US20170362822A1

US20170362822A1 - Damper frame

Info

Publication number: US20170362822A1
Application number: US15/623,927
Authority: US
Inventors: Jesse Karns; David Lee
Original assignee: Columbia Insurance Co; Taylor Devices Inc; Mitek USA Inc
Current assignee: Columbia Insurance Co; Taylor Devices Inc; Mitek USA Inc
Priority date: 2016-06-16
Filing date: 2017-06-15
Publication date: 2017-12-21
Also published as: NZ732837A; US20170362848A1; CA2970649C; US10370848B2; CA2970649A1; AU2017204003A1; CA2970642A1; AU2017204008A1

Abstract

A damper frame for dissipating seismic energy includes a structural frame and a damper assembly secured to the structural frame. The damper assembly includes a damper support secured to the structural frame. A damper is secured to the damper support adjacent a first end of the damper. A diagonal link is secured to the structural frame. A lever is secured to the damper support and the damper adjacent a second end of the damper opposite the first end of the damper. The first end of the damper is spaced vertically from the second end of the damper by a distance that is greater than a lateral distance between the first and second ends of the damper. The lever is connected to the diagonal link so displacement of the diagonal link relative to the damper support is amplified and transferred to the second end of the damper by the lever. The damper support includes a diagonal leg. The diagonal link and diagonal leg are arranged for telescoping movement relative to one another.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No. 62/350,853, filed Jun. 16, 2016, the entire contents of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to seismic protection for building systems, and more specifically to systems and methods for dissipating seismic energy.

BACKGROUND

In the construction of buildings, structural damage often provides energy dissipation over the course of a seismic event. Using structural damage to dissipate energy allows structures to be economically constructed. Dampers can be used to provide energy dissipation to structures, allowing structures to survive seismic events with little to no structural damage. The addition of viscous damping to wood framed structures can significantly increase seismic resistance and reduce building lateral displacements, thereby reducing damage to the structure. Although damping can be an effective method to reduce damage to a structure, viscous dampers have seen relatively little use in certain types of structures. Stiff low-rise structures, such as light-framed wood residential structures, have not been good candidates for damping because the effectiveness of the dampers is reduced due to the low displacement input into the dampers. At the point sufficient displacement and velocity is input into the damper, the structural damage due to that displacement is already significant. In addition, space for placement of dampers in light-framed wood residential structures is limited, as there is a growing demand for numerous windows and open floor plans. Placement of dampers in a horizontal position provides good displacement and energy dissipation, but takes up significant space. To use narrower frames, dampers are often positioned diagonally in a damper frame. The diagonal orientation of dampers in the frames results in a reduction of displacement to the dampers when compared to the displacement of the building because the damper is not aligned with the horizontal shifting associated with the seismic activity, thereby making the dampers less effective and less economical. In addition to reducing the displacement, the diagonal configuration amplifies the force in the damper, resulting in a need for a larger more costly damper.

SUMMARY

In one aspect of the invention a damper frame includes a structural frame and a damper assembly secured to the structural frame. The damper assembly includes a damper support secured to the structural frame and a damper secured to the damper support adjacent a first end of the damper. A diagonal link is secured to the structural frame. A lever is secured to the damper support and the damper adjacent a second end of the damper opposite the first end of the damper. The first end of the damper is spaced vertically from the second end of the damper by a distance that is greater than a lateral distance between the first and second ends of the damper. The lever is connected to the diagonal link so displacement of the diagonal link relative to the damper support is amplified and transferred to the second end of the damper by the lever. The damper support includes a diagonal leg. The diagonal link and diagonal leg are arranged for telescoping movement relative to one another.
Another aspect of the invention is a damper assembly including a damper support configured for attachment to a structural frame and a diagonal brace comprising an outer leg and an inner leg telescopically received in the outer leg. The diagonal brace is configured for attachment to the structural frame so that the diagonal brace extends diagonally within the structural frame. A lever is connected to the inner and outer legs of the diagonal brace so that the lever moves in response to telescoping movement of the inner and outer legs relative to one another. A damper has a first end secured to the support bracket and a second end secured to the lever so that movement of the lever requires movement of the first and second ends of the damper relative to one another.
Other objects and features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of one embodiment of a damper frame for use in light-framed structures; and

FIG. 2 is an enlarged, fragmentary front elevation of a damper assembly of the damper frame of FIG. 1.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, one embodiment of a damper frame is generally indicated at 110. The damper frame 110 includes a structural frame 112 and a damper assembly 114 configured to dissipate forces (e.g., forces due to seismic activity) in a building structure that includes the structural frame. The structural frame 112 is a generally rectangular frame including first and second vertical structural members (left and right members, respectively) 116, 118 and first and second horizontal structural members (top and bottom members, respectively) 120, 122 each secured to both of the vertical structural members. The structural members can be light gauge steel members, or any other suitable structural members.
As illustrated, the length L1 of the vertical members 116, 118 is greater than the spacing S1 between them. Relatedly, the generally rectangular shape of the area enclosed by the structural frame 112 has a height H1 that it greater than is width W1. For example, the ratio of the length L1 of the vertical structural members 116, 118 to the spacing S1 between them is suitably at least 2, and more suitably about 3. The spacing S1 between the vertical structural members 116, 118 is suitably no more than about 4 feet, and more suitably no more than about 3 feet. The structural frame 112 in the illustrated embodiment is sized and shaped so it can be installed in a wall within a single story of a building (e.g., in a single story building or on one of the floors of a multi-story building). For example, the spacing S2 between the horizontal structural members 120, 122 (which is equal to the length L1 of the vertical structural members 16, 18 in the illustrated embodiment) is suitably in the range of about 7 feet to about 12 feet (e.g., about 8 feet). It is understood that the top and bottom members 120, 122 may extend laterally beyond the vertical support members 116, 118. Other arrangements of the structural frame are within the scope of the present invention.
The damper assembly 114 includes a damper support 124 secured to the structural frame 112. The damper support 124 suitably includes a bracket 121 secured to the structural frame 112 (e.g., to the bottom structural member 122). In the embodiment illustrated in FIGS. 1 and 2, the bracket is secured to the structural frame 112 at a pivot point 137 at a corner of the frame where the bottom structural member 122 joins one of the vertical structural members (e.g., the left vertical structural member 116). As illustrated, the bracket 121 is suitably a generally triangular bracket secured to the frame 112 at one vertex. The damper support 124 also includes a leg 128 secured to the bracket 121. The leg suitably extends along a line extending from the apex of the bracket that is secured to the frame through the opposite side of the triangular bracket. For example, the bracket 121 suitably has the shape of an isosceles triangle and the leg 128 suitable extends along a line extending from the vertex that is secured to the frame 112 through the midpoint of the opposite side. The vertices of the triangular bracket 121 opposite the vertex that is secured to the frame extend laterally from opposite sides of the damper support leg 128. The leg 128 suitably extends from a location adjacent one of the corners of the structural frame 112 toward the opposite corner of the structural frame (e.g., diagonally from the lower left corner toward the upper right corner, as illustrated).
The damper assembly 114 also includes a diagonal link 134 that is secured to the structural frame 112 and extends angularly inward into the space enclosed by the members 116, 118, 120, 122 of the structural frame. The diagonal link 134 is secured to the structural frame 112 in a manner that transfers seismic energy from the structural frame to the diagonal link 134 during a seismic event. As illustrated in FIG. 1, for example, the diagonal link 134 is secured to the structural frame 112 at pivot point 136 adjacent a juncture of two structural members (e.g., at a corner of the structural frame). In the illustrated embodiment, the diagonal link 134 is secured to the structural frame 112 at a juncture of the top structural member 120 and the right vertical structural member 118. The diagonal link 134 extends inward toward the opposite vertical structural member 116. In the illustrated embodiment, the diagonal link extends from one of the corners of the structural frame toward the opposite corner (e.g., from the upper right corner toward the lower left corner, as illustrated). The diagonal link 134 and the leg 128 of the damper support 124 suitably extend along the same line.
One of the diagonal link 134 and the leg 128 of the damper support 124 is telescopingly received in the other. Collectively, the damper support leg 128 and the diagonal link 134 form a diagonal brace 138 extending within the structural frame 112. As illustrated, for example, the damper support leg 128 is telescopingly received within the diagonal link 134. Thus, the damper support leg 128 forms an inner leg of the diagonal brace 138 and the diagonal link 134 forms an outer leg of the diagonal brace. It is understood, however, that diagonal link could be received within the damper support leg. The diagonal brace 138 is suitably positioned and arranged within the structural frame so that seismic energy (e.g., energy that causes lateral displacement of the bottom structural member 122 relative to the top structural member 120) causes the inner leg 128 and outer leg 134 to move relative to one another as the telescoping brace 138 extends and retracts. The telescoping diagonal brace 138 is suitably secured to the frame 112 by pivot connections 136, 137 at opposite ends of the diagonal brace. Each of the telescoping legs 128, 134 is suitably a steel tube (e.g., a high-strength steel square tube), although other configurations are within the scope of the present invention.
The damper assembly 114 includes two dampers 132, 152 (broadly, shock-absorbing members). The dampers 132, 152 can be seismic dampers, such as fluid viscous dampers, or any other suitable shock-absorbing members configured to dissipate forces. The dampers 132, 152 are secured to the damper support 124 on opposite sides of the damper support leg 128. As illustrated in FIGS. 1 and 2, for example, the dampers 132, 152 are secured to the damper support bracket 121 at the vertices thereof opposite the vertex that is secured to the frame 112. One of the dampers 132 is pivotally secured to the support bracket 121 and extends upwardly generally along one of the vertical structural support members (e.g., the left member 116). The other damper 152 is secured to the damper support bracket 121 and extends diagonally toward the opposite vertical structural member (e.g., the right member 118). Damper 132 is oriented in a substantially vertical orientation. Damper 152 is in a less vertical orientation than damper 132 because it is more diagonally oriented than damper 132. Both dampers are oriented so the vertical spacing between their ends is greater than the lateral spacing between their ends (i.e., the angle between the dampers and horizontal is greater than 45 degrees). The dampers 132, 152 are positioned on opposite sides of the damper support leg 128 and the diagonal brace 138 formed by the diagonal support leg and the diagonal link 134. Moreover, the dampers 132, 152 are suitably substantially symmetrically arranged about the damper support leg 128 and diagonal brace 138.
The damper support 124 includes a bracket 130 mounted on the damper support leg 128 adjacent the end of the diagonal link 134. As illustrated in FIGS. 1 and 2, the bracket 130 extends laterally from opposite sides of the damper support leg 128. The damper assembly 114 includes a pair swing arms or levers 140, 170 pivotally connected to the damper support 124 and the ends of the dampers 132, 152. In the illustrated embodiment, the levers 140, 170 are metal plates, such as 0.5 inch thick steel plates. Each of the levers 140, 170 is suitably accompanied by a substantially identical lever (not shown) in registration therewith and attached to the respective damper 132, 152 and bracket 130 on opposite sides thereof so forces are distributed among the lever pairs. Referring to FIG. 1, one end the lever 140 is connected to the damper support 124 (e.g., the bracket 130) at a pivot point 144 and the opposite end of the lever is connected to the damper 132 at a pivot connection 146 at an end of the damper opposite the end of the damper that is connected directly to the damper support 124 (e.g. at the bracket 121 secured to the frame 112). The lever 140 extends from the pivot connection 144 where it is connected to the damper support 124 to the pivot connection 146 where it is connected to the damper 132 along a line that is generally perpendicular to the line of action of the damper 132. The lever 170 is suitably substantially identical to the lever 140 except that it is arranged to have an orientation that is symmetrical to the lever 140 about the damper support leg 128 and diagonal brace 138. The lever 170 is connected to the bracket 130 of the damper support 124 at a pivot connection 174 positioned symmetrically opposite pivot connection 144. The lever 170 extends to a pivot connection 176 with the damper 152 that is symmetrically opposite pivot connection 146. The lever 170 is also arranged so that it extends from pivot connection 174 to pivot connection 176 along a line that is substantially perpendicular to the line of action of damper 152.
The levers 140, 170 are thereby arranged so that when the levers begin to pivot, the initial movement of the dampers 132, 152 is aligned with the lines of action of the dampers. This facilitates efficient transfer of energy from the levers 140, 170 into the dampers 132, 152. This arrangement of the levers 140, 170 and dampers 132, 152 also minimizes lateral movement of the dampers (i.e., movement of the damper in a direction perpendicular to its line of action) in response to seismic energy. Minimizing lateral movement of the dampers 132, 152 also facilitates using a structural frame 112 that does not take up much lateral space. Moreover, this arrangement also facilitates use of smaller, less expensive dampers 132, 152.
The levers 140, 170 are also connected to the diagonal link 134 so that movement of the diagonal link relative to the damper support 124 (e.g., telescoping movement of the diagonal brace 138) requires movement of the levers (e.g., pivoting of the levers about pivot connections 144, 174, respectively. For example, as illustrated in FIGS. 1 and 2, a bracket 160 is mounted on the diagonal link 134 adjacent the end of the diagonal link. The bracket 160 extends laterally from opposite sides of the diagonal link 134 and therefore extends from opposite sides of the diagonal brace 138 formed by the diagonal link and the damper support leg 128. A pair of coupling links 164, 166 are pivotally connected to the levers 140, 170 at pivot connections 142, 172, respectively and also connected to the diagonal link 134 (e.g. via pivot connections with the bracket 130). The levers 140, 170 are thereby connected to the damper support 124 and the diagonal link 134 and arranged so that they move (e.g., rotate) in opposite directions when the diagonal link 134 moves relative to the damper support in a specific direction.
The linkage formed by the coupling link 164, lever 140, and damper 132 is suitably substantially identical to the linkage formed by the coupling link 166, lever 170, and damper 152 except that they are positioned on opposite sides of the damper support leg 128, diagonal link 134, and the diagonal brace 138 formed thereby and symmetrically arranged about the line extending along the diagonal link 134, damper support leg 128, and the diagonal brace 138. Referring to FIG. 2, the distance D1 between the pivot connections 142, 172 (where the levers 140, 170 are connected to the diagonal link 134) and the pivot connections 144, 174 (where the levers are connected to the damper support 124) is less than the distance D2 between the pivot connections 144, 174 and the pivot connections 146, 176 (where the levers are connected to the dampers 132, 152). Consequently, the levers 140, 170 amplify the displacement of the diagonal link 134 relative to the damper support 124 (e.g., amplify the displacement of the telescoping members 128, 134 of the diagonal brace 138) as this is transferred to the dampers 132, 152. Relatedly, the levers 140, 170 are arranged to amplify the velocity and also decrease the forces exerted on the dampers 132, 152 during a seismic event. During movement of the structural frame 112 (e.g., due to seismic forces), the displacement is amplified by the levers 140, 170 by a ratio of D2 to D1. In other words, the movement of the diagonal link 134 relative to the damper support leg 128 is magnified by the ratio D2:D1. In one embodiment, D1 is about 2 inches and D2 is about 11 inches, for an amplification of about 5.5. In the embodiment, illustrated in FIGS. 1 and 2, the mechanical advantage provided by lever 140 is substantially equal to the mechanical advantage provided by lever 170. However, other configurations are possible within the scope of the invention.
As seen in FIG. 1, the orientation of the dampers 132, 152 permits the damper frame 110 to be narrower than prior damper assemblies that included a horizontal damper. The damper assembly 114 magnifies the displacement as it is transferred to the dampers 132, 152, thereby amplifying the velocity of the dampers through the cyclic motion. In addition, the damper assembly 114 reduces the forces exerted on the dampers 132, 152 during a seismic event. The increase in displacement and velocity and the decrease in force to the dampers permit the use of smaller and cheaper dampers in the damper assembly 114. The narrower damper frame 110 and the smaller and cheaper dampers allow use of the damper frame in light-framed buildings, such as wood framed buildings.
Referring to FIG. 1, when the top structural member 120 moves in the direction of arrow C relative to the bottom structural member 122, the damper assembly links will move in corresponding directions designated by arrows C. As illustrated, when the top structural member 120 moves to the left, it pushes down on the diagonal link 134, which causes the diagonal link to slide down over the inner leg/damper support leg 128 of the telescoping brace 138. This causes the bracket 160 secured to the diagonal link 134 move down toward the bracket 130 the levers 140, 170 are mounted on, causing the coupling links 164, 166 to push down on the respective levers 140, 170 at pivot points 142, 172, causing the opposite end of the levers (e.g., at pivot points 146, 176) to move downward. Conversely, when the top structural member 120 moves in the direction of arrow D relative to the bottom structural member 122, the damper assembly links will move in corresponding directions designated by arrows D.
The diagonal link 134 only moves a fraction of the amount of the relative movement between the top and bottom structural members 120, 122. However, the levers 140, 170 amplify this movement as it is transferred to the respective dampers 132, 152. The levers 140, 170 also amplify the velocity of the movement as it is transferred to the dampers 132, 152, resulting in a reduction of the forces exerted on the dampers. The forces are resolved through the damper support bracket 121 into the ground or foundation of a building to which the damper frame 110 is secured. The amplified displacement and velocity 132, 152 allows the dampers to dissipate more energy. The higher velocity and lower force requirement for the dampers results in an effective use of the dampers, permitting smaller dampers to dissipate the same energy as a larger damper in a conventional chevron brace or toggle brace damper assembly. This effective use of the dampers also allows the dampers to be positioned to facilitate use of a narrower frame configuration. Space for installing damping devices in light-framed structures is limited, so the narrower frame 112 increases the applicability of the damper frame 110 while providing a significant ability to dissipate seismic energy.
The damper frame 110 can be sold and shipped to customers as an assembled damper frame (e.g., as seen in FIG. 1). Alternatively, the damper frame 110 can be sold and shipped to customers as a disassembled kit. The damper assembly 114 can be sold and shipped to customers separately, for use in any structure without requiring the structural frame 112 as shown.
The damper frame 110 as described above is useful in residential construction, such as single family and multi-family residences, and in other light-framed structures. Multiple damper frames can be used in the construction of a building. If the damper frame is shipped to a construction site already assembled, the possibility of miscalculation or incorrect connection in the field is reduced. The damper frame can be used in addition to and/or in place of other energy dissipation elements, such as shear walls and moment frames. The damper frame as described above offers several advantages in the construction of single or multi-level residential buildings. Because these buildings are smaller than commercial buildings (e.g., about 1-5 stories) and are wooden structures, typical damper frames with wide profiles and utilizing large, heavy, expensive dampers are not appropriate. The damper frame 110 has a narrow profile to permit use in light-framed buildings. The damper frame 110 amplifies forces to the dampers 132, 152 to permit use of smaller, lighter, and cheaper dampers. Some energy dissipation elements are permanently deformed during a seismic event to dissipate the energy. In comparison, the damper frame 110 described herein can be used over and over, as there is no permanent deformation required to dissipate energy.
Having described the 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.
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.
In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.
As various changes could be made in the above products without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Claims

What is claimed is:

1. A damper frame comprising:

a structural frame; and

a damper assembly secured to the structural frame, the damper assembly comprising:

a damper support secured to the structural frame;

a damper secured to the damper support adjacent a first end of the damper;

a diagonal link secured to the structural frame; and

a lever secured to the damper support and the damper adjacent a second end of the damper opposite the first end of the damper, the first end of the damper being spaced vertically from the second end of the damper by a distance that is greater than a lateral distance between the first and second ends of the damper, the lever being connected to the diagonal link so displacement of the diagonal link relative to the damper support is amplified and transferred to the second end of the damper by the lever,

wherein the damper support comprises a diagonal leg, the diagonal link and diagonal leg being arranged for telescoping movement relative to one another.

2. The damper frame of claim 1 wherein the damper has a substantially vertical orientation within the structural frame.

3. The damper frame of claim 1, wherein the structural frame is generally rectangular and comprises a vertical left structural member, a vertical right structural member, a horizontal top structural member extending between the left and right structural members, and a horizontal bottom structural member spaced from the horizontal top structural member and extending between the left and right structural members.

4. The damper frame of claim 3, wherein the diagonal link is connected to the structural frame in a manner such that movement of the top structural member relative to the bottom structural member during a seismic event causes displacement of the diagonal link relative to the damper support.

5. The damper frame of claim 1, wherein the damper is adjacent one of the vertical structural members.

6. The damper frame of claim 1 wherein the damper is a first damper and the lever is a first lever, the damper assembly further comprising:

a second damper connected to the damper support; and

a second lever,

wherein the second lever is secured to the damper support and secured to the second damper so the second damper extends between the lever and the damper support, a first end of the second damper being spaced vertically from a second end of the second damper by a distance that is greater than a lateral distance between the first and second ends of the second damper, the second lever being connected to the diagonal link so displacement of the diagonal link relative to the damper support is amplified and transferred to the second damper by the lever, the first and second levers being on opposite sides of a line of action of the diagonal link.

7. The damper frame of claim 6 wherein the damper assembly further comprises a first coupling link extending between the diagonal link and the first lever and indirectly connecting the diagonal link to the first lever and a second coupling link extending between the diagonal link and the second lever and indirectly connecting the diagonal link to the second lever.

8. The damper frame of claim 6, wherein the damper assembly comprises a bracket rigidly secured to the diagonal leg of the damper support and the first and second levers are pivotally secured to opposite sides of the bracket.

9. The damper frame of claim 6, wherein the first and second levers are arranged so they pivot in opposite directions in response to movement of the diagonal link relative to the damper support.

10. The damper frame of claim 6 wherein the first and second levers are pivotally connected to the damper support and a line extending from the pivotal connection between the first lever and the damper support to the connection between the first lever and the first damper is substantially perpendicular to a line of action of the first damper when the damper assembly is at rest and a line extending from the pivotal connection between the second lever and the damper support to the connection between the second lever and the second damper is substantially perpendicular to a line of action of the second damper when the damper assembly is at rest.

11. The damper frame of claim 1 wherein the lever is pivotally connected to the damper support and a line extending from the pivotal connection between the lever and the damper support to the connection between the lever and the damper is substantially perpendicular to a line of action of the damper when the damper assembly is at rest.

12. A damper assembly comprising:

a damper support configured for attachment to a structural frame;

a diagonal brace comprising an outer leg and an inner leg telescopically received in the outer leg, the diagonal brace configured for attachment to the structural frame so that the diagonal brace extends diagonally within the structural frame;

a lever connected to the inner and outer legs of the diagonal brace so that the lever moves in response to telescoping movement of the inner and outer legs relative to one another;

a damper having a first end secured to the support bracket and a second end secured to the lever so that movement of the lever requires movement of the first and second ends of the damper relative to one another.

13. The damper assembly of claim 12 wherein the lever is a first lever and the damper is a second damper, the assembly further comprising:

a second lever connected to the inner and outer legs of the diagonal brace so that the second lever moves in response to telescoping movement of the inner and outer legs relative to one another; and

a second damper having a first end secured to the support bracket and a second end secured to the second lever so that movement of the second lever requires movement of the first and second ends of the damper relative to one another,

the first and second levers being positioned on opposite sides of the diagonal brace.

14. The damper assembly of claim 13 wherein the first and second levers are arranged so they rotate in opposite directions in response to telescoping movement of the inner and outer legs relative to one another.

15. The damper assembly of claim 13 wherein the first and second levers are configured to amplify displacement of the inner and outer legs relative to one another as the movement is transferred to the first and second dampers.

16. The damper assembly of claim 13 wherein the first and second levers are pivotally connected to the damper support and a line extending from the pivotal connection between the first lever and the damper support to the connection between the first lever and the first damper is substantially perpendicular to a line of action of the first damper when the damper assembly is at rest and a line extending from the pivotal connection between the second lever and the damper support to the connection between the second lever and the second damper is substantially perpendicular to a line of action of the second damper when the damper assembly is at rest.

17. The damper assembly of claim 12 in combination with a structural frame, the diagonal brace being secured to the structural frame so the inner and outer legs thereof move telescopingly relative to one another during a seismic event.

18. The damper assembly of claim 12 wherein the lever is pivotally connected to the damper support and a line extending from the pivotal connection between the lever and the damper support to the connection between the lever and the damper is substantially perpendicular to a line of action of the damper when the damper assembly is at rest.