WO2013021349A1

WO2013021349A1 - Seismic-energy dissipator

Info

Publication number: WO2013021349A1
Application number: PCT/IB2012/054028
Authority: WO
Inventors: Walter Salvatore; Aurelio BRACONI
Original assignee: Università Di Pisa; Ilva S.P.A.
Priority date: 2011-08-08
Filing date: 2012-08-07
Publication date: 2013-02-14
Also published as: ITRM20110428A1

Abstract

Seismic-energy dissipator comprising an external carter; a frame housed inside said carter, configured to slide therealong and comprising a free end apt to be connected to an external structure; a pair of opposing elements arranged at opposite ends of the frame, said carter comprising, at each opposing element, a respective stopping abutment arranged so as to stop the sliding thereof toward the inside of the carter, said opposing elements being connected to said frame by respective dissipating elements; a pair of re-centering cables each having ends anchored to said pair of opposing elements.

Description

SEISMIC-ENERGY DISSIPATOR

DESCRIPTION

The present invention relates to a seismic-energy dissipator, for the seismic retrofitting of existing structures or the designing of new structures.

In general, seismic-energy dissipators of hysteretic type are devices that are mounted on structures to be protected in a seismic field; said devices are able to absorb and dissipate s eism-generated energy, preventing said energy from being transferred to the structure itself, damaging it.

Seismic-energy dissipators existing and commonly used today entail significant and evident drawbacks.

In particular, they have geometries and configurations such as not to guarantee structure re-centering at the end of the seismic event, decreasing structure safety towards subsequent shocks. Moreover, such a circumstance makes the replacing of dissipative elements less than easy, due to the strained state persisting in these elements even after the end of the seismic event.

Object of the present invention is to solve the above-mentioned drawbacks by providing a seismic-energy dissipator as substantially defined in claim 1.

A further object of the present invention is to provide a structure as substantially defined within the scope of claim 18.

Additional features of the invention are set forth in the corresponding dependent claims thereof.

The present invention, by overcoming the mentioned problems of the known art, entails several evident advantages.

The characteristic innovative techniques of the present invention may be schematized in the following points:

• stabilization of the dissipative elements (referred to as "fuses") by lateral stabilization systems of steel, in order to avoid instability phenomena in the inelastic field and allow an energy dissipation level not decreasing with the increase of the number of hysteretic cycles to which the dissipative device is subjected;

• possibility of easily replacing the fuses after each seismic event, with no need of costly interventions;

• ability of the dissipator subject of the present invention to quash residual deformations of the structure subsequently to the seism, thanks to the presence of cables having, post-tensioned, a high yield point, as will be detailed hereinafter. Thus, the seismic safety of the structure can be restored to original levels after each earthquake, but might also be enhanced thanks to the possibility of replacing the fuses;

• use of optimized-grade steel for the manufacturing of dissipative elements, or fuses, which perform just the task of absorbing seismic energy, deforming themselves. In such elements the near-totality of plastic deformations is concentrated, and therefore most of the seismic energy being inlet in the structure is dissipated, enabling a slight or nil damaging of the structure;

Therefore, the seismic-energy dissipator subject of the present invention entails the following innovative aspects:

• flexibility: the dissipator may be applied to different structural solutions: different both in geometry and materials (steel, reinforced concrete and masonry structures); the structural performances of the dissipator can be modified so as to meet the needs of the structure to be protected;

• repairability: the possibility of concentrating plastic deformations into dissipative elements (fuses) which may be replaced subsequently to the seismic event; the fuses are equipped with a lateral stabilization system made of steel, which prevents balance instability phenomena thereof under compressive loads;

• high performances: the fuses, made of steel, can be manufactured using steel grades deriving from application fields different from those commonly used in civil engineering;

• combining in a single system features independently developed beforehand: self-re-centering; prevented instability; repairability; applicability to many structures having different features.

Brief description of the drawings

Still further advantages, as well as the features and the operation steps of the present invention will be made apparent in the following detailed description of a preferred embodiment thereof, given by way of example and not for limitative purposes. Reference will be made to the figures of the annexed drawings, wherein:

Figure 1 shows in a side view a seismic-energy dissipator according to the present invention;

Figures 2-10 show in side views and in front views the various components of the dissipator of Figure 1 ;

Figure 11 shows in a perspective view the section of Figure 1 ;

Figures 12 and 13 schematically show the operation of the seismic-energy dissipator when subjected respectively to a compressive load and a tractive load;

Figures 14 and 15 show two photographic reproductions of components of the dissipator subject of the present invention.

Detailed description of the drawings

Referring to Figure 1 , a dissipator 1 subject of the present invention is shown in a side view, in order to internally show the components it comprises.

Always referring to Figure 1 , the dissipator 1 preferably has an elongated shape, and comprises an external carter 11 inside which a frame is housed comprising, as will be detailed hereinafter, a piston for load introduction, the frame being generally denoted in figure by reference number 12 and configured to be able to slide parallelly to an axis of the carter 11 according to a direction singled out in figure by letter a.

The movable frame 12 comprises a free end 121 equipped with means for connecting with an external structure (not depicted).

Moreover, the dissipator 1 comprises opposing elements 13 and 14 arranged at opposite ends of the movable frame 12, connected thereto each by respective dissipative elements 5 and 16, hereinafter referred to as "fuses".

The carter 11 comprises, at each opposing element 13 and 14, a respective stopping abutment 17 and 18, arranged so as to constitute a stopping point of its sliding toward the inside of the carter 11. For this reason, the stopping abutments 17 and 18 are facing each other.

The arrangement of the stopping abutments 17 and 18 with respect to the opposing elements 13 and 14, the latter connected to the movable frame 12 by the fuses 15 and 16, will be made clear in the explanation of the operation principle of the dissipator 1 when subjected to compressive or tractive loads.

Moreover, the two opposing elements 13 and 14 are coupled to each other by re- centering cables 19 and 20, which will be detailed hereinafter.

Finally, the carter 11 comprises one end 111 , opposite with respect to the free end 121 of the movable frame 12, it also equipped with means 111 for connecting with the external structure.

Referring now to next Figure 2, the external carter 11 is shown in a side view and in a front view.

The carter 11 , in the embodiment shown herein by way of a non-limiting example, comprises two sheet metals 112 and 113 of a thickness substantially equal to 10 mm, connected and shaped. As mentioned, the carter 11 has, at one end thereof, a drilled element 111 allowing the connecting, by pin joint, with the external structure to be protected.

Inside the carter 11 the stopping abutments 17 and 18 are obtained, which in the preferred embodiment described herein comprise each a first and a second pair of sheet metals, welded inside the carter, the pairs being facing each other as is evident in the front view along section line B-B.

The carter 11 further comprises closure side panels 114 and 115 (seen in the front sections along lines A-A and B-B), which have the task of stabilizing the sheet metals in order to prevent buckling phenomena due to compressions induced by external loads.

Referring to next Figure 3, the movable frame 12 is shown in a preferred embodiment thereof.

In particular, the frame 12 comprises a pair of hollow tubular profiles 122 and 123 parallel therebetween, preferably of square section, of dimensions 70 x 8.3 and 3100 mm long, preferably integrally connected to both ends by a welded joint and interposition of a plate 124 to hollow end profiles 125, of dimensions 160 x 80 x 10 and 190 mm long.

The profiles introduced above can be seen both in side section and in front section along lines A-A and B-B.

The two tubular profiles 122 and 123, in particular at their end portions 125 according to the preferred embodiment described herein, are connected therebetween by a transversal plate 128 - apt to connect the load introduction piston to the movable frame - a first anchoring plate 126 and a second anchoring plate 127, the latter depicted in greater detail in next Figure 4.

Referring to said figure, the anchoring plate 126 has a pair of welded sheet metals 1261 , provided with means for the reversible connection with the fuses (the latter not reported in figure). As can be seen in a front view of the first anchoring plate 126, it comprises four holes 1262, arranged in pairs along the sides of the two sheet metals 1261. Such holes serve, as it will be made evident hereinafter, for the inserting and the connecting of the fuses to such anchoring plate 126.

The anchoring plate preferably has dimensions equal to 144 mm of front width and 50 mm of thickness. The sheet metals 1261 have a length substantially equal to 123 mm. The second anchoring plate 127 is in all similar, and it also comprises a pair of sheet metals 1271 and four holes 1262, them also required for the inserting and the reversible connecting of the respective fuses. The second plate 127 comprises also a central through hole 1273, for the sliding insertion thereinside of the piston for load introduction in the movable frame 2, as will be described hereinafter.

Such a piston is described, and denoted by reference number 129, in the next Figure 5, to which now reference is made.

The piston is made, according to the preferred embodiment described herein, by a hollow tubular profile of a diameter of 88.9 x 3.2, having at its end 121 a drilled plate for the connecting by pin to the external structure. The plate, moreover, has another end 1291 equipped with a fork-shaped joint for the connection by friction bolts with the movable frame 12, and in particular with the transversal plate introduced hereto (and denoted by number reference 128 in the preceding Figure 3).

Along piston 129 a plurality of steel reeds are welded, suitably shaped and denoted in figure by reference 1292, to stabilize the piston during the introduction of compressive actions.

Referring to next Figure 6, the frame internal to the carter comprises a plurality of intermediate supporting elements 1200, each element connected to the pair of tubular profiles 122 and 123 and having a drilled portion apt to allow the insertion of the sliding piston 129. Therefore, the supporting elements are useful to decrease the free length of inflection of the piston. In particular, they are positioned at the reeds welded on the piston 129, in order to minimize play thereamong.

Figure 7 shows the piston 129, and in particular its end 1291 equipped with a fork-shaped joint for the connection with the transversal plate 128 by friction bolts.

Figure 8 shows in a front and a side view the two opposing elements 13 and 14, according to a preferred embodiment thereof.

The opposing elements 13 and 14 are made in a way entirely similar to the above- described anchoring plates.

In particular, the element 13 has a thickness equal to 50 mm and a pair of sheet metals 131 comprising means for the reversible connection with the respective fuses, as will be detailed hereinafter.

The element 13, having in a front view dimensions substantially equal to 176 x 428 mm, has four holes, placed side-by-side in pairs to the sheet metals 131 for the insertion of fuses.

The element 13 further comprises a pair of holes 133, for the insertion of the re- centering cables.

The opposing element 14 is entirely similar: in a front view, it has alike dimensions of 176 x 428 mm, a pair of sheet metals 141 comprising means f or the reversible connection with the fuses, and four holes 142 placed side-by-side in pairs thereto for the insertion of the fuses .

The element 14 comprises a respective pair of holes 143, them also required for the insertion of the re-centering cables. It preferably has a thickness equal to 70 mm and a central hole 144, preferably of a diameter of 106,3 mm, for the sliding insertion of the piston (not depicted). Referring to next Figure 9, the dissipative elements, or fuses, are depicted denoted by number reference 15. In Figure only one fuse is depicted, but it is clear that what is described in figure holds true for all fuses of the dissipator subject of the invention, as they are all substantially alike.

According to the preferred embodiment shown herein by way of example and not for limitative purposes, the dissipative element is substantially dog bone-shaped, comprising a central portion 151 and two end portions 152 and 153 provided with reversible connection means, said portions being required for the connection of the fuse on the one side to the respective opposing element, and on the other side to the respective anchoring plate (not depicted) by friction joints. As can be seen in the figure, the central portion has a reduced section with respect to the two end portions, for the connection of the fuse to the respective opposing elements and anchoring plates.

The fuse is preferably made of steel selected so as to exhibit a high ductility and a low yield point.

Referring to the illustrations below, the fuses, visible both in a front and in a side view, paired two by two, are equipped with a side stabilization system generally denoted by number reference 154, in order to avoid global buckling phenomena during the compression phase. Such a stabilization system is comprised of two sheet metals, shaped so as to allow fuses accommodation, and of a thickness preventing fuses skidding toward the inside.

Referring now to figure 10, the dissipator subject of the present invention comprises re-centering cables, each of which has ends anchored to the opposing elements.

In the figure an end portion of the cable 19 is depicted, yet it is understood that what described therefor likewise holds true for the other cable as well.

In particular, spiroidal-type cables have preferentially been selected, comprising, for each end, a cylindrical cable terminal adjustable with a threaded bar and denoted in figure by reference number 191.

The cable terminal 191 comprises a cylindrical element 1911 connected on the one side to the cable, e.g. by a chemical adhesive, and on the other side to a threaded bar 1912, enabling the anchoring thereof to the respective opposing element 14 and the tensioning thereof by means of a tightening bolt 1913.

Referring now to Figure 11 , the seismic-energy dissipator 1 is again depicted in a side section, and this time also the same section is present, in a perspective view. As will now be evident from the figure, the movable frame 12, inserted and constrained to slide along the axial direction a singled out by the carter 11 , comprises the tubular profiles 122 and 123 integrally connected to the piston 129 by the transversal plate

128, the piston 129 being connected to the external structure at its end 121.

The tubular profiles 122 and 123 rest on the opposing elements 13 and 14, which are connected therebetween by the post-tensioned re-centering cables 19 and 20.

The dissipator 1 further comprises, obtained inside the carter 11 and at the opposing elements 13 and 14, stopping abutments that, having each the shape of two pairs of sheet metals facing therebetween, advantageously act also as slide for the tubular profiles 122 and 123, between which they are arranged, as evident in figure.

As will be easily appreciated, the distance between the two facing sheet metals of each stopping abutment mus t necessarily be less than the thickness of the respective opposing element, so that precisely the sheet metals constitute a stopping point of the sliding of the latter toward the inside of the carter 11.

The opposing elements 3 and 14 are connected to the frame 12, respectively at the first anchoring plate 126 and at the second anchoring plate 127.

The fuses 15 and 16 are reversibly connected, by bolted joint, on the one side on the anchoring plate and on the other one on the opposing element.

In particular, two pairs of fuses are used to connect each anchoring plate to the respective opposing element, each pair of fuses arranged at the respective sheet metals by means of the holes obtained at the sides thereof, as highlighted above, and bolted thereat. Preferably, for each pair of fuses eight M10 bolts of class 8.8 were used.

The re-centering cables 19 and 20 are positioned inside the tubular profiles, and are constrained to the two opposing elements by means of the cylindrical cable terminals adjustable with threaded bars, in order just to be able to adjust the post-tensioning thereof.

The post-tensioning of the cables is precisely adjustable to the desired value by a suitable tightening of the end bolts.

Finally, the piston 129 is connected to the transversal plate 128 preferably by three friction bolts M24 of class 8.9.

Referring to next Figures 12 and 13, it is illustrated the operation principle of the seismic-energy dissipator according to the invention, respectively when subjected to a compressive load and when subjected to a tractive load.

Referring to the above figure, when the dissipator is in a quiescent condition (without any load applied thereon), the tubular profiles 122 and 123 are in contact with the opposing elements 13 and 14.

Imagine to constrain, e.g., the end 111 of the carter by means of a hinge joint and apply in a quasistatic manner an external force F at the end 121 of the piston, which, constrained to slide along the axial direction of the dissipator, places the latter under compression.

The force F is transmitted from the piston, through the transversal plate, to the tubular profiles, and therefrom to the opposing element 13.

When the force F exceeds the value of the total pre-compressive force exerted by the two cables 19 and 20, there are obtained the detachment of the opposing element 13 from the stopping abutments, and therefore the sliding of the frame 12 in the sense of the force F and the tractioning of the fuses 16, since the opposing element 14 in this case cannot slide toward the inside of the carter, as it is blocked by the respective stopping abutments 18.

In this configuration, the external force is therefore balanced by the traction present in the cables 19 and 20 and by the fuses 16 set in traction. With the decreasing of the external force (situation depicted by the bottom figure) the post-tensioned cables tend to bring the dissipator back to the initial configuration, thereby cancelling residual deformations.

In order for the dissipator subject of the invention to be effectively re-centering, the cables and the dissipative elements are advantageously configured so that the post- tensioning force of the cables be greater than the force required to stretch the dissipative elements under compression at the yield strength or beyond.

For the case of an application of the compressive load F, diagrams 12A show, from the left:

- hysteretic behavior of the dissipative elements: force - deformation pattern for the (unloaded) dissipative elements 17;

- hysteretic behavior of the dissipative elements: force - deformation pattern for the (tensioned) dissipative elements 16;

- overall behavior: stretching of the dissipator at the yield strength or beyond under compression;

For the case of compression unloading (bottom figure), diagrams 12B show from the left:

- hysteretic behavior of the dissipative elements: force - displacement pattern for the (unloaded) dissipative elements 17;

hysteretic behavior of the dissipative elements: force - deformation pattern for the dissipative elements 16 (stretched at the yield strength or beyond under compression);

- overall behavior: force - deformation pattern for the recovery of residual deformations (re-centering).

As can be seen, the external force - relative displacement diagram at the two ends of the dissipator assumes the flag-like shape typical of self-centering systems.

Referring to Figure 13, the dissipator operates according to the same principle when subjected to a tractive load.

In this case, the opposing element 13 is blocked by the stopping abutment 17 and therefore the fuses 17 are set in traction. Otherwise, the opposing element 14 begins to slide inside the carter when the tractive load F exceeds the post-tensioning load imparted to the cables.

The bottom figure shows the dissipator under tractive unloading conditions.

Likewise, for the case of application of the tractive load F, diagrams 13A show from the left:

- hysteretic behavior of the dissipative elements: force-deformation pattern for the dissipative elements 17 (tensioned) ;

- hysteretic behavior of the dissipative elements: force-deformation pattern for the dissipative elements 16 (stretched at the yield strength or beyond under compression);

- overall behavior: stretching of the dissipator at the yield strength or beyond under traction;

For the case of tractive unloading (bottom figure), diagrams 13B show from the left:

- hysteretic behavior of the dissipative elements: force - displacement pattern for the active dissipative elements 17 (stretched at the yield strength or beyond under compression) ;

- hysteretic behavior of the dissipative elements: force - deformation pattern for the non-active dissipative elements 16 (stretched at the yield strength or beyond under compression);

overall behavior: force - deformation pattern for the recovery of residual deformations (re-centering).

Finally, photographic reproductions 14 and 15 depict respectively the dissipative elements and the re-centering cables described above.

Moreover, it will be appreciated that the seismic-energy dissipator is decomposable and recomposable in all of its components, and therefore it could advantageously be provided in the form of an assembly kit.

The present invention has been hereto described with reference to a preferred embodiment thereof. It is understood that other embodiments might exist, all falling within the concept of the same invention, and all comprised within the protective scope of the claims hereinafter.

Claims

1. A seismic-energy dissipator (1) comprising:

• an external carter (11);

• a frame (12) housed inside said carter (11) configured to slide therealong and comprising a free end (121) apt to be connected to an external structure;

• a pair of opposing elements (13, 14) arranged at opposite ends of the frame (12), said carter (11) comprising, at each opposing element (13, 14) a respective stopping abutment (17, 18) arranged so as to stop the sliding thereof toward the inside of the carter (11), said opposing elements (13, 14) being connected to said frame (12) by respective dissipative elements (15, 16).

2. The seismic-energy dissipator (1) according to the preceding claim, further comprising a pair of re-centering cables (19, 20) each having ends anchored to said pair of opposing elements (13, 14).

3. The seismic-energy dissipator (1) according to the preceding claim, wherein each cable (19, 20) is of spiroidal type and comprises at each end a cylindrical cable terminal (191), said cable terminal (191) comprising a cylindrical element (1911) connected to an end threaded bar (1912) comprising a tightening bolt (1913) apt to cooperate with the respective opposing element (13, 14) for the anchoring and the tensioning of said cable (19, 20).

4. The seismic-energy dissipator (1) according to claims 3 or 4, wherein said cables (19, 20) and said dissipative elements (15, 16) are configured so that the post- tensioning force of the cables (19, 20) be greater than the force required to stretch said dissipative elements (15, 16) at the yield strength or beyond.

5. The seismic-energy dissipator (1) according to any one of the preceding claims, wherein said frame (12) comprises a pair of tubular profiles (122, 123), arranged along an internal wall of said carter (11), the tubular profiles (122, 123) being parallel therebetween and placed into contact with said pair of opposing elements (13, 14) when in a resting condition.

6. The seismic-energy dissipator (1) according to the preceding claim, wherein each cable (19, 20) is inserted inside a respective tubular profile (122, 123).

7. The seismic-energy dissipator (1) according to claims 5 or 6, wherein each stopping abutment (17, 18) comprises a first and a second pair of sheet metals, the sheet metals of each pair being facing each other so as to form a slide in which the respective tubular profile (122, 123) is arranged.

8. The seismic-energy dissipator (1) according to one of the claims 5 to 7, wherein said tubular profiles (122, 123) are connected by a transversal plate (128).

9. The seismic-energy dissipator (1) according to any one of the preceding claims, wherein said frame (12) comprises a sliding piston (129) inserted inside said carter (11) and comprising a first free end (121) apt to be connected with the external structure.

10. The seismic-energy dissipator (1) according to claims 8 and 9, wherein said sliding piston (129) comprises a second end (1291) apt to be connected to said transversal plate (128).

11. The seismic-energy dissipator (1) according to claims 9 or 10 and to one of the claims 5 to 8, comprising one or more intermediate supporting elements (1200) arranged along said carter (11), each element (1200) being connected to said pair of tubular profiles (122, 123) and having a drilled portion apt to allow the insertion of said sliding piston (129).

12. The seismic-energy dissipator (1) according to any one of the preceding claims, wherein said dissipative elements (15, 16) are reversibly connected to said frame (12) and to the respective opposing element (13, 14).

13. The seismic-energy dissipator (1) according to one of the claims 5 to 8 and one of the preceding claims, wherein said frame (12) comprises for each opposing element (13, 14) a respective anchoring plate (126, 127) fixed between said tubular profiles (122, 123), each anchoring plate (126, 127) comprising means (1261, 1271) for the reversible connection with said dissipative elements (15, 16).

14. The seismic-energy dissipator (1) according to any one of the preceding claims, wherein said dissipative elements (15) are substantially dog bone-shaped, comprising a central portion (151) having a reduced section and two end portions (152, 153) having reversible connection means.

15. The seismic-energy dissipator (1) according to any one of the preceding claims, wherein said carter (11) comprises means for connecting with the external structure at one end (111) thereof opposite to said free end (121) of said frame (12).

16. The seismic-energy dissipator (1) according to any one of the preceding claims, having a substantially elongated shape.

17. The seismic-energy dissipator (1) according to any one of the preceding claims, provided in the form of an assembly kit.

18. A structure, characterized in that it comprises a seismic-energy dissipator (1) according to any one of the preceding claims.