U.S. patent application number 13/985425 was filed with the patent office on 2014-01-30 for antiseismic support.
This patent application is currently assigned to POLITECNICO DI MILANO. The applicant listed for this patent is Daniele Cuminetti, Paolo Dubini, Daniela Ferroni, Riccardo Motta, Virginio Quaglini. Invention is credited to Daniele Cuminetti, Paolo Dubini, Daniela Ferroni, Riccardo Motta, Virginio Quaglini.
Application Number | 20140026498 13/985425 |
Document ID | / |
Family ID | 43976162 |
Filed Date | 2014-01-30 |
United States Patent
Application |
20140026498 |
Kind Code |
A1 |
Quaglini; Virginio ; et
al. |
January 30, 2014 |
ANTISEISMIC SUPPORT
Abstract
The present invention concerns an anti-seismic support for
supporting a construction engineering structure, which comprises a
support (14) having a concave sliding surface (17) and a sliding
block (16) with a convex sliding surface (16d) in sliding contact
with the concave sliding surface (17), the sliding block (16) being
capable of sliding with pendulum motion relative to the concave
surface (17) in response to an earthquake tremor or shock, the
device (11) comprising a sliding material (19) between the concave
sliding surface (17) and the convex sliding surface (16b), where
the friction coefficient between the sliding surfaces (16b, 17) is
above 10% when the device (11) is loaded with a pressure above 30
MPa and the sliding surfaces are caused to slide at a sliding speed
of more than 50 mm/s at a temperature of 20.degree. C. or more.
Inventors: |
Quaglini; Virginio; (Milan,
IT) ; Cuminetti; Daniele; (Milan, IT) ;
Dubini; Paolo; (Milano, IT) ; Motta; Riccardo;
(Milano, IT) ; Ferroni; Daniela; (Milano,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Quaglini; Virginio
Cuminetti; Daniele
Dubini; Paolo
Motta; Riccardo
Ferroni; Daniela |
Milan
Milan
Milano
Milano
Milano |
|
IT
IT
IT
IT
IT |
|
|
Assignee: |
POLITECNICO DI MILANO
Milan MI
IT
|
Family ID: |
43976162 |
Appl. No.: |
13/985425 |
Filed: |
February 20, 2012 |
PCT Filed: |
February 20, 2012 |
PCT NO: |
PCT/IB12/50749 |
371 Date: |
October 14, 2013 |
Current U.S.
Class: |
52/167.4 |
Current CPC
Class: |
E01D 19/046 20130101;
E04H 9/021 20130101 |
Class at
Publication: |
52/167.4 |
International
Class: |
E04H 9/02 20060101
E04H009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 21, 2011 |
IT |
MI2011A000257 |
Claims
1. An antiseismic device (11) for supporting a civil or
construction engineering structure, said device (11) comprising a
first support (14) having a concave sliding surface (17) and a
sliding block (16) having a convex sliding surface (16d) in sliding
contact with said concave surface (17), wherein said sliding block
(16) is capable of sliding with pendulum motion relative to said
concave sliding surface (17) in response to an earthquake tremor or
shock, the device (11) comprising a sliding material (19) that
forms one of: said concave sliding surface (17) and said convex
sliding surface (16b), wherein the coefficient of friction between
said sliding surfaces (16b, 17) is above 9% when the average
pressure between said sliding surfaces (16b, 17) is 30 MPa or more
and the sliding surfaces (16b, 17) are caused to slide at a sliding
speed of 50 mm/s or more at a temperature of 20.degree. C. or more,
said sliding material (19) comprising a polymeric material filled
with a polymeric, synthetic, ceramic or metal filler, wherein if
the the sliding material (19) undergoes the test defined by the
Standard EN15129:2009, Section 8.3.1.2.5 for antiseismic bearing
devices for buildings or the test defined by the US Standard
"AASHTO LRFD Bridge Design Specification", Section 15.10.1.2, it
exhibits less than 1.0 mm thickness reduction at the end of the
test.
2. A device (11) as claimed in claim 1, wherein said polymeric
material is PTFE.
3. A device (11) as claimed in claim 1, characterized in that the
filler is a metal only filler and comprises bronze.
4. A device (11) as claimed in claim 3, wherein the metal filler
comprises bronze only.
5. A device (11) as claimed in claim 1, wherein the metal filler is
from 30% to 60% by weight of said sliding material (19).
6. A device (11) as claimed in claim 1, wherein the sliding
material (19) has a thermal conductivity of more than 0.50
W/m*K.
7. A device (11) as claimed in claim 1, wherein friction between
said sliding surfaces (16b, 17) is less than 7%, when the mutual
sliding speed of the sliding surfaces (16, 17) is less than 10 mm/s
and the contact pressure between the sliding surfaces (16b, 17)
applied to the device (11) is at least 20 MPa.
8. A device (11) as claimed in claim 1, wherein in an oscillation
test of said device (11) in which the sliding speed between said
sliding block (16) and said first support (14) is at least 200
mm/s, the oscillation amplitude is at least 70% of the maximum
admissible oscillation permitted by the device (11) and the nominal
load is applied, during the third oscillation cycle the coefficient
of friction between the concave and convex sliding surfaces (16b,
17) of the device (11) is 10% or more.
9. A device (11) as claimed in claim 1, wherein in an oscillation
test of said device (11) in which the sliding speed between said
sliding block (16) and said first support (14) is at least 400
mm/s, the oscillation amplitude is at least 70% of the maximum
admissible oscillation permitted by the device (11) and the nominal
load is applied, during the third oscillation cycle the coefficient
of friction between the concave and convex sliding surfaces (16b,
17) of the device (11) is 10% or more.
10. A device (11) as claimed in claim 1, wherein the sliding
material (19) is mounted to the sliding block (16) either as a
sheet partially embedded in a corresponding seat formed on the
sliding block (16), or as a sheet applied using an adhesive or
mechanical fastening means and forms the convex sliding surface
(16b) of the sliding block (16).
11. A device (11) as claimed in claim 1, wherein the sliding
material (19) has a softening temperature above 250.degree. C.
Description
[0001] The present invention relates to an antiseismic support for
supporting civil or construction engineering structures, namely
including bridges.
[0002] Either term "civil engineering structure" or "construction
engineering structure" is used herein to designate civil
engineering structures such as buildings or bridges, but also silos
and tanks.
[0003] Antiseismic support devices are known in the art, which are
designed to be installed between the foundation of a civil
engineering structure (such as a building or a bridge) and the
structure itself, to protect it from an earthquake tremor or
shock.
[0004] "Pendulum" devices, like the one known from U.S. Pat. No.
4,644,714, are among the devices that accomplish this task: this
anti-seismic support comprises a lower support and an upper
support, which are joined to the structure to be supported and the
foundations of the structure respectively.
[0005] Both supports have a respective concave sliding surface and
are separated from each other by a slider. The slider has two
convex surfaces mating and in contact with the concave surfaces of
the upper and lower supports, to form a ball joint.
[0006] In the event of an earthquake tremor or shock, the slider
can slide with a pendulum motion relative to the first support,
thereby protecting the overlying structure from the effects of the
earthquake.
[0007] The sliding surface of the slider in contact with the
concave sliding surface of the first support is usually coated with
a sliding material to facilitate mutual sliding of the
surfaces.
[0008] As is known in the art, a composite material comprising PTFE
with carbon fibers or glass fibers is used as a sliding material.
The sliding material has a high friction coefficient, up to 20%,
which allow dissipation of a large amount of energy during rocking,
following an earthquake tremor or shock.
[0009] Nevertheless, these devices do not have an adequate wear
resistance and for this reason are not suitable for use in
supporting structures (such as bridges) that are subject to
continuous and frequent in-service movements even when no
earthquake occurs, e.g. due to thermal expansion, wind action, or
to a sudden change of the load supported by the structure.
[0010] In another prior art, according to EP 1 836 404, pendulum
anti-seismic bearing devices have been provided, which use a
different type of sliding material.
[0011] Particularly, according to EP 1 836 404, the sliding
material may be unfilled hard PTFE or UHMWPE. These materials
exhibit a high wear resistance, and a relatively low friction
coefficient, which allows them to accommodate the in-service
movements of structure, but prevents them from dissipating large
amounts of energy, as might be required in the case of a high
intensity earthquake.
[0012] In order to use the devices as disclosed in EP 1 836 404 in
highly seismic areas, it was proposed to apply viscous dampers to
the devices, for dissipating the high energy developed in the event
of a strong earthquake shock. This increases the dimensions and
costs of the device, due to the parts required in addition to those
conventionally used in this kind of supports.
[0013] A further drawback of prior art sliding materials is their
fast mechanical degradation due to the heat dissipated during the
earthquake: at high slip velocities, such as those generated by a
high-intensity earthquakes, high friction coefficient and extended
seismic excitation, the relative sliding motion of the slider
surfaces generates huge amounts of heat, causing fast degradation
of the properties of the sliding material.
[0014] Therefore, it would be desirable to provide an anti-seismic
support that is less exposed to degradation caused by the heat
generated by the sliding movement of the slider, while still
allowing heat generation by friction, i.e. dissipation of the
energy transmitted by the earthquake to the structure.
[0015] In the light of the above prior art, the object of the
present invention is to provide an anti-seismic support that can
solve the above mentioned prior art drawbacks.
[0016] Particularly, one object of the invention is to provide an
anti-seismic support that can be used to support bridges, e.g. road
or railroad bridges, and can withstand high-intensity and
long-lasting earthquakes.
[0017] A further object of the invention is to provide an
anti-seismic support that is not too large, has a simple structure
with a small number of parts and is reliable with time.
[0018] According to the present invention, these objects are
fulfilled by a device as defined in claim 1.
[0019] The features and advantages of the present invention will
become more apparent from the following detailed description of one
practical embodiment, which is given as a non-limiting example with
reference to the annexed drawings, in which:
[0020] FIG. 1 shows a sectional view of an anti-seismic support of
the invention;
[0021] FIG. 2 shows an enlargement of the sectional view of FIG.
1.
[0022] FIG. 1 shows an anti-seismic support 11 which is designed to
be installed among the foundations 13 of a construction engineering
structure, and the construction engineering structure 12
itself.
[0023] The anti-seismic support 11 is used to support the
construction engineering structure and protect it in the event of
an earthquake.
[0024] The construction engineering structure 12 may be a bridge,
e.g. a road or railroad bridge. Nevertheless, the bearing device 11
may be also employed to support buildings or other constructions,
such as silos and tanks.
[0025] The anti-seismic support 11 comprises an upper support 14
(or first support 14) having a concave sliding surface 17, and a
sliding block 16 in sliding contact with the sliding surface
17.
[0026] The sliding block 16 has a convex sliding surface 16b, which
contacts the concave sliding surface 17 of the upper support
14.
[0027] The sliding block 16 further comprises a convex joint
surface 20, facing away from the convex sliding surface 16b, which
is adapted to contact a corresponding concave joint surface 21,
formed in a second support 15.
[0028] In the figures, the second support 15 is located below the
sliding block 16 and will be mentioned hereinbelow as "lower
support 15".
[0029] Thus, the anti-seismic support 11 actually comprises two
supports 15, 14, which are separated by the sliding block 16. An
articulation joint is formed between the sliding block and one of
the two supports 15, 14 (15 in FIG. 1), and a slip joint is formed
between the sliding block 16 and the other of the two supports (14
in FIG. 1), to absorb earthquake-induced movements.
[0030] Obviously, while reference is expressly made in the drawings
and the description to a single configuration (with the
articulation joint below the sliding surface), the kinematically
opposite configuration (with the articulation joint above the
sliding surface) is possible and technically equivalent, and shall
be deemed to be implicitly disclosed herein.
[0031] Likewise, the configuration as shown in FIGS. 2a and 2b of
patent EP 1 806 404, in which the pendulum anti-seismic support
comprises two slip interfaces, instead of a slip interface and an
articulation joint, is also deemed to be incorporated herein by
reference.
[0032] Therefore, if the anti-seismic support comprises two slip
interfaces, the considerations relating to the slip interface of
the present invention shall be deemed to be equally applicable to
both interfaces of the anti-seismic support.
[0033] Preferably, the convex sliding surface 16b and the concave
sliding surface 17 have mating curvatures, to allow a pendulum
motion of this kind of devices 11; for instance, they may have a
spherical shape and hence have the same radius of curvature;
alternatively, other configurations may be envisaged, in which at
least one of the two surfaces has a variable radius of curvature,
for improved centering of the sliding block 16.
[0034] The upper support 14 is preferably in the form of a plate
and is preferably integrally joined, by known fastening means, to a
construction engineering structure to be supported. The upper
support 14 is preferably made of steel, but may be also made of
aluminum or another material.
[0035] During an earthquake tremor or shock, the sliding block 16
is adapted to slide along the concave sliding surface 17 with a
pendulum motion.
[0036] In the figures, the sliding block 16 is shown in its
equilibrium position, i.e. centered relative to the concave sliding
surface 17. The sliding block 16 is in this equilibrium position
before the earthquake and, depending on the interaction of certain
factors, including the type of earthquake, it can recover it at the
end of the earthquake.
[0037] The bearing device 11 comprises a sliding material 19 that
forms the concave sliding surface 17 of the upper support 14 or the
convex sliding surface 16b of the sliding block 16.
[0038] Advantageously, the sliding material 19 may be applied to
the sliding block 16 or the upper support 14 and may be placed in a
matingly shaped seat formed in the sliding block 16 or the upper
support 14. Advantageously, the sliding material has a thickness
(e.g. a constant thickness) greater than the depth (e.g. a constant
depth) of the seat in which it is embedded, thereby projecting out
of it.
[0039] Alternatively, the sliding material 19 may be applied to the
sliding block 16 or the upper support 14 using adhesives or
mechanical fastener means, such as screws and/or rivets; in this
case, the seat may be omitted.
[0040] Preferably, the sliding material 19 is applied to the
sliding block 16 and forms the convex sliding surface 16b of the
sliding block 16. The sliding material 19 may be in the form of a
sheet of material, e.g. having the thickness of a few
millimeters.
[0041] The sliding material 19 may include a polymeric material
with a polymeric, synthetic, ceramic or metal filler, carbon fiber
or glass fiber fillers being excluded from such alternatives.
[0042] The sliding material 19 has a relatively high friction
coefficient at velocities higher than those typically associated
with in-service movements, e.g. movements that displace the
elements fixed to the anti-seismic support 11 due to thermal
expansion, wind action or variable loads acting upon the surface,
or to viscous shrinkage of concrete. The concave sliding surface 17
of the upper support 14 and the convex sliding surface 16b of the
sliding block 16 may slide one upon the other with 9% friction or
more, or preferably 10% friction or more, if the device 11 has such
a load thereon that an average pressure (defined as the ratio of
the vertical load on the device to the projection area on a flat
surface of the curved contact surface of the convex sliding surface
16b of the sliding block 16 and the concave sliding surface 17 of
the upper support 14), of 30 MPa exists between the surfaces, with
a mutual sliding velocity of 50 mm/s or more.
[0043] Therefore, the bearing device 11 is adapted to dissipate a
large amount of energy, due to its high friction in case of
relatively high slip velocities, similar to those occurring in the
event of a high-intensity earthquake.
[0044] Furthermore, the sliding material has a high thermal
conductivity, of 0.50 W/m*K or more.
[0045] This relatively high thermal conductivity value allows fast
removal of heat from the contact surface of the sliding block 16
and the upper support 14. In fact, the earthquake energy is
dissipated and converted into thermal energy at the interface
between the convex sliding surface 16b of the sliding block 16 and
the concave sliding surface 17 of the upper support 14. In the
polymer materials that are typically used as a sliding material 19
in the prior art, thermal conductivity is much lower than 0.50
W/m*K. This prevented efficient removal of heat from the contact
surface and created peak temperatures in the sliding material 19,
possibly degrading the mechanical properties of the material. These
degradation effects may include softening of the sliding material
19, which affects its load withstanding capacity and/or reduction
of the friction coefficient of the polymer material, leading to a
reduced earthquake energy dissipation capacity and reduced
performances of the anti-seismic support.
[0046] The sliding material 19 as used in this invention is adapted
to support high heat generation on the sliding surfaces as compared
with prior art materials.
[0047] In the case of the present invention, the seismic isolation
device is characterized in that it uses, as a sliding material 19,
a material having a high thermal conductivity, which allows
temperature increase to be limited at the convex sliding surface
16b of the sliding block 16 and the concave sliding surface 17 of
the upper support 14.
[0048] Preferably, the thermal conductivity of the sliding material
is higher than 0.60 W/m*K, more preferably higher than 0.70 W/m*K,
and or lower than 0.90 W/m*K.
[0049] The sliding material 19 that is used in the device 11 also
has a high wear resistance.
[0050] Particularly, the properties of the sliding materials 19
typically undergo the wear test as set forth in EN 15129:2009 for
buildings, Paragraph 8.3.1.2.5 and or the US standard "AASHTO LRFD
Bridge Design Specification", Paragraph 15.10.1.2.
[0051] Therefore, the anti-seismic device 11 is adapted to also
withstand low-velocity movements, such as those that may occur when
the device 11 is installed in a structure that is required to
accommodate displacements (in-service movements) of the elements
fixed to the anti-seismic device 11 during its life, such as
bridges.
[0052] For instance, in-service movements in bridges may be caused
by vibrations due to heavy loads or by thermal expansion and may
lead to particularly long slip distances during the life of the
bridge.
[0053] Preferably, a wear test on the sliding material 19 in which
the sliding material 19 has a height of at least 2.0 mm from the
plane from which it projects (if it is inserted in an embedded
seat) or from the plane on which it is applied (if it is not
inserted in an embedded seat), with the application of pressure
ranging from 75% to 110% of the design pressure, and at a
temperature of 20.degree. C. +8.degree. C. and a velocity of 1 mm/s
or more, with a sliding distance of at least 1000 meters, results
in the sliding material 19 having its thickness reduced by less
than 1.0 mm.
[0054] Preferably, subject to the above specification of less than
1.0 mm thickness reduction, the sliding material 19 meets the life
test of EN15129:2009 for use in buildings, even in a variant
involving a sliding distance of more than 1000 m, more preferably a
sliding distance of 1600 m or more.
[0055] Preferably, the sliding material 19 comprises PTFE, more
preferably the polymer material of the sliding material 19 is
substantially or exclusively PTFE.
[0056] The use of PTFE as a polymer material affords a relatively
low friction coefficient at low slip velocities.
[0057] For instance, in friction tests with slip velocities of less
than 10 mm/s and with the device 11 loaded with the design load,
the friction developed due to the relative sliding motion of the
concave sliding surface 16b of the sliding block 16 and the concave
sliding surface 17 of the upper support 14 is less than 7%.
[0058] This allows accommodation of low-velocity in-service
movements, as possibly required by the structure, such as those
caused by wind, thermal expansion, sudden load changes on the
structure and viscous shrinkage of concrete.
[0059] Preferably, a filler, for instance a metal filler, for
instance in powder form is added to PTFE; for example, the filler
may be bronze powder.
[0060] Preferably, the metal filler is from 30% to 60%, more
preferably from 40% to 50% by weight. In a preferred embodiment,
the metal filler is about 45% by weight.
[0061] The presence of such amount of metal increases the thermal
conductivity of the sliding material 19 as compared with the normal
conductivity values that can be found in prior art polymer
materials.
[0062] In the preferred embodiment, in which PTFE is filled with
45% bronze powder, thermal conductivity is higher than 0.7 W/m*K,
and is preferably about 0.7 to 0.9 W/m*K.
[0063] Preferably, the sliding material is sintered and/or formed
into a sheet by compression molding. After molding, the sheet
material is processed to the desired thickness.
[0064] Preferably, the sliding material 19 as used in the device 11
has a thickness of about 8 mm and projects out of the sliding block
16 by about 3 mm, with about 5 mm thereof being embedded in the
sliding block 16.
[0065] The sliding block 16 of the figures has a sliding block body
16a, with a seat formed therein for receiving the sliding material
19. The seat is formed on a surface of the sliding block body 16a
which faces towards the concave sliding surface 17 of the upper
support 14. The sliding block body 16a is advantageously made of a
metal material, such as steel or an aluminum alloy.
[0066] As an alternative configuration, the sliding material 19 may
be applied to the surface of the sliding block 16 in contact with
the convex sliding surface 17 of the upper sliding block 14 by
adhesives or mechanical fastener means such as screws and/or
rivets.
[0067] The sliding block body 16a has a second convex surface 20,
facing away from the one on which the sliding material 19 is
applied. The surface 20 of the sliding block body 16a preferably
has a spherical shape. The sliding block 16 is rotatably coupled to
the lower support 15, thereby forming a ball joint. Particularly,
its convex surface 20 is received in a spherical concavity formed
in the lower support 15.
[0068] Preferably, the surface 20 lies on a layer of sliding
material 21, which is mounted on the lower support 15. Preferably,
the sliding material 21 consists of a highly-running sheet
material, i.e. having a low friction coefficient. For instance, the
sliding material 21 may be made from an appropriate known polymer
material having a friction coefficient of less than 7%. This joint
material may be suitably lubricated with lubricants known in the
art, to further reduce its friction coefficient.
[0069] Advantageously, in an oscillation test conducted with the
sliding block 16 and the upper support 14 moving at a relative
velocity of about 200 mm/s, or about 400 mm/s, with at least 70% of
the maximum oscillation amplitude admitted by the device 11 and
with a nominal load applied thereto, after three oscillation cycles
the friction coefficient between the concave sliding surface 17 and
the convex sliding surface 16b (i.e. those with the sliding
material 19 interposed therebetween) of the device 11 is 9% or
more, preferably 10% or more.
[0070] Advantageously, the sliding material 19 maintains a bearing
capacity of at least 30 MPa when it reaches a temperature of
200.degree. C.
[0071] The bearing capacity may be assessed, for instance, by a
compression test conducted on a 155 m diameter disk of sliding
material 19, with the method described in "Structural Bearings", by
H. Eggert and W. Kauschle, 2002, in which such 8 mm thick disk is
partially embedded in a metal support through 5 mm of its thickness
and subjected to constant pressure for 48 hours.
[0072] The bearing capacity is the pressure value at which the
deformation of the sliding material 19 under load stops within 48
hours and the height of the disk of sliding material 19 is reduced
by less than 2.0 mm.
[0073] Alternatively, the assessment may be based on the amount of
warping of the sliding material 19, which should be, for instance,
smaller than 6%, preferably smaller than 4%, e.g. smaller than 2%
of its maximum plan size, at the end of the third cycle of the
oscillation test as defined above, when conducted at a velocity of
200 mm/s or at a velocity of 400 mm/s.
[0074] Furthermore, the sliding material 19 preferably has a
softening temperature higher than 250.degree. C.
[0075] The above clearly shows that the objects of the present
invention have been fulfilled.
[0076] The anti-seismic support can provide earthquake protection
to structures like bridges, which must accommodate considerable
in-service sliding movements even when no earthquake occurs. In
fact, the anti-seismic support ensures high resistance to the wear
caused by mutual slipping of sliding surfaces.
[0077] The anti-seismic support is designed to withstand
high-intensity and long-lasting earthquakes, because the high
friction coefficients of the sliding surfaces allows dissipation of
a large amount of energy.
[0078] The anti-seismic device is reliable over time, even during a
high-intensity and long-lasting earthquake, as it can adequately
dissipate the thermal energy generated by friction, due to the high
thermal conductivity of the sliding material 11, which prevents the
temperature increase at the interface between the convex sliding
surface 16b of the sliding block 16 and the concave sliding block
17 of the upper support 14 from causing the sliding surface 11 to
soften and thus lead to a considerable reduction of its friction
coefficient.
[0079] Furthermore, the anti-seismic device has a relatively low
friction at a low slip velocity, which allows optimized
accommodation of in-service movements possibly required by the
construction engineering structure.
[0080] The sliding material also has a good weather resistance,
with very little or no moisture absorption.
[0081] Those skilled in the art will obviously appreciate that a
number of changes and variants may be made to the arrangements as
described hereinbefore to meet incidental and specific needs,
without departure from the scope of the invention, as defined in
the following claims.
[0082] The preferred embodiment of the invention as disclosed
herein is a device having spherical sliding surfaces, and symmetric
with respect to a vertical axis, in operation. Nevertheless it
shall be understood that, in a variant, the bearing device might
also have cylindrical sliding surfaces, with a substantially
horizontal axis of symmetry, in operation.
* * * * *