Which buildings are most resistant to earthquakes? Earthquakes and increasing the stability of buildings and structures. Resistance of the house to wind load

DECAYING OF THE SEISMIC EFFECT WITH DISTANCE FROM THE EPICENTER

The magnitude of an earthquake characterizes the energy of seismic waves emitted by its source, and the intensity of seismic tremors on the earth's surface depends on both the magnitude of the epicentral distance and the depth of the source.The given attenuation curves characterize the decrease in the intensity of seismic tremors with distance from the epicenter of earthquakes of different magnitudes with “normal” focal depths, the upper edge of which is located quite close to the earth’s surface. The deeper the source, the weaker the seismic effect at the epicenter and the slower it fades with distance.

// This effect can be compared to the intensity of illumination of a surface with a regular flashlight. The closer he is to her, the brighter the illumination at the shortest distance from him, but the faster it decreases with distance from the flashlight. When the flashlight itself moves away from the illuminated surface, the illumination in the center becomes dimmer, but this “less dangerous twilight” covers a fairly large area. //

POTENTIAL SITES OF SCENARIO EARTHQUAKES

In construction practice, along with probabilistic seismic hazard assessments determined on the basis of regulatory maps of seismic zoning of the territory of the Russian Federation - OSR-97, deterministic methods for calculating expected seismic impacts from so-called scenario earthquakes are often used, regardless of when they occur. In this case, an adequate selection of potential earthquake sources that pose the greatest danger to given areas and specific construction sites plays a decisive role.

An indispensable condition for the identification and seismological parameterization of potential earthquake foci (PEF), considered as scenarios, is reliance on the seismic geodynamic model of earthquake foci occurrence zones (EZZ zones), on the basis of which a set of official OSR-97 maps of federal significance was created.

When calculating theoretical (synthetic) accelerograms and the dynamic response of buildings and structures to seismic impacts, a number of geological and geophysical parameters of the structure and the environment in which seismic waves propagate (location of the source, its size and orientation in space, magnitude, seismic moment, attenuation of seismic waves of different lengths with distance, spectral influence of real soils and other factors).

Since deterministic estimates of the seismic effect obtained from scenario earthquakes are conservative, they often significantly overestimate the value of seismic intensity obtained by probabilistic methods. At the same time, such extreme seismic impacts may turn out to be extremely rare events that can often be neglected. In this regard, it is allowed to convert deterministic estimates into probabilistic ones that comply with the regulatory requirements of OSR-97 maps.

3D model of earthquake sources and potential sources, representing the greatest danger to the conditional city. 1 – lineaments, 2 – domains, 3 – sources of large earthquakes with magnitude M=6.8 and more, 4 – sources of earthquakes with M=6.7 and less, 5 – trajectories of seismic wave propagation from potential sources Z1 and Z2 of earthquakes towards the city.

This figure shows an example of the propagation of seismic waves from two potential sources of earthquakes - from a relatively small source Z1, located in the domain directly below the city, and from the largest source Z2, belonging to the lineament and located at a considerable distance from the city.

In the first case, the scenario earthquake is characterized by a moderate magnitude (no more than M=5.5) and a small depth of the source (no more than 10 km). In the second case, the source belongs to a high-rank lineament (magnitude M = 7.5) and has a fairly large extent (about 100 km).

Source Z1 generates a high-frequency spectrum of emitted waves that have a short duration and fairly high accelerations, which are mainly dangerous for low buildings. Conversely, low-frequency dynamic impacts from the Z2 source, which are characterized by relatively small accelerations compared to the Z1 event, pose a significant danger to high-rise construction sites due to their very long duration (possibly also high oscillation velocities and ground displacements) at low acceleration values.

The first results of stress tests of the BelNPP were presented in Minsk. They showed the resistance of the nuclear power plant under construction to extreme influences.

Construction of the BelNPP in Ostrovets, October 2017. Photo: Dmitry Brushko, TUT.BY

Conducted in 2016. They represent a one-time unscheduled test of a nuclear power plant’s resistance to extreme impacts. After the accident at the Japanese Fukushima plant, stress tests are carried out at nuclear power plants - operating and under construction. Today, journalists were presented with the first reports on the results of the inspection.

“The Belarusian nuclear power plant is resistant to similar events that occurred at Fukushima,” noted the head of the Department of Nuclear and Radiation Safety of the Ministry of Emergency Situations Olga Lugovskaya. — Buildings, structures, equipment are designed in accordance with the existing regulatory framework, safety margins are determined - this is a certain margin over the existing mandatory requirements.

Despite the fact that the BelNPP already has safety margins, the commission that conducted the stress tests decided to increase them.

“An action plan to strengthen safety reserves will be formed during this year, including with possible recommendations from European experts,” noted Olga Lugovskaya.

The head of the Department of Nuclear and Radiation Safety added that the stress tests even assessed the ability to withstand conditions that are extremely unlikely for the territory of Belarus: for example, strong earthquakes, flooding associated with a tsunami.

As the director of the Center for Geophysical Monitoring of the National Academy of Sciences of Belarus clarified Arkady Aronov, experts calculated two main parameters based on which the degree of seismic hazard is assessed. These are the design basis earthquake and the maximum design earthquake. The design basis earthquake was 6 points on a 12-point scale, the maximum design earthquake was 7 points on a 12-point scale.

— We came to the conclusion that it would be desirable to include in the program of work on the National Report work on creating a permanent seismic observation network to monitor geodynamic activity in the area of ​​the nuclear power plant. Despite the fact that our territory is located in a weak geodynamic region and it can in no way be compared with the conditions in which Fukushima was located,” said Arkady Aronov. — The program includes the creation of a local seismic control network. The temporary one is still there for the period of design and construction, but in the future this network will operate at all stages of the life of the nuclear power plant, including both the operational period and decommissioning. In the process of seismic control, the parameters will be constantly updated so that it is possible to review, clarify seismic impacts, and fully understand the seismic situation on-line.

— In addition, stress tests for the Belarusian NPP were also carried out for such natural factors, which with a very low probability may occur on the territory of Belarus. These are strong winds, squalls, very heavy rains, large hail, dust storms, heavy snowstorms, snowfalls, icing, fogs, droughts and extreme temperatures - the weather phenomena themselves and various combinations thereof. The consequences of power supply failures and losses of electrical carriers were also taken into account,” added Olga Lugovskaya.

- Minor changes - yes, there are. All of them will concern changes in the electrical part of the project - to increase safety margins in the scenario of a complete blackout of the station, - explained the deputy chief engineer of the Republican Unitary Enterprise "Belarusian Nuclear Power Plant" Alexander Parfenov.

Belarus has already sent a national report on a targeted reassessment of the safety of the Belarusian NPP (stress tests) to the European Commission. In the near future it should appear in the public domain on the ENSREG website and on the website of the Gosatomnadzor of Belarus. The national report was compiled by specialists from the Ministry of Natural Resources and Environment, the National Academy of Sciences, the Ministry of Emergency Situations, the Ministry of Foreign Affairs, and the Belarusian Nuclear Power Plant. In March 2018, European experts will come to Belarus to exchange views and proposals for the Belarusian National Report.

16.08.2016

Previously, we mainly focused on the parameters of the foundations of structures: accelerations, movement speeds, their periods (soils). The basis for any structure is a certain type of soil (rock). Therefore, in order for the rocks under the building to serve as a reliable foundation during their service life, not only during an earthquake, but also in normal times, it is necessary to know the physical-mechanical, chemical, hydrogeological, filtration properties of rocks and soil characteristics - how load-bearing element subject to various influences. In this subsection we will briefly discuss some practical issues regarding the behavior of soils during earthquakes. A more detailed analysis of the results of experimental and theoretical studies on the behavior of various soils under dynamic influences is given in the works.
In our opinion, the classic definition of soil as a complex material is given in the article by E. Faccioli and D. Resenditz, which says: “Soil is an aggregate of individual particles, the voids between which are filled with air or water. Consequently, soil is a two- or three-phase substance, the stress state of which can be fully described if the voltages corresponding to each phase are specified.”
According to the engineering-geological classification, rocks are divided (according to F.P. Savarensky with additions by V.D. Lomtadze) into 5 classes:
1. Rocky: andesites, basalts, sandstones and conglomerates with strong cement, limestones and dolomites are dense and durable.
2. Semi-rocky: weathered and highly fractured rocks of the first group, volcanic tuffs, tuffites and tuffaceous rocks, sandstones, shales, limestones and clayey dolomites, megrelians, chalk, siliceous rocks.
3. Loose unbound: sands, gravel, pebbles.
4. Soft knitted: clays, loams, sandy slurries, forest species.
5. Rocks of special composition, condition and properties: quicksand sands, sandy silts, saline clayey rocks, clayey silts, peats, soil, gypsum.
Most damage to buildings and structures during earthquakes is associated with low strength and soil collapses, which manifest themselves in the form of landslides, rock failure, soil liquefaction, delamination of embankments, loss of slope stability, and foundation precipitation. Soils provide one or another resistance to tension, compression and shear. The strength of a soil is determined mainly by its shear resistance, since compressive resistance is rarely exhausted; and the soil is almost not subject to stretching in real conditions.
Shear resistance of soils. Static resistance (ultimate strength) to soil shear is determined by the relation:

τ - shear resistance, o - normal stress along the fracture plane, σ0 - pore water pressure, tgφ - internal friction coefficient, φ - internal friction angle, c - adhesion. In (2.142), (σ-σ0) represents the effective normal stress determined by the soil structure, it is also called soil friction; the second term c in (2.142) is called cohesion. For loose soils there is no adhesion, i.e. c=0, for loams c=0.06-0.14, for clays c=0.35-0.65kg/cm2. The value of the angle of internal friction φ depends on the conditions of occurrence, porosity and density of the soil. With increasing density and decreasing porosity, the value of φ increases: for various silts φ = 13-16°, sandy clays - φ = 22-27°, sands - φ = 35-40°. When τ ≤ (σ-σ0)tgφ + c, soil shift (destruction) does not occur.
The main characteristics under dynamic loading are: shear modulus G for low-amplitude cyclic deformations, internal absorption, stress-strain relationship for large-amplitude cyclic deformations, and strength under cyclic loading. In soil subjected to alternating shear deformation, irreversible processes always take place, regardless of the level of loading. The stress-strain curve after several cycles takes the form of a closed loop, which has two main parameters: the average slope of the loop determines the shear modulus, and the area of ​​the loop determines the internal absorption. The amount of shear is influenced by the porosity coefficient, the degree of water saturation and the frequency of application of loads. As the shear amplitude y increases, the shear modulus G decreases. It has been established that Poisson's ratio under dynamic loads does not depend on frequency and varies within the range of 0.25-0.35 for non-cohesive soils and within 0.4-0.5 for cohesive soils. To measure internal friction forces, the following parameters are used: energy absorption coefficient Ω, logarithmic decrement δ and phase angle between force and deformation α. These parameters are interconnected by the following relationships:

Water saturation leads to an almost twofold increase in the decrement of fluctuations δ compared to soils in their dry state. For dry sands, the average value of δ at medium deformations (γ = 10v-3) reaches 0.2. Due to the large dependence of the values ​​of the shear modulus and vibration decrement on many factors, it is advisable to determine them experimentally for each specific soil using equipment specially designed for such tests.
Soil liquefaction. Sand saturated with water experiences liquefaction during intense vibrations. During an earthquake, the upper parts of such pounds lose their load-bearing capacity. As a result, structures built on these soils receive precipitation, and systems of engineering structures buried in the ground are destroyed and float up. The strength of sand under variable shear stress is proportional to the compression force. In the near-surface layer, where the compression force is small, the shear resistance is less than in deeper layers, so the likelihood of liquefaction is greater in the upper layers. Based on the results of special experiments, it was established that fine-grained sand liquefies faster than coarse-grained sand. Moistened sand also liquefies faster than dry sand. According to Okomoto, the experimentally determined maximum soil accelerations (in gals) at which its liquefaction occurs are given in Table 2.22.

Experimental studies by many scientists have shown that the higher the compression of sand and the lower the number of cyclic stresses, the higher the amplitude of recurrent stresses that cause liquefaction of the soil. The period of soil vibration has almost no effect on soil liquefaction.
The reaction of hard soils during earthquakes is similar to the reaction of an elastic system under shock impacts, during which the dynamic coefficient can reach 40-50, and the reaction of soft soils is similar to prolonged forced impacts, during which the dynamic coefficient can reach 5-10 times. Therefore, during earthquakes with a short duration, accelerations on rocky areas of soil should, in principle, be greater than on loose areas, and during earthquakes with a long duration, on the contrary, accelerations on loose areas should be greater.
Stability of slopes during earthquake. The main reason for the destruction of slopes during earthquakes is an increase in the intensity of seismic impact near the slope due to a sharp change in the terrain. There are known cases of an increase in the acceleration of the top of a cliff by 20-30% compared to the acceleration of the base. This effect is taken into account by many standards for earthquake-resistant construction, in particular French and Armenian ones. In addition, the destruction of slopes is also affected by a decrease in the strength and stability of the soil due to their vibration during an earthquake. Calculations to ensure slope stability during an earthquake are carried out as under normal conditions (without an earthquake), with additional consideration of horizontal and vertical inertial loads of the inert mass of soil from horizontal and vertical accelerations of the predicted earthquake. Unlike other structures, when calculating earthworks, the influence of the vertical component of an earthquake is quite large.

In the general case, with heterogeneous soils, to check the stability of the slope, the soil mass is divided into a large number of individual parts. Arbitrarily assigning the location of the center 0 and the radius of the circle r, after drawing the sliding surface, the soil mass is divided into a number of columns by vertical sections, as shown in Fig. 2.69. In the figure, one of these columns abсd is highlighted and the condition of equilibrium of forces is considered for it.
The sum of the moments of external forces (own weight plus horizontal and vertical inertia forces from the earthquake) relative to point 0 will be:

where y is the arm of the force kgW (kr is the seismicity coefficient in the horizontal direction) relative to point 0.
The sum of the moments of internal forces (internal friction force plus adhesion force) relative to point 0 will be:

To ensure slope stability, i.e. in order for the soil mass not to be subject to sliding (shear), it is necessary that

When calculating the slope, the minimum value of the ratio Mφ0/Mw0 is taken as the value of the safety factor. For normal conditions (in the absence of an earthquake) in the equations kg and kв are taken equal to zero.
Another, more simplified option for calculating stability taking into account seismic impact is that the stability calculation is carried out as in a conventional static calculation, but with a reduced value of the internal friction angle φ (slope rocks are artificially considered less strong depending on the strength of the earthquake). In this case, in formulas (2.144) and (2.145), the seismicity coefficients kr and kв are taken equal to zero, and the value of the angle φ is calculated using the formula

where φst is the real angle of internal friction of the rock, kg is the horizontal seismicity coefficient. So, for example, with kr=0.2 or kg=0.4, the angle of internal friction, in a simplified calculation of slope stability taking into account seismic effects, according to (2.147), must be taken respectively 8° and 15.6° less than the actual φst.
Soil pressure on retaining walls during earthquakes. The active soil pressure on retaining walls under normal conditions (without earthquakes) is determined by the Coulomb method, as shown in Fig. 2.70, where the following notations are adopted: w - weight of a soil mass of unit thickness, q - load on the soil surface, Q = cBC - force adhesion, R - friction force, P - pressure on the wall, φ - angle of internal friction of the soil, δg - angle of wall friction, usually taken equal to φ/2, BC - sliding plane.

The unknown forces P and R and the angle ψ0 are determined from the static equilibrium equations of the soil mass ABC. Mononobe, developing Coulomb's ideas, developed a method for determining the pressure P on a wall taking into account seismic influences. The effect of an earthquake is taken into account by changing the magnitude of the gravitational acceleration g and rotating it by an angle θ according to the formulas:

He obtained the following expressions for active Pa and passive pressure Pp. In this case, the pressure from the weight of the soil and from the external load on the soil surface are determined separately.
Active soil pressure (Fig. 2.71). The active pressure from the soil's own weight on the back side of the retaining wall is determined by the formula

Active soil pressure from external load on the surface is equal to:

where W is the volumetric weight of soil of unit thickness (kg/cm2), H is the height of the retaining wall, φ is the angle of internal friction of the soil, ψ is the angle of inclination of the wall, θ0 is the angle of inclination of the soil surface, ψ0 is the angle between the horizontal plane and the sliding plane, q is the intensity of external linear load (kg/cm2) on an inclined surface, the Ca coefficient is expressed by the formula:

The force Paw is applied at a distance of 2/3 of the height of the retaining wall from its top, and the force Paq is applied at the middle of the height of the wall and makes an angle δt to its surface.
Passive soil pressure(Fig. 2.72). Passive soil pressure on the back side of the wall from its own weight is determined by the formula:


Passive soil pressure from external load is determined by the formula:

The force Ppw is applied at a distance of 2/3 of the height of the retaining wall from its top, and the direction is perpendicular to the surface of the wall, the force pq is applied at the middle of the height of the wall and perpendicular to its surface. Formulas (2.150) and (2.151) show that in the case of a vertical retaining wall (δt = 0, ψ = 0) and a horizontal soil surface, with an increase in the seismicity coefficient kg, the active soil pressure increases, and the passive pressure decreases. At the same time, in comparison with normal conditions (kg = 0) for kg = 0.4, the active pressure at φ = 30° increases by 2.12 times, and the passive pressure decreases by 1.41 times.
The soil pressure on a retaining wall is determined under normal conditions by the difference between active and passive pressure (critical pressure). At the moment the wall begins to overturn, the soil pressure is determined only by the active pressure on the wall. Conversely, when force is applied to a retaining wall from the frontal surface, the soil pressure can reach passive pressure. This contributes to the stability of the retaining wall in critical condition.
Bearing capacity of soil during earthquakes. The bearing capacity of soil during strong earthquakes is significantly reduced. The quantitative characteristics of this reduction depend on many factors, the main one being the magnitude of the ground acceleration in the horizontal and vertical directions. If we assume that an earthquake leads to a decrease in the angle of internal friction of the soil compared to normal conditions, then based on the calculation of the bearing capacity of foundations under normal conditions, it is possible to determine their bearing capacity under seismic influences. This method of taking into account the influence of an earthquake on the bearing capacity of the soil was developed in the work of Sh. Okomoto. Below are the final expressions for determining the bearing capacity of point (round) and strip foundations, with general destruction of the soil from shear.
For a circular foundation with a radius R, the bearing capacity - Q is determined by the formula:

For a strip foundation with a loading width B, the linear load-bearing capacity (per unit width) is calculated by the formula:

where c is the specific cohesion of the soil, γ is the volumetric weight of the soil, Df is the depth of the foundation. The values ​​of the dimensionless coefficients Nc, Nq, Nγ, Nc", Nq" and Nγ" respectively for round and strip foundations, depending on the values ​​of soil acceleration in the horizontal and vertical directions kg and kv and the angle of internal friction of the soil φ are given in Table 2.23. B in the table, ks denotes the total seismicity coefficient:

Table data 2.23 at kс=0 correspond to the case of determining the value of the bearing capacity of foundations Q without taking into account the influence of an earthquake.

As the analysis of the table shows, with an increase in the seismicity coefficient ks (earthquake intensity), the bearing capacity of the soil decreases most significantly due to frictional resistance (Nγ), then the bearing capacity decreases due to deepening of the foundation (Nq) and, finally, the reduction in bearing capacity is the slightest due to clutch count (Nc).
Soil settlement. Under seismic influence, weakly consolidated soil becomes compacted and undergoes settlement. The maximum settlement value mainly depends on the amplitude of soil acceleration. When the horizontal acceleration of the soil reaches 300-400cm/sec2, the sandy soil on the Earth's surface flows and its condition changes greatly. The presence of a structure on the ground surface (additional vertical loading) greatly influences the settlement pattern depending on the weight of the structure and the frequency of ground vibrations. For critical structures, specific answers to these questions can only be obtained through special experimental model studies.
Stress in the soil from concentrated force. Due to the action of a concentrated force on the surface of a soil mass (Fig. 2.73), limited by a horizontal plane and having large (unlimited) dimensions in other directions, normal σz and tangential stresses τxy and τzx have the following values:

These formulas are known as Boussinesq's formulas and have great practical applications. For compressive stresses σz, a simpler formula is usually used:

The coefficients k are called Boussinesq coefficients. Their tabulated values ​​for various r/z ratios are given in many scientific textbooks on soil mechanics.
At the point of direct application of concentrated force, compressive stresses, as one would expect, reach very large values ​​and the soil undergoes plastic deformation. Therefore, for a certain hemispherical region around a concentrated force, formulas (2.158) are unacceptable. To obtain a more realistic stress picture, their values ​​are calculated at a certain distance (depth) below the point of application of the concentrated force. In the case of a uniformly distributed external load, to apply formulas (2.159), it can be divided into equal sections and considered as concentrated. In other words, a uniformly distributed load can, to a first approximation, be replaced by equivalent concentrated forces. The compressive stress σz at a given point in the soil in this case is calculated as the sum of the compressive stresses from each concentrated force according to the formula:

where n is the number of sections for dividing a uniformly distributed external load, ki is the Boussinesq coefficient, determined depending on the ratio ri/z for the i-th section. As the analysis of various examples shows, when using this method, depending on the length of the distributed load, the error in calculating σz does not exceed 6%.

Traditional methods and means of protecting buildings and structures from seismic influences include a large complex of various measures aimed at increasing the load-bearing capacity of building structures, the design of which is carried out on the basis of norms and rules developed by domestic and foreign construction experience that guarantee the seismic resistance of buildings and structures in areas with seismicity 7 , 8 and 9 points.

The design of buildings and structures in seismically hazardous areas begins with compliance with the general principles of earthquake-resistant construction, according to which all building materials, structures and design schemes used must ensure the lowest seismic loads. When designing, it is recommended to adopt, as a rule, symmetrical structural schemes and achieve a uniform distribution of structural rigidities and masses. In buildings and structures made from prefabricated elements, it is recommended to place joints outside the zone of maximum forces; it is necessary to ensure the homogeneity and solidity of structures through the use of reinforced prefabricated elements.

The choice of space-planning schemes, their shape and dimensions has a significant impact on the seismic resistance of buildings. The most preferred shapes of structures in plan are circle, polygon, square and similar shapes. However, such forms do not always meet planning requirements, so the most often used is a rectangular shape with parallel spans, without a difference in the heights of adjacent spans and without incoming corners. If there is a need to create complex shapes in the building plan, then it should be cut along its entire height into separate closed compartments of a simple shape. The design solutions of the compartments during an earthquake should ensure the independent operation of each of them. This is achieved by installing anti-seismic seams, which can be combined with temperature or sedimentary ones. Anti-seismic seams are carried out by installing paired walls, paired columns or frames, as well as by erecting a frame and a wall.

For a building height of up to 5 m, the width of such a seam should be at least 3 cm. For buildings of greater height, the width of the seam is increased by 2 cm for every 5 m of height.

In multi-storey buildings, a major role in their seismic resistance is played by the structures of interfloor floors and coatings, which work as rigidity diaphragms, ensuring the distribution of seismic loads between vertical load-bearing elements. Prefabricated reinforced concrete floors and roofing of buildings must be cast-in-place, rigid in the horizontal plane and connected to vertical load-bearing structures.

The side edges of the panels (slabs) of floors and coverings must have a keyed or grooved surface. For connection with an anti-seismic belt or for connection with frame elements in panels (slabs), reinforcement outlets or embedded parts should be provided.

The mass of the structure has a significant influence on the values ​​of seismic loads. Therefore, under the action of seismic forces, it is necessary to strive for the maximum possible reduction in the weight of structures and the resulting loads.

Non-load-bearing elements such as partitions and frame fillings are recommended to be lightweight, usually of large-panel or frame construction and connected to walls, columns, and, if the length is more than 3 m, to floors. In buildings of more than five floors, the use of hand-made brickwork partitions is not permitted. Partitions made of brick or stone should be reinforced along the entire length at least every 700 mm in height with rods with a total cross-section in the joint of at least 0.2 square meters. see. It is allowed to make suspended partitions with movement limiters from the plane of the panels.

Stone buildings suffer the most damage during earthquakes compared to other types of modern buildings.

The seismic resistance of stone buildings is determined by the strength of brick and stone, and also depends on the strength of their adhesion to the mortar. According to current regulatory documents, it is recommended that load-bearing brick and stone walls be erected, as a rule, from brick or stone panels, blocks manufactured in factories using vibration, or from brick or stone masonry using mortars with special additives that increase the adhesion of the mortar to the brick or stone .

To ensure seismic resistance, the choice of construction site is important - proximity to fault lines should be avoided. Changes are also made to the foundation of structures - “cushions” are created from concrete or polymer materials, thanks to which buildings slide or “float” during an earthquake and do not break along those lines where the greatest stress is created.

The most promising direction for increasing seismic resistance is seismic insulation of buildings. Seismic insulation involves detuning the vibration frequencies of a building from the prevailing frequencies of impact. This is what ensures a reduction in the mechanical energy received by the structure from the base.

Experts from Russia and foreign countries have proposed a variety of devices for seismic isolation systems and vibration energy absorbers of structures, as well as systems using alloys that remember the volumetric state, and other “intelligent” systems.

The following trends are observed in the world: the first is the use of pure seismic insulation of buildings, which is usually installed in the lower floors: rubber-metal supports of various modifications, with low and high damping, with and without a lead core, using various materials . There are also pendulum-type friction sliding supports. Both types of supports are used very widely in the world.

(Construction (Moscow), 03/30/2009)

The second direction is the use of damping (vibration damping), which has been known for a very long time and is constantly being improved. For high-rise construction, as a rule, a combination is used: seismic insulation is placed in the lower floor, and damping is installed along the height of the building. Now manufacturers offer a wide variety of dampers: metal, liquid, there are special alloys with memory, special damping walls; the latest devices, although relatively expensive, are quite effective.

The material was prepared based on information from open sources

Earthquake on demand

Earthquake scientists at the University of Nevada on Wednesday tested new highway bridge designs that were designed with innovative connecting elements that should better withstand dangerous ground tremors and prevent the structure from collapsing, burying people under thousands of tons of concrete and rebar.

was placed on a special stand to simulate movements of the earth's crust. The structure weighs 100 tons and is 21 meters long.

The tests were carried out a day after the devastating earthquake that occurred in Mexico. The shaking of the model continued for 30 seconds, during which time seismic sensors located on the columns and beam connections of the bridge recorded the movement of the structure and monitored the behavior of the new connecting elements.

Graduates from local technical universities attended the experiment and put their acquired knowledge into practice by measuring the effects of a bridge crash test. According to the preliminary report, during the initial inspection of the structure, no serious structural damage was noted.

“The bridge survived the experiment better than we expected.”, said Saeed Sayidi, a professor of civil and environmental engineering who led the project. He has been conducting similar research for more than 30 years, so he has considerable experience in such matters.

Already designed to withstand earthquakes, they are often unsafe for movement after large tremors. The designs tested used special types of connectors to connect precast pavement components, including ultra-high performance concrete, he said.

“Earthquakes themselves don’t kill people, they kill structures”, said Sayidi.

The elements had previously been tested individually, but had never before been combined into a bridge model subjected to realistic substrate movements. The model and amplitude of the tremors were taken from the 1994 earthquake that occurred in California, this corresponded to 7.5 points, which is a fairly serious test for the design.

Among other things, innovative connecting elements allow concrete and other elements to be secured to an existing bridge structure to speed up repair and reconstruction after a disaster.