US20180334826A1

US20180334826A1 - Asymmetric damping system for, and method of, protecting structures subjected to external dynamic forces

Info

Publication number: US20180334826A1
Application number: US15/841,547
Authority: US
Inventors: Saeed Towfighi
Original assignee: Wsp Usa Buildings Inc
Current assignee: Wsp Usa Buildings Inc
Priority date: 2017-05-17
Filing date: 2017-12-14
Publication date: 2018-11-22
Also published as: US10352058B2; US20180334824A1

Abstract

A structure having at least one generally horizontal flexural member extending between a pair of spaced-apart, upright columns, is protected from seismic forces by connecting one end of an elongated damping member to a first structural node on one of the columns, and by connecting an opposite end to a nodal junction on the flexural member. An undamped, rigid body is connected to the nodal junction and to a second structural node on the other of the columns. In response to the seismic forces, the rigid body is turned about the second structural node, the flexural member is flexed, an amplified force is exerted, and the damping member is displaced along an amplified working stroke.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. provisional application No. 62/507,617, filed May 17, 2017.

BACKGROUND

This disclosure generally relates to a system for, and a method of, protecting structures, such as multi-floor or single-floor buildings, subjected to external dynamic forces, such as earthquakes, winds, air bursts, and like lateral loads and environmental conditions and, more particularly, for efficiently and economically increasing the capability of such building structures to reliably withstand such disastrous environmental conditions by at least partly dissipating the energy produced by such external dynamic forces with a damping action.
It is generally known in the art of building construction to incorporate both concentric and eccentric, bracing elements to a building structure, as well as to incorporate both active and passive damping systems for dissipating energy, and for absorbing and resisting deformations and vibrations, caused by seismic disturbances and like external dynamic forces. See, for example, U.S. Pat. Nos. 2,053,226; 3,418,768; 4,922,667; 5,065,552; 5,147,018; 5,152,110; 5,347,771; 5,491,938; and 6,397,528. It is also known to isolate a base of the building structure, but such base isolation is typically very costly and not readily feasible for most buildings.
Yet, as advantageous as these known construction techniques have been, the level of energy dissipation has not always proven to be high enough to justify the cost for the achieved improvement in performance. Accordingly, it is desirable to efficiently and economically increase the performance of such building structures to reliably withstand such disastrous environmental conditions by more significantly dissipating the energy caused by such external dynamic forces with a damping action.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views, together with the detailed description below, are incorporated in and form part of the specification, and serve to further illustrate embodiments of concepts that include the claimed invention, and explain various principles and advantages of those embodiments.

FIG. 1 is a simplified schematic elevational view of a multi-floor building structure equipped with an asymmetric damping system in accordance with one embodiment of the present disclosure.

FIG. 2 is a view analogous to FIG. 1, but of another embodiment in accordance with the present disclosure.

FIG. 3 is a view analogous to FIG. 1, but of still another embodiment in accordance with the present disclosure.

FIG. 4 is a simplified diagram showing displacement of components of the system of FIG. 1 on a representative floor of the building structure when subjected to external dynamic forces.

FIG. 5 is a view analogous to FIG. 1, but of yet another embodiment on a representative floor in accordance with the present disclosure.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present disclosure.
The system and method have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

DETAILED DESCRIPTION

One aspect of this disclosure is directed to an asymmetric damping system for, and a method of, protecting a structure, for example, a multi-floor or single-floor building, when subjected to external dynamic forces, such as earthquakes, winds, air bursts, and like lateral loads and environmental conditions. The structure has at least one generally horizontal flexural member, e.g., a floor beam and/or a floor slab, extending between a pair of spaced-apart, upright columns. Preferably, a plurality of such flexural members are arranged in mutual parallelism between the columns, each floor of the building having a corresponding respective flexural member.
The system includes an elongated damping member having one end operatively connected to a first structural node on one of the columns, and an opposite end operatively connected to a nodal junction on the flexural member. Preferably, but not necessarily, the nodal junction is located centrally or midway of the flexural member between the columns. The damping member extends from the first structural node to the nodal junction along a first inclined or diagonal direction. The damping member has a damping element that is displaceable along the first inclined direction. In the preferred embodiment, the damping element may constitute a piston mounted in, and movable relative to, a cylinder, in which an inert operating viscous fluid, such as silicone, is accommodated. Any force-velocity and/or force-displacement sensitive damping element, or any number of such damping elements could be used.
The system further includes an undamped, rigid body operatively connected to the nodal junction, and operatively connected to a second structural node on the other of the columns. As used herein, the term “rigid body” is defined as a solid body in which deformation is zero or so small that it can be neglected. The distance between any two given points on a rigid body remains constant in time regardless of external dynamic forces exerted on it. The rigid body is turnable about the second structural node or center of rotation in response to the external dynamic forces for flexing the flexural member, for exerting an amplified force, and for displacing the damping element along an amplified working stroke along the first inclined direction to protect the structure from the external dynamic forces. The flexed flexural member stores energy during its flexing, and acts to return to its original position when no longer subjected to the external dynamic forces.
In one embodiment, the rigid body is a triangle having three sides and includes an elongated stiffening brace as one of its sides. The brace has one end operatively connected to the nodal junction, and an opposite end operatively connected to the second structural node. The brace extends from the second structural node to the nodal junction along a second inclined or diagonal direction that is different from the first inclined direction. The first and second inclined directions may be mirror-symmetrical and form a chevron- or V-like configuration with its apex at the nodal junction. In another embodiment, the rigid body may constitute either a shear wall or a truss. For example, a reinforced concrete shear wall may be advantageously employed as the rigid body. As used herein, the term “asymmetric” is intended to mean that there is no symmetry at opposite sides of the nodal junction, i.e., a damping member and a rigid body are located at the opposite sides of the nodal junction, rather than, for example, two damping members that are symmetrically located at the opposite sides of the nodal junction, or two rigid bodies that are symmetrically located at the opposite sides of the nodal junction.
Referring now to FIG. 1 of the accompanying drawings, a multi-floor building 10 is constructed of at least two generally upright or vertical columns 12 extending upwardly from, and built on, a foundation 20, and at least one generally horizontal flexural member 14, and preferably, a plurality of such flexural members 14, connected to, and spanning, the columns 12 in mutual parallelism, each floor having a respective or corresponding flexural member 14. Advantageously, each flexural member 14 is a floor beam and/or a floor slab. Although the building 10 of FIG. 1 has been illustrated as having five floors, this is merely exemplary, because the number of floors is arbitrary.
Upon exposure to a lateral load, such as a seismic force or a like external dynamic time-varying force, the building 10 experiences deformations, vibrations and stresses, and at least some, if not all, of the flexural members 14 and the columns 12 exhibit a localized flexing or bending movement or distortion. This disclosure is directed to an asymmetric damping system for, and a method of, protecting the building 10 when subjected to such external dynamic forces to reliably withstand such external dynamic forces by at least partly dissipating the energy produced by such external dynamic forces with a damping action.
More particularly, the system includes at least one elongated damping member 16, and, as shown in FIG. 1, a plurality of such damping members 16, preferably one for each floor, each damping member 16 having one end operatively connected to a respective first structural node 18 on one of the columns 12, and an opposite end operatively connected to a respective nodal junction 22 on a respective flexural member 14. Preferably, but not necessarily, each nodal junction 22 is located centrally or midway of the respective flexural member 14 between the columns 12. Each damping member 16 extends from the respective first structural node 18 to the respective nodal junction 22 along a first inclined or diagonal direction, which, as shown in FIG. 1, has a rising slope, as considered from left to right. Each damping member 16 has a damping element 24 that is displaceable along the first inclined direction.
In the preferred embodiment, the damping element 24 resembles an automobile shock absorber in that it typically consists of a piston, preferably of hardened, hand-polished, stainless steel coated with Teflon (trademark) mounted in, and movable along a working stroke relative to, a cylinder, also constituted of a hardened stainless steel, and in which an inert operating viscous fluid, such as silicone, is accommodated. The fluid advantageously has a flashpoint in excess of 600 degrees F., and is thus classified as nonflammable and noncombustible. The silicone is preferably a pure fluid polymer that cannot settle out or break down into components. The cylinder is preferably sealed to prevent oxidation of the silicone. Various working strokes are available depending on the magnitude of the force applied to opposite ends of the damping element 24. Other damping elements, for example, friction damping elements, visco-elastic damping elements and, in brief, any force-velocity and/or force-displacement sensitive damping element, or number of such damping elements, could be used. The damping element 24 absorbs energy as a function of the relative velocity or displacement of the piston as dictated by the velocity or displacement of the neighboring flexural members 14 and columns 12.
The system further includes at least one undamped, rigid body, and preferably a plurality of such rigid bodies, preferably one for each floor. As used herein, the term “rigid body” is defined as a solid body in which deformation is zero or so small that it can be neglected. The distance between any two given points on a rigid body remains constant in time regardless of the external forces exerted on it. As shown in FIG. 1, each rigid body may be configured, in one embodiment, as a triangle. The longest side or hypotenuse of the triangle is an elongated stiffening brace 28 having one end operatively connected to the respective nodal junction 22, and an opposite end operatively connected to a respective second structural node 26 on the other of the columns 12. A second side of the triangle extends generally horizontally from the respective nodal junction 22 along a respective flexural member 14 to an upper structural node 26. A third side of the triangle extends generally vertically from the upper structural node 26 along the column 12 to a lower structural node 26. Each brace 28 extends from the respective second structural node 26 to the nodal junction 22 along a respective second inclined or diagonal direction that is different from the first inclined direction. As shown in FIG. 1, each second inclined direction has a falling slope, as considered from left to right. The first and second inclined directions may, as shown in FIG. 1, be mirror-symmetrical and form a chevron- or V-like configuration with its apex at each nodal junction 22. In another embodiment, as best shown in FIG. 2, each rigid body may be configured as either a shear wall 30, or as a truss having criss-crossed or single diagonal braces. For example, a mass of solid material, e.g., reinforced concrete, may be advantageously employed as the shear wall 30. As used herein, the term “asymmetric” is intended to mean that there is no symmetry at opposite sides of the nodal junction 22, i.e., the damping member 16 and the rigid body are located at the opposite sides of the nodal junction 22, rather than, for example, two damping members 16 that are symmetrically located at the opposite sides of the nodal junction 22, or two rigid bodies that are symmetrically located at the opposite sides of the nodal junction 22.
Each rigid body, e.g., each triangle that includes the brace 28 or each shear wall 30, is turnable as a unit about its respective second structural node 26 or center of rotation in response to the external dynamic forces for flexing the corresponding flexural member 14, for exerting an amplified force, and for displacing the respective damping element 24 along an amplified working stroke, as explained in more detail below in connection with FIG. 4, along the first inclined direction to protect the building 10 from the external dynamic forces. Each flexed flexural member 14 stores energy during its flexing, and acts to return to its original position when no longer exposed to the external dynamic forces.
In accordance with this disclosure, not every floor needs to have its own damping member 16, or its own rigid body. Thus, as shown in FIG. 2, the first, third, and fifth floors have no rigid body. Also, the orientation of the damping member 16 on the fifth floor is opposite to that on the other floors. As shown in FIG. 3, a single brace 28 need not span one floor, but can span a plurality of floors, such as the first and second floors. Also, a single damping member 16 need not span one floor, but can span a plurality of floors, such as the fourth and fifth floors. In addition, more than two columns 12 may be provided. Furthermore, the building 10 is not restricted to only one type of rigid body, but different rigid bodies may be employed in the same building. The nodal junctions 22 need not be located centrally or midway of the respective flexural member 14 between a pair of adjacent columns 12, but can be located at any point on a respective flexural member 14. Each nodal junction 22 on the flexural members 16, as well as each structural node on the columns 12, is preferably a pivot point, but may also be a fixed interconnection point. Also, each nodal junction 22 need not be a common pivot point for both the damping member 16 and the rigid body 28, 30, because the connection point for the damping member 16 may be slightly spaced laterally and horizontally away from the connection point for the rigid body 28, 30. Other variations are also contemplated.
In FIG. 3, the triangular and rectangular areas enclosed by dashed lines denote rigid bodies whose joint movement flexes a corresponding flexural member. For a steel structure, the rigid body may advantageously be configured as a truss type arrangement of elements that includes a segment of one column, preferably at least one story in elevation, a segment of a flexural member, and at least one diagonal damping member. For a concrete structure, the rigid body may advantageously be configured as a solid wall of any shape and incorporating a segment of a column and a segment of at least one flexural member.
As shown in the diagram of FIG. 4 in which a representative floor is modeled, the vertical height between adjacent stacked floors is designated as H, the horizontal distance between adjacent columns is designated as L, and the length of the rigid brace 28 is designated as D. If a lateral force F is applied to this floor, then the flexural member 16 and the columns 12 will be displaced to the illustrated dashed line positions, in which the brace 28 has rotated about the structural node 26 over an angular distance A, and the nodal junction 22 will move both downwardly and horizontally towards the left over an angular distance B. Since D is greater than H, the angular distance B is greater than the angular distance A. Put another way, the distance D2 is greater than D1. This causes the stroke of the damping element 24 to be correspondingly greater, and the amplified damper movement is more effective than heretofore in dissipating more of the energy of the force F.
As described so far, the damping member 16 and the rigid body generally lie in a common plane. However, as shown in FIG. 5, the damping member 16 and the rigid body can also generally lie in different planes that intersect one another, such as in a corner of the building 10 where the walls meet at right angles.
In the foregoing specification, specific embodiments have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the invention as set forth in the claims below. For example, although the structure to be protected has been described and illustrated as being a building 10, other structures, including non-stationary and non-land-based structures, could also benefit from this invention. Also, the external dynamic forces need not be seismic forces or winds, but could also be vibrations whose effects to a machine or like apparatus are to be mitigated. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present teachings.
The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.
Moreover in this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” “has,” “having,” “includes,” “including,” “contains,” “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises, has, includes, or contains a list of elements does not include only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a,” “has . . . a,” “includes . . . a,” or “contains . . . a,” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises, has, includes, or contains the element. The terms “a” and “an” are defined as one or more unless explicitly stated otherwise herein. The terms “substantially,” “essentially,” “approximately,” “about,” or any other version thereof, are defined as being close to as understood by one of ordinary skill in the art, and in one non-limiting embodiment the term is defined to be within 10%, in another embodiment within 5%, in another embodiment within 1%, and in another embodiment within 0.5%. The term “coupled” as used herein is defined as connected, although not necessarily directly and not necessarily mechanically. A device or structure that is “configured” in a certain way is configured in at least that way, but may also be configured in ways that are not listed.
The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various embodiments for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter.

Claims

I claim:

1. An asymmetric damping system for protecting a structure when subjected to external dynamic forces, the structure having at least one generally horizontal flexural member extending between a pair of spaced-apart, upright columns, the system comprising:

an elongated damping member having one end operatively connected to a first structural node on one of the columns and an opposite end operatively connected to a nodal junction on the flexural member, the damping member extending from the first structural node to the nodal junction along a first inclined direction, the damping member having a damping element that is displaceable along the first inclined direction; and

an undamped, rigid body operatively connected to the nodal junction and operatively connected to a second structural node on the other of the columns, the rigid body being turnable about the second structural node in response to the external dynamic forces for flexing the flexural member, for exerting an amplified force, and for displacing the damping element along an amplified working stroke along the first inclined direction to protect the structure from the external dynamic forces.

2. The system according to claim 1, wherein the rigid body has three sides and includes an elongated stiffening brace as one of its sides, the brace having one end operatively connected to the nodal junction and an opposite end operatively connected to the second structural node, the brace extending from the second structural node to the nodal junction along a second inclined direction that is different from the first inclined direction.

3. The system according to claim 1, wherein the rigid body includes one of a shear wall and a truss.

4. The system according to claim 1, wherein the nodal junction on the flexural member is a common pivot point pivotably connected to both the damping member and the rigid body.

5. The system according to claim 1, wherein the damping member and the rigid body generally lie in a common plane.

6. The system according to claim 1, wherein the damping member and the rigid body generally lie in different planes that intersect one another.

7. An asymmetric damping system for protecting a multi-floor building when subjected to external dynamic forces, the building having a pair of spaced-apart, upright columns and a plurality of generally horizontal flexural members in mutual parallelism, each flexural member extending on each floor between the columns, the system comprising:

at least one elongated damping member having one end operatively connected to a first structural node on one of the columns and an opposite end operatively connected to a nodal junction on at least one of the flexural members, the at least one damping member extending from the first structural node to the nodal junction along a first inclined direction, the at least one damping member having a damping element that is displaceable along the first inclined direction; and

at least one undamped, rigid body operatively connected to the nodal junction and operatively connected to a second structural node on the other of the columns, the at least one rigid body being turnable about the second structural node in response to the external dynamic forces for flexing the at least one flexural member, for exerting an amplified force, and for displacing the at least one damping element along an amplified working stroke along the first inclined direction to protect the building from the external dynamic forces.

8. The system according to claim 7, further comprising additional elongated damping members, each additional damping member having one end operatively connected to additional first structural nodes on the one column and an opposite end operatively connected to additional nodal junctions on others of the flexural members, the additional damping members extending from the additional first structural nodes to the additional nodal junctions along additional inclined directions that are parallel to the first inclined direction, each additional damping member having an additional damping element.

9. The system according to claim 7, further comprising additional rigid bodies including additional elongated stiffening braces, each having one end operatively connected to additional nodal junctions on others of the flexural members and an opposite end operatively connected to additional second structural nodes on the other column, the braces extending from the additional second structural nodes to the additional nodal junctions along additional second inclined directions that are parallel to the second inclined direction.

10. The system according to claim 7, further comprising additional rigid bodies, each including one of a shear wall and a truss.

11. The system according to claim 7, further comprising additional elongated damping members and additional rigid bodies, and wherein only selected ones of the floors contain the additional damping members and the additional rigid bodies.

12. A method of protecting a multi-floor building when subjected to external dynamic forces, the building having a pair of spaced-apart, upright columns and a plurality of generally horizontal flexural members in mutual parallelism, each flexural member extending on each floor between the columns, the method comprising:

operatively connecting one end of at least one elongated damping member to a first structural node on one of the columns;

operatively connecting an opposite end of the at least one elongated damping member to a nodal junction on at least one of the flexural members;

configuring the at least one damping member to extend from the first structural node to the nodal junction along a first inclined direction, and to have a damping element that is displaceable along the first inclined direction;

operatively connecting at least one undamped, rigid body to the nodal junction;

operatively connecting the at least one rigid body to a second structural node on the other of the columns; and

configuring the at least one rigid body to turn about the second structural node in response to the external dynamic forces for flexing the at least one flexural member, for exerting an amplified force, and for displacing the at least one damping element along an amplified working stroke along the first inclined direction to protect the building from the external dynamic forces.