CH625302A5 - - Google Patents

Description

The invention relates to a spatially floating body protected from ground vibrations, in particular structure, machine or isolator station, which is connected via mechanical isolators, which are designed to be elastic in all directions, to a base rigidly attached to the subsurface.

Building safely in earthquake-prone areas is a challenging task for modern architecture.

Despite years of intensive research and development, the results have so far been unsatisfactory, and it has not been possible to secure a building properly in the event of extreme earthquakes under all conditions. Various new proposals for earthquake protection systems have become known in the past 20 years. One of these proposals deals with energy destruction by vibration absorbers installed in the building roof (Wirsching P.H., Campbell G.W .: Minimal structural response under random excitation using the vibration absorber; International Journal of Earthquake Engineering and Structural Dynamics, Vol. 2,1974). Another proposal concerns the storage of the superstructure of the building on horizontally movable roller bearings with elastic elements to build up restoring forces (Matsushita K., Izumi M .: Studies on mechanismes to decrease earthquake forces applied to buildings; Proceedings of the 3rd World Conference on Earthquake Engineering , London, 1965). Finally, it has also been proposed to hang the superstructure in order to separate it from the direct influence of the vibrations (Oto Lanios C J. et al: Study of the behavior of a hanging building under the effect of an earthquake; Proceedings of the 4th World Conference on Earthquake Engineering, Santiago de Chile, 1969).

All of these and related ideas have so far not had a major impact on the conventional, so-called earthquake-friendly design, which is used for earthquakes up to medium intensities. This type of construction provides good protection for human life for such earthquakes and offers sufficient stability for the buildings, however, taking structural damage into account until it is ready for demolition. Protection is insufficient at high earthquake intensities. Infrastructure buildings in areas with a high earthquake risk are particularly problematic. Such buildings are subject to considerable danger in the event of sudden, unexpected earthquakes or earthquake-like effects. These are specifically facilities for public needs with vital functions (hospitals, administrative and command centers); of traffic (large bridges, train station facilities, tunnels); energy needs (dams, power plants, fuel deposits); the industrial sector (chemical plants, explosives manufacturing); military use; as well as buildings with a large concentration of people (high-rise buildings, congress and cinema buildings, protective structures). The existence of some of these structures in areas at high risk of earthquakes basically depends on the possibility of technically realizing the integral earthquake protection. There is therefore a clear need for an improved earthquake protection option.

This leads to the following problem:

The conventional, earthquake-proof design is based on the knowledge that the fundamental natural building frequencies are almost inevitably in the resonance range of the earthquake reaction spectra. The kinetic energy that is transmitted to these buildings by the ground vibrations is transformed into structural deformations. As long as these structural deformations remain in the elastic range, the buildings will not be damaged. If, however, shocks occur that cause deformations in the load-bearing elements of the building that exceed the flow limit of the material, there are fallow phenomena that can lead to the collapse of the building.

Decisive progress in the seismic safety of buildings was achieved when it was possible to remove the structural deformations, which in the previous construction mainly take place in the upper structure of the building, from this area at risk of breakage. In this regard, CH-PS 450.675 proposes to arrange flexible zones in the form of highly elastic insulators between the superstructure of the building and its foundation, so that a floating bearing arrangement is created.

The method is known from the storage of machine foundations, and its use on buildings has already been described in specialist journals (Hubacher C., Stauda-cher E., Siegenthaler R .: earthquake protection in construction; Neue Zürcher Zeitung, Technikbeilagen, February 9, 1970) . It is a real, spatially floating bearing that can be distinguished from the horizontally floating bearing. While the isolators in the latter are only highly elastic in the horizontal plane (Delfosse GC: The G APEC System - A new highly effective aseismic system; Proceedings of the 6th World Conference on Earthquake Engineering, New Delhi, 1977), the former allows free movement in in all directions, including vertical.

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Although the advantages of this earthquake protection system were known, it was not known that the floating storage could be improved through suitable additional technical measures up to integral protection against the strongest known earthquakes. s

The usual methods of demonstrating earthquake safety are assessed below:

For the exact mathematical examination of a conventionally designed building, the mechanical properties of all four elements of the system, i.e. i »Buildings, insulators, foundations and floors. The mass, damping and stiffness distribution in the superstructure, the insulators, the foundation and the subsoil must be included in the mathematical system model if you want to reliably determine its dynamic reactions due to a given earthquake stress.

However, the calculation methods commonly used today, which are proposed in the legal building standards with the aid of greatly simplified finite element models, cannot meet the needs of integral earthquake protection. The spectral analysis using the usual mean spectra gives results with a possible error range of several 100%, while the cost of a modal or linear incremental analysis must be measured against the building shell cost. It should be borne in mind that, for integral earthquake protection, those exposed elements of the structure must in principle be found, the failure of which can be the initial cause of the system collapse. - How can integral earthquake protection actually be demonstrated in practice? 30th

There is also an important gap in the technique of load case definition: There is no direct mathematical relationship between the seismological earthquake strength data using estimated intensities or measured magnitudes and quantities used in engineering such as the maximum acceleration of a signal. - How should the relationship between earthquake risk maps and legal load case regulations be established?

The criticism thus refers to the fact 40

- That structural earthquake protection works with an inadequately known load case and with calculation methods that simplify the actual conditions in an impermissible manner;

- that the usual finite element models for a precise 45 examination of buildings cannot be detailed enough or are too expensive to use if the resolution is high (poor economy or insufficient precision of the results);

- that the material laws of many building materials (e.g. steel and concrete) are too little known for the higher-frequency components of earthquake excitation.

This means that the earthquake stress on the buildings calculated by convention must be viewed as an unreliable estimate, which can be exceeded many times in practice.

The limited earthquake protection mandate on which the known earthquake standards are based is in line with these findings. This requires:

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- that the buildings can withstand the earthquake that regularly recurs on the site with as little damage as possible, and

- that the protection of human life takes precedence over building protection in the event of intense or extreme earthquake tremors. 65

The reason why the protection mandate has so far been reduced in this way is not only because it was uneconomical to demand more consistent structural protection measures for all buildings in high-seismic regions. Up until now, there has been no way, in practice, to technically implement the integral earthquake protection or to prove it mathematically. For this, the computational proof would have to be carried out in such a way that those exposed structural elements whose failure are the initial cause of the system collapse could actually be found. Finally, there was considerable legal uncertainty in the determination of the load case, for which science has so far not provided any recognized engineering basis for definition.

The aim of the present invention is to eliminate the disadvantages mentioned and to implement the integral earthquake protection of buildings in practice. The technical measures proposed below are intended to be able to repeatedly and without damage absorb the strongest vibrations that have been measured on the building site to date or that can be expected there from previously defined or known causes. The technical measures should be such that the achievable integral protection can be proven in a simple, reliable and economical way by calculation or experiment.

In an expanded scope of the task of the invention, the protection of buildings against vibrations of a general nature is also to be effected. In addition to the natural earthquakes, artificial earthquakes as a result of nuclear or conventional bomb explosions as well as explosions, plane crashes, bullet impacts and other shock-like impacts are also possible. In addition to buildings, shelters, energy systems, military systems, large machines and isolator stations should also be able to be protected. Not only the actual building ground of free-standing buildings, but also a cavern rock, a machine chassis or a part of the building itself as the carrier of endangered devices can take on the role of the shaken medium. Of course, the above list does not claim to be complete. As a dangerous event, e.g. also saw a plane crash on a reactor building in which a large machine is located.

In the case of a spatially floating body of the type mentioned at the outset, the objects are achieved according to the invention in such a way that between the highest of the six lowest system natural frequencies, referred to as the basic frequencies, of the vibration element consisting of the body (D) and the isolators (C) and the deepest of the as Upper frequencies designated higher system natural frequencies, there is an area referred to as a natural frequency hole, in which the oscillation element has no natural frequencies, the natural frequency hole being intended to lie in the resonance range of the decisive design reaction spectrum of the vibration.

If the body is a building, its spatially floating storage is achieved by means of horizontally and vertically highly elastic damping elements (mechanical isolators), which are inserted between the two parts of the building by separating the superstructure from its foundation. The six fundamental frequencies of the vibration element can be relocated to a zone with a corresponding mass distribution of the superstructure and the stiffness distribution of the insulators, which are below the frequency of the resonance range of the design reaction spectrum of the vibration.

The superstructure receives a spatially rigid training. For this purpose, it is designed in a box-like or honeycomb-like manner, the outer walls being constructed to be continuous and load-bearing. In this way, an earthquake-compatible design of the structure is achieved, which as such is also required for unprotected structures in the earthquake standards. This measure leads to an increase in the upper frequencies of the structure above the

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upper limit of the spectral resonance range.

The foundation stiffly stuck in the building ground forms a rigid unit with it, whereby the foundation can be designed as a continuous plate, as a trough or as a specially designed mezzanine. The vertical rigidity of the subsoil should be at least six to nine times greater than the vertical isolator rigidity, so that the influence of soil compliance on the calculation method can be neglected when verifying protection.

As a result of this conception of the structure and the isolators, a natural frequency hole of the structure is formed in the resonance range of the reaction spectrum of typical strong earthquakes.

Thanks to the measures according to the invention, the building withstands the largest strong earthquake measured or to be expected on the site. It is integrally protected against earthquakes. This means the ability of the protected building area to repeatedly repeat extreme earthquake vibrations without elasto-plastic deformations, i.e. Destruction to survive the structure.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawings. Show it:

1 schematically shows a structure which stands on earthquake that is at risk of earthquakes,

2 shows a Fourier amplitude spectrum of an earthquake vibration,

3 schematically shows a mechanical isolator,

Fig. 4 shows a cross section through an insulated shelter in a cavern and

Fig. 5 is a perspective, exploded view of a standard building for the computational and experimental verification of integral earthquake protection.

The endangered structure D shown in FIG. 1 is connected to the foundation B and the environment, e.g. the ground A, connected. Pi and P2 denote the reference points of a measurable vibration wave E, e.g. an earthquake, expressed in the time domain T as spatial translational and rotational acceleration [DÈ (T)].

Any spatial, dynamic movements in the surrounding medium A that are transferred to the bearing area C of the structure D are to be understood here as vibrations. They can run intermittently or as periodic or pseudo-periodic vibrations.

Such dynamic or extreme vibrations of the support C are to be regarded as intense or extreme vibrations, which threaten the mechanical integrity of the structure D or impermissibly or completely impede its normal use as long as no specific protective measures have been taken.

The vibrations can be defined deterministically as time or frequency functions or probabilistically in the form of dimensioning spectral forms. The specific character of the vibrations is described as a Fourier amplitude and phase spectrum or as a so-called reaction spectral form. The relevant variables are the frequency content of the signal, i.e. the spectral distribution of the amplitudes as a function of frequency and the maximum acceleration of the signal for calibration purposes.

The earthquake reaction spectrum shown schematically in FIG. 2 is a typical form of a seismic design spectrum, the possible fundamental frequencies and the lowest upper frequencies of the proposed vibration body consisting of the structure D and the elastic support C being shown. Such a rated response spectrum is calculated from one or more suitably calibrated time functions. With the help of a calculation method known per se, the maximum movement reaction of a simple, undamped vibrator to the selected excitation is determined and plotted as a function of the natural frequency of the vibrator. For typical earthquake ground vibrations, it has a central frequency band with large amplitudes. This band is called Designated resonance range of the reaction spectrum.

In FIG. 2, F denotes the frequency and Sa the reaction spectral shape of the vibration in the acceleration range. Samait is the peak or maximum value of the spectral acceleration in the resonance range, and SaR is its reference or limit value, the corresponding cut-off frequencies of the resonance range being designated Fi and F2.

The upper and lower limits of the entire spectral frequency bandwidth F result from the specific character of the vibrations against which the proposed technical measures are used. The resonance range that describes the building frequencies at risk from excitation is eliminated from the amplitude spectrum as that central zone II, the spectral acceleration of which exceeds the limit value SaR. This limit value SaR can be expressed as a function of the maximum value Sama *, e.g. SaR = 0.8 X Samax. Below the resonance zone II is zone I for the lower, less dangerous fundamental frequencies and above is zone III for the upper frequencies.

The fundamental natural frequencies of most buildings fall entirely into Zone II of the schematic earthquake Fourier amplitude spectrum. The corresponding range of this resonance zone for solid floors is between 1.6 Hz and 6.0 Hz (empirical values). This results in the following zone widths:

Zonel: <1.6 Hz Zone II: between 1.6 Hz and 6.0 Hz Zone III:> 6.0 Hz

It should be noted that statements about the natural frequencies of the structure refer to the entire vibrating body, formed from the superstructure D and the insulators C surrounding it (FIG. 1), and not to individual sub-areas of the superstructure.

The type of vibration hazard of unprotected structures that are to be protected by the proposed technical measures is delimited as follows:

a) Risk of collapse for buildings of conventional construction with excitable natural frequencies in zone I. Excitation of the foundation B can cause impermissibly large deformations in the supporting structure of the building D. This leads to destruction on exposed load-bearing elements: threats to the mechanical integrity (collapse or becoming unusable) of partial areas or the overall structure.

b) Risk of resonance for structures of conventional construction with excitable natural frequencies in Zone II or devices inside the structure D. The resonance excitation of the structure results in an overuse of the affected elements: damage to partial areas, to the overall structure or to objects inside the structure .

c) Risk of brittle fracture for buildings of conventional construction with excitable natural frequencies in Zone III. The vibrations of the floor have a frequency content that triggers shock-like stress conditions on the structure: brittle fracture destruction. The brittle fracture destruction presupposes a brittle reaction behavior of the claimed materials in the excited frequency band.

d) Risk of overuse due to differential support movements. The passage of a vibration 5

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Wave from pi to p2 (Fig. 1) can lead to impermissibly large differential support displacements for structures D with considerable external dimensions: damage caused by the structure's tendency to stand out locally from the supports.

Damage from combinations of claims of the mentioned claims a) to d) are included; many of the unprotected structures typically have excitable natural frequencies in Zones II and IH.

The proposed technical measures to achieve integral earthquake protection and the possibility of simple mathematical verification of this protection are explained for easy understanding using the example of a building under extreme earthquake effects. They can be transferred directly to the related use cases.

The superstructure D to be protected of the building is supported on the foundation B via insulators C, which in turn is firmly attached to the subsoil A (FIG. 1). The schematic ground movement is marked with E.

The protected superstructure D generally includes all parts of the building that are not permanently embedded in the ground. The superstructure D can be supported directly on the foundation or lie on the basement levels embedded in the ground, which in this case act as an additional foundation.

The mechanical isolators C have a double function, because on the one hand they have to control the vibration behavior of an elastic system and on the other hand they have a damping effect. Accordingly, the schematically illustrated insulator according to FIG. 3 has a damping element C. 2 and a spring element C. 1. In the case of a possible technical design of an insulator, a head plate and a base plate are glued to natural rubber plates in such a way that the insulator can be firmly connected to the superstructure or the foundation. The natural rubber sheets are in turn glued to each other according to a special manufacturing method in order to be able to absorb extreme pressure, tensile and shear deformations. The isolators are designed so that they are highly elastic in all directions.

Natural rubber support bodies are preferred because they achieve better damping values compared to steel springs and generally meet the elasticity requirements with sufficient resistance to aging.

When the system is at rest, insulators must absorb the static superstructure and introduce them into the foundation. Their geometric positions and individual stiffness are therefore dictated by the mass distribution in the superstructure and cannot be influenced without complex technical measures; i.e. that vertical loads at the level of the foundation generally have to be absorbed where they occur, whereby the following types of training are conceivable: insulator carpet made of identical elements; Insulator carpet with individually adapted elements; terraced arrangement; free positioning.

The following variants of the foundation can occur: classic foundation with additional elements to accommodate the earthquake protection system (foundation lays directly on the ground); Mezzanine that separates the basement from the upper floor and houses the additional elements of the earthquake protection system.

Regardless of the variant chosen, the formation of the foundation must meet the following requirements: conception as a support area with great rigidity in all directions; Prevention of uncontrolled relative movements between the support points; Protection of the insulators against harmful environmental influences; easy access to

Isolator control, maintenance and replacement; flawless absorption of classic load cases (dead weight, payload, wind and snow).

As a further embodiment of the invention, a shelter D is shown in FIG. 4, which is supported by insulators C on the walls of a cavern.

It has now been arithmetically proven that the following three technical measures must be taken to ensure that buildings that are floating are integrated against earthquakes:

- The six basic frequencies 1-6 of the system must be moved to Zone I (Fig. 2). This is done with the help of mechanical isolators, which are highly elastic in all directions (including vertical). The two lowest basic frequencies

I, 2 should be approximately one third of the lower cut-off frequency Fi of the resonance range or below, while the top fundamental frequency 6 may rise to just below the cut-off frequency Fi in the event of an earthquake.

- The superstructure of the building must be designed so stiff that the upper frequencies 7- o'clock of the isolated system all come to Zone III. For this purpose, a so-called box or honeycomb-like structure of the superstructure selected: the outer walls of the building are designed to be load-bearing, they are continuous, solid and only partially interspersed with openings. Their interlocking effect among themselves and with the ceilings, inner walls and columns is to be ensured by construction measures known per se. Relative movements at nodes, element boundaries and construction sections must be excluded thanks to suitable training. A honeycomb-shaped formation occurs when the ceilings and the load-bearing inner walls are included for the internal bracing of the box.

- The foundation must form a rigid whole with the ground. For this, a solid foundation must be selected, e.g. Rock, solid rock or suitable consolidated alluvions, whose vertical stiffness is at least six to nine times greater than the insulator stiffness. The foundation itself is generally designed as a continuous slab or as a trough. As a result, relative movements between the support points can be reduced to negligible sizes and the influence of soil elasticity is negligible for the calculation process.

These proposed technical measures have the following effects:

- In the resonance range of the design spectral shape (zone

II, Fig. 2), a zone is formed without natural frequencies of the system: natural frequency hole in the resonance range of the excitation spectrum.

- Since the fundamental system natural frequencies are all very low, only greatly reduced, higher-frequency components of the ground excitation E are transferred to the superstructure. This eliminates the risk of brittle fractures in the superstructure.

- Thanks to the rigid design and high insulation, there is no longer a risk of collapse for the superstructure.

- Any differential bearing displacements during the passage of a shaft movement are recorded "at the source" (relative movement between the highly elastic insulators), which greatly reduces the risk of overloading the superstructure.

There are also considerable simplifications for the mathematical model:

- The superstructure may also be treated like a rigid body in the final main arithmetic of vibration analysis for computational purposes. He now only has the s

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six degrees of freedom of the rigid body in space. In practice, this does not affect the quality of the results compared to the "exact solution".

- The influence of the ground elasticity can be neglected for computational purposes if the unloaded so-called “free-field natural frequencies” of the floor are at least two and a half to three times as high as the highest basic frequency of the floating building. In this case, it is no longer necessary to take into account the interaction between building / building site.

- The influence of the upper frequencies (from 7th system frequency) on the vibration stress of the protected building area may be neglected for computational purposes.

- Thanks to its rigid construction, resonance problems in the protected building area can be dealt with locally. An interaction between locally resonant parts and the protected building area is eliminated thanks to its rigid design.

The practical feasibility of proof of safety against extreme vibrations is part of the task for integral vibration protection. The following procedure is considered suitable to provide this evidence in the event of extreme earthquake stress. It is based on the fact that, by appropriately defining the load case, extreme earthquakes can be distinguished from the standard earthquakes that occur regularly in a high seismic region in terms of strength and character. The definition of the load case can be suitably transferred to other dynamic stress conditions. The security verification is carried out in the following stages:

1st stage

Definition of extreme and standard quakes, valid for the construction site

2nd stage

Proof of the seismic safety of the building without an earthquake protection system against the load case of standard earthquakes in accordance with the regulations of the earthquake standards of the region concerned, assuming a restriction to elastic deformations according to the standard

3rd stage

Find the most unfavorable directions of incidence by rotating the three-dimensional design quakes around the foundation to determine the extreme reactions - repetitive spectral or modal calculation under extreme albums

4th stage

Investigation of the behavior of the extremal movement and force quantities with systematic variation of the mass and stiffness distribution on the building with earthquake protection system - parameter analysis by repetitive spectral calculation in the most unfavorable directions of incidence

5th stage

Determination of the extreme movement and force quantities of the overall system and of system areas on the building with earthquake protection system - modal or incremental calculation with extreme design earthquakes in the most unfavorable directions of incidence

6th stage

Incorporation of the extreme earthquake reactions into the static calculation and the structural design - actual safety verification

7th stage

Investigation of the local risk of resonance - calculation with finite element models for building sections and the determined kinematic reactions (5th stage) as input functions

For stages 4-6, the structure must be introduced as a spatially defined mathematical model. The structural resolution should go into so much detail that the analysis allows the exposed elements to be found that are the first to experience elasto-plastic deformations.

In order to experimentally confirm the mathematical proof of safety, the model of a standard building was created and subjected to a vibration that corresponds to the most movement-intensive earthquakes that are currently known.

The standard building shown in an exploded view in FIG. 5 has a clear, clear structure with a statically and dynamically clearly conceivable concept. The floor plan is point-symmetrical, and the design is monolithic, compact and box-like, so that a strong, rigid construction is guaranteed. The superstructure is again marked with D, the insulators with C and the foundation with B. The storey ceilings Dl, the roof D.2, the core D.3 with the staircase, the inner and outer walls D.4 and the supports D. 5 contribute to the internal bracing of the building.

This standard building can be considered a representative representative of a “tower tower”.

The technical feasibility of the integral earthquake protection could be verified with this building. The natural frequency hole according to the invention formed in the resonance range of the earthquake design spectrum.

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Claims (9)

625 302 1. Body that is protected against vibrations from the ground and floats in space, which is connected via mechanical isolators, which are elastic in all directions, to a base rigidly attached to the ground, characterized in that between the highest (6) of the six referred to as fundamental frequencies lowest natural system frequencies (1-6) of the vibration element consisting of the body (D) and the isolators (C) and the lowest (7) of the higher natural system frequencies (7, 8 ...) referred to as upper frequencies, there is an area called a natural frequency hole, in which the vibration element has no natural frequencies, the natural frequency hole being in the resonance range of the decisive design reaction spectrum of the vibration. 2. Body according to claim 1, characterized in that the two lowest fundamental frequencies (1 and 2) are not more than 40% of the highest fundamental frequency (6). 2nd PATENT CLAIMS 3. Body according to claim 1, characterized in that the highest fundamental frequency (6) does not exceed 1.6 Hz and the lowest upper frequency (7) does not fall below 6.0 Hz. 4. Body according to claim 1, characterized in that it is box-shaped or honeycomb-shaped, the outer walls being designed to be continuous and load-bearing. 5. Body according to claim 4, characterized in that the elements carrying in the interior are used for its stiffening. 6. Body according to claim 1, characterized in that the base (B) is designed as a continuous plate or as a trough. 7. Body according to claim 1, characterized in that a rigid base is present. 8. Body according to claim 1, characterized in that the vertical stiffness of the insulators is at least six times smaller than the vertical stiffness of the substrate and the vertical stiffness of the body itself. 9. Body according to claim 1, characterized in that it is a building, a machine or an isolator station.