EP2288753B1

EP2288753B1 - Bearings acting as energy dissipating devices

Info

Publication number: EP2288753B1
Application number: EP08749531.3A
Authority: EP
Inventors: Agostino Marioni
Original assignee: ALGA SpA
Current assignee: ALGA SpA
Priority date: 2008-04-09
Filing date: 2008-04-09
Publication date: 2016-03-30
Anticipated expiration: 2028-04-09
Also published as: WO2009124589A1; ES2571033T3; EP2288753A1

Description

The present invention relates to bearings acting as energy dissipating devices. An example of such a bearing may be found in US 4 617 769 A . They are employed particularly, but not exclusively, in structures impervious to seismic occurrences, as for example in bridges.
Pot or spherical bearings are frequently used for constructions such as bridges or the like. They comprise a bearing basement, a pressure pad arranged inside the bearing basement, a bearing cap which engages the inside of the bearing basement and is supported on the pressure pad. They are high resistant to horizontal actions. As for an example their capacity can be from 50 to 10,000 tons and more.
As for an example, pot bearings are sold by the Company ALGA under the commercial reference ALGAPOT. As for another example spherical bearings are sold by the company ALGA under the commercial reference ALGALINK SFERON.
Said pot or spherical bearings are suitable for transmitting in safety high horizontal loads but can not withstand alone to significant horizontal strains or displacements as it may occur when an earthquake happens.
Therefore energy dissipating devices have been developed for rendering a structure impervious to seismic occurrences. Said structures usually comprise dampers that are deformable in the elastic field or beyond the elastic limit thereby dissipating the deformation by hysteresis of the material of the damper, principally in form of heat.
Anti-seismic devices are of great importance for the strength of buildings and a European Standard draft has been drawn up by the Technical Committee CEN/TC340, "Anti-seismic devices", to deal with this matter and published in April 2007 under reference prEN15129.
This European standard covers the design of devices that are provided in structures with the aim of modifying their response to seismic action. It specifies functional requirements and general design rules in the seismic situation, material characteristics, manufacturing and testing requirements as well as acceptance, installation and maintenance criteria.
Hysteretic dampers are ruled by Chapter 6, Displacement Dependent Devices, of said European Standard draft.
Base isolators connected with hysteretic dampers have been disclosed in said document, namely in Annex J which gives examples of combined devices where for example a slider is combined with shock transmission units, or a slider is combined with tapered pin steel hysteretic elements, or a sliding guided pot bearing is combined with E-shaped hysteretic elements and shock transmission units.
Said last example corresponds to figure JJ.3 of said document and is appended in the present document as figure 1: this comprises the features of the preamble of claim 1 .
The hysteretic seismic isolator 1 of figure 1 comprises a pot bearing 2 combined with two E-shaped hysteretic dampers 3 and shock transmission units 4. The pot bearing 2 is arranged on a sliding surface of a sliding plate 5. Said pot bearing 2 is conformed so as to slide only along a groove 6 that forms a directional guide. The two external legs of the E-shaped dampers 3 are articulated with the plate 5 and the central legs of said dampers are articulated with the bearing pot 2.
This solution is used for example for base isolated continuous bridges connected to one abutment that require on the piers devices that shall be free to move longitudinally to compensate creep, shrinkage, temperature variation, but shall be able to move in a transverse direction in case of an earthquake, then deforming the dampers to dissipate energy.
It is also possible to use another close embodiment where a unidirectional hysteretic isolator comprises a pot bearing arranged on two stacked sliding plates and where the sliding plates are guided in perpendicular directions thanks to two orthogonal grooves. Two E-shaped dampers are part of said device, where the two external legs of said dampers are articulated to the plate on which the pot bearing can slide in one direction and the central legs are articulated to said pot bearing. One of the sliding plates allows a free movement whilst the other one provide a movement in a perpendicular direction in case of earthquake, thus deforming the dampers to dissipate energy.
Although preceding hysteretic seismic isolators are commonly used, drawbacks still exists, namely due to their costs.
It is an object of the present invention to solve the cost problem of seismic isolators and to provide a device with simplified parts arranged so as to decrease costs and possibly enhance the efficiency.
The previously mentioned problem is solved by a bearing acting as energy dissipating device according to claim 1.
The design of the bearing according to the invention is greatly simplified in comparison to the prior art devices because the sliding surface does not need to be machined to form a groove in it.
Furthermore each damper is articulated with the bearing upper part in only one point.
This allows an increased sliding freedom of the bearing upper part on the bearing upper part.
According to embodiments of the present invention, the following feature may be added and/or combined:

the dampers may deform essentially in a plane parallel to the plane (X, Y) when a shearing occurs between the bearing basement base and the bearing cap;

According to an embodiment of the present invention one extremity of each damper is hinged to the pressure pad. According to a non limitating example a corresponding pressure pad has a lower plane surface contacting the sliding surface of the bearing basement base and an upper surface corresponding to a hollow sphere part; an extremity of each damper is hinged to a protuberant part, as for example a flat protuberant part, comprising a hole and linked to the pressure pad; the bearing cap has a lower spherical surface which abuts against an upper surface of said pressure pad and a plane upper surface on which a structural part may lie on.
According to another embodiment of the present invention, one extremity of each damper is hinged to the bearing cap.
According to still another embodiment of the present invention, the bearing upper part also comprises a bearing wall which forms a bearing basement with the bearing basement base and where the pressure pad is mounted within said bearing basement, the bearing cap extends within said bearing basement and has a lower portion which abuts against the upper surface of the pressure pad, where the lower surface of the basement wall and the lower surface of the pressure pad can slidingly move on the sliding surface and where one extremity of each damper is hinged to the basement wall.
According to the last embodiment, the arrangement of the basement wall, the pressure pad and the bearing cap may be of different types:

according to an embodiment, the basement wall, the bearing cap and the pressure pad have a common rotation axis (Z), perpendicular to the plane (X, Y);
according to a further embodiment, said arrangement is configured so as the pressure pad is, at rest, a cylinder which axis is Z, Z being perpendicular to the plane (X, Y), with two surfaces substantially parallel to the plane (X, Y), the basement wall is a hollow cylinder which axis is Z and which inside surface is contacted by a least part of the cylindrical surface of the pressure pad and the lower surface of the pressure pad contacts the sliding surface of the bearing basement base. The pressure pad may consist of rubber. Said arrangement is comparable to a pot bearing, and for example can be close to a previously mentioned ALGAPOT pot bearing;
according to another further embodiment, said arrangement is configured so as the pressure pad has, at rest, a substantially spherical surface with Z as a symmetry axis and a plane surface where the substantially spherical surface contacts a spherical part of the lower portion of the bearing cap and the plane surface contacts the sliding surface of the bearing basement base. The pressure pad may consist of aluminium and for example comprises polished aluminium surface to provide low-friction rotation. Said arrangement is comparable to a spherical bearing, and for example can be close to a previously mentioned ALGALINK SFERON bearing;
although said both arrangements are preferred ones, other arrangements are possible.

According to an embodiment of the present invention the sliding surface of the bearing basement base is a combination of stainless steel and a sliding material such as PTFE.
According to an embodiment of the present invention the extremities of the dampers are hinged to the bearing upper part and to the bearing basement base thanks to cylindrical hinges.
According to another embodiment, the hinges are spherical.
According to an embodiment of the present invention, at rest, the lines incorporating the two hinging points of each damper are parallel one to another and to the X axis. These features are advantageous because it allows the bearing upper part to slide freely on the bearing basement base in the direction perpendicular to the X axis, thus the Y axis. The free slide along the Y axis is limited to plus/minus Y_max. Thus the displacement along the X axis of the bearing upper part leads to the deformation of the dampers and to energy dissipation, whereas the displacement along the Y axis up to +/- Y_max does not lead to the deformation of the dampers. Would the bearing upper part displaced further to + Y_max or - Y_min, then the dampers would deform and dissipate energy. According to this embodiment a unidirectional hysteretic seismic isolator is provided without the use of guides as previously disclosed.
According to an embodiment of the present invention, the number of dampers is even, as for example equal to two, and the extremities of the dampers hinged to the basement wall of a pair of said dampers are arranged in a plane parallel to the plane (X, Y) symmetrically to the axis Z.
The invention also relates to an anti-seismic device comprising at least one bearing according to the invention. Said device may comprise several bearings according to the invention, as for example mounted on a sole plate.
The invention also relates to a bridge comprising at least a pier and a bridge floor wherein at least a bearing according to the present invention or an anti-seismic device according to the present invention is arranged between at least a pier and the bridge floor.
According to an embodiment of the present invention, the plane (X, Y) of the bearings arranged in said bridge is a substantially horizontal plane.
According to an embodiment of the present invention, the bearings of the bridge are unidirectional hysteretic seismic isolators of the invention, as described above, and the X axis of each of said bearings are aligned.
Non limiting embodiments of the invention will now be described with reference to the accompanying drawings wherein:

figure 1 is a prior art hysteretic seismic isolator here above described;
figure 2 is a front view of a bearing acting as energy dissipating device, at rest, according to the present invention;
figure 3 is a top view of the bearing of figure 2, at rest (X = Y = 0) ;
figure 4 is a partial cross sectional view of the bearing of figures 2 and 3, according to line III-III;
figures 5.1 to 5.8 diagrammatically illustrate the cinematic of the bearing of the figures 2 to 4 when displacements occur in the plane (X, Y).

Skilled artisans 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 improve the understanding of the embodiments of the present invention. The same numeral references in the different figures correspond to a same part. The wordings "upper" and "bottom" or "lower" indicate positions relative to parts as drawn in a diagram where the bearing basement base is placed in a horizontal position as shown in figures 2 and 4.
The bearing 10 acting as energy dissipating device of figures 2 to 5 includes a bearing basement 20 + 30 which comprises a base 20 and a wall 30. According to said embodiment the base 20 is a horizontal plate comprising a sliding surface 25. Said plate can be arranged on bridge piers thanks to pins 90. According to the present non limiting embodiment, the bearing basement wall 30 is a hollow cylinder which axis of symmetry is, at rest, the Z axis. Said wall 30 has a lower plane surface 35 which may slide on the sliding surface 25.
A pressure pad 50, as for example made of aluminium, is mounted within the bearing basement 20 + 30. The lower surface 55 of the pressure pad 50 may slide on the sliding surface 25.
According to the present non limiting embodiment the pressure pad 50 is a part of a sphere where its upper surface 52 is spherical and its lower surface comprises an annular planar surface 55. Said pressure pad 50 has, at rest, a rotation axis Z. The lower part of the pressure pad has a recess to hold a suitable sliding material, such as for example PTFE. A bearing cap 40 extends within the bearing basement 20 + 30 and has a lower portion 42 which abuts against an upper surface 52 of the pressure pad 50. Said bearing cap 40 has, at rest, a rotation axis Z. According to the present non limiting embodiment, the lower surface of the bearing cap 40 is cylindrical.
The bearing cap 40 has an annular portion 44 which transfers the horizontal load to the bearing basement wall 30, allowing relative rotation of said two parts.
The upper surface 46 of the bearing cap 40 is intended to receive a structural part of a construction, such as for example a concrete beam of a bridge floor. An upper pin 45 is provided to maintain said structural part in a corresponding hole. Other anchorage means are possible, such as connection of the bearing cap with a structural part thanks to cementitious or epoxy mortar, or to connecting bolts.
According to said embodiment, the bearing upper part comprises the bearing basement wall 30, the pressure pad 50 and the bearing cap 40.
According to the present non limiting embodiment two dampers 100 are provided. Said dampers are C-shaped metallic rods with two flattened extremities 105.
Each extremity 105 comprises a hole 107.
A first extremity of said dampers is hinged to a flat protuberant part 38 of the bearing basement wall 30, thanks to a cylindrical hinge 60.
The second extremity of said dampers is hinged to the bearing basement base 20 thanks to a cylindrical hinge 70.
Said cylindrical hinge 70 comprises an annular part 72 welded on the bearing basement base 20 thanks to a welding bead 80. It further comprises a screw 74, which lower part is screwed in said annular part 72 and which upper part comprises a threading. The corresponding extremity 105 of the damper 100 is arranged so as internal surface of the hole 107 may contact the external surface of the screw 74 and be free to rotate.
A bearing 76 is placed on the top of the screw 74 and of said extremity 105 of the damper 100 to let the damper 100 rotate around the axis of the cylindrical hinge 70.
A cylindrical plate 78 is placed on said bearing 76 and a screw 75 is placed on said plate 78 and screwed in the threading of the screw 74.
According to said embodiment, the dampers 100 may deform essentially in a plane parallel to the plane (X, Y) when a shearing occurs between the bearing basement base 20 and the bearing cap 40.
According to said embodiment the two lines incorporating the two hinging points (center of 60 and center of 70) of a damper are parallel one to another and parallel to the X axis. The extremities 105 hinged to the basement wall 30 thanks to the flat protuberant parts 38 are arranged symmetrically to the axis Z in the (X, Y) plane. The angle θ is about 150°.
The cinematic of a bearing 10 acting as energy dissipative device of figures 2 to 4 is exemplified on figures 5.
The configuration at rest of said bearing 10 is illustrated on figure 3, where X = Y = 0.

The positions of the axis of the bearing basement wall, 30, according to the figures 5, are reported in Table I. Said axis may move between +/- X_max and +/- Y_max. The X_max value is limited, for example by the maximum displacement along the X axis before the bearing basement wall 30 contacts the damper extremity hinged thanks to the hinge 70.

TABLE I

	X	Y
Figure 5.1	0	Y_max
Figure 5.2	0	- Y_max
Figure 5.3	X_max	0
Figure 5.4	- X _max	0
Figure 5.5	X_max	Y_max
Figure 5.6	- X_max	Y_max
Figure 5.7	X_max	- Y_max
Figure 5.8	- X_max	- Y_max

The Y_max value corresponds to the maximum displacement along the Y axis that the bearing basement wall 30 can do before the dampers 100 being deformed. The bearing basement wall 30 may slide further to + Y_max or - Y_max, but if it does the dampers 100 will deform and dissipate energy.
Thus the dampers 100 of figures 5.1 and 5.2 do not deform and the bearing basement wall 30 can freely slide on the bearing basement base 20. The bearing 10 can thus accommodate freely strains between the bearing cap 40 and the bearing basement base 20 along the Y axis.
When strains occurs that would lead the axis of the bearing basement wall 30 to slide in the X axis direction, the dampers 100 deform and act to dissipate energy as shown on figures 5.3 to 5.8.
The bearing 10 acting as energy dissipating device of figures 2 to 5 acts thus as a unidirectional hysteretic seismic isolator without the use of guides as in the prior art of figure 1.
Said bearing 10 is greatly simplified compared to the bearing 1 of figure 1 and the cost of said bearing 10 may be significantly reduced.
According to an example of the bearing 10 acting as energy dissipating device of the invention:

the supported vertical load is 12 000 kN,
the horizontal load at yield of the hysteretic damper 100 is 800 kN,
the free longitudinal movement is +/- 500 mm,
the transversal movement under earthquake is +/- 150 mm,
the overall dimension in plan (X, Y) of the bearing 10 is 1100 mm.

The invention has been described above with the aid of embodiments without limitation of the general inventive concept which appears from the claims.

Claims

A bearing (10) acting as energy dissipating device which includes a bearing basement base (20) parallel to a plane (X, Y) and a bearing upper part comprising a pressure pad (50) and a bearing cap (40) which abuts against an upper surface (52) of the pressure pad (50) characterised in that the upper part comprises a lower surface (35, 55) parallel to the plane (X, Y) that can slidingly move in all directions on a sliding surface (25) of the bearing basement base (20) and where said bearing (10) includes two C-shaped metallic dampers (100) having two extremities (105), one extremity being hinged to the bearing upper part and the other extremity being hinged to the bearing basement base (20), the dampers being geometrically so arranged that they define a segment ([-Y_max; Y_max]) of a first direction (Y) of said plane (X, Y) along which the bearing upper part is adapted to slide without causing a deformation of the dampers whereas a slide of the bearing upper part along a second direction (X) of said plane (X, Y) and perpendicular to the first direction causes a deformation of the dampers.
The bearing of preceding claim wherein the dampers (100) may deform essentially in a plane parallel to the plane (X, Y) when a shearing occurs between the bearing basement base (20) and the bearing upper part.
The bearing of any of preceding claims wherein one extremity of each damper (100) is hinged to the pressure pad.
The bearing of claim 1 or 2 wherein one extremity of each damper (100) is hinged to the bearing cap.
The bearing of claim 1 or 2 wherein the bearing upper part also comprises a bearing wall (30) which forms a bearing basement (20 + 30) with the bearing basement base (20) and where the pressure pad (50) is mounted within said bearing basement (20 + 30), the bearing cap (40) extends within said bearing basement (20 +30) and has a lower portion (42) which abuts against the upper surface (52) of the pressure pad (50), where the lower surface (35) of the basement wall (30) and the lower surface (55) of the pressure pad (50) can slidingly move on the sliding surface (25) and where one extremity of each damper (100) is hinged to the basement wall (30).
The bearing of claim 5 wherein the basement wall (20), the bearing cap (40) and the pressure pad (50) have a common rotation axis (Z), perpendicular to the plane (X, Y).
The bearing of claim 6 wherein the pressure pad is, at rest, a cylinder which axis is Z, with two surfaces substantially parallel to the plane (X, Y), the basement wall is a hollow cylinder which axis is Z and which inside surface is contacted by a least part of the cylindrical surface of the pressure pad and the lower surface of the pressure pad contacts the sliding surface of the bearing basement base.
The bearing of claim 6 wherein the pressure pad (50) has, at rest, a substantially spherical surface (52) with Z as a symmetry axis and a plane surface (55), where the substantially spherical surface (52) contacts a spherical part of the lower portion (42) of the bearing cap (40) and the plane surface (55) contacts the sliding surface (25) of the bearing base (20).
The bearing of any of preceding claims wherein the extremities (105) of the dampers (100) are hinged to the bearing upper part and to the bearing basement base thanks to cylindrical hinges (70).
The bearing of any of preceding claims wherein, at rest, the lines incorporating the two hinging points of each damper (100) are parallel one to another and to the X axis.
The bearing of any of preceding claims wherein the number of dampers (100) is even, as for example equal to two, and wherein the extremities (105) hinged to the bearing upper part of a pair of said dampers are arranged in a plane parallel to the plane (X, Y) symmetrically to the axis Z.
An anti-seismic device comprising at least one bearing according to any of preceding claims.
A bridge comprising at least a pier and a bridge floor wherein at least a bearing according to any of claims 1 to 11 or an anti-seismic device of claim 12 is arranged between at least a pier and the bridge floor.
The bridge of claim 13 comprising a plurality of bearings (10) which each incorporate the features of claim 10 and wherein the X axis of each of the bearings are aligned.