Abstract:
A link-fuse joint resists bending moments and shears generated by seismic loading. A joint connection includes a first plate assembly having a first connection plate including a first diagonal slot formed therethrough. A second plate assembly has a second connection plate including a second diagonal slot formed therethrough. The second diagonal slot is diagonally opposed to the first diagonal slot. The second connection plate is position such that at least a portion of the second diagonal slot aligns with a portion of the first diagonal slot. A pin is positioned through the first diagonal slot and the second diagonal slot. The joint connection accommodates a slippage of at least one of the first and second plate assemblies relative to each other when the joint connection is subject to a seismic load and without significant loss of clamping force.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a link beam joint that is utilized in a structure that is subject to seismic loads. In particular, the link beam joint is a link-fuse joint that lengthens dynamic periods and reduces the forces that must be resisted within shear wall or frame construction of structures so that the walls or frames can withstand seismic activity without sustaining significant damage. 
         [0003]    2. Description of the Related Art 
         [0004]    Structures have been constructed, and are being constructed daily, in areas subject to seismic activity. Special considerations must be given to the design of such structures. In addition to normal loading conditions, the walls and frames of these structures must be designed not only to accommodate normal loading conditions, but also those loading conditions that are unique to seismic activity. For example, link beams within shear walls are typically subject to cyclic motions during seismic events. To withstand such loading conditions, structures subject to seismic activity must behave with ductility to allow for the dissipation of energy under those extreme loads. 
         [0005]    In conventional systems, reinforced link beams subject to seismic loads have been designed with the beams fully connected directly to reinforced concrete shear walls with fully developed reinforcing bars. These beams are designed to elastically resist service wind and frequent earthquake events and are designed to plastically perform or hinge during severe earthquake events. 
         [0006]    Since link beam length-to-depth ratios are relatively small, shear will typically control the behavior of the beams. For large shear forces, diagonal reinforcement arranged in elevation in the shape of an “X” is typically required. In other cases where shear forces are large, embedded structural steel members are placed within the reinforced concrete beams to resist the load. In all cases, these beams are designed to permanently deform in a severe seismic event. Reinforcing bars and structural steel, if used permanently, deform and concrete cracks or spalls. Energy is dissipated and beams act with ductility but plastically deform with conventional designs. 
         [0007]    In steel braced frames, steel beams located between braces are designed to fuse during extreme seismic events. The behavior is similar to beam links used in eccentrically braced frames. These beams are designed to yield and plastically deform, protecting the bracing members and columns and the overall integrity of the structure. 
         [0008]    Although current link beam designs may be able to withstand a seismic event, the damage caused by the joints&#39; inability to function elastically, raises serious questions about whether conventional structures can remain in service after enduring seismic events. A need therefore exists for shear wall and steel braced frame structures that can withstand a seismic event without experiencing significant beam or joint failure, so that the integrity of the structure remains relatively undisturbed even after being subject to seismic activity. 
       SUMMARY OF THE INVENTION 
       [0009]    A “link-fuse” joint consistent with the present invention enables a shear wall or steel braced frame to withstand a seismic event without experiencing significant beam or joint failure. The link-fuse joint is also referred to as a joint connection herein. The link-fuse joint is generally utilized in a link beam assembly. The link-fuse joint may be incorporated, for example, into the reinforced concrete shear walls or steel braced frames of a building or other structure subject to seismic activity and improves the structure&#39;s dynamic characteristics by allowing the link-fuse joint to slip under extreme loads. This slippage changes the structure&#39;s dynamic characteristics by lengthening the structure&#39;s fundamental period and softening the structure, which allows the structure to exhibit elastic properties during seismic events. By utilizing the link-fuse joint, it is generally not necessary to use shear walls or steel frames and link beams as large as typically used for a similar sized structure to withstand an extreme seismic event. Accordingly, overall building costs can also be reduced through the use of a link-fuse joint consistent with the present invention. 
         [0010]    The link-fuse joint may be employed in a link beam, where the beam attaches to neighboring walls or frames of a structure. In the link-fuse joint, a plate assembly within a beam is designed to mate and be held together by a pin assembly extending through connection plates that extend outward from the plate assembly. Additionally, the plate assembly has diagonally opposed slots. The plate assembly may be secured together, for example, by a threaded rod, multiple threaded rods, multiple high-strength steel bolts, and the like. These connections allow for the slotted plates to slip relative to each other when subject to extreme seismic loads without a significant loss in clamping force. Movement in the joint may be further restricted by treating the faying surfaces of the plate assembly with brass. The brass shims used within the connection possess a predetermined load-displacement behavior and excellent cyclic attributes. 
         [0011]    The friction developed from the clamping force within the plate assembly with the brass shims against the steel surface prevents the joint from slipping under most service loading conditions, such as those imposed by wind, gravity, and moderate seismic vents. The threaded rod(s) or high-strength bolts are torqued to provide a slip resistant connection by developing friction between the connected surfaces. However, under extreme seismic loading condition, the level of force applied to the connection exceeds the product of the coefficient of friction times the normal rod or bolt clamping force, which causes the joint to slip in a planer direction while maintaining connectivity. 
         [0012]    The sliding of the joint during seismic events provides for the transfer of shear forces and bending moment from the link beams to the shear walls or braced frames. This sliding dissipates energy, which is also known as “fusing.” This energy dissipation reduces potential damage to the structure due to seismic activity. 
         [0013]    In accordance with devices consistent with the present invention, a joint connection is provided. The joint connection comprises a first plate assembly having a first connection plate including a first diagonal slot formed therethrough. A second plate assembly has a second connection plate including a second diagonal slot formed therethrough. The second diagonal slot is diagonally opposed to the first diagonal slot. The second connection plate is position such that at least a portion of the second diagonal slot aligns with a portion of the first diagonal slot. A pin is positioned through the first diagonal slot and the second diagonal slot. The joint connection accommodates a slippage of at least one of the first and second plate assemblies relative to each other when the joint connection is subject to a seismic load and without significant loss of clamping force. 
         [0014]    Although a joint connection consistent with the present invention will slip under extreme seismic loads to dissipate the energy, the joints will, however, remain elastic due to their construction. Furthermore, the joint generally does not becomes plastic nor yields when subjected to the loading and the slip. This allows, for example, a shear wall structure utilizing the joint connection to remain in service after enduring a seismic event and resist further seismic activity. 
         [0015]    Other features of the invention will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the invention, and be protected by the accompanying claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    The accompanying drawings, which are incorporated in an constitute a part of this specification, illustrate an implementation of the invention and, together with the description, serve to explain the advantages and principles of the invention. In the drawings, 
           [0017]      FIG. 1  is a perspective view of one embodiment of a link beam joint assembly consistent with the present invention; 
           [0018]      FIG. 2  is an exploded front view of the link beam joint assembly illustrated in  FIG. 1 ; 
           [0019]      FIG. 2   a  is a front view of a pin assembly used to connect the slotted plate assembly; 
           [0020]      FIG. 3  is an exploded top view of the link beam joint assembly illustrated in  FIG. 1 ; 
           [0021]      FIG. 3   a  is a side view of the pin assembly used to connect the slotted plate assembly; 
           [0022]      FIG. 4  is a cross sectional view of the plate assembly of  FIG. 2  taken along line IV-IV′,  FIG. 5  is a cross sectional view of the plate assembly of  FIG. 2  taken along line V-V′; 
           [0023]      FIG. 6  is a cross sectional view of the plate assembly of  FIG. 2  taken along line VI-VI′; 
           [0024]      FIG. 7  is a side view of a single threaded thru-rod pin assembly; 
           [0025]      FIG. 8  is a side view of a multiple threaded thru-rod pin assembly; 
           [0026]      FIG. 9  is a side view of a multiple high-strength bolt pin assembly; 
           [0027]      FIG. 10  is a front view of one embodiment of the link joint assembly consistent with the present invention; 
           [0028]      FIG. 11  is a top view of one embodiment of the link joint assembly consistent with the present invention; 
           [0029]      FIG. 12  is a front view of the link beam joint assembly consistent with the present invention as it would appear with the link-fuse joint displaced when subject to extreme loading conditions; and 
           [0030]      FIG. 13  is a perspective view of the link beam joint assembly consistent with the present invention as it would appear with the link-fuse joint displaced when subject to extreme loading conditions. 
       
    
    
       [0031]    Corresponding reference characters indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0032]    Reference will now be made in detail to an implementation in accordance with a link-fuse joint consistent with the present invention as illustrated in the accompanying drawings. The link-fuse joint enables a shear wall or steel braced frame to withstand a seismic event without experiencing significant beam or joint failure. The link-fuse joint may be incorporated, for example, into the reinforced concrete shear walls or steel braced frames of a building or other structure subject to seismic activity and improves the structure&#39;s dynamic characteristics by allowing the link-fuse joint to slip under extreme loads. This slippage changes the structure&#39;s dynamic characteristics by lengthening the structure&#39;s fundamental period and softening the structure, which allows the structure to exhibit elastic properties during seismic events. By utilizing the link-fuse joint, it is generally not necessary to use shear walls or steel frames and link beams as large as typically used for a similar sized structure to withstand an extreme seismic event. Accordingly, overall building costs can also be reduced through the use of a link-fuse joint consistent with the present invention. 
         [0033]      FIG. 1  is a perspective view of one embodiment of a link beam joint assembly  10  consistent with the present invention. Although the illustrative embodiment of  FIG. 1  is described as applied to a structure consisting of reinforced concrete, one skilled in the art may also utilize a link-fuse joint  19  in structures comprising other materials, such as structural steel and/or composite materials, e.g., a combination of structural steel and reinforced concrete. The link-fuse joint may be used between columns within a braced frame, for example. 
         [0034]    As seen in  FIG. 1 , the illustrative link beam joint assembly  10  includes walls  12   a  and  12   b  connected via beams  14   a  and  14   b.  In the illustrative example, the walls  12   a,    12   b  are reinforced concrete walls. The walls may alternatively comprise different materials, such as steel columns and the like. The beams may be, for example, concrete beams, steel beams, and the like. Embedded plates  28   a,    28   b  are secured to a respective beam  14   a,    14   b,  for example by being welded to the beam and/or secured within the beam&#39;s concrete material. Spaced-apart connection plates  16   a,    16   b  extend from an end of embedded plate  28   b.  Spaced-apart connection plates  18   a,    18   b  extend from an end of embedded plate  28   a.  The connection plates may be, for example, steel plates and the like and connect to the embedded plate, for example, by being welded to the embedded plate. 
         [0035]    Connection plates  16   a,    16   b  and connection plates  18   a,    18   b  are connected to each other via a link-fuse joint  19 . To create the link-fuse joint  19 , the respective connection plates  16   a,    16   b  and  18   a,    18   b  are connected to each other via a pin assembly  20  that extends through the sets of connection plates  16   a,    16   b  and  18   a,    18   b.  The pin assembly  20  may comprise, for example, structural steel or another suitable material. In the illustrative example, connection plates  16   a,    16   b  are positioned as inner plates between outer connection plates  18   a,    18   b.  Each set of inner connection plates  16   a,    16   b  and outer connection plates  18   a,    18   b  abut against one another when the joint  19  is complete. As further described below, connecting the connection plates  16   a,    16   b  and  18   a,    18   b  together via the pin assembly  20  through opposing slots  30  and  31  in plates  16   a,    16   b  and  18   a,    18   b,  respectively, creates the link-fuse joint  19  consistent with the present invention. 
         [0036]    In the illustrative example, there are two connection plates  16   a  and  16   b  that abut against two connection plates  18   a  and  18   b.  One having skill in the art will appreciate that each side of the link-fuse joint may comprise a different number of connection plates. For example, one side of the joint may include two connection plates  16   a  and  16   b  and the opposite side of the joint may include a single, wider connection plate  18 . There may be one or more connection plates on each side of the joint. Further, there may be a different number of connection plates on each side of the joint. 
         [0037]      FIG. 2  is an exploded front view of the link beam joint assembly  10  illustrated in  FIG. 1 . This view illustrates the connection plates  16   a  and  18   a  as they would appear when the joint  19  is disconnected. In the illustrative example, the connection plates  16   a  and  18   a  are welded to the respective embedded plates  28   a,    28   b  and extend away from the embedded plates. 
         [0038]    Inside connection plates  16   a,    16   b  and outside connection plates  18   a,    18   b  each include a diagonal slot  30  and  31 , respectively. These slots are diagonally opposed with a reference angle θ, typically 0° to 90°. These diagonally opposed slots allow for an imposed lateral or vertical moment in the plane of the walls  12   a  and  12   b.    
         [0039]      FIG. 2   a  is a front view of an illustrative pin assembly  20 , which includes a structural steel pin (or threaded rod)  21 , four steel nuts  22 , and eight steel washers  24 . The pin  21  is inserted into the diagonal slots  30  and  31  in the connection plates  16   a,    16   b  and  18   a,    18   b.  The pin  21  is then restrained to the connection plates with steel washers  24  and torqued steel nuts  22 . The steel washers  24  are located under the steel nuts  22 . The pin  21  is aligned through diagonally opposite slots  30  and  31 . One having skill in the art will appreciate that the pin assembly components may comprise materials other than those described above with respect to the illustrative example. Further, the pin assembly configuration may be adapted to include fewer or a greater number of components, such as additional washers or nuts. 
         [0040]      FIG. 3  is an exploded top view of the link beam joint assembly  10  illustrated in  FIG. 1 . This view depicts the placement of the inner connection plates  16   a,    16   b  and the outer connection plates  18   a,    18   b.  The position of the diagonal slots  30  and  31  is also shown in this figure. As illustrated, connection plate  16   a  includes slot  30   a,  connection plate  16   b  includes slot  30   b,  connection plate  18   a  includes slot  31   a,  and connection plate  18   b  includes slot  31   b.  In the illustrative example, the connection plates  16   a,    16   b  and  18   a,    18   b  extend directly outward from the embedded plates  28   a,    28   b,  and parallel to the respective link beams  14   a,    14   b.  In the illustrative example, the connection plates  16  and  18  are placed equidistant from one another relative to the center line of the plate assembly. 
         [0041]    Illustrated in  FIG. 3   a,  is a top view of the pin assembly  20  used to connect the plates  16   a,    16   b  and  18   a,    18   b.  This view illustrates how the pin  21 , which is a threaded steel rod in the example, is fastened to the connection plates  16   a,    16   b  and  18   a,    18   b  with steel nuts  22  over steel washers  24 . Brass shims  26  are placed between steel washers  24  and connection plates  16   a,    16   b  and  18   a,    18   b.    
         [0042]      FIG. 4  is a cross sectional view of the plate assembly  18  of  FIG. 2  taken along line IV-IV′. The section illustrates the cross-section of the outer connection plates  18   a,    18   b.  In addition, this view illustrates the position of the diagonal slots  31   a,    31   b  relative to the horizontal center line axis  40  of the beam  14   a  taken along line IV-IV′. 
         [0043]      FIG. 5  is cross sectional view of the plate assembly  16  of  FIG. 2  taken along line V-V′. The section illustrates the cross-section of the inner connection plates  16   a,    16   b.  This view illustrates the position of the diagonal slots  30   a,    30   b  relative to the horizontal center line axis  50  of the beam  14   b  taken along V-V′. 
         [0044]      FIG. 6  is a cross sectional view of the plate assembly  16   a,    16   b  of  FIG. 2  taken along line VI-VI′. This view illustrates the connection of plates  16   a,    16   b  normal to the embedded steel plate  28  with their position relative to the centering axis  60  of beam  14   b  and wall  12   b  beyond. 
         [0045]      FIG. 7  is a top view of the completed pin assembly  20  used to connect inner connection plates  16   a,    16   b  and outer connection plates  18   a,    18   b  utilizing a single steel threaded thru-rod  21 . This illustrative pin assembly includes a completely threaded steel rod  21 , steel nuts  22  used for torquing the rod, steel washers  24 , and brass shims  26 .  FIG. 7   a  is a side view of the completed pin assembly  20 . 
         [0046]      FIG. 8  is a top view of another embodiment of the completed pin assembly  20  used to connect inner connection plates  16   a,    16   b  and outer connection plates  18   a,    18   b  utilizing multiple steel threaded thru-rods  32 . This pin assembly includes multiple threaded steel rods  32 , steel nuts  33  used for torquing the rods, steel washers  24 , brass shims  26 , and a steel spacer plate  36  used to keep the rods aligned. Spacer plate  36  may use standard diameter holes to match the rod diameter.  FIG. 8   a  is a side view of the completed pin assembly  20  that utilizes multiple steel threaded thru-rods  32 . 
         [0047]      FIG. 9  is a top view of yet another embodiment of the completed pin assembly  20  used to connect inner plates  16   a,    16   b  and outer plates  18   a,    18   b  utilizing multiple high-strength steel bolts  34 . This pin assembly includes high-strength steel bolts with threads excluded from the shear plane  34 , steel nuts  35  used for torquing the bolts, steel washers  24 , and brass shims  26 .  FIG. 9   a  is a side view of the completed pin assembly  20  that utilizes multiple high-strength steel bolts  34 . 
         [0048]      FIG. 10  is a front view of one embodiment of the link beam joint assembly  10  as it would appear with the connection plates  16   a,    16   b  and  18   a,    18   b  connected via the link-fuse joint  19 . This view illustrates the placement of the pin assembly  20  through connection plates  16   a,    16   b  and  18   a,    18   b.  This connection may be accomplished, for example, with a single thru-rod  21 , multiple thru-rods  32 , or multiple high-strength bolts  34 . As explained previously, the diagonally opposed slots  30  and  31  in the connection plates  18   a,    18   b  and  16   a,    16   b,  respectively, allow the connection plates to slide relative to one another when subject to extreme seismic loads. As the connection plates move, they are held together via the pin  20 , yet are enabled to move as the pin  20  travels within the slots. The slipping that occurs between the plates  16   a,    16   b  and  18   a,    18   b  transfers to embedded plates  28   a,    28   b,  thereby dissipating energy at the joint  19 . 
         [0049]    To control slippage between the connection plates  16   a,    16   b  and  18   a,    18   b,  when subject to standard load conditions, such as wind, gravity and moderate seismic events, one or more brass shims  26  may be placed, for example, between the connection plates and/or between the connection plates and adjacent washers. The coefficient of friction of the brass, or other material that is used, against the cleaned mill surface of structural steel, or other material, is very well understood and can be accurately predicted. For example, the shear force that will initiate slip can be determined using Equation 1 below: 
         [0000]      F=μ s N   (Equation 1) 
         [0000]    where, F is the shear force that will initiate slip, μ s  is the coefficient of static friction (e.g., 0.30 for brass clamped between steel plates), and N is the clamping force introduced into the connection by the torquing the thru-rod  21  or  32  or bolts  34 . Thus, the amount of shear that the joint  19  can bear before a slip or rotation will occur between connection plates  16   a,    16   b  and  18   a,    18   b  can be determined. 
         [0050]    Further, bolt tensioning in the steel bolts  21 ,  32  or  34  is not lost during the slipping process. Therefore, the frictional resistance of the joint  19  is maintained after the shear wall/link beam/joint motion comes to rest following the slippages between the connections plates  16   a,    16   b  and  18   a,    18   b.  Thus, the link-fuse joint  19  should continue not to slip during moderate loading conditions, even after undergoing extreme seismic activity. 
         [0051]      FIG. 11  is a top view of one embodiment of the link beam joint assembly  10 . This view illustrates the positioning of the connection plates  16   a,    16   b  and  18   a,    18   b,  relative to one another, when the joint  19  is connected, as well as embedded plates  28 . As shown in this illustrative example, shims  26  may be positioned, for example, between the connection plates (e.g., between connection plate  16   a  and connection plate  18   a ), between the connection plates and interior washers (e.g., between connection plate  16   b  and washer  24 ), and/or between the connection plates and exterior washers (e.g., between connection plate  18   b  and washer  24 .) 
         [0052]      FIG. 12  is a side view and  FIG. 13  is a perspective view of the link-fuse joint  19  as it would appear slipped when placed under a severe seismic load. When subject to seismic loads, shear forces and bending moments are introduced into the wall  12   a,    12   b  from ground motions due to seismic activity. When the loads are extreme, the link-fuse joint  19  will slip, as shown in  FIG. 12  and  FIG. 13 . The joint  19  will slide about the pin  21  (or  32  or  34 ) connection, which is created through the introduction of the pin assembly  20  into the connection plates  16   a,    16   b  and  18   a,    18   b  while using diagonally opposed slots  30  and  31 . Shear loads are transferred to the link beam  14   a,    14   b  then to the shear wall  12   a,    12   b  through this pin connection. In the illustrative example, the wall  12   a  has shifted, for example, toward the upper left relative to the joint  19 , such that the pin  21  has slid to the base of slot  31 , while the pin  21  has not changed position within slot  30 . The pin  21  could however change position within slot  30  during overall shifting of the structure. Thus, the diagonally opposed slots enables the pin  21  to maintain a connection within the joint  19  when the walls  12   a,    12   b  move relative to each other. 
         [0053]    Accordingly, with the slip of the link-fuse joint, energy is dissipated. The dynamic characteristics of structure are thus changed during a seismic event once the onset of slip occurs. This period is lengthened through the inherent softening, i.e., stiffness reduction, of the structure, subsequently reducing the effective force and damage to the structure. 
         [0054]    The foregoing description of an implementation of the invention has been presented for purposes of illustration and description. It is not exhaustive and does not limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practicing the invention. The scope of the invention is defined by the claims and their equivalents. 
         [0055]    For example, other applications of the link-fuse joint  19  within a building frame may include the introduction of the joint  19  into other structural support members in addition to the beam, such as the shear wall  12 , primarily at the base of the shear walls  12 . Other materials may be considered for the building frame and joint  10 , including, but are not limited to, composite resin materials such as fiberglass. Alternate structural steel shapes may also be used in the link-fuse joints  19 , including, but not limited to, built-up sections, e.g., welded plates, or other rolled shaped such as channels. Alternative materials (other than brass) may also be used between the connection plates  16   a,    16   b  and  18   a,    18   b  to achieve a predictable slip threshold. Such materials may include, but not be limited to, Teflon, bronze or steel with a controlled mill finish. Steel, Teflon, bronze or other materials may also be used in place of the brass shims  26  in the plate end connection. 
         [0056]    When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0057]    As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.