler depicted in Figure 15 utilizes a compression load transfer mechanism to splice rebars, allowing the utilization of rebars that cannot be spliced with the tensile couplers currently available on the market. This innovative coupler comprises two primary units that encapsulate the spliced rebar. A tensile force applied at the end of the coupler is transferred to the other end through compression of the rebar placed inside the coupler. The shown prototype presents a proof - of-concept design. However, this design can be altered in many ways.

[0071] The development of this coupler was motivated by the current inventor group’s research on the use of Shape Memory Alloy (SMA) bars in the construction industry. Splicing to these bars is either costly or unreliable. The currently disclosed coupler spliced to rebars will allow for dissipation of seismic forces. The currently disclosed coupler can act as a fuse that absorbs seismic energy, thereby reducing structural damage. The currently disclosed coupler introduces a truly innovative feature: the ability to have a fuse material within its inner chamber. This fuse is formed as a solid compressible core. In structural engineering, the term “fuse” refers to a sacrificial element that experiences damage, thereby protecting surrounding elements. In the event of damage, the repair is done by replacing the fuse. This concept is used in Earthquake Engineering as the seismic design philosophy allows damage to occur. Using SMA bars as the fuse material presents an additional advantage: the residual seismic inelastic deformations are significantly reduced or perhaps even eliminated, simplifying the repair process following seismic activity and allowing structures to remain functional with short downtime.

[0072] There are two distinct behaviours for SMA: shape memory effect (SME) and superelasticity. The coupler utilizes the superelastic behaviour of SMA. There exist three primary families for SMAs: nickel -titanium (NiTi) alloys, copper-based alloys, and iron-based alloys. The majority of previous research on structural applications utilized NiTi and copper-based alloys.

[0073] The 2011 Christchurch earthquake is a poignant example of significant seismic damage and loss of functionality in buildings. The primary cause was steel yielding, which absorbed the seismic energy at the cost of irreversible deformations and a permanent incline. This damage led to prolonged service disruptions, as it necessitated extensive repairs or reconstruction. This damage underscored the need for improved seismic design strategies focusing on life safety and maintaining building functionality post-earthquake. Such insights have since influenced revisions in building codes and the adoption of more robust design approaches globally, including stricter performance-based standards.

[0074] Integrating SMA in the chamber of the currently disclosed coupler will significantly reduce or even approach elimination of the observed irreversible deformations and permanent inclination experienced, for example, in the 2011 Christchurch earthquake. SMAs possess the unique selfcentering property, allowing them to absorb and dissipate seismic energy without experiencing any residual deformations. Restoring the structure to its initial condition following the seismic activity eliminates the need for extensive repairs or demolition.

[0075] Proof-of-Concept Coupler: Mild steel is known for its widespread availability and reasonable cost. Therefore, the coupler was manufactured using mild steel. Figure 16 illustrates the stress-strain behaviour of the mild steel, characterized by a yield strength of 420 MPa and an ultimate strength of 440 MPa. The yield strength signifies the maximum load the steel can bear before its behaviour transitions from elastic to plastic. Below this threshold, the material is expected to deform elastically, reverting to its original shape once the applied stress is removed. This threshold serves as a critical limit for engineers in structural design. The ultimate strength represents the maximum load the material can endure before failure occurs.

[0076] The coupler was designed to remain elastic and undamaged when the steel bars are tensioned, i.e., the steel bar placed within the coupler will yield before the coupler reaches its yield strength.

[0077] Test set-up: Figure 15 illustrates the prototype sleeve featuring a central compression chamber designed for the internal core bar. The chamber dimensions (sleeve length, wall thickness, and clearance) are optimized based on FE simulation geometry (see Example 3) and hierarchy constraints from ISO 15835-1 to achieve concentric load transfer and satisfy the hierarchical yield ratios outlined in Example 3.

[0078] • Test frame: 520 kN Tinius-Olsen screw-driven universal testing machine, calibrated per ASTM E4 (2013) to ensure traceable force measurements with <±1 %.

[0079] • Specimen grips: Custom wedge grips with spherical scats per ASTM E8 (2013), maintaining axial alignment and minimizing secondary bending (< 2 % of axial load).

[0080] • Instrumentation and loading control: Two 100 mm LVDTs measured the relative slip (displacement) between rebars and the sleeve, while a 50 mm LVDT tracked the global elongation of the assembly. Strain gauges were affixed mid-length on the 015 mm core bar and external Grade 60, 20M (019.5 mm) rebars. The crosshead was driven at a constant rate of 0.015 mm / mm / min (Method C per ASTM E8) to capture accurate elastic-plastic transitions. This strain rate corresponds to a quasi-static rate appropriate for structural materials. All instrumentation meets ISO 15630-1 (2019) specifications for rebar testing.

[0081] • Specimens (see Figure 17): o C-REF: Bare 15 M mild steel bar, loaded monotonically to ~3 % strain, then partially unloaded and reloaded (see Figure 17B). o C-COUP: Same 15M bar enclosed in sleeve with external rebars, tested using the same protocol. The unload-reload cycle simulates the first seismic displacement reversal, with a slip threshold of < 0.1 mm required for reliable rc-cngagcmcnt (sec Figure 17C).

[0082] Results: Two tensile tests (C-REF and C-COUP) were performed following the same loading regimen. As shown in Table 8 and Figure 18, both specimens reached ~3 % global strain. The coupled specimen successfully transferred load and re-engaged the core. • Bar size & grade: Grade 60 20M rebars (0 ~ 19.5 mm) represent typical reinforcement in plastic-hinge regions for mid-rise frames; testing this size offers a conservative proxy for larger bars with lower strain demands.

[0083] • Core-to-sleeve hierarchy: The 015 mm mild-steel core was selected to yield at approximately 90 kN, which is approximately 15-20% below the external rebars, meeting the hierarchy ratios outlined in Example 3 and sacrificial fuse design guidelines.

[0084] • Strain demand: The 3% global strain targets ductile-link demands under a Design Basis Earthquake (2.5-3% per ACI 318 and EN 1998-1).

[0085] • Load path: The unload / reload to < 50 % peak emulates the initial seismic reversal; reengagement within < 0.1 mm slip assures continued performance during cyclic loading

[0086] • Fixture performance: The testing frame and self-aligning wedge grips limited secondary bending to < 2 % axial load, aligning with ASTM E8 tolerances and ensuring deformation was localized to the splice.

[0087] Despite the limited sample size (ISO 15835-1 requires three specimens per bar size for qualification), these tests capture the primary loading, strain demand, and geometric conditions expected in seismic coupler applications.

[0088] LVDTs recorded residual slip < 0.05 mm, a figure well below the 0.1 mm re-engagement threshold specified in ISO 15835-1 (static & seismic categories) and confirmed in EOTA 160129 coupler guidelines.

[0089] Although ISO 15835-1 recommends three specimens per bar size for full qualification, two specimens are acceptable for proof-of-concept validation, confirming core-first yielding, low slip, and re-engagement behaviour..

[0090] Table 8. Summary of Experimental Results in Example 2. Tension test discussion: The tension tests were conducted to evaluate the effectiveness of the proposed load transfer mechanism in splicing rebars while preserving the load-deformation behaviour akin to a single, continuous rebar. For the tension tests, the two bars connected to the coupler were selected to have a higher strength than the bar placed within the coupler to simulate the intended use with Shape Memory Alloy (SMA) bars.

[0091] The tensile tests were conducted using a 520 kN Tinius Olsen Universal Testing Machine following ASTM A370 standards. The Tinius Olsen Universal Testing Machine has a stationary base and a mobile upper frame. The specimen under examination is secured to the stationary base at one end and to the mobile frame at the other using clamps. As the upper frame is elevated, moving away from the stationary base, tensile forces are applied to the clamped specimen, as shown in Figure 17A.

[0092] Two tensile tests were performed to ascertain whether the load transfer mechanism facilitated by the coupler would emulate the targeted behaviour: one with a continuous 15M rebar and another with a 15M rebar inserted within the coupler, as illustrated in Figures 17B and 17C.

[0093] The results, depicted in Figure 18, are presented in the form of load-displacement curves. The load-displacement behaviours of the two tests were similar, indicating the proposed coupler's suitability for effectively splicing rebars and transferring the tensile forces through the proposed compressive mechanism. The behaviour was governed by the tension behaviour of the continuous 15M bar in the first test and the compression behaviour of the 15M bar placed within the coupler in the second test.

[0094] The initial displacements up to approximately 10 mm are due to deformation of the bar and deformations within the setup. After 10 mm, the deformations were only associated with the bar elastic deformation (region 1 in Figure 18). If the load was removed within this region, the bars would return to their original length.

[0095] At a load of about 90 KN, the 15M bars yielded in tension in the first test and in compression in the second test. This point marked the transition from elastic to plastic behaviour, Point 2 in Figure 18. In the second test, the bars connected to the coupler remained unaffected due to their higher strength.

[0096] Beyond the yielding point, the material experiences substantial deformation without a corresponding increase in stress. This stage is referred to as the yield plateau (region 3 in Figure 18). The yield plateau behaviour observed in the coupler test mirrored that of the 15M continuous bar test. The observed minor differences in deformations are expected in experimental studies. After reaching the yield point, the load was reduced and then increased again to mimic the expected loading and unloading of the bars during seismic activities. This unloading and loading activity is marked as Region 4 in Figure 18. Both the continuous bar and the coupler behaved in the same manner, affirming the coupler's suitability for seismic applications.

[0097] These results confirm that the prototype coupler effectively transfers axial force through compression of the internal core bar, achieving the intended yielding hierarchy while maintaining elastic behaviour in the sleeve. Compared to the reference specimen, the coupled assembly exhibited a modest (~4%) increase in initial stiffness without affecting yield capacity, indicating composite action without premature slip.

[0098] During the unload-reload cycle, the internal core re-engaged seamlessly, with residual slip < 0.05 mm — well below the 0.1 mm threshold permitted by ISO 15835-1 and EOTA specifications. The load-displacement curve retraced the original elastic branch, indicating negligible strength degradation and full recovery of axial stiffness.

[0099] Strain-gauge measurements confirmed that plastic deformation localized within the 015 mm mild-steel core, while the surrounding Grade 60 rebars and sleeve remained elastic. This response satisfies the force-hierarchy limits of 0.80 F_y, frame and 0.90 F_y, bar outlined in Example 3. Post-test visual inspection revealed minor local buckling of the core. However, there was no measurable deformation of the sleeve, verifying that the sleeve possessed the necessary strength margin (>25% above rebar yield) for seismic applications.

[0100] Although the mild-steel core lacks self-centering capability, the results confirm the intended axial load path and validate the coupler's core-first yielding behaviour. These outcomes establish a performance baseline for SMA-core development and meet the preliminary qualification requirements for mechanical couplers as specified in ISO 15835-1.

[0101] In short, the tests demonstrated that the current design could transfer the tension forces through compression within the coupler.

[0102] Upon reviewing the test results, a question may arise regarding emphasis on tension tests, and why is compression not as significant of a concern as tension. The answer relates to concrete construction being better suited to withstand compression forces than tension forces. More specifically, given concrete's low tensile resistance, it can only withstand compression forces, while the rebars provide the necessary tensile resistance. However, concrete does not eliminate effect of compression forces, and when subjected to a sufficient compression, concrete may undergo a slight contraction. As an integral part of the concrete structure, the disclosed coupler will also experience this slight contraction. This contraction is typically sufficiently small so as to induce small compression in the coupler's external body (for example, in the first and second frames), but without impacting the solid compressible core.

[0103] Experimental Exemplification: Experimental Example 3 (finite element study).

[0104] A finite element (FE) study was conducted using ANSYS to extend the experimental validation and assess the structural response of the coupler under tensile loading. The simulations aimed to verify the intended force hierarchy and evaluate coupler performance across different core / sleeve material combinations.

[0105] Example 3.1 : Model Geometry and Mesh.

[0106] The FE model included the coupler sleeve, external reinforcing bars, and internal solid compressible core. A structured hexahedral mesh was used and refined in stress-critical regions. Mesh convergence was verified via ANSYS's automated h-refmement utility until changes in total reaction force and sleeve peak stress were below 5% across iterations.

[0107] Example 3.2: Material Model Definitions.

[0108] The SMA solid compressible core was modelled using the built-in ANSYS SMA material model, which captures superelastic plateau behaviour, hysteresis, transformation-induced stiffness changes, and residual strain effects. Mild steel cores used standard multilinear isotropic hardening. Sleeve and external rebars were modelled with bilinear elastoplastic properties derived from Tables 5, 6, and 7 and relevant standards (e.g., ASTM A572, EN 10025-6). Table 9 and Figure 19 define the hysteresis model for the SMA core material.

[0109] Table 9. SMA Material Parameters Defining the Hysteresis Envelope in Figure 19.

[0110] Example 3.3: Boundary Conditions and Loading Protocol.

[0111] Displacement-controlled axial loading was applied at the ends of the external rebars to simulate both monotonic and cyclic tensile conditions. A full three-dimensional model of the coupler assembly was used without invoking geometric or loading symmetry. Contact interfaces (core-sleeve, sleeve-rebar) were modelled using bonded or unbonded definitions, depending on the intended mechanical behaviour and connection details of each material pair. The cyclic protocol included unloading and reloading sequences to evaluate re-engagement behaviour, hysteresis characteristics, and residual slip at strain levels up to approximately 4%.

[0112] Example 3.4: Simulation Matrix.

[0113] This example defines the five FE cases, which cover a range of core and sleeve material pairings, and outlines the modelling assumptions used for each case (see Table 10).

[0114] The finite element study included five material pairings (core and sleeve), representing performance tiers from premium SMA-based options to cost-effective mild steel control cases. The rationale for each combination is summarized in Table 10. These simulations aimed to verify the capacity hierarchy, self-centering, and residual slip characteristics under seismic tensile demands. Key FE-Model Assumptions are:

[0115] • Element type: SOLID 186, 20-node hexahedral elements with reduced integration; average element edge length ~ 1.25 mm after convergence.

[0116] • Mesh strategy: Automatic h-refinement via ANSYS Convergence Utility, continued until changes in peak reaction force (AF_pcak) and maximum von Mises stress (Ao_v,max) were both < 5 % between successive passes.

[0117] • Contact formulation: Augmented Lagrange method; dry steel -to-steel friction coefficient g = 0.20 applied at core-sleeve and sleeve-rebar interfaces.

[0118] • Material law - SMA cores: Built-in ANSYS superelastic SMA model used with tension-compression symmetry enabled; isotropic hardening applied post-plateau using parameters calibrated from Tabrizikahou et al. (2022).

[0119] • Material law - steel (sleeve and rebar): Bilinear elastoplastic with isotropic hardening; elastic modulus E = 200 GPa, tangent modulus E_t = 0.01 E after yield.

[0120] • Loading protocol: Displacement-controlled axial loading up to 4% global strain; unloaded to zero force; reloaded to 4% to assess hysteresis and re-engagement.

[0121] • Boundary conditions: Axial loads applied via reference nodes rigidly coupled to rebar ends, with zero rotation degrees of freedom to maintain pure axial tension.

[0122] • Solver settings: Large-deformation analysis enabled; Newton-Raphson residual tolerance set to 5*10A-4; automatic time stepping (min step size = lx!0A-4) to ensure convergence.

[0123] Example 3.5: Verification and Validation.

[0124] This example describes the validation procedure used to compare simulation outputs against experimental results, along with the acceptance criteria for assessing model accuracy. Numerical accuracy was evaluated by comparing FE simulations against the proof-of- concept tensile test (C COUP), illustrated in Figure 18 and summarized in Table 8, using five independent verification metrics:

[0125] 1. Initial elastic stiffness: Defined as the slope of the load-displacement curve between 0% and 0.15% bar strain.

[0126] 2. First-yield load: Corresponding to the force at 0.2% offset strain on the core stress-strain curve.

[0127] 3. Peak load at 4% global strain: The maximum force reached before unloading.

[0128] 4. Energy dissipation at 4% global strain: Computed as the area enclosed by the first unload-reload hysteresis loop, normalized by core-bar volume.

[0129] 5. Residual slip: The permanent slip recorded after the first full displacement cycle.

[0130] The simulation was considered validated if all the following criteria were met: (1) ±10 % agreement for stiffness, first yield, and peak load; and (2) Residual slip within ±0.02 mm of the experimental value.

[0131] Case V in Table 10 met these thresholds, confirming that the mesh density, contact formulations, and nonlinear material models adequately captured the core coupler mechanics. Figure 20 overlays the simulation and test results for the load-displacement response.

[0132] Key metrics from the five simulated cases are presented in Tables 11 and 12, demonstrating high fidelity correlation across material pairings.

[0133] Table 10. FE Simulation Matrix: Core / Sleeve Pairings.

[0134] The use of different core materials — such as steel, aluminum, FRP, and shape-memory alloys (SMAs) supports a modular coupler design. In this approach, the sleeve geometry and connection interfaces remain standardized across variants, while the solid compressible core can be selected or replaced based on project-specific performance objectives or post-event maintenance needs. This modularity enables the coupler to function as a replaceable structural fuse, allowing damaged or overstrained cores to be swapped without altering the surrounding concrete or reinforcement.

[0135] Example 3.6: Simulation Results and Evaluation Criteria.

[0136] This example presents the key simulation results, including yield sequence, energy dissipation, and residual slip, and establishes the performance criteria used to determine whether intended hierarchical criteria were met.

[0137] Simulation outcomes were evaluated using load-displacement curves, core stress-strain responses, energy dissipation capacity, and residual slip measurements. Key numerical outputs are summarized in Tables 11 and 12, while representative plots are shown in Figures 20-22.

[0138] The results confirm that the calibrated FE models reproduce the intended performance hierarchy across all five material pairings:

[0139] • Core-first yielding: Inelastic deformation initiated in the core before sleeve yielding, satisfying the condition F_y,core< 0.80 F_y, frame.

[0140] • Bar protection: Inelastic deformation initiated in the core prior to the external rebars, maintaining F_y,core < 0.90 F_y,bar to prevent bar plasticity.

[0141] • Elastic sleeve behaviour: In all cases, the sleeve remained elastic up to at least 1.25 F_y,bar, satisfying the overstrength requirements for seismic design. This observation is clearly shown in Figure 21, as the top range is set to represent stresses between 0.8 F_y, frame and 1.0 F_y, frame.

[0142] These simulation findings align with experimental observations and validate the coupler's performance under seismic loading protocols, confirming that the target force hierarchy and deformation limits are achieved.

[0143] Table 11. Key Numerical Outputs from FE Simulations.

[0144] Table 12. Capacity -Hierarchy Verification Summary.

[0145] Example 4.7: Threshold Rationale & Out-of -Range Scenarios.

[0146] The proposed force hierarchy thresholds — F_y, core / F_y,bar< 0.90,

[0147] F_y,core / F_y, frame < 0.80, and F_y, frame / F_y, bar > 1.25 — define the mechanical sequencing beneficial for the coupler to function as intended under seismic loading. These ratios are informed by both international design codes and validated simulations, and they satisfy three critical criteria for engineering reliability:

[0148] 1. Tunable and Quantifiable: The force ratios differentiate the currently disclosed coupler from existing literature and existing commercially available solutions by establishing a tunable and quantifiable capacity hierarchy.

[0149] 2. Workability Standard: It defines clear mechanical boundaries for reliable performance under seismic demands, serving as technical design limits.

[0150] 3. Future-Proofing: By expressing requirements as force ratios, rather than material types, the approach accommodates future core and frame alloys without requiring redesign of the coupler geometry.

[0151] Example 3.7.1: Alignment with Seismic Capacity Design Codes.

[0152] Seismic codes such as ACI 318-19, AISC 341-22, and Eurocode 8 establish overstrengthbased design principles to enforce yielding in ductile components — typically referred to as fuses — prior to more brittle or non-replaceable elements. This philosophy aligns with the proposed thresholds:

[0153] * F_y,core / F_y,bar < 0.90 ensures that the core yields before the reinforcing bar, reducing bar damage and avoiding strain localization or buckling.

[0154] * F_y,core / F_y, frame < 0.80 prevents premature yielding of the sleeve, preserving confinement and axial force transfer.

[0155] * F_y, frame / F_y, bar > 1.25 aligns with overstrength factors (Qo, yOv) in Eurocode 8 and AISC 341, ensuring the sleeve remains elastic as the rebar yields.

[0156] Together, these limits allow the coupler to maintain anchorage, dissipate energy, and exhibit self-centering performance under cyclic earthquake loading.

[0157] Example 3.7.2: Simulation-Based Validation and Violation Cases.

[0158] These hierarchy ratios were validated through finite element (FE) simulation, which confirmed the intended sequencing and mechanical response under seismic demand. Two violation cases illustrate the risks of exceeding these thresholds.

[0159] Violation Case I: Rebar Yields Before Core.

[0160] In this simulation, the core was assigned a yield stress of 475 MPa, while the rebar had a lower yield stress of 345 MPa. These values resulted in a force ratio exceeding the specified upper limit of 0.90. The outcome highlights a fundamental breakdown in the intended force hierarchy. The von Mises stress contours (Figure 23) revealed that the external rebars yielded before the core began to transform, thereby preventing the activation of the superelastic plateau, which is key to energy dissipation and self-centering. Plastic strain plots (Figure 24) confirmed that all inelastic deformation was concentrated in the rebars, while the core remained entirely elastic and inactive.

[0161] The stress-strain response of the rebar (Figure 25) exhibited a residual strain of approximately 0.0175 mm, indicating permanent deformation and a loss of self-centering capability. Meanwhile, the core's stress-strain curve (Figure 26) showed only elastic behaviour; no stress plateau or phase transformation was observed, further confirming that the core did not engage as intended.

[0162] In conclusion, when the core is too strong relative to the rebar, the coupler's energy dissipation and self-centering mechanisms are not triggered. Instead, the reinforcement sustains irreversible damage, and the structural benefits of the coupler are forfeited.

[0163] Violation Case II: Sleeve Yields Before Core.

[0164] In this case, the core's yield stress was again set at 475 MPa, but the sleeve (frame) was assigned a lower yield stress of 345 MPa. These values resulted in a force ratio exceeding the specified upper limit of 0.80.

[0165] Von Mises stress plots (Figure 27) showed that the sleeve was plastified before the core, disrupting the intended force transfer sequence. The plastic strain contours (Figure 28) revealed significant deformation in the sleeve, including ovalization and instability, both of which compromised the confinement necessary for reliable axial load transfer and self-centering.

[0166] Furthermore, the stress-strain curve for the sleeve (Figure 29) confirmed the presence of residual strain after unloading, indicating permanent deformation and a reduction in stiffness and seismic resilience. The sleeve did not remain elastic as required for proper core activation and recentering.

[0167] This violation case illustrates that if the sleeve is under-strength relative to the core, the structural integrity of the coupler is compromised. The core cannot engage properly, the sleeve yields prematurely, and the coupler fails to fulfill its intended role in seismic performance.

[0168] These case studies are further supported by Table 13, which summarizes the predicted failure modes that occur when capacity hierarchy limits are violated. The table outlines the consequences of exceeding each ratio, including bar buckling, sleeve ovalization, loss of selfcentering, and permanent slip — all of which are undesirable outcomes in seismic applications. Table 13. Consequences of Violating Capacity -Hierarchy Ratios.

[0169] Example 3.7.3: Engineering Justification and Material-Uncertainty Design.

[0170] These thresholds serve as quantitative standards for workability. They define the boundaries within which the coupler advantageously performs:

[0171] • They distinguish the currently disclosed coupler by embedding stress-based limits into the design, which are not present in conventional splices.

[0172] • They ensure functional safety, maintaining hierarchy and resilience when experiencing seismic action.

[0173] • They are future-proof, applicable to emerging SMA and high-strength steel alloys without material-specific requalification.

[0174] These thresholds are thus not empirical guesses but codifiable, repeatable performance criteria that can distinguish the currently disclosed coupler from existing mechanical splices.

[0175] The force hierarchy ratios provide a universal, enforceable design rule that governs the proper sequencing of yielding and elastic behaviour within the coupler. Maintaining these limits is advantageous to enabling the coupler's self-centering and energy-dissipating performance while ensuring structural safety. Violation leads to predictable and undesirable failure modes (see Table 13), confirming that these thresholds are technically significant.

[0176] Experimental Exemplification: Experimental Example 4 (comparative analysis of core materials).

[0177] Table 14 summarizes the key attributes that inform the selection of core materials for seismic coupler applications. Each row captures the principal advantages, limitations, and optimal use case for a given alloy, allowing designers to weigh trade-offs between performance, cost, fatigue resistance, and fabrication ease. The primary conclusion is that NiTi and NiTiNb shape memory alloys deliver the highest overall performance, particularly in terms of self-centering capability and low-cycle fatigue resistance. However, these benefits come at a significantly higher material and processing cost. Cu-Al-Mn SMA offers a mid-range option with acceptable superelastic behaviour and easier fabrication, making it an attractive choice for cost-conscious seismic retrofits. In contrast, Fe-Mn- Si SMA and mild steel are best suited for sacrificial fuse applications, especially where low cost or weldability is prioritized over reusability.

[0178] To validate these selections, finite element (FE) simulations were conducted using the ANSYS software. Material models were calibrated against the data described in Examples 2 and 3. The simulated hysteresis loops showed strong agreement with lab observations, confirming that:

[0179] • Core yielding consistently precedes sleeve and rebar yielding (i.e., the force hierarchy conditions F_y,core < 0.80 F_y, frame and < 0.90 F_y,bar are met),

[0180] • The sleeve remains elastic up to at least 1.25 F_y,bar, and

[0181] • SMA cores demonstrate negligible residual strain after unloading, confirming effective self-centering behaviour.

[0182] Together, these results confirm that all candidate materials, when properly paired with matching sleeve steels, satisfy the mechanical hierarchy and deformation recovery criteria required for seismic applications, consistent with the provisions of ISO 15835-1 and ACI 318.

[0183] Table 14. Key Attributes for Selection of the Seismic Coupler Cores.

[0184] Experimental Exemplification: Experimental Example 5 (review of experimental examples and glossary of selected terms).

[0185] The combined experimental tests and validated finite element simulations demonstrate that the proposed coupler reliably transfers axial tension through a compression -core mechanism, while enforcing the intended yielding hierarchy: the core yields first, followed by the reinforcing bars, and the sleeve remains elastic up to at least 1.25 times the yield strength of the reinforcing bars, F_y,bar.

[0186] In the proof-of-concept tensile test (C COUP), the coupler achieved a yield force of approximately 91 kN — slightly exceeding the design target — re-engaged after unloading with less than 0.05 mm residual slip, and exhibited no measurable sleeve deformation. These outcomes confirm secure load transfer with low slip and repeatable axial performance under cyclic conditions.

[0187] Finite element simulations were conducted for five core-sleeve material pairings, ranging from high-performance (NiTi / S690QL) to cost-optimized (Cu-Al-Mn / S550QL) configurations. One pairing — using a mild-steel core — was physically tested and matched simulation results within ±10% for stiffness, yield force, and peak load. The other four simulations, calibrated against this benchmark, produced consistent performance trends. Across all cases, residual slip was reproduced to within 0.02 mm, supporting the model's reliability in evaluating untested materials. Implications for seismic engineering include:

[0188] • Self-centering performance: NiTi and NiTiNb cores exhibit stable hysteresis and minimal residual drift, enabling immediate re-occupancy following Design Basis Earthquake (DBE) or Maximum Considered Earthquake (MCE) events.

[0189] • Cost-tiered design: Cu-Al-Mn and Fe-Mn-Si cores satisfy the force hierarchy at reduced material cost, offering feasible options for retrofits or mid-importance structures in moderate hazard zones.

[0190] • Sacrificial fuse option: A mild-steel core encased in an elastic sleeve serves as a disposable energy-dissipating element, suitable for applications such as bridges or industrial facilities where post-event replacement is acceptable.

[0191] • Fabrication compatibility: All sleeves are fabricated from standard quenched- and-tempered or HSLA steels, allowing integration into conventional welding and rebar connection workflows. Performance tier is governed solely by core material selection.

[0192] In certain high-risk applications — such as nuclear reactors located in seismic zones — it may be desirable to design the mechanical coupler such that the solid compressible core reaches failure before any yielding occurs in the coupler sleeve. This conservative force hierarchy ensures that all inelastic and potentially failure-level deformation is localized within a replaceable core element, while the surrounding coupler sleeve remains fully elastic and structurally intact. Such an approach enhances post-event inspectability, prevents damage from propagating into the primary load path, and facilitates controlled, modular replacement. Although this condition requires the core's ultimate axial capacity to be lower than the yield strength of the sleeve — imposing more stringent material and geometric constraints — it may be justified in safety-critical infrastructure where structural integrity, containment, and reparability under extreme seismic demand are paramount.

[0193] These findings confirm that the coupler design is inherently modular and tunable — from premium self-centering solutions to low-cost sacrificial variants by substituting the internal core while preserving a common sleeve architecture. This flexibility supports a unified detailing philosophy adaptable to a wide spectrum of seismic performance objectives and economic constraints. Table 15. Glossary of Selected Terms.

[0194] Experimental Exemplification: (reference list).

[0195] • American Institute of Steel Construction (AISC). (2022). Seismic Provisions for Structural Steel Buildings (AISC 341-22). Chicago, IL, USA. • Alam, M. S., Youssef, M. A., & Nehdi, M. (2007). Utilizing shape memory alloys to enhance the performance and safety of civil infrastructure: A review. Canadian Journal of Civil Engineering, 34(9), 1075-1086. https: / / doi.org / 10.1139 / 107-038

[0196] • American Concrete Institute. (2019). ACI 318-19 - Building Code Requirements for Structural Concrete and Commentary. Farmington Hills, MI, USA. • ASTM International. (2019). ASTM A36 / A36M- 19 - Standard Specification for Carbon Structural Steel. West Conshohocken, PA, USA. • ASTM International. (2019). ASTM A564 / A564M 19 - Standard Specification for Hot-Rolled and Cold-Finished Age-Hardening Stainless Steel Bars and Shapes. West

[0197] Conshohocken, PA, USA.

[0198] • ASTM International. (2021). ASTM A572 / A572M-21el - Standard

[0199] Specification for High-Strength Low- Alloy Columbium -Vanadium Structural Steel. West Conshohocken, PA, USA.

[0200] • ASTM International. (2023). ASTM A1034 / A1034M-23 - Standard Specification for Mechanical Splices for Steel Reinforcing Bars. West Conshohocken, PA, USA.

[0201] • ASTM International. (2013). ASTM E4-13 - Standard Practices for Force Verification of Testing Machines. West Conshohocken, PA, USA.

[0202] • ASTM International. (2013). ASTM E8 / E8M-13 - Standard Test Methods for Tension Testing of Metallic Materials. West Conshohocken, PA, USA.

[0203] • Cai, J., Mao, S., Liu, Y., Cui, L., Zhang, J., Zhang, Z., & Han, X. (2022). Nb / NiTi laminate composite with high pseudoelastic energy dissipation capacity (~30 MJ / m3). Materials Today Nano, 19, Article 100238.

[0204] • Dillinger. (2024). Dillimax 690 - High Strength Fine Grained Structural Steel, Quenched and Tempered - Technical Data Sheet. Dillingen, Germany. Retrieved from https: / / data.shs.hdw.agency / app / uploads / 2024 / 06 / DILLIMAX_690_0 l_2024_E.pdf

[0205] • European Committee for Standardization (CEN). (2019). EN 10083-3:2019 - Steels for quenching and tempering Part 3: Technical delivery conditions for alloy steels. Brussels, Belgium.

[0206] • European Committee for Standardization (CEN). (2019). EN 10025-6:2019 — Hot rolled products of structural steels - Part 6: Technical delivery conditions for high yield strength structural steels in the quenched and tempered condition. Brussels, Belgium.

[0207] • European Committee for Standardization (CEN). (2013). EN 10149-2:2013 - Hot-rolled flat products made of high yield strength steels for cold forming - Part 2: Delivery conditions for thermomechanically rolled steels. Brussels, Belgium.

[0208] • European Committee for Standardization (CEN). (2004). EN 1998-1:2004 - Eurocode 8: Design of Structures for Earthquake Resistance - Part 1: General Rules, Seismic Actions and Rules for Buildings. Brussels, Belgium. • European Organisation for Technical Assessment (EOTA). (2020). EAD 160129-00-0301 - Couplers for Mechanical Splices of Reinforcing Steel Bars. Brussels, Belgium.

[0209] • Greiner, C., Oppenheimer, S. M., & Dunand, D. C. (2005). High strength, low stiffness, porous NiTi with superelastic properties. Acta Biomaterialia, 1(6), 705-716. https: / / doi.Org / 10.1016 / j.actbio.2005.07.005

[0210] • Han, X., Cai, J., Mao, S., Liu, Y., Cui, L., Zhang, J., Zhang, Z., & Han, X. (2022). Nb / NiTi laminate composite with high pseudoelastic energy dissipation capacity. Materials Today Nano, 19, Article 100238.

[0211] • International Organization for Standardization (ISO). (2018). ISO 15835- 1:2018 - Steels for the reinforcement of concrete - Reinforcement couplers for mechanical splices of bars - Part 1 : Requirements. Geneva, Switzerland.

[0212] • International Organization for Standardization (ISO). (2019). ISO 15630- 1:2019 - Steel for the reinforcement and prestressing of concrete - Test methods - Part 1: Reinforcing bars, wire rod and wire. Geneva, Switzerland.

[0213] • NLMK Clabccq. (2025). Qucnd 700® Extra High-Strength Structural Steels - Product Datasheet. Clabecq, Belgium. Retrieved from https: / / eu.nlmk.com / upload / iblock / b45 / nlmk_europe_ plate_quend.pdf

[0214] • Pareek, S., Suzuki, Y., Araki, Y., Youssef, M. A., & Meshaly, M. (2018). Plastic hinge relocation in reinforced concrete beams using Cu-Al-Mn SMA bars. Engineering Structures, 175, 765-775. https: / / doi.Org / 10.1016 / j.engstruct.2018.08.072

[0215] • Tabrizikahou, A., Kuczma, M., Lasecka-Plura, M., Noroozinejad Farsangi, E., Noori, M., Gardoni, P., & Li, S. (2022). Application and modelling of shape-memory alloys for structural vibration control: State of- the art review. Construction and Building Materials, 342, Article 127975. https: / / doi.Org / 10.1016 / j.conbuildmat.2022.127975

[0216] • Youssef, M. A., Alam, M. S., & Nehdi, M. (2008). Experimental investigation on the seismic behaviour of beam-column joints reinforced with superelastic SMAs. Journal of Earthquake Engineering, 12(7), 1205-1222. https: / / doi.org / 10.1080 / 13632460802003082

[0217] An illustrative version and several variants of a mechanical coupler for reinforcing bars have been described above without any intended loss of generality. Further examples of modifications and variation are now provided. Still further variants, modifications and combinations thereof are contemplated and will be apparent to the person of skill in the art. It is to be understood that illustrative variants or modifications are provided to enhance the understanding of the person of skill in the art and are not intended as limiting statements.

[0218] For example, the coupler may be manufactured from a variety of materials. The coupler frame and the core can be made of the same material or of different materials. Any material, approved for construction, can be used including but not limited to mild steel, carbon steel, stainless steel, fibre-reinforced plastics, aluminum, and shape memory alloy. In certain examples, the coupler core can be made of steel (including for example mild steel, carbon steel, and stainless steel), fibre-reinforced plastics, aluminum, or shape memory alloy, and the coupler frame can be made of steel, such as mild steel, carbon steel, or stainless steel, and the collapsible chamber being formed by a combination of the first and second frames can also be made of steel, such as mild steel, carbon steel, or stainless steel. The coupler frame may be designed to remain elastic and not undergo inelastic deformations while being tensioned or compressed. Concepts of capacity design should be applied to ensure that damage is only affecting the core material. As the main design force is tensile, the tensile force leading to apparent yielding in the core material must be less than the apparent yielding in the external bars. Material safety factors that account for the potential variability in the material properties need to be applied during this process.

[0219] As another example of variation, the coupler may be designed to be readily disassembled to replace a solid compressible core. For example, the coupler sleeve comprises a detachable component, and the solid compressible core is configured to be replaceable following removal of surrounding concrete and disassembly of the coupler sleeve and optionally detachment of a connected rebar.

[0220] In an example of a coupler design: (i) the coupler frame shall remain elastic under an axial load not less than 1.25 the external-bar yield force (Fy, bar) and need not be designed for forces greater than this value; (ii) the force at which the core experiences inelastic deformation must not exceed 0.90 Fy, bar; and (iii) inelastic deformation of the core shall initiate at a force not greater than 0.80 the frame yield force (Fy, frame), ensuring a minimum 20 % capacity margin between core and frame.

[0221] In all examples, the coupler core is configured to experience inelastic deformation at a force less than the force required for the first and second frames of the coupler to undergo inelastic deformation. In all examples, the coupler core is configured to initiate inelastic deformation at a lesser force than the rebars connected to the coupler, and the rebars connected to the coupler are configured to initiate inelastic deformation at a lesser force than the first and second frames of the coupler.

[0222] In all examples, the solid compressible core is configured to initiate inelastic deformation at a lesser force than the coupler sleeve, the first frame and / or the second frame.

[0223] In some examples, such as examples prioritizing robust isolation from seismic shock, the solid compressible core is configured to experience inelastic deformation and failure at an axial force less than the yield force of the coupler sleeve, the first frame and / or the second frame.

[0224] In all examples, the solid compressible core is configured to initiate inelastic deformation at a lesser force than a rebar connected to the coupler sleeve, and the rebar connected to the coupler sleeve is configured to initiate inelastic deformation at a lesser force than the coupler sleeve.

[0225] In some examples, such as examples prioritizing robust isolation from seismic shock, the solid compressible core is configured to experience inelastic deformation and failure at an axial force less than the yield force of the coupler sleeve, and a rebar connected to the coupler sleeve is configured to initiate inelastic deformation at an axial force less than the yield force of the coupler sleeve.

[0226] In some examples, the yield force of the coupler sleeve and reinforcing bar may exceed the ultimate axial force of the core; this represents a conservative design condition, particularly those involving high-strength or superelastic core materials.

[0227] In many examples, the coupler will be configured to withstand a minimum axial force equivalent to about 1.25 times the tensile yield force of the exterior rebars that are connected to the coupler.

[0228] In many examples, the force at which the core material experiences inelastic deformations will not exceed about 90% of the yield force of the external rebars.

[0229] In many examples, the force at which the core material experiences inelastic deformations will not exceed about 80% of the yield force of the coupler.

[0230] Throughout this specification, the term F_y, frame refers to the yield force of the coupler frame, comprising Frame 1 and Frame 2, which together form the coupler sleeve or housing of the coupler. This excludes the solid compressible core. Although the terms frame and coupler are sometimes used interchangeably in engineering practice, this specification uses frame specifically to refer to the load-resisting outer shell of the coupler without the core. When interpreting force hierarchy expressions (e.g., F_y,core / F_y, frame), F_y, frame denotes the axial force at which either Frame 1 or Frame 2 (or both) would initiate inelastic deformation, as determined under monotonic axial loading per ASTM E8.. F_y, frame may be used interchangeably with F_y, sleeve as the yield force or inelastic deformation criteria for the coupler sleeve as a whole as tested by ASTM E8 will also often apply to the first frame (Frame 1) and the second frame (Frame 2) of the coupler.

[0231] The terms reinforcing bar and rebar may be used interchangeably, as rebar is a commonly used shortened or abbreviated word to express the term reinforcing bar.

[0232] In certain high-risk examples — such as nuclear reactors located in seismic zones — it may be desirable to design the mechanical coupler such that the solid compressible core reaches failure before any yielding occurs in the coupler sleeve (comprising Frame 1 and Frame 2). This conservative force hierarchy ensures that all inelastic and potentially failure-level deformation is localized within a replaceable core element, while the surrounding coupler sleeve remains fully elastic and structurally intact. Such an approach enhances post-event inspectability, prevents damage from propagating into the primary load path, and facilitates controlled, modular replacement. Although this condition requires the core's ultimate axial capacity to be lower than the yield strength of the sleeve — imposing more stringent material and geometric constraints — it may be justified in safety-critical infrastructure where structural integrity, containment, and reparability under extreme seismic demand are paramount.

[0233] In certain examples, to ensure controlled and safe deformation behaviour, the coupler may be designed such that the yield or inelastic initiation force of both the reinforcing bar and the coupler frame (Frame 1 and Frame 2) exceeds the ultimate axial force capacity of the solid compressible core. This condition, while conservative, ensures that the core undergoes all intended energy dissipation through inelastic deformation, while the bar and frame remain fully elastic even up to core failure. However, in practical applications — particularly where material tolerances are tightly controlled — relaxed yield force ratios such as 0.90-0.95 for core-to-bar, 0.80-0.85 for core- to-frame, and 1.10-1.25 for frame-to-bar may be considered. These relaxed ranges offer design flexibility, though they reduce the safety margin compared to the conservative yield force targets of <0.90, <0.80, and >1.25, which were validated through experimental testing and numerical simulation.

[0234] The yield and ultimate forces for each coupler component shall be determined in accordance with recognized standards for structural testing. For reinforcing bars, yield strength (F_y,bar) and ultimate tensile strength (F_u,bar) shall be established using standard tensile testing procedures as defined in ASTM A370 or ISO 6892, depending on jurisdictional requirements. The coupler sleeve comprises two opposing halves — Frame 1 and Frame 2 — which together form a coupler sleeve with collapsible chamber that houses the solid compressible core. Yield and ultimate forces for both the solid compressible core and the assembled coupler sleeve shall be derived from monotonic axial tests conducted in accordance with ASTM E8 for metallic materials. Yield force shall correspond to the initiation or onset of inelastic deformation: plastic yielding for steel components and stress-induced phase transformation for shape memory alloy (SMA) cores.

[0235] In certain examples, to ensure that inelastic deformation remains confined to the solid compressible core, the coupler is designed to enforce a force hierarchy in which the core undergoes inelastic deformation first, while both the reinforcing bar and the coupler frame (comprising Frame 1 and Frame 2) remain elastic. This is achieved by proportioning the yield strengths of the components. Based on experimental and numerical validation, a conservative set of target ratios includes: a core-to-bar yield force ratio of less than 0.90, a core-to-frame yield force ratio of less than 0.80, and a frame-to-bar yield force ratio greater than 1.25 (core-to-frame may be used interchangeably with core-to-sleeve, and frame-to-bar may be used interchangeably with sleeve-to-bar). These thresholds have been shown to reliably prevent premature yielding of the bar or sleeve, thereby preserving system integrity and enabling post-event core replacement. Alternatively, relaxed ratios closer to unity may be considered — such as 0.90-0.95 for core-to-bar, 0.80-0.85 for core-to-frame, and 1.10-1.25 for frame-to-bar — particularly in applications where manufacturing tolerances are tightly controlled and material properties are well characterized. However, reducing these strength margins increases the risk of undesired yielding in the frame or rebar, potentially leading to non-recoverable damage, sleeve ovalization, bar slippage, or loss of confinement. For this reason, conservative ratios are recommended in applications that prioritize damage localization, ductility, and reparability.

[0236] As another example of variation, the first and second frames are often configured and aligned so that the first longitudinal axis defined by the first frame is co-axial with the second longitudinal axis defined by the second frame. While a co-axial alignment is a typical configuration, an offset from co-axial alignment may be tolerated and accommodated provided that the first and second frames can be combined to form an overlapped section, thereby forming the collapsible chamber. As such, even when the first and second frames are offset from a co-axial alignment, alignment of the first longitudinal axis will at least be limited by the circumference of the second frame, and alignment of the second longitudinal axis will at least be limited by the first frame, such that an adjacent alignment of first and second frames approaching lapped splicing is expressly avoided. Typically when offset from co-axial, the first longitudinal axis will be aligned to be closer to the second longitudinal axis than to the circumference of the second frame, and the second longitudinal axis will be aligned to be closer to the first longitudinal axis than to the circumference of the first frame.

[0237] As another example of variation, the coupler and its collapsible chamber can hold any type of SMA. When exposed to specific thermal or mechanical stimuli, shape memory alloys (SMAs) can return to a predetermined shape or size. These materials exhibit two distinct behaviours: the shape memory effect (SME) and the pseudoelastic effect. The SME allows the alloy to revert to its original shape upon heating after deforming at a lower temperature, driven by a reversible phase transformation between martensite and austenite phases. On the other hand, the pseudoelastic effect, or superelasticity, enables SMAs to undergo substantial, reversible deformations at a constant temperature higher than the austenite finish temperature. This phenomenon occurs due to a stress-induced transformation between austenite and martensite phases.

[0238] There are three primary families of SMAs: nickel -titanium (NiTi) alloys, copper-based alloys, and iron-based alloys. Copper- and iron-based SMAs are often viewed as cost-effective alternatives to NiTi SMAs due to their favourable shape memory properties, damping capacity, and other functional characteristics. However, practical applications of these alternatives are hindered by several challenges. Copper-based SMAs face issues such as phase stabilization, transition hysteresis, aging, and brittleness, which cast doubt on their long-term viability in engineering applications. Similarly, iron-based SMAs, despite their cost advantages and ease of production through conventional steel-making processes, suffer from low shape recovery percentages, limiting their practical utility.

[0239] NiTi SMAs, known as Nitinol, are celebrated for their high shape recovery rates and robust engineering properties, making them the preferred choice for commercial applications. These alloys exhibit excellent ductility, corrosion resistance, and performance in low-cycle fatigue and strain-controlled environments. However, their complex and expensive production processes, including the need for vacuum or inert atmosphere melting and frequent annealing due to work hardening, constrain their broader commercial use. In contrast, copper-based SMAs, while not matching NiTi's superior shape memory properties, offer advantages such as lower production costs and easier fabrication using conventional metallurgy. Iron-based SMAs, though cost- effective, fall short in shape memory capacity and exhibit significant transformation hysteresis, further limiting their competitive edge against NiTi and copper-based SMAs in practical applications.

[0240] In summary, current literature and technical knowledge indicates that NiTi SMAs are the most demanding and costly to process but exhibit the highest elastic response with reported maximum recoverable strain of up to 8% typically. Copper-based alloys provide the second- highest elastic response, with maximum recoverable strain of up to 5% typically, while iron-based SMAs typically have a recoverable strain of less than 5%. NiTi SMAs demonstrate a higher degree of SME, followed by copper-based alloys and iron-based alloys. In terms of material workability, iron-based SMAs outperform NiTi-based materials, while copper-based alloys are the least workable.

[0241] Further variation of the coupler can be guided by targeted finite element analyses and validated experimental research presented in the experimental examples. Representative material property profiles were compiled for candidate materials (binary NiTi, NiTiNb, Cu-Al-Mn, Fe- Mn-Si, and mild steel), and finite element modeling conducted using ANSYS confirmed that inelastic deformation initiates in the core before the frame, satisfying force hierarchy requirements (core yield force < 0.80 F_y, frame and < 0.90 F_y,bar); see Tables 5 and 6 for representative material properties). Comparative compressibility and energy absorption analyses further confirmed that these candidate materials possess sufficient deformation capacities and cyclic hysteretic behaviours, consistent with the targeted mechanical performance criteria.

[0242] Embodiments described herein are intended for illustrative purposes without any intended loss of generality. Still further variants, modifications and combinations thereof are contemplated and will be recognized by the person of skill in the art. Accordingly, the foregoing detailed description is not intended to limit scope, applicability, or configuration of claimed subject matter.

Claims

1. WHAT IS CLAIMED IS:

1. A rebar coupler comprising: a coupler sleeve comprising a collapsible chamber; a solid compressible core located in the collapsible chamber; the solid compressible core resisting a collapsing motion of the collapsible chamber by opposing surfaces of the solid compressible core abutting opposing interior surfaces of the collapsible chamber as the collapsible chamber moves from a relative expanded position to a relative collapsed position.

2. A rebar coupler comprising: a coupler sleeve comprising an elongate first frame and an elongate second frame; the first frame defining a first central longitudinal axis, the first frame comprising a first connector positioned a first distance from a first transverse plate oriented transverse to the first central longitudinal axis, the first connector configured for coupling or attachment of a first rebar; the second frame defining a second central longitudinal axis, the second frame comprising a second connector positioned a second distance from a second transverse plate oriented transverse to the second central longitudinal axis, the second connector configured for coupling or attachment of a second rebar, the first frame and the second frame slidably engaged to overlap the first distance and the second distance to define a third distance extending from the first transverse plate to the second transverse plate, the first frame and the second frame combining to form a collapsible chamber defining an interior space for holding or capturing a solid compressible core, the interior space defined by a longitudinal dimension equal to the third distance, the first longitudinal axis aligned to be substantially parallel to the second longitudinal axis.

3. The rebar coupler comprising: a coupler sleeve comprising a first frame and a second frame; the first frame comprising a first connector and a first transverse plate, the first connector for securing or fixing a first rebar, the first transverse plate for engaging or abutting a first end of a solid compressible core, the solid compressible core positioned between the first connector and the first transverse plate;the second frame comprising a second connector and a second transverse plate, the second connector for securing or fixing a second rebar, the second transverse plate for engaging or abutting a second end of the solid compressible core, the solid compressible core positioned between the second connector and the second transverse plate, the second transverse plate positioned between the solid compressible core and the first connector; an overlapped section of the first frame and the second frame forming a collapsible chamber to hold the solid compressible core, the first transverse plate and the second transverse plate forming opposing longitudinal ends of the collapsible chamber; the first frame and the second frame slidably engaged so that tension applied to one or both of the first connector and the second connector causes a decrease in longitudinal distance of the collapsible chamber as defined by the spacing between the first transverse plate and the second transverse plate, and the solid compressible core resists the decrease in longitudinal distance.

4. A rebar coupler comprising: a coupler sleeve comprising a first frame and a second frame; the first frame comprising a first connector for securing or fixing a first rebar, the first connector attached by the first frame to a first transverse plate for engaging or abutting a first end of a solid compressible core; the second frame comprising a second connector for securing or fixing a second rebar, the second connector attached by the second frame to a second transverse plate for engaging or abutting a second end of the solid compressible core; the first frame and the second frame positioned to provide a sequential longitudinal spatial ordering in forward or reverse of the first connector followed by the second transverse plate followed by the second end of the solid compressible core followed by the first end of the solid compressible core followed by the first transverse plate followed by the second connector; the first frame and the second frame providing an overlapped section, the overlapped section comprising the first transverse plate, the second transverse plate and the solid compressible core, the first transverse plate and the second transverse plate forming opposing longitudinal ends of a collapsible chamber to hold the solid compressible core; the first frame and the second frame slidably engaged so that tension applied to one or both of the first connector and the second connector causes a decrease in longitudinal distance of thecollapsible chamber as defined by the spacing between the first transverse plate and the second transverse plate, and the solid compressible core resists the decrease in longitudinal distance.

5. The coupler of any one of claims 1-4, wherein the solid compressible core is configured to initiate inelastic deformation at a lesser force than the coupler sleeve, the first frame and / or the second frame.

6. The coupler of any one of claims 1-4, wherein the solid compressible core is configured to experience inelastic deformation and failure point at an axial force less than the yield force of the coupler sleeve, the first frame and / or the second frame.

7. The coupler of any one of claims 1-4, wherein the solid compressible core is configured to initiate inelastic deformation at a lesser force than a rebar connected to the coupler sleeve, and the rebar connected to the coupler sleeve is configured to initiate inelastic deformation at a lesser force than the coupler sleeve.

8. The coupler of any one of claims 1-4, wherein the solid compressible core is configured to experience inelastic deformation and failure point at an axial force less than the yield force of the coupler sleeve, and a rebar connected to the coupler sleeve is configured to initiate inelastic deformation at an axial force less than the yield force of the coupler sleeve.

9. The coupler of any one of claims 2-4, wherein the first frame includes a first detachable component.

10. The coupler of claim 9, wherein the first detachable component is the first transverse plate.

11. The coupler of any one of claims 2-4, wherein the second frame includes a second detachable component.

12. The coupler of claim 11, wherein the second detachable component is the second transverse plate.

13. The coupler of claim 3 or 4, wherein the first frame includes a first detachable component that is the first connector or the first transverse plate.

14. The coupler of claim 3 or 4, wherein the second frame includes a second detachable component that is the second connector or the second transverse plate.

15. The coupler of claim 3 or 4, wherein the first frame defines a first longitudinal axis, the second frame defines a second longitudinal axis, and the first longitudinal axis is co-axial with the second longitudinal axis.

16. The coupler of claim 3 or 4, wherein the first frame defines a first longitudinal axis, the second frame defines a second longitudinal axis, the first longitudinal axis is offset from co-axial alignment with the second longitudinal axis, the first longitudinal axis aligned to be closer to the second longitudinal axis than to the circumference of the second frame, and the second longitudinal axis aligned to be closer to the first longitudinal axis than to the circumference of the first frame.

17. The coupler of any one of claims 1-16, wherein the solid compressible core is made of mild steel, carbon steel, stainless steel, fibre-reinforced plastics, aluminum, or shape memory alloy.

18. The coupler of claim 17, wherein the shape memory alloy is a nickel-titanium (NiTi) alloy, a copper-based alloys, or an iron-based alloy.

19. The coupler of claim 17, wherein the shape memory alloy is selected from the group consisting of nickel-titanium (NiTi), nickel-titanium-niobium (NiTiNb), copper-aluminum-manganese (Cu- Al-Mn), and iron-manganese-silicon (Fe-Mn-Si).

20. The coupler of any one of claims 1-19, wherein the coupler sleeve is made of mild steel, carbon steel, or stainless steel.

21. The coupler of any one of claims 1-20, wherein the collapsible chamber forms an interior rectangular prism shape.

22. The coupler of any one of claims 1-20, wherein the collapsible chamber forms an interior cylindrical shape.

23. The coupler of any one of claims 1-22, wherein the solid compressible core is configured to experience inelastic deformation at a yield force equal to or less than about 0.80 times the yield force that causes inelastic deformation of the coupler sleeve.

24. The coupler of any one of claims 1-23, wherein the solid compressible core is configured to experience inelastic deformation at a yield force equal to or less than about 0.90 times the yield force that causes inelastic deformation of a rebar connected to the coupler sleeve.

25. The coupler of any one of claims 1-24, wherein the coupler sleeve remains elastic under an axial force equal to or greater than about 1.25 times the yield force of the reinforcing bar.

26. The coupler of any one of claims 1-25, wherein the coupler is configured to enforce a capacitybased force hierarchy such that: a) the axial force at which the solid compressible core initiates inelastic deformation is less than or equal to 0.90 times the yield force of a rebar; b) the axial force at which the solid compressible core initiates inelastic deformation is less than or equal to 0.80 times the yield force of the coupler sleeve; and c) the coupler sleeve remains elastic under an axial force equal to or greater than 1.25 times the yield load of the reinforcing bar.

27. The coupler of any one of claims 1 -25, wherein the coupler is configured to satisfy a capacitybased force hierarchy defined by one or more of the following ratio ranges: a) the axial force at which the solid compressible core initiates inelastic deformation is between 0.90 and 0.95 times the yield force of a reinforcing bar connected to the coupler; b) the axial force at which the solid compressible core initiates inelastic deformation is between 0.80 and 0.85 times the yield force of the coupler frame (comprising Frame 1 and Frame 2); c) the axial force at which the coupler frame initiates yielding is between 1.10 and 1.25 times the yield force of the reinforcing bar.

28. The coupler of any one of claims 1-25, wherein the yield force of the coupler sleeve and the yield force of the rebar both exceed the ultimate axial force of the solid compressible core, the solid compressible core is made of a superelastic shape memory alloy (SMA) material.

29. The coupler of any one of claims 1-25, wherein the coupler sleeve comprises a detachable component, and the solid compressible core is configured to be replaceable following removal of surrounding concrete and disassembly of the coupler sleeve and optionally detachment of a rebar.

30. The coupler of any one of claims 1-29, wherein the coupler is self-centering.

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