Abstract:
A toggle linkage for incorporation into a frame of a structure, such as a building, including a first link having a shock absorber therein, a first end on the first link connected to a first area of the frame, a second link having a first end connected to a second area of the frame remote from the first area, a second end on the second link, a third link having a first end connected to a third area on the frame remote from the first and second areas, a second end on the third link, a second end on the first link connected proximate the second end of the second link, and the second ends of the second and third links being connected to each other by a metal plate which is welded therebetween and which flexes in the direction of its thickness and not in the direction of its width so as to maintain the longitudinal axes of the second and third links in the same plane when the toggle linkage is activated by a seismic event as before the toggle linkage was activated.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an improved seismic isolation structure utilizing a toggle linkage. 
     By way of background, there are in use two common types of seismic isolation devices utilizing viscous dampers. One type is a diagonal brace structure incorporating a viscous damper, which is placed in a frame of a structure, such as a building. Another type of device is a Chevron structure which is placed in the frame of a building. The seismic displacement which is opposed by the foregoing seismic isolation devices is the horizontal displacement between the floors of a building or between various levels of other structures, such as bridges, and it is this displacement which must be used to drive the viscous damper. However, in diagonal and Chevron isolation devices, the damper has a very small displacement as the various levels of a structure move relative to each other, thereby requiring large, heavy, short stroke dampers which are relatively expensive both in initial cost of fabrication and cost of installation. By way of broad example, the relative movement between floors of a building could be on the order of a fraction of an inch. Thus, for example, in a rectangular frame of a building wall having a dimension of about 22 feet horizontally and 20 feet vertically and having a diagonal of about 30 feet, the change in length of the diagonal would be only a fraction of an inch. This small fraction of an inch in change in length of a diagonal constitutes the stroke which has to be applied to the viscous damper, thereby necessitating the above-mentioned relatively large, heavy, short stroke dampers. Another type of seismic isolation device which is known in the prior art is a toggle linkage such as shown in opened Japanese patent application Sho 63-114069 (Patent No. 1-284639). The advantage of a toggle linkage is that it essentially magnifies relatively small movements between levels of a structure, that is, it provides a motion which is larger than the motion produced by the change in length of a diagonal brace or by the movement of a Chevron brace. Thus, a toggle brace permits the use of relatively inexpensive long stroke, relatively light hydraulic dampers and also permits the use of other types of long stroke shock absorbers. However, toggle linkages with clevis types of connections at the junctions of the links of a toggle linkage have certain deficiencies, namely, (1) there is too much play at the clevis so that the shifting of the floors of a building is not fully transmitted by the links of the toggle linkage to the damper, and (2) the clevis connection inherently permits out-of-plane buckling which further diminishes the amount of floor shifting which is effectively transmitted to the toggle linkage. It is with overcoming the foregoing deficiency of toggle linkages having a clevis connection that the present invention is concerned. 
     SUMMARY OF THE INVENTION 
     It is the object of the present invention to provide an improved seismic isolation device utilizing a toggle linkage having a solid connection at the junction of the links so that (1) the magnification of the relatively small movements between levels of the structure provided by the toggle linkage is fully transmitted to the shock absorber associated with the toggle linkage and (2) there is no out-of-plane buckling of the toggle linkage at the junction of the links. Other objects and attendant advantages of the present invention will readily be perceived hereafter. 
     The present invention relates to a seismic isolator for placement in a frame of a structure comprising a first link having a shock absorbing member therein, a first end on said first link for connection to a first area on said frame, a second end on said first link, a second link having a first end for connection to a second area on said frame remote from said first area, a second end on said second link, a third link having a first end for connection to a third area on said frame remote from said first and second areas, a second end on said third link, and a solid joint without relatively movable parts connecting said second ends of said second and third links to each other. 
     The present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic perspective view of the improved toggle linkages of the present invention installed in a building; 
     FIG. 2 is a schematic view of the action of the toggle linkage which causes the shock absorber to operate in tension; 
     FIG. 3 is a schematic view of the action of the toggle linkage which causes the shock absorber to operate in compression; 
     FIG. 4 is a view, partially in cross section, of an improved toggle linkage of the present invention in a frame of a building and having a solid joint between certain links and solid joints between these links and the building; 
     FIG. 5 is a fragmentary view, partially in cross section, taken substantially along line 5--5 of FIG. 4; 
     FIG. 6 is a fragmentary cross sectional view taken substantially along line 6--6 of FIG. 5 and showing the solid connection between one end of the toggle linkage and the building frame; 
     FIG. 7 is a view, partially in cross section, of a modified form of the improved toggle linkage utilizing I-beams and having a solid connection between certain links and solid connections between these links and the building frame; 
     FIG. 8 is a fragmentary view, partially in cross section, taken substantially along line 8--8 of FIG. 7; and 
     FIG. 9 is a fragmentary cross sectional view taken substantially along line 9--9 of FIG. 8. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1 a building frame 10 is schematically shown having a plurality of toggle linkage seismic braces 11 in its framework with each toggle linkage 11 being located within a rectangular frame having four sides, such as AB, BC, CD and AD, and the building 10 having three floors 12, 14 and 16. As is well known, when building 10 is subjected to a seismic shock, the floors 12, 14 and 16 will shift relative to each other in a horizontal direction. Thus, the rectangular frames, such as ABCD, will slightly distort into parallelogram configurations. 
     In FIGS. 2 and 3 the frame portion ABCD of FIG. 1 is schematically shown by itself. FIG. 2 shows floor 16 shifted to the left relative to floor 14, and FIG. 3 shows floor 16 shifted to the right relative to floor 14. Thus, in FIG. 2 when floor 16 shifts to the left, the corner A of frame ABCD will move to the left to the point A&#39;, and corner D will move to the point D&#39; so that rectangle ABCD now becomes parallelogram A&#39;BCD&#39;. In FIG. 3 floor 16 is shown as shifting to the right relative to floor 14 by an amount equal to DD&#39;. Therefore, the rectangle ABCD now becomes parallelogram A&#39;BCD&#39;. 
     As noted above toggle linkage seismic isolation brace structures are utilized to permit the use of relatively low force, long stroke dampers or shock absorbers with the attendant advantage of lower cost. In FIGS. 2 and 3 a toggle brace structure is disclosed wherein the building frame ABCD is reinforced by a toggle brace linkage which includes links BE and DE and a link AE having a suitable shock absorber such as a liquid damper, liquid spring or combination thereof 22 therein, or any other suitable type of shock absorber, as discussed hereafter. 
     By way of example, in frame ABCD sides AD and BC are 264 inches long, and sides AB and CD are 240 inches long. Link BE is 178.71 inches long and link DE is 178.32 inches long. When frame ABCD is a rectangle, that is, before it is deflected, link AE is 184.99 inches long. Furthermore, it is preferable that the shock absorber 22 should have a liquid spring characteristic so that it places links BE and DE in tension. 
     When there is a seismic shock which causes floor 16 to shift to the left in FIG. 2 by an amount of 0.3 inches, so that the corner A moves to point A&#39; and corner D moves to point D&#39;, link AE will elongate from 184.99 inches to 187.61 inches, that is, by an amount of 2.62 inches because links BE and DE will move to positions BE&#39; and DE&#39;, respectively. Thus when link AE is elongated, the shock absorber 22 will tend to counter this elongation and it can be seen that the stroke is 2.62 inches. 
     When floor 16 shifts to the right relative to floor 14, as shown in FIG. 3, corner A will move to point A&#39; and corner D will move to point D&#39;. At this time link BE will move to position BE&#39; and link DE will move to position D&#39;E&#39;. The foregoing being the case, link AE will become shortened to link A&#39;E&#39; which has a length of 180.29 inches from the original length of AE of 184.99 inches. Thus, the difference in length between link AE and link A&#39;E&#39; is 4.70 inches. Thus when link AE is elongated, the shock absorber 22 will tend to counter this elongation and it can be seen that the stroke is 4.70 inches. 
     In accordance with one aspect of the present invention, a solid joint 20 (FIG. 4) is provided between links 17 and 19 of the toggle linkage 11 which also includes link 21 in which shock absorber 22 is located. Links 17 and 19, which correspond to links BE and DE, respectively, of FIGS. 2 and 3, are hollow cylindrical metal members having longitudinal axes 17&#39; and 19&#39;, respectively, which lie in a plane when the toggle linkage is not subjected to a seismic event. 
     The solid joint 20 between links 17 and 19 is a high strength steel plate 29 acting as a single plane to provide a blade-type flexure. Plate 29 has its ends 30 and 31 welded into slots 30&#39; and 31&#39;, respectively, in the ends of links 17 and 19, respectively. Plate 29 has a thickness dimension T (FIG. 4) and a width dimension W (FIG. 5). When the frame ABCD distorts to a parallelogram, as shown in FIGS. 2 and 3, plate 29 will flex in the direction of its thickness T. However, plate 29 will not flex in the direction of its width W because of the relatively larger bending moment of inertia of this width dimension, and accordingly there will be no movement of the longitudinal axes 17&#39; and 19&#39; of links 17 and 19, respectively, out of the original plane which they occupied before a seismic event. In other words, there is no out-of-plane buckling of links 17 and 19. 
     In accordance with another aspect of the present invention, the outer ends 23 and 24 of links 17 and 19, respectively, are rigidly connected to the corners of frame ABCD by solid joints in the following manner. A plate 25 is welded into slots 26 in link end 23, and plate 25 is in turn welded to frame corner B. A plate 27 is welded into slots 27&#39; in link end 24, and plate 27 is in turn welded to frame corner D. Thus there are solid joints between the ends of links 17 and 19 and the frame of the building. The solid joints of this type are perfectly satisfactory because of the very small amounts of angular movement between the building frame and links 17 and 19 during a seismic event. The foregoing solid joints avoid any lost motion between the building frame and links 17 and 19 during a seismic event. Also the plates 25 and 27 of the solid joints at B and D resist out-of-plane buckling of links 17 and 19 for the same reason set forth above relative to plate 29, namely, the larger bending moment of inertia of these plates in their width directions. In other words, all motion of the frame ABCD is transmitted to the links 17 and 19 of the toggle linkage 11, considering that there is no loss of motion therebetween. 
     Link 21 includes a hydraulic shock absorber 22 wherein the cylinder 22&#39; has one end rigidly connected to rod 28&#39; and the other end of rod 28&#39; is pivotally connected at frame corner A at 28 by means of a clevis joint 30. The piston 31 of shock absorber 22 is pivotally connected to link 19 proximate joint 20 by a clevis joint 32. These clevis joints will not produce any significant lost motion, considering that the forces are transmitted substantially in the direction of the axis of link 21. The shock absorber 22 can be a fluid damper, or a liquid spring, or combinations of both or other types of shock absorbers, as discussed hereafter. Preferably, however, the shock absorber 21 should be a liquid spring so that it will place the toggle links 17 and 19 in tension, although this is not necessary. It will be appreciated that when the foregoing links are placed in tension, the link 21 in which the liquid spring is located will be in compression. 
     Thus the combination of no loss of motion between links 17 and 19 at solid joint 20 and at the solid joints provided by plates 25 and 27 at the frame corners B and D along with the absence of out-of-plane buckling at joint 20 and at frame corners B and D results in the transmission of the totality of movement of the deflection of frame ABCD during a seismic event to link 21 in which shock absorber 22 is located. 
     In FIGS. 7-9 an alternate embodiment of the present invention is disclosed. The only differences between the embodiment of FIGS. 7-9 and that of FIGS. 4-6 are three-fold. Firstly, the links 17a and 19a are in the form of I-beams rather than the hollow cylindrical links 17 and 19. Secondly, the links 17a and 19a are placed in compression if shock absorber 22a in link 21a is a liquid spring. Thirdly, the outer ends of links 17a and 19a are of a configuration so that they can be welded directly to the frame of the building, that is, they do not have solid joints such as plates 25 and 27 of FIGS. 4-6 therebetween. However, as noted above, the shock absorber can be a liquid spring, or a damper of any type, or a combination of a liquid spring and damper. However, a liquid spring such as shown in U.S. Pat. No. 5,462,141, dated Oct. 31, 1995, is preferred, and the subject matter relating to FIGS. 2-7 of this patent is incorporated herein by reference. 
     In FIGS. 7-9 links 17a and 19a have their inner ends welded to plate 20a which is analogous to plate 20 of FIGS. 4-6. Also, in FIGS. 7-9 the outer ends of links 17a and 19a are welded directly to frame portions B and D at 33 and 34, respectively, whereas in FIGS. 4-6, solid movable joints in the form of metal plates 25 and 27 are used to produce slight angular movements. It will be appreciated that there can be the direct welding of the links 17a and 19a to the frame in certain instances because of the very slight angular movements in these areas. One end of link 21a, namely, the piston 32&#39; of shock absorber 22a, is connected to link 19a at clevis joint 32a and the cylinder of the shock absorber 22a is connected to the building frame at C by clevis joint 28a. 
     While the solid joints have been shown above as comprising welded plates such as 20, 25, 27 and 20a, it will be appreciated that, if desired, these plates can be rigidly secured by bolts or rivets between the parts which they connect, if desired or required, and these modifications will also comprise solid joints. Also, while clevis joints have been shown at the ends of links 21 and 21a, it will be appreciated that any other type of joints can be used for connecting links 21 and 21a between the other parts of the toggle linkage and the frame of the building. 
     Liquid springs of the type which can also be used are shown in U.S. Pat. Nos. 4,582,303 and 4,064,977, and dampers such as shown in U.S. Pat. Nos. 4,638,895, 4,815,574 and 4,867,286 may also be used, and other types of non-liquid shock absorbers may also be used. 
     While the foregoing description has specifically described shock absorbers in the form of hydraulic energy absorbing devices, it will be appreciated that the toggle linkage is not limited thereto but may also be used with other types of energy absorbing devices including but not limited to viscoelastic rubber damping elements, such as shown in U.S. Pat. No. 4,910,929, hysteretic (friction) damping elements and yieldable steel damping elements, such as shown in U.S. Pat. No. 4,910,929, said patents being incorporated herein by reference. 
     While preferred embodiments of the present invention have been disclosed, it is will be appreciated that it is not limited thereto but may be otherwise embodied within the scope of the following claims.