U.S. patent application number 15/531773 was filed with the patent office on 2017-09-21 for yielding link, particularly for eccentrically braced frames.
The applicant listed for this patent is Cast Connex Corporation. Invention is credited to Constantin Cristopoulos, Juan-Carlos De Oliveira, Michael Gray, Tarana Haque, Kyla Tan.
Application Number | 20170268252 15/531773 |
Document ID | / |
Family ID | 56090748 |
Filed Date | 2017-09-21 |
United States Patent
Application |
20170268252 |
Kind Code |
A1 |
Gray; Michael ; et
al. |
September 21, 2017 |
YIELDING LINK, PARTICULARLY FOR ECCENTRICALLY BRACED FRAMES
Abstract
A structural yielding link, particularly for use in an
eccentrically braced frame arrangement or in a linked column frame
arrangement having a first end having a means for connecting to a
face of a first beam and a second end having a means for connecting
to a face of a second beam; a first variable cross-section portion
and a second variable cross-section portion extending from the
first end and from the second end, respectively; and a constant
cross-section portion joining the first variable cross-section
portion and the second variable cross-section portion.
Inventors: |
Gray; Michael; (Whitby,
CA) ; De Oliveira; Juan-Carlos; (Pickering, CA)
; Cristopoulos; Constantin; (Toronto, CA) ; Haque;
Tarana; (Vaughan, CA) ; Tan; Kyla; (Toronto,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Cast Connex Corporation |
Toronto |
|
CA |
|
|
Family ID: |
56090748 |
Appl. No.: |
15/531773 |
Filed: |
December 1, 2014 |
PCT Filed: |
December 1, 2014 |
PCT NO: |
PCT/CA2014/051147 |
371 Date: |
May 31, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E04H 9/028 20130101;
E04B 1/98 20130101; E04B 2001/2451 20130101; E04B 1/2403 20130101;
E04B 2001/2496 20130101; E04H 9/0237 20200501; E04H 9/021 20130101;
E04H 9/024 20130101; E04B 2001/2457 20130101; F16F 7/12 20130101;
E04B 2001/2442 20130101; E04H 9/025 20130101 |
International
Class: |
E04H 9/02 20060101
E04H009/02; E04B 1/98 20060101 E04B001/98; E04B 1/24 20060101
E04B001/24 |
Claims
1. A structural yielding link comprising: a first end having a
means for connecting to a face of a first beam or column and a
second end having a means for connecting to a face of a second beam
or column; a first variable cross-section portion and a second
variable cross-section portion extending from said first end and
from said second end, respectively; a constant cross-section
portion joining said first variable cross-section portion and said
second variable cross-section portion.
2. The structural yielding link according to claim 1 for use in an
eccentrically braced frame arrangement or in a linked column frame
arrangement.
3. The structural yielding link according to claim 1, wherein said
first and said second variable cross-section portions are hollow
along at least a portion of lengths thereof.
4. The structural yielding link according to claim 1, wherein said
first variable cross-section portion and said second variable
cross-section portion have a cross-section tapering from said
respective first and second end portions towards said constant
cross-section portion such that a width of said first and second
variable cross-section portions at said respective first and second
end portions is greater than a width at said constant cross-section
portion.
5. The structural yielding link according to claim 4, wherein said
first and said second variable cross-section portions are hollow
and have an interior wall thickness which is greater at said first
and second end portions, respectively than proximate said
constant-cross section portion.
6. The structural yielding link according to claim 1, wherein said
variable cross-section portions are designed, sized and otherwise
dimensioned to promote near simultaneous yielding along a
substantial portion of the yielding link when subjected to a
linearly varying bending moment diagram.
7. The structural yielding link according to claim 1, wherein said
first and said second variable cross-section portions have a width
defined by a higher-order function; whereby said higher-order
function promotes yielding of the link when the link is subjected
to load(s) causing a linearly varying bending moment diagram.
8. A structural link according to claim 1, wherein said first and
said second variable cross-section portions are defined such that
the cross sectional area along the length of the link is constant;
whereby said constant cross sectional area promotes a constant
axial strain along the length of the link when the link is
subjected to any axial load.
9. A structural link according to claim 8, wherein said constant
cross sectional area is achieved by a flange located at the
flexural neutral axis of the cross section.
10. The structural yielding link according to claim 1, further
comprising a transition region between said first and second ends
and said first and second variable cross-section portions,
respectively; where said transition region includes a thickened
material portion for limiting stress and strain occurring during
yielding of the link from propagating to said means for connecting
to said end faces of said first and second beams.
11. The structural yielding link according to claim 1, wherein said
variable cross-section portions are designed, sized and otherwise
dimensioned to promote yielding along a substantial portion of the
yielding link.
12. The structural yielding link according to claim 4, wherein said
first and said second variable cross-section portions are hollow
and have an interior wall thickness which is constant throughout
said first and second variable cross-section portions.
13. The structural yielding link according to claim 1, wherein said
first variable cross-section portion and said second variable
cross-section portion have a cross-section tapering from said
respective first and second end portions towards said constant
cross-section portion such that a depth of said first and second
variable cross-section portions at said respective first and second
end portions is greater than a depth at said constant cross-section
portion.
14. An eccentrically braced frame arrangement comprising a first
column and a second column; a beam connecting said first column and
said second column; said beam having a first portion connected to
said first column, a second portion connected to said second column
and a yielding link connecting said first portion and said second
portion; at least one brace having a node end connected proximate
an end of said first column and another end connected to an end of
said first portion proximate said yielding link; wherein said
yielding link comprises a first end having a means for connecting
to an end face of said first portion and a second end having a
means for connecting to an end face of said second portion; a first
variable cross-section portion and a second variable cross-section
portion extending from said first end and from said second end,
respectively; a constant cross-section portion joining said first
variable cross-section portion and said second variable
cross-section portion.
15. The eccentrically braced frame arrangement according to claim
14, wherein said first and said second variable cross-section
portions are hollow along at least a portion of lengths
thereof.
16. The eccentrically braced frame arrangement according to claim
14, wherein said first variable cross-section portion and said
second variable cross-section portion have a cross-section tapering
from said respective first and second end portions towards said
constant cross-section portion such that a width of said first and
second variable cross-section portions at said respective first and
second end portions is greater than a width at said constant
cross-section portion.
17. The eccentrically braced frame arrangement according to claim
16, wherein said first and said second variable cross-section
portions are hollow and have an interior wall thickness which is
greater at said first and second end portions, respectively than
proximate said constant-cross section portion.
18. The eccentrically braced frame arrangement according to claim
14, wherein said variable cross-section portions are designed,
sized and otherwise dimensioned to promote yielding along a
substantial portion of the yielding link.
19. The eccentrically braced frame arrangement according to claim
14, wherein said first and said second variable cross-section
portions have a width defined by a higher-order function; whereby
said higher-order function promotes yielding of the link when the
link is subjected to load(s) causing a linearly varying bending
moment diagram.
20. An eccentrically braced frame arrangement according to claim
14, wherein said first and said second variable cross-section
portions are defined such that the cross sectional area along the
length of the link is constant; whereby said constant cross
sectional area promotes a constant axial strain along the length of
the link when the link is subjected to any axial load.
21. An eccentrically braced frame arrangement according to claim
20, wherein said constant cross sectional area is achieved by a
flange located at the flexural neutral axis of the cross
section.
22. The eccentrically braced frame arrangement according to claim
14, further comprising a transition region between said first and
second ends and said first and second variable cross-section
portions, respectively; where said transition region includes a
thickened material portion for limiting stress and strain occurring
during yielding of the link from propagating to said means for
connecting to said end faces of said first and second beams.
23. The eccentrically braced frame arrangement according to claim
14, wherein said variable cross-section portions are designed,
sized and otherwise dimensioned to promote yielding along a
substantial portion of the yielding link.
24. The eccentrically braced frame arrangement according to claim
16, wherein said first and said second variable cross-section
portions are hollow and have an interior wall thickness which is
constant throughout said first and second variable cross-section
portions.
25. The eccentrically braced frame arrangement according to claim
14, wherein said first variable cross-section portion and said
second variable cross-section portion have a cross-section tapering
from said respective first and second end portions towards said
constant cross-section portion such that a depth of said first and
second variable cross-section portions at said respective first and
second end portions is greater than a depth at said constant
cross-section portion.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to building frame
structures, and particularly to yielding links for use is building
frame structures, especially eccentrically braced frames or linked
column frames.
BACKGROUND OF THE INVENTION
[0002] Eccentrically braced frames (EBFs) are a commonly used,
high-ductility lateral load resisting system, generally implemented
in steel building constructions. The brace(s) in an EBF are
arranged such that at one end the brace(s) are connected to a frame
node and at the other end the brace(s) are connected to a beam. In
the case where the EBF has one brace per frame, the brace work
point is located away from the node defined by the beam column
intersection. In the case where the EBF has two braces per frame,
the braces do not share a node at center of the beam. Rather, each
brace is slightly more inclined, thus moving the two brace end
points away from the centre of the beam. In both configurations,
the eccentric brace geometry results in shear and bending being
applied to a short portion of the continuous beam. This portion of
the beam is commonly referred to as the link, or yielding link.
During an earthquake, the system is designed such that the link
yields in shear or flexure (or a combination of both), thereby
limiting the force that can develop in the other structural
elements and absorbing seismic energy in a stable manner.
[0003] Typically, the link portions of EBFs have been wide flange
(W-sections), rectangular hollow sections (HSS), or built-up box
sections. EBFs exhibit excellent ductility capacity and perform
well after an earthquake. However, after a severe seismic event,
the links are somewhat damaged and can require repair or
replacement. This led to the development of replaceable links for
EBFs.
[0004] In an EBF with replaceable links, the link is a separate
component from the rest of the beam element(s). The replaceable
link is the yielding element of this system and the remaining beam
element(s) are intended to remain elastic. This component is bolted
or welded to the beam such that there is a predominantly rigid
connection capable of transmitting the shear force or bending
moment required to yield the link element. Prior research on
replaceable links has focused on link elements created from
weld-fabricated rolled sections such as W-sections, channels,
rectangular hollow structural sections, and build-up box sections.
All of these concepts have been continuous, prismatic, constant
cross-section sections that yield either in constant shear or in
flexural hinging at the ends of the links.
[0005] A linked column frame is an arrangement that utilizes
replaceable links in a modified structural configuration. The
behaviour of the link in the linked column frame is the same as it
is in the eccentrically braced frame, thus any link developed for
eccentrically braced frames may be equally applicable to a linked
column frame, and indeed have been applied to link column frames in
the prior art.
[0006] It is an object of the invention to provide a replaceable
yielding link providing at least one improvement over the prior
art.
SUMMARY OF THE INVENTION
[0007] According to one embodiment of the invention, there is
provided a structural yielding link having a first end having a
means for connecting to a face of a first beam or column and a
second end having a means for connecting to a face of a second beam
or column; a first variable cross-section portion and a second
variable cross-section portion extending from the first end and
from the second end, respectively; and a constant cross-section
portion joining the first variable cross-section portion and the
second variable cross-section portion.
[0008] In one aspect of the invention, the structural yielding link
is used in an eccentrically braced frame arrangement or in a linked
column frame arrangement.
[0009] In another aspect of the invention, the first and the second
variable cross-section portions are hollow along at least a portion
of lengths thereof.
[0010] In another aspect of the invention, the first variable
cross-section portion and the second variable cross-section portion
have a cross-section tapering from the respective first and second
end portions towards the constant cross-section portion such that a
width of the first and second variable cross-section portions at
the respective first and second end portions is greater than a
width at the constant cross-section portion.
[0011] In another aspect of the invention, the first and the second
variable cross-section portions are hollow and have an interior
wall thickness which is greater at the first and second end
portions, respectively than proximate the constant-cross section
portion.
[0012] In another aspect of the invention, the variable
cross-section portions are designed, sized and otherwise
dimensioned to promote near simultaneous yielding along a
substantial portion of the yielding link when subjected to a
linearly varying bending moment diagram.
[0013] In another aspect of the invention, the first and the second
variable cross-section portions have a width defined by a
higher-order function; whereby the higher-order function promotes
yielding of the link when the link is subjected to load(s) causing
a linearly varying bending moment diagram.
[0014] In another aspect of the invention, the first and the second
variable cross-section portions are defined such that the cross
sectional area along the length of the link is constant; whereby
the constant cross sectional area promotes a constant axial strain
along the length of the link when the link is subjected to any
axial load.
[0015] In another aspect of the invention, the constant cross
sectional area is achieved by a flange located at the flexural
neutral axis of the cross section.
[0016] In another aspect of the invention, there is further
provided a transition region between the first and second ends and
the first and second variable cross-section portions, respectively;
where the transition region includes a thickened material portion
for limiting stress and strain occurring during yielding of the
link from propagating to the means for connecting to the end faces
of the first and second beams.
[0017] In another aspect of the invention, the variable
cross-section portions are designed, sized and otherwise
dimensioned to promote yielding along a substantial portion of the
yielding link.
[0018] In another aspect of the invention, the first and the second
variable cross-section portions are hollow and have an interior
wall thickness which is constant throughout the first and second
variable cross-section portions.
[0019] In another aspect of the invention, the first variable
cross-section portion and the second variable cross-section portion
have a cross-section tapering from the respective first and second
end portions towards the constant cross-section portion such that a
depth of the first and second variable cross-section portions at
the respective first and second end portions is greater than a
depth at the constant cross-section portion.
[0020] According to another embodiment of the invention, there is
provided an eccentrically braced frame arrangement having a first
column and a second column; a beam connecting the first column and
the second column; the beam having a first portion connected to the
first column, a second portion connected to the second column and a
yielding link connecting the first portion and the second portion;
at least one brace having a node end connected proximate an end of
the first column and another end connected to an end of the first
portion proximate the yielding link; wherein the yielding link
includes a first end having a means for connecting to an end face
of the first portion and a second end having a means for connecting
to an end face of the second portion; a first variable
cross-section portion and a second variable cross-section portion
extending from the first end and from the second end, respectively;
and a constant cross-section portion joining the first variable
cross-section portion and the second variable cross-section
portion.
[0021] In one aspect of this embodiment, the first and the second
variable cross-section portions are hollow along at least a portion
of lengths thereof.
[0022] In another aspect of this embodiment, the first variable
cross-section portion and the second variable cross-section portion
have a cross-section tapering from the respective first and second
end portions towards the constant cross-section portion such that a
width of the first and second variable cross-section portions at
the respective first and second end portions is greater than a
width at the constant cross-section portion.
[0023] In another aspect of this embodiment, the first and the
second variable cross-section portions are hollow and have an
interior wall thickness which is greater at the first and second
end portions, respectively than proximate the constant-cross
section portion.
[0024] In another aspect of this embodiment, the variable
cross-section portions are designed, sized and otherwise
dimensioned to promote yielding along a substantial portion of the
yielding link.
[0025] In another aspect of this embodiment, the first and the
second variable cross-section portions have a width defined by a
higher-order function; whereby the higher-order function promotes
yielding of the link when the link is subjected to load(s) causing
a linearly varying bending moment diagram.
[0026] In another aspect of this embodiment, the first and the
second variable cross-section portions are defined such that the
cross sectional area along the length of the link is constant;
whereby the constant cross sectional area promotes a constant axial
strain along the length of the link when the link is subjected to
any axial load.
[0027] In another aspect of this embodiment, the constant cross
sectional area is achieved by a flange located at the flexural
neutral axis of the cross section.
[0028] In another aspect of this embodiment, there is further
provided a transition region between the first and second ends and
the first and second variable cross-section portions, respectively;
where the transition region includes a thickened material portion
for limiting stress and strain occurring during yielding of the
link from propagating to the means for connecting to the end faces
of the first and second beams.
[0029] In another aspect of this embodiment, the variable
cross-section portions are designed, sized and otherwise
dimensioned to promote yielding along a substantial portion of the
yielding link.
[0030] In another aspect of this embodiment, wherein the first and
the second variable cross-section portions are hollow and have an
interior wall thickness which is constant throughout the first and
second variable cross-section portions.
[0031] In another aspect of this embodiment, the first variable
cross-section portion and the second variable cross-section portion
have a cross-section tapering from the respective first and second
end portions towards the constant cross-section portion such that a
depth of the first and second variable cross-section portions at
the respective first and second end portions is greater than a
depth at the constant cross-section portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Embodiments will now be described, by way of example only,
with reference to the attached Figures, wherein:
[0033] FIG. 1 is an elevation view of a yielding link in an
eccentrically braced frame according to one embodiment of the
invention.
[0034] FIGS. 2A, 2B and 2C show side, top and end views,
respectively, of the yielding link of FIG. 1.
[0035] FIG. 3 is a perspective view of the yielding link of FIG.
1.
[0036] FIG. 4 is an elevation view of a yielding link in an
eccentrically braced frame according to another embodiment of the
invention.
[0037] FIGS. 5A, 5B and 5C show side, top and end views,
respectively, of the yielding link of FIG. 4.
[0038] FIG. 6 is a perspective view of the yielding link of FIG.
4.
[0039] FIG. 7 is an elevation view of a yielding link in a
single-brace eccentrically braced frame according to another
embodiment of the invention.
[0040] FIGS. 8A, 8B and 8C show side, top and end views,
respectively, of the yielding link of FIG. 7.
[0041] FIG. 9 is a perspective view of the yielding link of FIG.
7.
[0042] FIG. 10 is an elevation view of a yielding link in a linked
column frame according to another embodiment of the invention.
[0043] FIGS. 11A, 11B and 11C show side, top and end views,
respectively, of the yielding link of FIG. 10.
[0044] FIG. 12 is a perspective view of the yielding link of FIG.
10.
[0045] FIG. 13 is a reference diagram showing key variables in the
design of the yielding link according to the invention.
DETAILED DESCRIPTION
[0046] Embodiments of the invention provide a replaceable yielding
link with a cross-section that varies along at least a portion of
the length of the yielding link. The yielding link is intended to
be used in eccentrically braced frame (EBF) arrangements, or in
linked column frame arrangements which exhibit similar structural
responses to force-applying events as EBF arrangements. For the
purposes of this disclosure, the terms "link" and "yielding link"
are used interchangeably. The cross-section of the link is
preferably shaped, and otherwise dimensioned such that the change
in moment resistance along the length of the link substantially
matches the moment diagram that results from the applied forces.
This enables the link to yield in flexure along a substantial
portion of its length, thereby reducing the inelastic strains
resulting from a given amount of plastic link rotation, when
compared to the prismatic, constant cross-section links of the
prior art. Reducing the inelastic strains in the link increases the
displacement capacity of the link and its resistance to low cycle
fatigue fractures, thus increasing the ductility of the EBF as a
whole. Reducing the inelastic strains also enables the design of
more compact, efficient links that provide equal or better
performance when compared to the prismatic, constant cross-section
links of the prior art. This compact design results at least in
easier transport of the link and facilitates replacement following
yielding.
[0047] A variable cross-section which promotes yielding along
substantially the full length of the link could be achieved in a
number of ways. For example, if the cross-section is rectangular or
square shaped, the link's width out of the plane of the frame could
be varied, the link's depth could be varied, or the thickness of
the link's walls could be varied. Any combination of these could
also result in a shape that promotes near simultaneous yielding
along substantially the full length of the link.
[0048] The theoretical concept of varying the cross-sectional shape
of a building element to promote spread in yielding or for use as
energy dissipation mechanisms in base isolated structures has been
accomplished in other prior art applications. (For example, see (i)
Tsai et al. 1993. Design Of Steel Triangular Plate Energy Absorbers
For Seismic-Resistant Construction. Earthquake Spectra. Vol. 9, No.
3: pp. 505-528; (ii) Gray et al. 2014. Cast Steel Yielding Brace
System For Concentrically Braced Frames: Concept Development And
Experimental Validations. Vol. 140. No. 4: Paper Number 04013094;
and (iii) Japanese Patent Application No. 62-051290 (Publication
No. 63-219928) filed Mar. 6, 1987 by Kajima Corp.) However, to the
knowledge of the applicants, varying cross-sections have not been
used in any form of eccentrically braced frames to increase
performance of the yielding link elements, nor have they been used
as link elements in a linked column frame exhibiting behaviour
analogous to eccentrically braced frames. Furthermore, the
adaptations and structural details described herein relating
particularly to improving any one of performance, efficiency or
ease of construction of the link implemented within an
eccentrically braced frame or a linked column frame differ from the
prior art of which the applicant is aware.
[0049] Embodiments of the link as herein described are intended to
replace the continuous beam yielding element of an eccentrically
braced frame with a replaceable element. The link is comprised of a
yielding segment and two connections, at the ends of the yielding
segment. The link is intended for the protection of the structural
frame of a building from excessive damage during cyclic dynamic
loading conditions (such as an earthquake) by absorbing the
majority of the energy and limiting the forces that must be
resisted by the structure as a whole. Cyclic dynamic loading
conditions refers to repeated cycles of flexural yielding,
including the increase in strength that is expected as the
replaceable link reaches large inelastic strains (due to
over-strength and second-order geometric effects). When a building
using the tapered replaceable link is subjected to such loading
conditions, the building structure cyclically deforms laterally.
These cyclic lateral deformations result in cyclic deformations in
which the yielding segment of the link is in double curvature.
Under severe loading, the cyclic link deformations cause the link
to yield, and to behave in a non-linear manner.
[0050] The yielding segment of the tapered replaceable link is
shaped based on the expected combination of bending, shear and
axial forces such that it will yield flexurally along nearly all of
its length. The combination of these forces can vary depending on
the structural loading, frame geometry, and location of the link
(in the centre of the beam, at the beam column connection, or in a
linked column frame). The cross sectional geometry of the link
varies along its length (in the direction of the beam axis) such
that at any given section its extreme fibers will yield at the same
magnitude of externally applied bending moment. This bending moment
would be considered the yield bending moment. Continuous yielding
along the length of the yielding segment is advantageous over
yielding at discrete locations along the length of the link,
because, for links of equal length, continuous yielding will result
in lower plastic strains for a given link rotation, and therefore
higher ductility, than prior art links. Increasing the ductility of
an eccentrically braced frame link decreases the likelihood for
structural collapse or expensive structural repair.
[0051] In addition, at any point along the length of the link the
cross-section has sufficient strength to resist the externally
applied shear and axial forces that would be associated with the
maximum bending moment that would be expected, which is limited by
the link's non-linear behaviour and the typical range of
deformations for an eccentrically braced frame structure. One
possible means of resisting the applied axial forces could be to
select the tapering of the cross section such that, in addition to
matching the flexural resistance to the applied bending moment, the
cross sectional area of the link remains constant along its entire
length. In this case, the stress resulting from any magnitude of
applied axial force would be constant along the length of the link.
When yielding in flexure, such a link would exhibit distributed
plasticity along nearly its entire length, regardless of the
magnitude of the applied axial force. In the presence of variable
axial forces, a link without this feature (i.e. a link with a
varying cross sectional area) could potentially yield in a discreet
location, rather than exhibiting uniformly distributed flexural
yielding along its length. One possible means of achieving constant
cross sectional area could be a thickened flange located at the
flexural neutral axis of the section. Such a flange would attract
much of the applied axial load, but not contribute significantly to
the flexural strength. Another possible means of achieving constant
cross sectional area would be to taper the thickness of the web(s)
or side walls of the section to compensate for loss of area
resulting from tapering the flange(s) or top and bottom walls of
the section to achieve flexural yielding along substantially the
full length of the link.
[0052] Further, the transition between the yielding portions of the
link and the end connection region could be thickened or otherwise
shaped in such a manner so as to limit inelastic strain from
spreading into the connection region. This would ensure that
yielding only occurs in the yielding portion, thus avoiding
fracture in the connection region.
[0053] Specific embodiments adhering to these principals will now
be described.
[0054] Referring now to FIGS. 1-3, there is shown a first
embodiment of the invention in which a yielding link 10 is used to
connect adjacent beams 12 in an eccentrically braced frame
arrangement 5. As described earlier, the frame is considered
eccentrically braced since the braces 8 are not connected at a
common working node of the frame 5 at their ends proximate the
beams 12. The link 10 has a substantially rectangular cross-section
15 that is hollow along a portion of its length, as indicated by
the dashed-line portions 20 in FIGS. 2A and 2B. Variable
cross-section portions 25 of the link, beginning proximate either
ends of the link have a constant depth and a varying width, and are
preferably hollow throughout, or substantially hollow throughout.
In the centre of the link 10, there is a constant cross-section or
solid portion 60, which adjoins the two variable portions 25, and
define termination points 65 of the hollow portions 20. For the
purposes of this application, "depth" is defined as the direction
perpendicular to the ground on which the frame is assembled or
along the z-axis in FIG. 3, and "width" is defined as a direction
parallel to the ground and perpendicular to the elongate axis of
the beams to which the link is attached or along the y-axis in FIG.
3.
[0055] The thicknesses of the top 30 and bottom 35 walls of the
variable portion varies linearly. That is, the material thickness
of the wall bounding a top surface 40 of the variable portion with
a top surface of the hollow portion 20 is linearly variable, as
illustrated. Meanwhile, the thickness of the side walls 45 is held
constant. That is, the material thickness of the wall bounding the
sidewall 50 of the variable portion 25 and the sidewall of the
hollow portion 20 is constant.
[0056] The variation in the width from w to w1 to w2 of the
variable portion 25 may be linear in some embodiments, but is most
preferably defined by a higher-order function that is defined to
ensure that the hollow portions 20 of the link 10 yield
simultaneously when subjected to a linearly varying, double
curvature bending moment diagram, combined with shear, axial, and
torsional forces at the ends 55 of the link 10. An example and
derivation of such a higher order function is provided in the
Example further below in this description.
[0057] The vertical walls 45 of the hollow sections 20 and the
solid centre 60 of the yielding portion 70 of the link 10 are
designed to have adequate shear and axial strength for the combined
forces that could be applied within the expected range of
deformations in a typical eccentrically braced frame building or a
link column frame, depending on the application. The cross section
of the link also includes an optional flange 57 at the neutral axis
that has been shaped, and otherwise dimensioned such that the cross
sectional area of the link remains constant throughout the yielding
portions. The flange 57 is preferably located at a mid-region of
the link, and extends across the length of the link. The transition
region 67 between the end connection 55 and the yielding portion 70
of the link 10 includes additional material to increase the
thickness so as to ensure that stress and strain resulting from
flexural or shear yielding does not propagate into the connection
ends 55 during cyclic loading. Practically, the ends 55 and the
transition region 67 are designed, sized, and otherwise dimensioned
to prevent failure or yielding of the link 10 at the connection
with either beam 12 or at a portion of the link 10 proximate this
connection. The specific dimensions of the link 10 and sizing of
each of the elements described above will be dependent upon the
specific implementation and will be calculable by one skilled in
the art in view of this description.
[0058] Referring now to FIGS. 4-6, there is shown a second
embodiment of the invention in which a yielding link 110 is used to
connect adjacent beams in an eccentrically braced frame arrangement
105. The link 110 has a substantially rectangular cross-section 115
that is hollow along a major portion of its length, as indicated by
the dashed-line portions 120 in FIGS. 5A and 5B. Variable
cross-section portions 125 of the link have a constant depth and a
varying width. The varying, and in particular, tapering width as
illustrated is designed to promote yielding along the entire length
of the variable cross-section portions 125. At the centre of the
link 110, there is a solid portion 160, which adjoins the two
variable cross-section portions 125.
[0059] The thicknesses of the top 130 and bottom 135 walls of the
variable cross-section portion 125 is maintained constant, in
distinction to the embodiment of FIGS. 1-3. In this embodiment, the
walls of the variable cross-section portion 125 and of the solid
portion 160 are designed, sized and otherwise dimensioned to have
adequate shear and axial strength for the combined forces that
could theoretically be applied within the expected range of
deformations in a typical eccentrically braced frame structure.
Additional details of this embodiment may be as described with
respect to the embodiment of FIGS. 1-3.
[0060] In a third embodiment of the invention, as illustrated in
FIGS. 7-9 there is shown a yielding link 210 having a substantially
rectangular cross-section 215 that is hollow along all of its
length, as indicated by the dashed-line portions 220 in FIGS. 8A
and 8B. Variable cross-section portions 225 of the link have a
varying depth and a constant width and wall thickness within the
variable cross-section portions 225. The varying, and in
particular, tapering depth as illustrated is designed to promote
yielding along the entire length of the variable cross-section
portions 225. At the centre of the link 110, there is a hollow,
constant depth portion 260, which adjoins the two variable
cross-section portions 225.
[0061] The thicknesses of the top 230 and bottom 235 walls of the
variable cross-section portion 225 is maintained constant. The
walls of the variable cross-section portion 225 and of the hollow,
constant depth portion 260 are designed, sized and otherwise
dimensioned to have adequate shear and axial strength for the
combined forces that could theoretically be applied within the
expected range of deformations in a typical eccentrically braced
frame structure. Additional details of this embodiment may be as
described with respect to the embodiment of FIGS. 1-3.
[0062] In other contemplated alternatives, the yielding segment of
the link may have cross-sections other than substantially
rectangular cross-sections as described in the previous
embodiments. The cross-section may be any shape or configuration
that has a variable, and preferably tapered, cross-section such
that flexural yielding along a substantial portion of the length of
the link is promoted. On example of this is shown in the embodiment
of FIGS. 10-12 where a link 300 has a primarily "I" shaped cross
section. The width w of the flanges 305 of the "I" shape varies
along the length of the link, thus providing for the variable
cross-section. The varying cross-section of the flanges 305 is
intended to promote yielding along most of the length of the
yielding segment of the link. In this embodiment the web 310 of the
"I" section is designed to have adequate shear and axial strength
for the combined forces that could be applied within the expected
range of deformations in a typical eccentrically braced frame
building. The thickness of the web 310 is tapered along the length
of the link such that at any section the yield moment matches the
applied bending moment (thereby resulting in distributed flexural
yielding) and the cross sectional area is constant (thereby
resulting in a uniform axial strain along the length).
[0063] Other variable cross-sections, and in particular tapered
cross-sections are also contemplated. Any of the above described
embodiments could be used in a variety of eccentrically braced
frame configurations (for example, the link in the centre of the
beam or the link at the beam column intersection) or in linked
column frame configurations. Other shapes and cross-sections are
known in the art, and to which the teachings of this invention in
respect of one or more of the variability of the cross-sections,
the hollow portion within the variable cross-section portion or the
solid centre portion having a constant cross-section may be applied
to prior art link cross-sectional shapes. This statement is not
intended to limit the invention to requiring each of the variable
cross-section portion, hollow portion within the variable
cross-section portion and the constant cross-section centre portion
in combination as essential features. Rather, the invention is only
limited by the claims that follow this description.
[0064] There are a number of means by which the link can be
connected to the other elements of the structural frame, be it the
eccentrically braced frame or a linked column frame. For example,
in the embodiment FIG. 1, the link 10 is shown at the centre of a
chevron-type eccentrically braced frame 5. The link 10 is connected
to the beams of the frame with a bolted end-plate type connection.
To accommodate this type of connection the ends of the yielding
segment of the link have large, vertically oriented plate elements
7 that bolt to corresponding end plates 3 on the ends of the beam
elements of the structural frame. This connection would be designed
to have the strength to resist the combination of bending moment,
shear and axial force that would be induced in the expected range
of deformations in a typical eccentrically braced frame building.
Another feature of this implementation would be a small, protruding
extension of the plate extending within the hollow of the yielding
segment, in order to increase the rigidity at the intersection of
the end plate and the yielding segment of the link 10, thereby
ensuring the deformations are isolated within the yielding segment
of the link.
[0065] The embodiment of FIG. 4 is also shown at the centre of a
chevron type eccentrically braced frame. This embodiment is
connected to the webs of the beams of the brace with a bolted shear
connection via plates 107.
[0066] The link 210 of FIG. 7 is shown at the beam column
intersection of a single brace eccentrically braced frame 205. The
link 210 is connected to the beam and the face of the column via a
welded connection. At the end of the yielding portion the walls 230
of the end portions 225 are made thicker than the walls 230, 235 in
the variable cross-section portion 225. This additional material
thickness is provided to ensure that yielding does not propagate to
the vicinity of the weld. The welded joint between the tapered
replaceable link and the end plate of the beam, or the face of the
column, can be achieved with fillet welds or groove welds, or other
weld details.
[0067] The embodiment of FIG. 10 is shown in a linked column frame
300 having columns 360 and 370 of adjacent column frames, which are
linked by the links 300. This embodiment is shown with a bolted end
plate type connection which would bolt to the faces of the two
columns in the system.
[0068] Other end connection configurations are possible but not
illustrated, provided the end connection is designed to resist the
combination of bending moment, shear and axial force that would be
induced in the expected range of deformations in a typical
eccentrically braced frame building, would not change the primary
function or behaviour of the replaceable link.
[0069] The various embodiments of the link as herein described may
be formed by casting, which provides a manner for creating the
optionally complex or higher order tapering of the variable
cross-section portion of the link of some embodiments. It is also
noteworthy that such casting processes permit for the hollow
portions, and variable thickness of certain walls as described
above, as the link can be manufactured to have complex or detailed
geometries both on the outer portions and within the hollow
portions as well, such as the varying wall thickness as described
in some embodiments above. Casting the link as a single body would
also eliminate the need to weld various plates together within the
yielding region. This would eliminate the potential for premature
fractures, which is a risk when welds are subjected to large
inelastic strain. Cast would also eliminate sharp geometric
transitions which could create undesirable stress concentrations in
the yielding region.
EXAMPLE
[0070] While linear tapered cross-sections are contemplated in the
variable cross-section portion of the link, as herein described,
there are additional advantages to providing a tapering which
follows a higher order function in defining segments of the
variable cross-section of the link. In order to implement the
variable cross-section link of FIGS. 1-3, and in particular with a
higher order function defining the tapering and variable
cross-section, applicant has contemplated one example of defining
the profile of the tapering width of the variable
cross-section.
[0071] Referring to FIG. 13, a profile of the link 1305 is derived
from the following derivation defining the profile of the tapering
of the width of the section, b(x), which considers the plastic
capacity of the flanges (top and bottom walls) of the box section
and ignores the any contribution from the webs of the box section
as being negligible. It is assumed that the link is deformed in
double curvature. The assumed applied shear on the link, V, is
combined with the length of the link to define applied moment at
any point, x, along the length of the link. The applied moment is
in turn used to define profile of the section. The generalized
profile of the tapering as a function of the applied shear, V,
yield strength of the material, F.sub.y, depth of the section, d,
and the tapering of the flange thickness, h(x), is presented in the
following equation:
b ( x ) = V ( L - 2 x ) 2 h ( x ) F y [ d - h ( x ) ]
##EQU00001##
[0072] In the particular embodiment of interest the thickness of
each flange, h(x), varies linearly from thick at the end to thin in
the middle of the yielding link. The equation describing the flange
thickness at any point, x, along the length of the yielding portion
of the link, is presented below as a function of the maximum flange
thickness, h.sub.max, minimum flange thickness, h.sub.min, and the
length of the yielding portion, L.sub.y:
h ( x ) = h max ( 1 - x L y ) + h min x L y ##EQU00002##
[0073] Substituting these two equations would give the specific
equation defining the width of the flange along the length of the
link between the connection end (x=0) to the inner end of the
yielding portion of the link (x=L.sub.y).
b ( x ) = V 2 F y .times. ( L - 2 x ) dh max - h max 2 + [ - dh max
+ dh min + 2 h max 2 - 2 h max h min ] ( x L y ) - [ h max - h min
] 2 ( x L y ) 2 ##EQU00003##
[0074] The side walls of the link include a ridge located at the
section's neutral axis which is proportioned such that the
cross-sectional area of the link at any location is the same
despite the tapering width of the link. The area of the external
flanges, A.sub.flanges(x), was determined based on the following
equation:
A.sub.flanges(x)=2[b(0)h.sub.max-b(x)h(x)]
[0075] In this particular embodiment the transition region between
the yielding portions and the end connections includes thickened
segments which limit the spread of plastic strain into the
connection region.
[0076] This is example is intended to show one way in which the
variable cross-section could be generated in accordance with the
principles set forth in this description, and is not intended to
limit the invention in any manner. As discussed earlier, the
variable cross-section portion could also be a linearly variable
profile or be defined by a lower order function that that described
in this example.
[0077] Various other modifications may be made or alternatives
implemented without departing from the invention, which is defined
solely by the claims that now follow.
* * * * *