WO1998041716A1

WO1998041716A1 - Earthquake-proof device for buildings and engineered constructions

Info

Publication number: WO1998041716A1
Application number: PCT/FR1998/000552
Authority: WO
Inventors: Bruno Domange; Alfred Krief; John B. Mander; Gokhan Pekcan
Original assignee: The Research Foundation Of State University Of New York; Jarret S.A.
Priority date: 1997-03-19
Filing date: 1998-03-19
Publication date: 1998-09-24
Also published as: AU7049298A; FR2761099B1; JP2001516410A; FR2761099A1

Abstract

The invention concerns an earthquake-proof device for buildings and engineered constructions characterised in that it comprises pre-stressed cables (A1, A2, B ...) fixed at one of their ends to a ground structure (22) supporting the building or construction and at their other end to a high storey structure (24) of the building or construction, said cables (A1, A2, B ...) being stretched along an optimised curve by calculation based on the structural features of the building or construction, the cable being stretched in a plane passing through the horizontal displacement direction which needs to be limited.

Description

ANISISMIC DEVICE FOR BUILDINGS AND WORKS OF ART

The present invention relates to an anti-seismic device for buildings and engineering structures as well as to buildings and engineering structures equipped with such devices. The protection of buildings and engineering structures against earthquakes is a well known problem, for the resolution of which many solutions have been proposed, generally quite expensive, difficult to maintain and relatively effective.

The invention relates to a device of new design, relatively inexpensive, reliable and easy to maintain and verify.

An additional advantage of the invention is that it could even be applied after the fact to unprotected works already built.

The anti-seismic device for buildings and engineering structures according to the invention is characterized in that it comprises prestressed cables fixed, at one of their ends, to a ground structure supporting the building or the work, and to their other end, at a high storey or high structure of the building or structure, said cables being stretched following a curve optimized by calculation as a function of the construction characteristics of the building or structure, the cable being stretched in a plane passing through the horizontal direction of movement which one wishes to limit.

By soil structure is meant any structure of the building or of the structure rigidly linked to the ground, such as for example a ground floor or basement floor, or even a lower floor.

Advantageously, at least one tension damping spring is provided on each prestressed cable.

Preferably, the device comprises at least one traction damping spring which is mounted in the vicinity of the lower end for anchoring the cable to the ground structure, which damping spring is prestressed in tension to a value greater than that of the prestressing of the cable which hangs thereon.

Preferably, the upper end of the cable is fixed towards an upper part of the building or of the structure, at a certain distance from its top.

To define the curve which the cable follows, there are provided guide elements, advantageously at least at certain floors, walls or posts of the building or the structure. According to another characteristic of the device of the invention, the guiding elements in the passage of a structure of the building or of the structure, such as in particular floors, walls or posts, can advantageously be trotters energy dissipators.

Preferably, at least three, and preferably at least four aforementioned prestressed cables are provided, oriented in a horizontal direction different from the space.

Even more preferably, at least two parallel cables for each protected horizontal direction are provided, and said two cables are each arranged towards the opposite faces of the protected building or structure. Other characteristics, objects and advantages of the invention will appear more clearly with the aid of the description which follows, given with reference to the appended drawings, in which:

Figure 1 is a schematic view illustrating the operating principle of a device designed according to the invention. FIG. 2 shows on a larger scale the detail surrounded II in FIG. 1.

Figure 3 very schematically shows the whole of a building to be protected.

Figure 4 shows schematically the layout of cables in a building of the type shown schematically in Figure 3. Figure 5 shows an exploded view of the base plane, the top plane and the upper plane of anchoring cables of the diagram in Figure 4, this view to understand how the cables are arranged in space in relation to the four directions indicated.

Figure 6 shows how two of the cables work, in the case of a force undergone by the building in the direction indicated by the arrow in this figure. Figure 7 shows schematically the layout of a cable in the building.

FIG. 8 shows on a larger scale the anchor in low fixing of the cable at the level of the circle marked NUI in FIG. 7.

Figure 9 shows on a larger scale how the cable passes through a building floor, as marked in IX in the figure

7.

FIG. 10 shows the displacement and the deformation of a cable during a movement of the building in the direction of arrow A parallel to the plane in which this cable is stretched. Figure 11 shows schematically an example of implementation for the protection of an eight-story building.

Referring to Figure 1, there is schematically illustrated a building referenced as a whole 10 resting on the ground 11 and having a number of floors, three of which have been referenced 12, 13, 14, 15. According to Invention, to protect such a building or structure against earthquakes, a number of cables are provided in the building which will be routed, for example as will be explained in more detail with reference to Figures 4 to 6 which follow.

In FIG. 1, a cable 16 has been illustrated stretched between a point on the ground 17 where it is anchored and a point 18 on the upper floor 15 of the structure.

According to the invention, as already mentioned, the cable 16 is prestressed in tension.

In addition, towards the lower part of the cable, as illustrated in 19, a tension damping spring is also provided, which is also prestressed in traction, which will make it possible to absorb stresses in deformation of the cable and dissipate the corresponding energy and also to ensure and maintain the prestress of cable 16 over time. As will be explained below, the preload of the shock absorber spring is advantageously chosen to be greater than that of the cable. As illustrated in FIG. 2, there is advantageously provided for each passage of the cable 16 through a floor such as the floor 12 a trotting device 20 which will slow down the movement movements of the cable during an earthquake tending to deform the building, as will be explained in more detail, in particular in relation to FIG. 6.

The general principle of the invention being thus set out, it will be assumed that the device is applied to a building such as a tower 21 illustrated in FIG. 3 of square, rectangular parallelepiped section, 30 meters side at the base and of

100 meters high, for example around 33 floors.

Referring to FIG. 4, the same structure 21 has been shown diagrammatically, but only the base perimeter on the ground referenced 22, the summit referenced 23 and a relatively high intermediate stage referenced 24, for example, have been shown. level between the 21st and the 27th floor in the example shown of a tower of about 33 floors.

In the same figure 4, the four directions of the building have been referenced by the arrows A, B, C, D, for example North-South, South-North, East-West, West-East. To retain the building which would be subjected to a thrust in the direction of arrow A (FIG. 6) are provided in the illustrated example two cables Al, A2 whose bottom and top anchor points have been respectively referenced al, a2 in plane 22 and a, a'2 in plane 24.

These cables are stretched in vertical planes parallel to direction A.

It is clear that if the building is subjected to a deformation which tends to move its apex 23 in the direction of arrow A, the cables A1, A2 will be subjected to an additional traction as a result of the lengthening of the distance separating the points al, a'1 and a2, a'2. Advantageously, the two cables A1, A2 are close to the corresponding lateral faces of the building, ie here, with respect to the plane of the figures

4 and 6, the front and rear respectively. In the same way, to resist a push in the direction of arrow B, two cables are provided which are directed in a vertical direction parallel to the direction of arrow B.

In FIG. 4, in order not to overload the figure, only one cable B (towards the rear face of the building) has been shown anchored at b and b 'respectively in planes 22 and 24.

In FIG. 5, on the other hand, the respective anchor points bl, b'I of a first cable B (close to the front face of the building) and b2, b have been shown so as to allow their location to be clearly identified. '2 the second cable B (close to the rear face of the building and corresponding to that illustrated in Figure 4).

In the same way, two cables are provided in vertical planes parallel to the arrow C whose implantation or anchoring points at the level of the planes 22 and 24 have been referenced respectively cl, c2 and c'1, c'2, and in the same way two other cables in vertical planes parallel to arrow D to resist a thrust in the direction of arrow D, cables anchored respectively in plane 22 and in plane 24 at the points referenced dl, d2, d ' 1, of 2.

It can be seen in FIG. 5 that, advantageously, the anchor points al-cl, bl-c2, dl-b2, a2-d2 are combined, as are the anchor points at the plane 24 b'l- d'2, a'1-d'l, a'2-c'2, b'2-c'l; in this way, for eight cables, each of which two arranged in parallel will be put into action to resist the movement of movement of the building in one direction, it will suffice to provide four anchors on the ground and four anchors on the upper floor. If we want to better distribute the forces, we can advantageously separate the low and high anchor points from each other.

But in general, we will adopt a symmetrical position of the cables working in opposition to, in the resting state of the building or the structure, to balance the compressive forces that the cables apply to it. Referring to Figures 7 and 8, we illustrated how an anchorage could be made at ground level. In FIG. 7, the tower 21 has been represented by referencing, in order not to overload the figure, only one floor of three floors and a single cable 16, which is stretched in a practically vertical plane between a point of anchoring to the ground 11 and an anchoring point at the level of the floor referenced 24. At the level of the anchoring to the ground, as can be seen more clearly in FIG. 8, there is interposed between the lower end of the cable 16 and the lower floor 22 resting on the ground a traction damping spring 19 which may for example be of the JARRET type (registered trademark), as explained below in the example given. Two joints 25, 26 allow perfect alignment in tension of the shock absorber spring 19 with the prestressed cable 16.

The anchoring of the axis 25 can be obtained by a square piece 27 suitably anchored to the floor 22 and to a support structure post 28. As can be seen more clearly in FIG. 9, at each passage of the floor, as as the intermediate floor 29, a trotter 30 is advantageously provided which slows down the movement of the cable 16 and will make it possible to dissipate energy during a movement of movement of the building

In a simulation example, as illustrated in FIG. 10, the device of the invention was applied comprising the eight cables stretched as previously exposed to a tower 100 meters high comprising approximately 33 floors on a square base of 30 meters by 30 meters.

Each cable is linked to the building at one end, the low end referenced A0 on the ground by means of a traction damping spring of the type previously indicated, and at the other high end referenced A7 on the floor surface of the 23rd floor.

The cables are tensioned with a pretension of around 300kN. The shock absorber spring has a pretension of 350kN, that is to say it is always placed in the initial installation position; in other words, it is not working at this stage. At each level, the cable crosses the floor through a hole 32 forming a cable guide element (Figure 9); so as not to overload the figure, the holes have only been referenced from three floors to three floors (figure 10).

The holes are usually not aligned so that the cable follows a certain curve and compresses the floor with a force F (Figure 9) depending on the angle formed between the cable and the vertical. However, it will be observed that a substantially straight curve can be chosen for the cable.

In the stable state of rest, the building is vertical, and the eight cables generate equal and opposite forces for all the floors, which forces cancel each other out.

During a deformation in a direction of the building, for example direction A, only the two cables whose traces a, a, a2, a'2 on the horizontal plane are parallel to this direction will work more (these are the only which are subject to extension). Figure 6 shows the two cables A1, A2 stretched during a deformation of the building in the direction mentioned.

Figure 10 shows the cable movements when the top of the building moves 1 meter in direction A.

In an example of a feasible solution, the cable would be made of steel strands and would have a section of diameter about 41 millimeters, or an initial stress of 300 Mpa, which corresponds, after all calculations, (reduced to an effective section of cable from 1320 mm ² x 0.85) to around 340 kN.

Ll = length in place of the cable between points A0 and A7: 77.9 meters.

Cable weight: about 700 kg. The working length L0 of the cable at rest, before installation is such that L0 = AOAl + Al A2 + A2A3 + A3A4 + A4A5 + A5A6 + A6A7 - initial elongation (prestressing) = 77.9 m - 0.111 m = 77.789 m.

Assuming an initial lateral displacement of 1 meter for the top of the building (1 hundredth of its height) the distance A0A7 becomes equal to 78.165 meters, an extension of 265 millimeters.

This value corresponds to an extension of the cable added to the extension of the shock absorber spring. If the cable is made to work up to 550 Mpa (or 630 kN), this gives an additional lengthening of the cable due to the deformation of the building by 102 millimeters, hence a spring stroke of 163 millimeters (265 - 102 = 163).

A JARRET shock absorber with the characteristic traction stroke 170 millimeters, prestressing 350 kN, maximum reaction 700 kN meets the requirements, with an initial prestressing greater than that of the cable, and a maximum resistance greater than that taken up to absorb deformation.

Such an apparatus would have as an approximate volume D = 300 millimeters, L = 900 millimeters. Figure 9 shows trotters stuck between the cable and the floor.

These will dissipate energy during the deformation of the building. Indeed, the cable in lengthening, will move relative to the floor and their contact points will move along the cable. Such trotters can be constituted for example by molded plastic parts with high resistance which rub on the cable or by jaws having friction surfaces which are applied by force to the cable, either directly or indirectly.

In FIG. 11, the results of a simulation carried out on a homogeneous eight-storey building, referenced 33 as a whole, comprising eight floors, referenced 34 to 41, illustrated above a ground surface referenced 42, have been illustrated. .

It was assumed that the building was of substantially square section and had dimensions of floor area of the order of 50 meters, each floor being at a height of 2.80 m above the next floor (and the floor for the floor 34), each floor having a thickness of 30 cm and a mass of the order of 40 tonnes.

It was also assumed that the floors rested on posts without interposition of sails, of identical stiffness, the horizontal stiffness between two floors and also between the ground and the first floor being assumed to be 10 Mega Newtons / m. To protect the building, a total of sixteen cables stretched at the rate of four, used in vertical planes, symmetrically with respect to the center of the structure, were used to retain the building in each of the four horizontal directions of space, as previously explained with reference to Figures 4 to 6.

In FIG. 11, in order not to overload the drawing, a single cable, referenced 43 has been shown, the lower end of which is anchored to a shock absorber spring referenced 44 and the upper end of which is anchored to the last floor of the floor 41 .

The cables can be anchored to the shock absorber springs as illustrated and explained in relation to FIG. 8.

In the example shown, it has been assumed that there was no trotting element when the floors passed.

Each cable being made up of seven T15S class 1 860 strands (cross section of steel = 1 050 mm ² - maximum admissible force = 1 562 kN for the cable), an optimized curve is illustrated in figure 11 or have been plotted on the abscissa the distance of the holes in each floor from the low anchor point and on the ordinate, the height of the floor crossed.

Thus, for example, for the floor of the second floor referenced 35, the cable passage hole is 34.73 meters from the lower anchoring end at this second floor.

Under these conditions, the length of the cable in place will be 57.70 meters. It will be prestressed to 600 kN and a JARRET damper spring with a prestress of 680 kN and a maximum admissible force of 1,000 kN will be used as the shock absorber spring.

Such a device which has a static stiffness of 200 kN / m fits into a housing with a diameter of 350 mm and a length of 1000 mm.

Claims

1 - Anti-seismic device for buildings and engineering structures, characterized in that it comprises prestressed cables (16) fixed at one of their ends to a ground structure (22) supporting the building or the work and to their other end of a high-rise floor structure of the building or structure, said cables being stretched following a curve optimized by calculation as a function of the construction characteristics of the building or structure, the cable being stretched in a vertical plane containing the horizontal direction of movement that we want to limit.

2 - Device according to claim 1, characterized in that guide elements (32) of the cable (16) are provided at least at certain floors, walls or posts of the building or the structure. 3 - Device according to claim 1 or 2, characterized in that on each prestressed cable (16) is provided at least one traction damping spring (19).

4 - Device according to claim 3, characterized in that the shock absorber spring is prestressed to a level of prestress greater than that of the cable.

5 - Device according to claim 3 or claim 4, characterized in that at least one tension damping spring is mounted in the vicinity of the lower end of anchoring the cable to the ground structure.

6 - Device according to any one of the preceding claims, characterized in that the upper end of the cable is fixed towards an upper part of the building or structure, at a certain distance from its top.

7 - Device according to any one of the preceding claims, characterized in that the passage of the structures of the building or of the structure, such as in particular floors, walls or posts, are provided with trotting devices (30) for braking movements cable movement (16) and energy dissipation. 8 - Device according to any one of the preceding claims, characterized in that there is provided at least three and preferably at least four aforementioned prestressed cables oriented in different horizontal directions of the space. 9 - Device according to claim 8, characterized in that at least two parallel cables for each protected horizontal direction are provided, said two cables being each disposed towards the opposite faces of the building or protected structure.

10 - Building or structure protected against earthquakes, characterized in that it comprises an anti-seismic device according to any one of the preceding claims.