WO2016071879A1

WO2016071879A1 - Seismic retrofitting buckling restrained brace

Info

Publication number: WO2016071879A1
Application number: PCT/IB2015/058588
Authority: WO
Inventors: Al-sadoon A. ZAID
Original assignee: University Of Ottawa
Priority date: 2014-11-07
Filing date: 2015-11-06
Publication date: 2016-05-12
Also published as: CN107109841A; CA2966846A1

Abstract

A method and apparatus is disclosed for providing lateral support against buckling for a load-carrying inner core steel bar at a region between the end of a buckling restrained brace assembly and steel plates of structural frame joint assembly. Lateral support against buckling at the transition zone between a buckling restrained brace and a supporting frame member is provided through a specialized mechanical end brace comprising a plurality of lateral support structures configured for slidable inter-fitting engagement in response to axial deformation of a load-carrying inner core steel bar. In this manner, axial force is only carried by the load- carrying inner core steel core bar with continuous lateral restraint.

Description

SEISMIC RETROFITTING BUCKLING RESTRAINED BRACE

BACKGROUND Field of the Invention

[0001] The present invention relates to retrofitting of structural frames and more specifically to steel bracing for lateral drift control in reinforced-concrete frame buildings for seismic applications. The proposed retrofitting technique can also be implemented as the main seismic force resisting system for steel frames and for new construction.

Related Art

[0002] Existing non-ductile or limited ductility reinforced- concrete buildings such as those built before enhancements in seismic provisions in building codes m a y pose a significant risk, for example, when subjected to strong earthquakes. Such conventional buildings were designed and built primarily to resist wind and/or gravity loads only, with less understanding of seismic demands and design detailing than is currently understood. The vulnerable stock of buildings include: residential, commercial, schools, hospitals, and other critical/non-critical facilities. In general, current seismic code requirements are significantly more comprehensive and stringent than those of the pre 1970 era. In other words, ductile design and detailing requirements prescribed in newer codes to reduce seismic vulnerabilities were not implemented in the majority of existing older buildings. These vulnerabilities include lacking one or more parameters of strength, stiffness, and ductility. Therefore, a large number of existing building inventories worldwide are seismically deficient and may possess a significant threat to life safety and economic well- being of society. As a result, there has been an increasing interest and specifically after recent major earthquakes to perform seismic risk mitigation and strengthen older buildings to control lateral drifts and to reduce seismic deformation demands. SUMMARY

[0003] The foregoing needs are met, to a great extent, by the present invention wherein, according to a first broad aspect, the present invention provides an apparatus comprising a first lateral support structure having a first base and a plurality of first longitudinal members extending from the first base, and a second lateral support structure having a second base and a plurality of second longitudinal members extending from the second base. Each first longitudinal member slidably interfits between a pair of second longitudinal members of the plurality of second longitudinal members, wherein each second longitudinal member slidably interfits between a pair of first longitudinal members of the plurality of first longitudinal members. The first base may include a first opening and the second base includes a second opening that are configured to receive an elongated member extending through the first opening and the second opening wherein the plurality of first longitudinal members and the plurality of second longitudinal members surround and laterally restrain a motion of the elongated member when the elongated member extends through the first opening and the second opening.

[0004] According to a second broad aspect, the present invention provides a method comprising adjusting a relative axial relationship between a first lateral support structure and a second lateral support structure of a longitudinal assembly to thereby maintain an axially aligned and structurally continuous arrangement for the longitudinal assembly of the first and the second lateral support structures, wherein the first lateral support structure is in an slidable interfitting engagement with the second lateral support structure.

[0005] According to a third broad aspect, the present invention provides an apparatus comprising a buckling restrained brace and two lateral end-support units coupled to the buckling restrained brace, wherein the buckling restrained brace comprises an elongated member extending through a lateral restraining system. Each of the two lateral end-support units comprises a first lateral support structure and a second lateral support structure, wherein the first lateral support structure comprises a first base and a plurality of first longitudinal members extending from the first base, and wherein the second lateral support structure comprising a second base and a plurality of second longitudinal members extending from the second base. Each first longitudinal member slidably interfits between a pair of second longitudinal members of the plurality of second longitudinal members. Similarly, each second longitudinal member slidably interfits between a pair of first longitudinal members of the plurality of first longitudinal members. The first base includes a first opening and the second base includes a second opening configured to receive the elongated member that extends through the first opening and the second opening, wherein the plurality of first longitudinal members and the plurality of second longitudinal members surround and laterally restrain a motion of the elongated member when the elongated member extends through the first opening and the second opening.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention.

[0007] FIG. 1 is a perspective view of a yielding core element of a Buckling Restrained Brace (BRB) assembly.

[0008] FIG. 2 is a perspective view of conventional BRB structure comprising the yielding core element in a lateral restraint configuration.

[0009] FIG. 3 is a side view of a conventional BRB structure comprising a yielding core element and a lateral support housing unit.

[0010] FIG. 4 is a side view of a yielding core element and lateral support housing illustrated side by side.

[0011] FIG. 5 is cross-sectional end-view of a conventional BRB structure illustrating the external and internal reserve spaces used to prevent direct bearing in a conventional BRB configuration. [0012] FIG. 6 is a cross-sectional side view of an exemplary BRB assembly showing the core section and two end-elements at either ends of the core section, according to one embodiment of the present invention.

[0013] FIG. 7 is a cross-sectional view of a buckling restrained brace core section, according to one embodiment of the present invention.

[0014] FIG. 8 is a cross-sectional side view of an exemplary load-bearing core element, according to one embodiment of the present invention.

[0015] FIG. 9 is a cross-sectional side view of an exemplary all-threaded load-bearing core element, according to one embodiment of the present invention.

[0016] FIG. 10 is a cross-sectional side view of an exemplary end-element, according to one embodiment of the present invention.

[0017] FIG. 11 is perspective view of a section of an exemplary end-element, according to one embodiment of the present invention.

[0018] FIG. 12 is a cross-sectional axial view of an exemplary end-element, according to one embodiment of the present invention.

[0019] FIG. 13 is a cross-sectional front view of an exemplary end-elements according to one embodiment of the present invention.

[0020] FIG. 14 is a cross-sectional 90°-rotated front view of an exemplary end-element, according to one embodiment of the present invention.

[0021] FIG. 15 is a frontal image of an exemplary end-element configured to provide continuous lateral end support for a yielding core element extending through it, according to one embodiment of the present invention.

[0022] FIGS. 16, 17 and 18 are elevated views of a BRB connection assembly components, according to one embodiment of the present invention.

[0023] FIG. 19 is an illustration of a BRB assembly configuration within a testing frame, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions

[0024] Where the definition of terms departs from the commonly used meaning of the term, applicant intends to utilize the definitions provided below, unless specifically indicated.

[0025] For purposes of the present invention, it should be noted that the singular forms, "a," "an" and "the," include reference to the plural unless the context as herein presented clearly indicates otherwise.

[0026] For purposes of the present invention, directional terms such as "top," "bottom," "upper," "lower," "above," "below," "left," "right," "horizontal," "vertical," "up," "down," etc., are used merely for convenience in describing the various embodiments of the present invention. The embodiments of the present invention may be oriented in various ways. For example, the diagrams, apparatuses, etc. , shown in the drawing figures may be flipped over, rotated by 90° in any direction, reversed, etc.

[0027] For purposes of the present invention, a value or property is "based" on a particular value, property, the satisfaction of a condition or other factor if that value is derived by performing a mathematical calculation or logical operation using that value, property or other factor.

[0028] For purposes of the present invention, the term "compression stress" refers to physical or mechanical stress developed due to application of force along a longitudinal axis.

[0029] For purposes of the present invention, the term "compressive deformation" refers to structural deformation that may develop due to presence of compression stress.

[0030] For purposes of the present invention, the term "cored base portion" refers to a base structure that comprises one or more hollow sections extending along or in parallel to its longitudinal axis.

[0031] For purposes of the present invention, the term "hinge" refers to a jointed or flexible device or structure that holds two parts together so that one can move relative to the other. The movement may be translational or rotational in two dimensional or three dimensional space. The term hinge may also refer to a single continuous piece of material which folds or pivots upon itself. The term hinge may also refer to means that connects two solid objects, allowing only a limited angle of rotation between them. A hinge may be constructed of flexible material or of moving components. Further, a hinge may be a specially constructed section of one or both of the solid objects to which it is connected, or it may be separate self-contained assembly which is then attached to said solid objects.

[0032] For purposes of the present invention, the term "individually removable unit" refers to a specific element, structure, object or component that fulfills a specific function as part of a larger system comprising an assembly of elements, structures, objects or components, wherein the specific element, structure, object or component may be removed without comprising the structural, operational or functional integrity of the system.

[0033] For purposes of the present invention, the term "individually replaceable unit" refers to a specific element, structure, object or component that fulfills a specific function as part of a larger system comprising an assembly of elements, structures, objects or components, wherein the specific element, structure, object or component may be replaced without comprising the structural, operational or functional integrity of the system.

[0034] For purposes of the present invention, the term "lateral restraining end-element" refers to a single or composite structure or system that provide lateral support at an end section of an element, unit, or object in order to prevent any lateral displacement in the element, unit or object.

[0035] For purposes of the present invention, the term "lateral restraining end element" refers to single or composite structure or system that provide lateral support at the end section of a structure in order to prevent any lateral displacements in the structure.

[0036] For purposes of the present invention, the term "lateral support structure" refers to a structure, element or object that provides lateral support for another structure, element or object.

[0037] For purposes of the present invention, the term "lateral support structure" and the term "end-element" are interchangeably used. [0038] For purposes of the present invention, the term "lateral support" refers to a physical or mechanical support provided around an outside perimeter of an object in order to prevent or restrict movement, displacement or deformation of the object in the lateral direction.

[0039] For purposes of the present invention, the term "lateral" or "laterally" refers to the line, axis, or direction perpendicular to the longitudinal direction, which within the plane of the structure or device.

[0040] For purposes of the present invention, the term "laterally restrained" refers to a condition, state, or property whereby movement, displacement or deformation in the lateral direction is being restricted or inhibited, for example by another structure disposed laterally in relation to the object being laterally restrained.

[0041] For purposes of the present invention, the term "longitudinal gap" refers to a gap that exists along the longitudinal axis between two more structures. The longitudinal gap may be occupied of by another structure or it may be left as a void.

[0042] For purposes of the present invention, the term "longitudinal member" refers to a structure that extends mostly in the longitudinal direction away from its starting base or position.

[0043] For purposes of the present invention, the term "pinned-end connection" refers to a connection between two or more structures made- by securing in-place an overlaid portion of the two or more structures to one-another, for example with a bolt, to thereby form a hinged connection between the two or more structures.

[0044] For purposes of the present invention, the term "relatively slidable inter-fitting structures" refers to structures configured for slidable inter-fitting engagement in relation to one another, for example a structure with structural features that are arranged and shaped in order to fit into complementary cut-away portions of another structure having similar structural features and vice versa.

[0045] For purposes of the present invention, the term "slidable inter-fitting engagement" refers to a condition, configuration or arrangement whereby interaction between two or more structures involves sliding of structural features from one structure into complementary voids or cut-away portion that may exists in or between structural features of the other structure and vice versa.

[0046] For purposes of the present invention, the term "slidable inter-fitting structures" is interchangeably referred to as "lateral support structures" or "lateral support elements."

[0047] For purposes of the present invention, the term "tensile deformation" refers to a structural deformation resulting from the presence, exertion or application of tensile force.

[0048] For purposes of the present invention, the term "tensile force" refers to a stretching force or load pulling at one or both ends of a body along its longitudinal length. Tensile force is applied to a material, structure or body that acts away from the surface it is applied to. In other words it acts to pull the material or object apart.

[0049] For purposes of the present invention, the term "tensile" refers to a state or condition of being under tension or having a stretching force applied.

[0050] For purposes of the present invention, the term "tension" refers to a uniaxial force tending to cause the extension of a body or a balancing force within that body resisting the extension.

[0051] For purposes of the present invention, there term "structurally continuous arrangement" refers to an axial arrangement between two or more structures wherein no cross-sectional or longitudinal gap or gaps exists between the two or more structures in the arrangement, i.e., either one structure starts at the point where the other structure ends along the axial line of arrangement, or there is a structural overlap, along a common axial line, between the two or more structures such that there is structural continuity along the axial line of arrangement from the point the first structure starts all the way up to the point where the last structure ends.

Description

[0052] While the present invention is disclosed with references to certain embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it has the full scope defined by the language of the following claims, and equivalents thereof. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the invention.

[0053] Among a number of effective retrofitting techniques that have been implemented to retrofit existing buildings, the present invention contemplates the use of steel bracing. In particular the use of steel buckling restrained braces (BRB) to retrofit seismically deficient reinforced concrete frame building has shown superior seismic performance efficiency and promise relative to conventional bracing.

[0054] Buckling restrained braces are considered a relatively new type of seismic force resisting system. Conventional braces withstand both compressive and tensile forces and consist of different steel sections designed to avoid rupture under tensile stresses and buckling under compression. Buckling of these braces is a function of the slenderness ratio of the load-bearing member, which is a ratio of the effective length to the least radius of gyration of the cross section. Therefore, large cross-sectional areas are usually specified to avoid buckling failure in compression and subsequent damage to the framing structural integrity. To overcome such challenges, the concept of buckling restraining was developed.

[0055] The main concept of buckling restraint is to decouple the stress resistance of the main yielding steel core from the flexural buckling resistance that is provided by the lateral casing. Lateral bracing of the compression carrying load element provides lateral restraint against buckling along the braced length of the load carrying core, leaving un-restrained segments vulnerable to buckling under compressive load. Frames retrofitted with BRBs illustrate that failure occurs mainly in the external and internal reserve gaps that are part of the system and are configured as such to circumvent the load carrying element, or any part of the frame connection assembly from directly bearing upon the lateral restraining structure of the BRB. In other words, the brace yielding segment is un-restrained within these gaps, but is given a larger cross-sectional area to serve as a stiffener. Therefore these segments are prone to fail in buckling. Failure at steel core ends due to in-plane and out-of-plane bending moments is an oft-reported phenomenon. [0056] Considering the ease of installation of braces and relevant associated costs, BRBs are predominantly pre-manufactured and installed by specialized companies and suppliers, rather than built locally on the construction sites. This leads to additional costs for design, development, materials, transportation, installation, and quality control processes. Additionally, these commercial braces need to be inspected and evaluated for reliability after major earthquakes. If replacement is necessary, the entire brace (i.e., the steel core and the restraining system) must be replaced, since they are cast integrally as a unit.

[0057] Select embodiments of the present invention are directed towards addressing the above shortcomings of current BRBs including the vulnerability of un-restrained segments of the brace due to the presence of reserve gaps. Consequently, in accordance to one aspect of the present invention an apparatus and method for achieving an effective retrofit technique using buckling restrained braces is disclosed.

[0058] Embodiments of the present invention disclose a new design concept for a buckling restrained brace assembly that upgrades either, existing, repaired, and/or virgin reinforced concrete structures built according to previous state-of-art practice prior to the enactment of modern building codes. In accordance to another aspect of the present invention, a method and apparatus is disclosed for enhancing the performance of steel buckling restrained braces (BRB) used to retrofit seismically deficient reinforced concrete frame buildings. The proposed braces can also be implemented as the main seismic force resisting system in new construction. Thus, disclosed embodiments provide a design concept based upon restraining an entire length of a yielding core bar through a specially designed mechanical end brace. This eliminates any unsupported gaps that make the yielding core susceptible to buckling. Additionally, disclosed embodiments of the BRB structure may be assembled locally such as on construction sites. Furthermore, in accordance to another embodiment of the present invention, if replacements are required after major earthquakes, only the yielding core bar may require replacing rather than the entire brace system, rendering the disclosed exemplary seismic retrofit technique both structurally sound and economically feasible. [0059] FIG. 1 illustrates a conventional yielding core bar 100 comprising an upper end 104 and a lower end 106. An un-bonding material 108 covers a main body region 110 of the yielding core bar 100. The yielding core bar 100 has four rectangular arms 112, 114, 116 and 118 that extend the length of yielding core bar 100 and are the same size. Rectangular arm 112 is at 90° angle with respect to rectangular arms 114 and 118, rectangular arm 114 is at 90° angle with respect to rectangular arms 112 and 116, rectangular arm 116 is at 90° angle with respect to rectangular arms 114 and 118 so that yielding core bar 100, made from ductile steel, has a cross-shaped cross-section.

[0060] FIG. 2 illustrates a conventional buckling-restrained brace (BRB) structure 200 comprising a lateral bracing structure 204 in which the yielding core bar 100 is mounted therein. Lateral bracing structure 204 may be made of concrete, steel, composite, or any other suitable material for implementation within structural framework. Lateral bracing structure 204 provides lateral stiffness to yielding core bar 100 when yielding core bar 100 deforms laterally so that yielding core bar yields in-elastically in compression as well as in tension. Un-bonding material 108 on the yielding core bar 100 ensures that the axial forces are resisted only by the yielding core 100. Un-bonding material 108 prevents bonding between the yielding core bar 100 and lateral bracing structure 204 such that no axial load is transferred to the lateral bracing structure 204. A fill material 205 (which may comprise materials such as mortar, concrete, etc.) is disposed between un-bonding material 108 and an outer casing 206 of the lateral bracing structure 204. Fill material 205 provides additional resistance to buckling. BRB structure 200 may be viewed as a damper that dissipates significant and similar energy under tension and compression stress conditions..

[0061] FIGS. 3 and 4 illustrate another conventional BRB structure 300 and the elements comprising the same. BRB 300 includes a yielding core element 304 mounted inside a casing 306. Yielding core element 304 is the load carrying component and is typically made of steel.

Casing 306 is a hollow steel casing that functions as a bucking restraining system. Occupying the hollow space interposed between casing 306 and yielding core element 304 is filler material 308 (indicated by dashed lines inside casing 306) thus providing additional lateral restraint to the yielding core element 304. Yielding core element 304 has a restrained yielding portion 312, two restrained non- yielding transition portions 314 and two unrestrained non- yielding portions 316. Each unrestrained non-yielding segment 316 includes two arms 318 between which there is a gap 320.

[0062] Restrained yielding portion 312 is laterally restrained by the surrounding filler material 308 and casing 306. Restrained non-yielding transition portions 314 form end extensions of the restrained yielding portion 312 that are located inside casing 306 and have a larger cross sectional in order to ensure an elastic behavior. Each un-restrained non-yielding portion 316 is an extension of a restrained non-yielding transition portion 314 that extends past an end 322 of casing 306. Each un-restrained non-yielding portion 316 provides a connection point for BRB 300 to a frame of structure employing BRB 300. In steel structures, the connection may occur via a bolting or welding operations.

[0063] The yielding core element (bar) shown in FIGS. 3 and 4 may have an un-bonding insulator applied to each of the restrained yielding portions to provide a gap to thereby prevent or minimize frictional force transfer to the surrounding filling material and casing. Un-bonding insulator may be composed of materials such as Styrofoam™, silicon rubber sheets, grease, vinyl sheets, masking tape, asphalt paint, an air gap, etc. When an air gap is employed, the size of the air gap is based on the maximum strain in the yielding steel core segment and lateral deformations expected while the BRB is subjected to compressive stresses. Poisson's ratio of the yielding steel core both in the elastic and plastic ranges may be used to assess these lateral deformations.

[0064] In general, BRB assemblies are connected to the frame building through the load carrying element comprising a restrained yielding steel segment. There is no connection between the braced frame structure and the lateral restraining system. This implies that the load carrying element will be shortened when the BRB is subjected to compression stresses, while the length of surrounding casing, providing lateral restraint to the load carrying element, remains constant. Therefore, external and internal reserve gaps are used to prevent the load carrying element or any part of the frame connection assembly from directly bearing upon the lateral restraining system.

[0065] FIG. 5 illustrates an end portion of a conventional BRB assembly 500 comprising a yielding core bar 502 that is utilized as a load carrying element and a lateral restraining system 503 for providing lateral restraint to the yielding core bar 502. The lateral restraining system 503 may comprise a hollow casing 504 and filler material 505 occupying a space between hollow casing 504 and yielding core bar 502. Restrained non-yielding segment 506 of yielding core bar 502 may comprise internal reserve gaps 507, 508 and 510 disposed between yielding core bar 502 and filler material 505. Internal reserve gaps may circumvent yielding core bar 502 from directly bearing against filler material 505 when yielding core bar 502 experiences axial compression. Internal reserve gaps 507, 508 and 510 may further contain an un-bonding material 512. Un-restrained non-yielding segment 516 of yielding core bar 502 may comprise an exterior gap 520 physically separating an end 522 of the lateral restraining system 503 and supporting joints 524 that may form a part of a frame connection assembly. Exterior gap 520 prevents supporting joints 524 or any other part of a frame connection assembly from directly bearing against lateral restraining system 503, as the yielding core bar 502 experiences axial deformation due to a compressive load.

[0066] Therefore, the presence of the exterior gaps, as shown in FIG. 5, leads to a shorter casing length relative to length of the BRB assembly. The end portions of the core bar are laterally un-restrained within the external gaps and are, thereby, prone to buckling. In order to impede failure at the steel core ends due in-plane and out-of -plane bending, proper stiffening may be required at these core segments. In contrast, if no gap is provided or if the gap provided is not sufficient, the load will bear against the lateral supporting structure and the brace may experience pre-mature buckling failure at its mid-length.

[0067] In accordance to one embodiment of the present invention, an exemplary retrofit methodology comprises a single diagonal buckling restrained brace capable of performing up to the full compression and tension capacities of the load-carrying element. Select embodiments of the present invention employ the brace to be connected to steel joints surrounding the beam and columns near the frame joints. Yielding in both tension and compression produces a system with approximately the same lateral strength, stiffness and energy dissipation capacities during reverse cycling loadings.

[0068] As previously stated, in order to prevent a load-carrying element from directly bearing against the lateral supporting component of the BRB assembly, external gaps are provided at each end of the BRB between the lateral supporting component and the supporting joints such as, for example, gusset plates or mechanical hinge or any other connection details. These gaps serve to prevent any physical coupling between supporting joint members and lateral supporting structure as the yielding core axially deform under compressive load so that no load bears against the lateral supporting structure. However, the load-bearing or the load-carrying core element (i.e., yielding steel core bar) is un-restrained within these gaps and, therefore, these segments are prone to buckling. Local buckling failure at the steel core ends due to in-plane and out-of-plane bending are among the primary causes of buckling failure in BRB systems. Therefore, these regions are critical design areas requiring improvement as best served by the instant invention.

[0069] FIG. 6 illustrates a cross-sectional side-view of a ready-to-be installed BRB assembly 600 in accordance with one embodiment of the present invention. Ready-to-be installed BRB assembly 600 features an exemplary BRB assembly 602 (without end-hinges 610) comprising of a core segment 604 and lateral end- support unit 606 for providing a transition mechanism between the core segment 604 and the supporting frame member (i.e., base plate 608) at a frame connection point (i.e., end-hinge 610) which comprises a laterally unrestrained length 613 of a load-bearing core element 612. BRB 602 is connected, at either ends, for example, to a base plate 608 of end-hinge 610 through a load-bearing core element 612. Lateral end-support unit 606 comprises two lateral support structure 614 and 616, interchangeably referred to as end-elements 614 and 616. Lateral support structure 614 and 616 are configured for slidable inter-fitting engagement in a structurally continuous arrangement along a common axial line. In addition, lateral support structures or end- elements 614 and 616 are co-axially arranged upon a load-bearing core element 612. Clearance gaps 618 provide a passage for unrestrained relative axial movement between end- elements 614 and 616 (inter-slidable with one another). This enables unrestrained axial deformation of load-bearing core element 612. End-elements 614 and 616 (inter-slidable with one another) provide continuous lateral support along the entire unrestrained length 613 of load-bearing core element 612 from the end of core segment 604 up to base plate 608. The lateral end-support unit 606 is implemented to provide an exterior gap 619 between base plate 608 (frame joints) and top surface 620 of outer casing 621 at either end of the BRB. External gap 619 allows for deformation of the frame structure without interference from structural components of BRB. The exterior gaps 619 between base plate 608 and top surface 620 of outer casing 621 (i.e., where the lateral end-support unit 606 extends past the outer casing 621 of the BRB 602 to connect to the frame joint) allows for axial deformation of load- bearing core element 612 without interference from structural components of the BRB. An end portion 622 of load-bearing core element 612 may extends beyond base plate 608 in order to facilitate attachment of load-bearing core element 612 to, for example, base plate 608 of end-hinge 610.

[0070] In conventional BRB assemblies, conventional yielding core bars are designed to sustain damage in order to prevent catastrophic destruction to a frame structure (such as during a seismic event). While otherwise preventing damage to the structure at a prescribed location in which a conventional yielding core bar is installed, components of the aforementioned yielding core bar (e.g., restrained non-yielding segment 506 of yielding core bar 502) may become permanently wedged such as within the lateral brace structure. This sort of catastrophe would, otherwise, make the yielding core bar 502 virtually and practically impossible to remove from the BRB assembly. As a result, the entire BRB assembly would need to be replaced in order to restore proper bracing and integrity to the frame structure at this location for future seismic or other catastrophic events.

[0071] In contrast, advantages of the disclosed invention provide an improved yielding core bar design within a novel BRB assembly. Improvements to the disclosed BRB assembly 602 provide continuous buckling restraint for load- bearing core element 612 without employing altered structural or specialized designs of load-bearing core element 612 which might otherwise become prohibitive for individual replacement after a seismic event. For example, the load-bearing core element 612 eliminates additional structure features that may prohibit removal/replacement of load-bearing core element 612 after a seismic event unlike convention yielding core bar designs.

[0072] A cross-sectional view of core segment 604 is illustrated in FIG. 7. Core segment 604 comprises a load-bearing core element 612 disposed within a filling material 714. The filling material 714 may traverse along the length of core segment 604. Load-bearing core element 612 along with the filling material 714 may be inserted inside a steel pipe 718. Steel pipe 718 may be encased by filler material 720 (e.g., high flow cement-based concrete) and outer casing 621 (also referred to as hollow segment section tube casing or HSS). A clearance gap 724 may be created between the filling material 714 from one side and the steel pipe 718 on the other side to allow for the expansion of load-bearing core element 612 in compression, and minimize or eliminate the transfer of axial force(s) between load-bearing core element 612 and surrounding filler 720 and outer casing 621.

[0073] FIG. 8 illustrates a cross-sectional side view 800 of an exemplary load-bearing core element 802. In order to have a controlled yielding segment, the load-bearing core element 802 may have a reduced-area bar section 803 along a length 804 in the core segment 604 and unreduced-area bar sections 805 and 806 along lengths 807 and 808, respectively (i.e., through end-support 606 at each end.) The reduced-area bar section 803 may be surrounded by filling material 714 along a length 804 in the core segment 604. The unreduced-area bar section 805 may comprise a threaded section 811 and an unthreaded section 812. Similarly the unreduced-area bar section 806 may comprise a threaded section 814 and an unthreaded section 816. The threaded sections 811 and 814 of the unreduced-area bar section 805 and 806 may traverse sections 622, 608 and 619 of the load-bearing core element 802. In the exemplary load-bearing core element 802, area reduction for reduced- area bar section 803, extending along core segment 604, may be achieved, for example, by shaving off (machining) some of the steel from the outer surface of the load-bearing core element 802.

[0074] A cross-sectional side view 900 of an exemplary all-threaded load-bearing core element 902 is illustrated in FIG. 9. Similar to exemplary load-bearing core element 802, all- threaded load-bearing core element 902 may have a reduced-area bar section 903 along a length 904 in the core segment 604 and unreduced-area bar sections 905 and 906 along lengths 907 and 908, respectively (i.e., through end-support 606 at each end.) The reduced- area bar section 903 may be surrounded by filling material 714 along a length 904 in the core segment 604. The unreduced-area bar sections 905 and 906 of the all-threaded load-bearing core element 902 may traverse sections 622, 608 and 606 of the all-threaded load-bearing core element 802. In the exemplary all-threaded load-bearing core element 902, area reduction for reduced-area bar section 803 may be achieved by increasing thread depth of threading 810 in the reduced-area bar section 803 relative to threading 812 in the unreduced- area bar sections 805 and 806.

[0075] An epoxy and sand or bar threads can serve as filling 714 around the load-bearing core element 612. epoxy and sand or bar threading.

[0076] In accordance to one embodiment of the present invention, filling material 714 may comprise epoxy composition disposed around a reduced- area bar section of the load- bearing core element . In some embodiment of the present invention filling material 714 may comprise sand-based filler material. Other embodiments may comprise a combination of epoxy and sand as filling material 714. In alternative embodiments of the present invention, external surface of threading in the reduced-area bar section of the load-bearing core element , such as, for example, in the all-threaded load-bearing core element 902, may serve as filling material 714.

[0077] According to one designed embodiment, Load-bearing core element 612 may have a diameter of approximately 44.5 mm at the end-support units 606 (unreduced-area bar section) and a diameter of approximately 31.8 mm at the core segment 604 (reduced-area bar section). The difference between the bar diameters at the two regions, 606 and 604, may be filled by filling material 714 (i.e., epoxy and/or sand if the bar is machined or bar threads if the bar is threaded). Load-bearing core element 612 may then be inserted inside steel pipe 718. In one disclosed configuration, steel pipe 718 is designed with an approximately 46.5 mm inner diameter. Upon insertion of load-bearing core element 612 and the filling 714 within steel pipe 718, a clearance gap, 724, of approximately 1 mm all around is created between load-bearing core element 612 and steel pipe 718.

[0078] According to one embodiment, the clearance gap 724 is based on the maximum anticipated longitudinal strain of the load-bearing core element and on the Poisson's ratio of approximately 0.3 and 0.5 in the elastic and inelastic ranges, respectively, in accordance to the material properties of the load-bearing core element. At approximately 3% lateral drift of the frame, the bar transverse strain is expected to be around 0.3ey + 0.5 x 14.5ey, resulting in total transverse strain of approximately 1.51% corresponding to a lateral expansion of approximately 0.7 mm. The clearance gap, 724, may be selected to account for slightly larger strains in the load-bearing core element 612 within the core segment 604.

[0079] Some disclosed embodiments provide high flow cement-based concrete, for example, Sikacrete-08 SCC (self-consolidation concrete), to be utilized as filling material 720 between steel pipe 718 and the outer steel casing 621. Outer steel casing 621 is designed for sufficient flexural strength that exceeds the yield strength of the restrained yielding core. The - flexural strength of the buckling resistance of the HSS section is sufficient to provide a compressive force resistance factor of safety relative to the restrained core ultimate strength.

[0080] The structural details and mechanical operation of the lateral end-support unit 606 are further disclosed in FIGS. 10, 11, 12, 13, 14 and 15, in accordance to select embodiments of the present invention. Referring to FIG. 6 and FIG. 10, the lateral end-support unit 606 is implemented using end-elements 614 and 616 (represented as slidable inter-fitting structures). First end-element 614 may be connected to base plate 608 of end-hinge 610 of a frame connection assembly using, for example, four perimeter screws 1000. Second end- element 616 may be connected with, for example, four perimeter screws 1001 to the outer casing 621 near the end of the buckling-restrained core segment 604 as shown in FIG. 6 and FIG. 10. First end-element 614 and second end-element 616 may be configured for slidable inter-fitting engagement with each other in order to, for example, forms an interlocking zone 1002.

[0081] Referring to FIGS. 6, 10, 11 and 12, end-elements 614 and 616 (slidable inter- fitting structures) both comprise a cored base portion 1003 and 1010, respectively. End- elements 614 may further comprise a plurality of circumferentially disposed longitudinal members 1104, 1106 and 1108 extending along a longitudinal axis away from the cored base portion 614. End-elements 616 may further comprise a plurality of circumferentially disposed longitudinal members 1112, 1114 and 1116 extending along a longitudinal axis away from the cored base portion 616. Longitudinal members 1104, 1106, 1108 may axially extend away from the cored base portion 614 in such a way as to laterally restrain the motion of an elongated member (such as, for example, load-bearing core element 612) extending through the cored opening of cored base portion 614. Longitudinal members 1112, 1114, 1116 may axially extend away from cored base portion 616 in such a way as to laterally restrain the motion of an elongated member (such as, for example, load-bearing core element 612) extending through the cored opening of the cored base portion 616. The elongated member (e.g., load-bearing core element 612) is laterally restrained along the entire length of end- elements 614 and 616. The entire length of end-element 614 comprises the longitudinal length through the cored base portion 1003 and the length of longitudinal members 1104, 1106 and 1108. The entire length of end-element 616 comprises the longitudinal length through the cored base portion 1010 and the length of longitudinal members 1112, 1114 and 1116.

[0082] The laterally closed structural arrangement (illustrated in FIG. 11) formed in the inter-locking zone 1117 by the over-lapping interleaved arrangement of longitudinal members 1104, 1106 and 1108 of end-element 614 and longitudinal members 1112, 1114 and 1116 of end-element 616, prevents the two end-elements 614 and 616 from separating (i.e., moving out of an overlapped arrangement of respective longitudinal members) when load- bearing core element 612 is in tension. This will prevent the formation of any laterally unsupported regions within the configuration of lateral end- support units 606 (e.g., see FIG. 6).

[0083] Referencing FIGS. 10, 11 and 12 end-element 614 having a cylindrical base portion 1003 and three longitudinal members 1104, 1106 and 1108 extending from cylindrical base portion 1003 may be configured in a slidable inter-fitting engagement with end-element 616 having a cylindrical base portion 1010 and three longitudinal members 1112, 1114 and 1116 extending from cylindrical base portion 1010.

[0084] As illustrated in FIGS. 10, 11, 12, 13 and 14, longitudinal members 1104, 1106 and 1108 extend from cylindrical base portion 1003 of first end element 614. Longitudinal members 1112, 1114 and 1116 extend from cylindrical base portion 1010 of second end- element 616. In one disclosed embodiment, the aforementioned longitudinal members have respective interior surfaces that may be configured such that they together form a cylindrically-shaped inner surface when each longitudinal member of the first end-element slidably interfits between a pair of longitudinal members of the second end-element (i.e., within a complementary cut-away portion of the second end-element) and each longitudinal member of the second end-element slidably interfits between a pair of longitudinal members of the first end-element (i.e., within a complementary cut-away portion of the first end- element.)

[0085] Functioning as an improved yielding core bar, load-bearing core element 612 is configured having a prescribed diameter and grade, and extends through buckling-restrained core segment 604 and lateral end-support units 606 comprising of end-elements 614 and 616. Lateral end-support units 606 eliminate any unsupported gaps that may make the yielding core bar susceptible to buckling. Consequently, the lateral end-support units 606 along with the buckling-restrained core segment 604 provide lateral restraint for the entire length of the load-bearing core element 612. One of many attachment configurations may be employed to secure load-bearing core element 612. For example, load-bearing core element 612 may be threaded at its ends and bolted to joint base plates 608 at either side of BRB 602 with for example a nut 1018. The lateral end-support unit 606 may be configured to allow unrestrained relative translational movement of two end-elements 614 and 616 along an axial direction across an external gap 619 and clearance gap 618. External gap 619 and clearance gap 618 may be designed to accommodate compressive and tensile axial deformations, respectively, which may be required at the targeted ultimate drift of a structural frame. As a result, continuous lateral restraint is provided for load-bearing core element 612 along its entire length and within lateral end- support units 606. As such, lateral end support units 606 functionally act as compressible lateral brace structures that prevent lateral displacement while allowing for bi-directional axial displacement of an elongated member (e.g., load- bearing core element 612) extending there through.

[0086] FIGS. 13 and 14 represent a cross section side-view 1300 and 90°-rotated cross section side-view 1400 of a lateral end- support unit 606 for a load-bearing core element 612 in a buckling-restrained brace assembly. FIG. 15 illustrates a frontal photographed image

1500 of a lateral end-support unit 606 that illustrates the continuous lateral restraining mechanism poised to enact when the load-bearing core element 612 is placed under tension and/or compression. As further observed from FIGS. 13, 14 and 15, each lateral end-support unit comprises of two inter-slidable structures, namely end-elements 614 and 616, each comprising a cylindrical cored base portion (also referred to as cored end sections) 1003 and 1010, respectively. In accordance to one embodiment of the present invention, an exemplary configuration, as shown in FIGS. 10, 11, 12 13, 14 and 15, may comprise three longitudinal members 1104, 1106 and 1108 associated with end-element 614, that may be offset in relation to three longitudinal members 1112, 1114 and 1116, associated with end-element 616. The offset may be an axial or a rotational offset implemented in such a way as to allow longitudinal members 1104, 1106 and 1108 of first end-element 614 and longitudinal members 1112, 1114 and 1116 of second end-element 616 to slide past one another and in- between each other to thereby form a closed hollow cored section as illustrated in the exemplary configurations of FIGS. 11 and 12.

[0087] Referencing FIGS. 6, 10, 11, 12, and 15 in order to minimize frictional forces, a gap 1202 may be maintained between the inter-sliding longitudinal members 1104, 1106 and 1108 of end-element 614 and longitudinal members 1112, 1114 and 1116 of end-element 616. Referencing FIG. 12, there may further be a gap 1204 between lateral end-support unit 606 (not shown in FIG. 12) and outer casing 621. Friction may further be reduced by greasing the gap 1202 between the said longitudinal members in the interlocking zone 1002 and gap 1204 between lateral end-support units 606 and the outer casing 621 in order to further facilitate free relative translational movement of end-elements 614 and 616. In select embodiments, gap 1202 is approximately 5 mm and gap 1204 is approximately 1 mm all around. Disclosed embodiments may also provide longitudinal members 1104, 1106, 1108 that extend from the cylindrical cored end portion 1003 of end-element 614 and longitudinal members 1112, 1114, 1116 that extend from the cylindrical cored end portion 1010 of end- element 616 being capable of free relative translational movement along a common longitudinal axis. Longitudinal members 1104, 1106, 1108, 1112, 1114, 1116 may also be configured to a length of approximately 140 mm each.

[0088] Referencing FIGS. 10, 11 and 15 the laterally restrained zone 1502 may be divided into three transition zones comprising a clearance gap 1504 on one of the laterally restrained zone 1502 (wherein lateral support is provided by the three solid longitudinal members 1104, 1106 and 1108 that extend from the end-element 614), a clearance gap 1506 on another end of laterally restrained zone 1502 (wherein lateral support is provided by the three solid longitudinal members 1112, 1114 and 1116 that extend from the end-element 616), and interlocking zone 1002, in a middle of the laterally restrained zone -1302 (wherein lateral support is provided by an interleaved arrangement of longitudinal members from both inter-slidable end-elements 614 and 616). Before the BRB is loaded, load-bearing core element 612 is laterally restrained across clearance gap 1504 and 1506 by the three longitudinal members 1104, 1106 and 1108 from one end, and three longitudinal members 1112, 1114 and 1116 from the other end, wherein each of the one end and the other end extend from end-elements 614 and 616, respectively. Within the interlocking zone 1002, load-bearing core element 612 is laterally restrained by an inter-fitting arrangement of longitudinal members from end-elements 614 and 616. Therefore, based on the mechanism devised in accordance to an embodiment of the invention, the load-bearing core element 612 is fully restrained against buckling over its entire length, i.e., from joint to joint.

[0089] In a disclosed embodiment, laterally restrained zone 1302, between the cored cylindrical base portions 1003 and 1010 (associated with end-elements 614 and 616, respectively) is approximately 200 mm long. This section may be divided into three segments. Top and bottom segments correspond to clearance gap 1504 and 1506 that permit axial deformations in response to compression of the load-bearing core element 612 (when the core is subjected to compression). Top and bottom segments corresponding to clearance gap 1504 and 1506 are approximately 60 mm each. A middle segment, of approximately 80 mm length, corresponds to interlocking zone 1002and serves to prevent the two end-elements 614 and 616 of the lateral end-support unit 606 from separating (i.e., developing a longitudinal gap in their structural arrangement) when the load-bearing core element 612 is in tension.

[0090] In one disclosed embodiment, cylindrical cored base portion 1003 is approximately 60 mm thick, disposed inside hollow steel casing 621. Cylindrical cored base portion 1010 may be secured to the outer casing 621 at an end of core segment 604 with a retaining structure, such as, for example, four perimeter screws 1001 for engaging screw hole locations 1508. The cylindrical cored base 1003 may be approximately 170 mm thick connected to thick joint steel plate 608 of a frame connection assembly by another retaining structure such as, for example, four perimeter screws 1000 (shown in FIG 10) for engaging screw hole locations 1510. [0091] According to one embodiment of the present invention, the lengths of the components are based on the geometry of the frame at approximately 3% lateral drift. In one embodiment a prescribed length of yielding core is approximately 1565 mm at the core segment 604; and approximately 430 mm at lateral end-support units 606; and the thickness of steel plates -608 is approximately 57 mm. At this drift, the predicted elongation of the length of load-bearing core element 612 (in its entire length based on BRB assembly 602) is approximately 70.5 mm (35.3 mm at each brace end) , corresponding to a global bar strain of approximately 2.9%, which is approximately 14.5 times the bar yielding strain, ey, of about 0.2%.

[0092] In another disclosed embodiment, end-elements 614 and 616 comprise a cored cylindrical base portion having an inner diameter of approximately 46.5 mm and an outer diameter of approximately 150 mm. The end-elements may be configured to accommodate a gap of approximately 60 mm of tensile and compressive axial deformations. Lateral end- support unit 606 may be inserted inside steel outer casing 621 of BRB assembly 604 to create an approximately 60 mm longitudinal gap between top surface 620 of the outer casing 621 and the base plates 608 of frame connection assembly at each end of the BRB assembly, in accordance to described embodiments of the present invention. However, other embodiments may produce a longitudinal gap approximately in a range of 50 mm to 100 mm for typical frame buildings.

[0093] FIG. 16, 17 and 18 illustrates primary components and the assembled structure for an exemplary mechanical steel hinge 1600 for coupling a BRB to a frame structure, in accordance to one embodiment of the present invention. The exemplary mechanical steel hinge 1600 comprises two hinge parts 1602 and 1604 as illustrated in FIG. 14 and FIG. 15, respectively. A single high strength bolt 1606 of approximately 44.5 mm diameter may be used to attach the two hinge parts 1602 and 1604 together to form a pinned-end connection

1608 as illustrated in FIG. 16. The purpose of pinned connection 1608 is to eliminate secondary moments at the ends of the load-bearing core bar 1610. The hinge part 1602 may comprise a thick steel plate 1612 that secures the load-bearing core element (steel core yielding bar) 1610 at both ends. Two plates 1614 of approximately 25.4 mm thickness may be welded onto the approximately 57.2 mm thick end plate 1612. The plates may be fabricated with a bolt hole 1616 of approximately 44.5 mm diameter to connect to hinge part 1604 of the connection assembly, which in turn is connected to the concrete frame. The connecting bolt 1606 which connects the two hinge parts 1602 and 1604 provides the hinging mechanism, thus ensuring concentric force application on load-bearing core bar 1610. A rectangular cut out 1618 of approximately 127 mm x 254 mm may be provided in the two steel plates 1614 for the purpose of providing sufficient space to secure nuts 1620 of the steel core yielding steel bar 1610. Hinge part 1604 of the pin connection 1608 may comprise of approximately 50.8 mm thick steel plate 1622 which may comprise an approximately 44.5 mm diameter bolt hole 1624 to connect with hinge Part 1602. Steel plate 1622 may be welded to an end plate 1626.

[0094] One exemplary BRB configuration 1900 is shown in FIG. 19. In the exemplary configuration 1900, a steel brace 1902 is placed diagonally at an angle of approximately 41 degrees with respect to the foundation level 1904. The BRB 1902 is comprised of a core section 1903 (approximately 1565 mm in length) and two lateral end-support units 606 coupled to opposite ends of the core segment which comprises a conventional buckling- restrained brace. Lateral end-support units 606 ( approximately 430 mm in length) allow unrestrained axial deformations of the load-bearing core element 612. The total brace length of approximately 2425 mm incorporates a core section and two lateral end-support units at either end of the core section. The BRB may be assembled and then connected to hinge part 1602 of the connection assembly 1608 by, for example securing nuts 1620 on the threaded ends 1906 of the load-bearing core element 612 as shown in FIG. 19. Thereafter, the brace may be inserted into the frame 1907 and secured by a bolt 1606 (through bolt hole 1616) to hinge part 1604 of the connection 1608. Hinge part 1604 may be welded to a steel bearing assembly 1908 that is, in turn, connected to the joints of the frame. Two springs 1909 and 1910 may be fastened between opposites sides of the outer casing 621 at the lower lateral end-support unit 606 region and the base plate 608 of end-hinge 610 in order to maintain the external gap 619. Two additional HSS 1911 and 1912 of approximately 254 mm x 254 mm x 13 mm may be placed on the outer faces of the frame 1907 as shown in FIG. 17. [0095] Having described the many embodiments of the present invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. Furthermore, it should be appreciated that all examples in the present disclosure, while illustrating many embodiments of the invention, are provided as non-limiting examples and are, therefore, not to be taken as limiting the various aspects so illustrated.

Claims

WHAT IS CLAIMED IS:

An apparatus comprising:

a first lateral support structure comprising a first base and a plurality of first longitudinal members extending from the first base; and

a second lateral support structure comprising a second base and a plurality of second longitudinal members extending from the second base,

wherein each first longitudinal member slidably interfits between a pair of second longitudinal members of the plurality of second longitudinal members, wherein each second longitudinal member slidably interfits between a pair of first longitudinal members of the plurality of first longitudinal members, wherein the first base includes a first opening and the second base includes a second opening configured to receive an elongated member that extends through the first opening and the second opening,

wherein the plurality of first longitudinal members and the plurality of second longitudinal members surround and laterally restrain a motion of the elongated member when the elongated member extends through the first opening and the second opening.

The apparatus of claim 1 wherein the apparatus is configured such that the plurality of first longitudinal members extending from the first base of the first lateral support structure partially extends past the plurality of the second longitudinal members extending from the second base of the second lateral support structure.

The apparatus of claim 1 wherein a clearance gap is configured between each first longitudinal member and each second longitudinal member when the each first longitudinal member slidably interfits between a pair of second longitudinal members and vice versa.

4. The apparatus of claim 3 wherein the clearance gap minimizes frictional forces and allows a free relative translational movement between the plurality of first longitudinal members and the plurality of second longitudinal member.

5. The apparatus of claim 1, wherein the plurality of longitudinal members of the first lateral support structure and the plurality of longitudinal members of the second lateral support structure each comprise three longitudinal members.

6. The apparatus of claim 1, wherein the first opening is cylindrically-shaped, wherein the second opening is cylindrically-shaped and wherein the plurality of first longitudinal members and the plurality of second longitudinal members having interior surfaces that together form a cylindrically-shaped inner surface.

7. The apparatus of claim 1, wherein the elongated member comprises a load-bearing core element.

8. The apparatus of claim 7, wherein the load- bearing core element is individually removable from the apparatus.

9. The apparatus of claim 7, wherein the load-bearing core element is individually replaceable from the apparatus.

10. The apparatus of claim 7, wherein the load-bearing core element is coupled to a hinge at each end of a buckling-restrained brace assembly for ensuring concentric force on the load-bearing core element.

11. The apparatus of claim 10, wherein the first lateral support structure provides a longitudinal gap to the hinge at each end of the buckling-restrained brace assembly in order to allow for an axial deformation when the load-bearing core element is subjected to compression.

12. The apparatus of claim 11, wherein the longitudinal gap is approximately 50 mm to 100 mm.

13. The apparatus of claim 10, wherein the hinge comprises a first hinge part and a second hinge part, wherein the first hinge part is coupled to the load-bearing core element and wherein, the second hinge part is coupled to a frame joint.

14. The apparatus of claim 13, wherein the load-bearing core element is threaded at each end and connected to the first hinge part at either end of the buckling-restrained brace assembly.

15. The apparatus of claim 13, wherein the first hinge part and the second hinge part are coupled together with a bolt to form a pinned-end connection.

16. The apparatus of claim 15, wherein the bolt provides a hinging mechanism for ensuring concentric force on the load-bearing core element.

17. A method comprising:

adjusting a relative axial relationship between a first lateral support structure and a second lateral support structure of a longitudinal assembly to thereby maintain an axially aligned and structurally continuous arrangement for the longitudinal assembly of the first and the second lateral support structures, wherein the first lateral support structure is in a slidable interfitting engagement with the second lateral support structure.

18. The method of claim 17, wherein the first lateral support structure and the second lateral support structure are coaxially arranged upon an end portion of a load-bearing core element in a buckling-restrained brace assembly.

19. The method of claim 18, wherein the first lateral support structure is coupled to an end of the load-bearing core element at a frame connection point and configured for an inter-fitting engagement with the second lateral support structure coupled to an end of the buckling restrained brace.

20. The method of claim 18 wherein, the first lateral support structure and the second lateral support structure comprise a cored base portion having a plurality of circumferentially disposed longitudinal members extending axially away from the cored base portion.

21. The method of claim 18 wherein, the slidable interfitting engagement between the first and the second lateral support structures is facilitated by a relative rotational offset between the first and the second lateral support structures.

22. An apparatus comprising:

a buckling restrained brace; and two lateral end- support units coupled to the buckling restrained brace,

wherein the buckling restrained brace comprises an elongated member extending through a lateral restraining system,

wherein each of the two lateral end-support units comprises a first lateral support structure and a second lateral support structure,

wherein the first lateral support structure comprises a first base and a plurality of first longitudinal members extending from the first base, and

wherein the second lateral support structure comprising a second base and a plurality of second longitudinal members extending from the second base, wherein each first longitudinal member slidably interfits between a pair of second longitudinal members of the plurality of second longitudinal members, wherein each second longitudinal member slidably interfits between a pair of first longitudinal members of the plurality of first longitudinal members, wherein the first base includes a first opening and the second base includes a second opening configured to receive the elongated member that extends through the first opening and the second opening,

23. The apparatus of claim 22, wherein the two lateral end-support units are coupled to opposite ends of the buckling restrained brace.

24. The apparatus of claim 22, wherein the apparatus is initially configured such that the plurality of first longitudinal members extending from the first base of the first lateral support structure partially extends past the plurality of the second longitudinal members extending from the second base of the second lateral support structure.

25. The apparatus of claim 24, wherein a clearance gap is configured between each first longitudinal member and each second longitudinal member when each first longitudinal member slidably interfits between a pair of second longitudinal members and vice versa. 26. The apparatus of claim 25 wherein the clearance gap minimizes frictional forces and allow a free relative translational movement between the plurality of first longitudinal members and the plurality of second longitudinal member.

27. The apparatus of claim 22, wherein the plurality of longitudinal members of the first lateral support structure and the plurality of longitudinal members of the second lateral support structure each comprise three longitudinal members.

28. The apparatus of claim 22, wherein the first opening is cylindrically-shaped, wherein the second opening is cylindrically-shaped and wherein the plurality of first longitudinal members and the plurality of second longitudinal members have interior surfaces that together form a cylindrically-shaped inner surface. 29. The apparatus of claim 23, wherein the elongated member comprises a load-bearing core element.

30. The apparatus of claim 29, wherein the load-bearing core element is individually removable from the apparatus.

31. The apparatus of claim 29, wherein the load-bearing core element is individually replaceable from the apparatus.

32. The apparatus of claim 29, wherein the apparatus is a buckling-restrained brace assembly, wherein the load-bearing core element is coupled to a hinge at each end of the buckling-restrained brace assembly for ensuring concentric force on the load- bearing core element. 33. The apparatus of claim 32, wherein the first lateral support structure provides a longitudinal gap to the hinge at each end of the buckling-restrained brace assembly in order to allow for an axial deformation when the load-bearing core element is subjected to compression.

34. The apparatus of claim 33, wherein the longitudinal gap is approximately 50 mm to 100 mm.

35. The apparatus of claim 32, wherein the hinge comprises a first hinge part and a second hinge part, wherein the first hinge part is coupled to the load-bearing core element and wherein the second hinge part is coupled to a frame joint.

36. The apparatus of claim 35, wherein the apparatus is a buckling-restrained brace assembly, wherein the load-bearing core element is coupled at each end and retained to a base plate of the first hinge part at either end of the buckling-restrained brace assembly.

37. The apparatus of claim 36, wherein the load-bearing core element is threaded at each end and connected to the first hinge part at either end of the buckling-restrained brace assembly.

38. The apparatus of claim 35, wherein the first hinge part and the second hinge part are coupled together with a bolt to form a pinned-end connection.

39. The apparatus of claim 38, wherein the bolt provides a hinging mechanism for ensuring concentric force on the load-bearing core element.