When erecting stone structures in seismic areas, additional requirements are imposed on materials:
The surfaces of stone and brick must be cleaned of dust before laying;
In mortars intended for the construction of masonry, Portland cement should be used as a binder;
Natural sand should be used as a filler in mortar mixtures; the use of fine-grained and dune sands enriched with sifted stone mining waste with a particle size of 1.5-2.5 mm is allowed; it is not allowed to use cement mortars without plasticizers;
When choosing cements for mortars, it is necessary to take into account the influence of air temperature on their setting time. Masonry of bricks and ceramic stones should be carried out in compliance with the following additional requirements: masonry of stone structures should be carried out to the full thickness of the structure in each row; horizontal, vertical transverse and longitudinal joints of the masonry must be filled completely with mortar with cutting of the mortar on the outer sides of the masonry;
The masonry of walls in places where they are mutually adjacent is erected only at the same time;
The bonded rows of masonry, including backfill rows, are laid from whole stone and brick;
The laying of brick pillars and piers with a width of 2.5 bricks or less should be done only from whole bricks, with the exception of cases where incomplete bricks are needed for bandaging masonry seams;
Temporary breaks in the masonry being erected should end only with an inclined groove and be located outside the areas of structural reinforcement of the walls; the bent ends of the vertical connections of the anti-seismic belt should be released (for control) onto one of the internal surfaces of the wall being built.
When accepting stone structures carried out in seismic areas, the work performed on the installation of a reinforced belt at the level of the top of foundations, floor-by-floor anti-seismic belts, fastening of thin walls and partitions, as well as the adhesion strength of the mortar to the wall stone material are subject to intermediate acceptance.
When making masonry in dry and hot climates, special attention is paid to maintaining the mobility of the mortar before it is laid in the structure. For this purpose, the mortar is protected from moisture loss, delamination and heating by sunlight during the transportation of the mortar and the laying process itself.
Before laying in a structure, ceramic bricks must be generously moistened or immersed in water for the time necessary for optimal moisture. When there are breaks in the masonry, you cannot leave a layer of mortar on the freshly laid masonry; continuation of the masonry after the break must be started by abundantly wetting the surface of the masonry with water. To protect the masonry from premature evaporation of moisture from the mortar, the laid part of the structure is covered with moisture-absorbing materials, periodically moistened, and, if possible, additional sun protection coatings are installed.
Under these conditions, it is necessary to maintain the viability of the solution until it is laid. The loss of water from the solution through evaporation during transportation and storage leads to a sharp decrease in its mobility and acceleration of cement hydration processes, which negatively affect the quality and labor intensity of the masonry.
The main measures aimed at maintaining the viability of the solution are: the use of cement that has a long setting time, the use of water-retaining additives when preparing the solution, transportation and storage of the solution
on site in closed containers or covered with moisture-proofing material.
It is mandatory to moisten the brick before laying.
When reconstructing existing buildings, there is often a need to increase the overall stability and solidity of the masonry, increase the strength characteristics of the masonry elements, and replace individual sections of weakened masonry.
The solidity of masonry is increased when cracks occur in it. They are sealed by injecting cement or polymer mortar through specially prepared holes. Holes in the masonry are made in vertical and inclined areas - after 0.8...1.5 m, in horizontal areas - after 0.2...0.5 m. The cement mortar is pumped with a mortar pump, the polymer composition is injected into the masonry from a special balloon with a manual syringe.
The technological execution of the process is the same for different methods. Holes with a diameter of 25...35 mm are drilled into the masonry structure, into which steel tubes 15...20 cm long are inserted, embedded in the masonry with cement mortar. Cracks on the surface are sealed (covered) with cement-sand mortar. After a day, they begin injection, which is carried out in horizontal tiers from bottom to top.
The load-bearing capacity of masonry is increased by strengthening it with clips, which significantly reduce the lateral expansion of the masonry and increase the resistance of the masonry to longitudinal force.
Steel frames are used to strengthen rectangular walls and pillars. It consists of vertical steel corners installed on the mortar at the corners of the reinforced element and clamps made of strip or round steel, welded or bolted to the corners. The resulting structural solution is carefully caulked with a rigid cement-sand mortar, often over a metal mesh.
The reinforced concrete cage includes vertical reinforcing bars with a diameter of 6...12 mm with transverse clamps with a diameter of 4...10 mm, located at a distance between them of 100...150 mm; concrete coating - according to calculation, but usually within 60... 120 mm.
A reinforced mortar cage is similar to a reinforced concrete one, but in it the reinforcement frame is covered with a layer of cement-sand plaster 30...40 mm thick. This type of clip can be used to reinforce elements of any cross-section when a large degree of reinforcement is not required. The advantages of a mortar casing are its small thickness, lower labor intensity and cost of the device compared to a reinforced concrete casing.
Rolled profiles are used for local reinforcement of walls and partitions. Beams from a channel or I-beam are installed on both sides of the wall and they are tightened with bolts. Plastering with cement-sand mortar is carried out over a metal mesh.
Replacement of elements of stone structures is carried out when it is inappropriate to use other methods of strengthening. Replacing structures requires the preliminary arrangement of their temporary fastening for the period of work, after which it is possible to dismantle the heavily damaged masonry and make a new one. Simultaneous dismantling of adjacent walls is not allowed. During the masonry process, horizontal seams are reinforced with steel mesh; work is performed on high-grade bricks and mortar.
Often, under the influence of aggressive groundwater, foundations and basement walls are destroyed.
One scientist figuratively said about seismicity that “our entire civilization is being built and developed on the lid of a cauldron, inside of which terrible, unbridled tectonic elements are boiling, and no one is safe from the fact that at least once in their life they will not find themselves on this bouncing lid.”
These “funny” words interpret the problem quite loosely. There is a strict science called seismology (“seismos” in Greek means “earthquake”, and this term was coined about 120 years ago by the Irish engineer Robert Male), according to which the causes of earthquakes can be divided into three groups:
· Karst phenomena. This is the dissolution of carbonates contained in the soil, the formation of cavities that can collapse. Earthquakes caused by this phenomenon are usually of low magnitude.
· Volcanic activity. An example is the earthquake caused by the eruption of the Krakatoa volcano in the strait between the islands of Java and Sumatra in Indonesia in 1883. Ash rose 80 km into the air, over 18 km 3 fell, and this caused bright dawns for several years. The eruption and sea wave over 20 m high led to the death of tens of thousands of people on neighboring islands. However, earthquakes caused by volcanic activity are observed relatively rarely.
· Tectonic processes. It is because of them that most earthquakes occur on the globe.
“Tektonikos” translated from Greek means “build, builder, structure.” Tectonics is the science of the structure of the earth’s crust, an independent branch of geology.
There is a geological hypothesis of fixism, based on the idea of the inviolability (fixedness) of the positions of the continents on the Earth's surface and the decisive role of vertically directed tectonic movements in the development of the earth's crust.
Fixism is opposed to mobilism, a geological hypothesis first expressed by the German geophysicist Alfred Wegener in 1912 and suggesting large (up to several thousand km) horizontal movements of large lithospheric plates. Observations from space allow us to speak about the unconditional correctness of this hypothesis.
The Earth's crust is the upper shell of the Earth. There is a distinction between continental crust (thickness from 35...45 km under the plains, up to 70 km in the mountains) and oceanic (5...10 km). The structure of the first has three layers: upper sedimentary, middle, conventionally called “granite,” and lower “basalt”; in the oceanic crust there is no “granite” layer, and the sedimentary layer has a reduced thickness. In the transition zone from the continent to the ocean, an intermediate type of crust (subcontinental or suboceanic) develops. Between the Earth's crust and the Earth's core (from the surface of Mohorovicic to a depth of 2900 km) is the Earth's mantle, which makes up 83% of the Earth's volume. It is believed that it is mainly composed of olivine; Due to the high pressure, the mantle material appears to be in a solid crystalline state, with the exception of the asthenosphere, where it is possibly amorphous. The temperature of the mantle is 2000...2500 o C. The lithosphere includes the earth's crust and the upper part of the mantle.
The interface between the Earth's crust and the Earth's mantle was identified by the Yugoslav seismologist A. Mohorovicic in 1909. The speed of longitudinal seismic waves when passing through this surface increases abruptly from 6.7...7.6 to 7.9...8.2 km/s.
According to the theory of “planar tectonics” (or “plate tectonics”) by Canadian scientists Forte and Mitrovica, the earth’s crust throughout the entire thickness and even slightly below the Mohorovicic surface is divided by cracks into plane-platforms (tectonic lithospheric plates), which carry the load of oceans and continents . 11 large plates have been identified (African, Indian, North American, South American, Antarctic, Eurasian, Pacific, Caribbean, Cocos plate west of Mexico, Nazca plate west of South America, Arabian) and many small ones. The slabs have different heights. The seams between them (the so-called seismic faults) are filled with a material that is much less durable than the material of the slabs. The plates seem to float in the earth's mantle and continuously collide with one another at their edges. There is a schematic map that shows the directions of movement of tectonic plates (relatively relative to the African plate).
According to N. Calder, there are three types of joints between slabs:
A crevice formed when plates move away from each other (North American from Eurasian). This results in an annual increase of 1 cm in the distance between New York and London;
A trench is an oceanic depression along the boundary of plates as they approach each other, when one of them bends and plunges under the edge of the other. This happened on December 26, 2004, west of the island of Sumatra during the collision of the Indian and Eurasian plates;
Transform fault - sliding of plates relative to each other (Pacific relative to North American). Americans sadly joke that San Francisco and Los Angeles will sooner or later unite, since they are on different sides of the Saint Andreas seismic fault (San Francisco is on the North American plate, and the narrow Californian section, together with Los Angeles, is on Pacific) about 900 km long and move towards each other at a speed of 5 cm/year. When an earthquake occurred here in 1906, 350 km of the indicated 900 shifted and froze with a displacement of up to 7 m. There is a photograph that shows how one part of a California farmer’s fence shifted along the fault line relative to the other. According to the predictions of some seismologists, as a result of a catastrophic earthquake, the California Peninsula could be torn away from the mainland along the Gulf of California and turn into an island or even sink to the bottom of the ocean.
Most seismologists attribute the occurrence of earthquakes to the sudden release of elastic deformation energy (elastic release theory). According to this theory, long-term and very slow deformations - tectonic movement - occur in the fault area. This leads to the accumulation of stress in the slab material. The stresses grow and grow and at a certain point in time reach the limiting value for the strength of rocks. Rock rupture occurs. The rupture causes a sudden rapid displacement of the plates - a push, elastic recoil, resulting in seismic waves. Thus, long-term and very slow tectonic movements transform into seismic movements during an earthquake. They have high speed due to the rapid (within 10...15 s) “discharge” of the accumulated enormous energy. The maximum earthquake energy recorded on Earth is 10 18 J.
Tectonic movements occur along a significant length of the plate junction. The rupture of rocks and the seismic movements caused by it occur at some local section of the junction. This area can be located at different depths from the Earth's surface. This area is called the source or hypocentral region of the earthquake, and the point in this region where the rupture began is called the hypocenter or focus.
Sometimes not all the accumulated energy is “discharged” at once. The unreleased part of the energy causes stress in new bonds, which after some time reaches the limiting value for the strength of rocks in certain areas, as a result of which an aftershock occurs - a new rupture and a new push, but of lesser force than at the time of the main earthquake.
Earthquakes are preceded by weaker tremors - foreshocks. Their appearance is associated with the achievement in the massif of such stress levels at which local destruction occurs (in the weakest areas of the rock), but the main crack cannot yet form.
If the source of the earthquake is located at a depth of up to 70 km, then such an earthquake is called normal; at a depth of more than 300 km, it is called deep-focus. At intermediate focal depths, earthquakes are called intermediate. Deep-focus earthquakes are rare; they occur in the area of ocean basins, are distinguished by a large amount of released energy and, therefore, have the greatest effect on the Earth's surface.
The effect of earthquakes on the Earth's surface, and consequently their destructive effect, depend not only on the amount of energy released during a sudden rupture of material at the source, but also on the hypocentral distance. It is defined as the hypotenuse of a right triangle, the legs of which are the epicentral distance (the distance from the point on the Earth’s surface where the intensity of the earthquake is determined to the epicenter - the projection of the hypocenter onto the Earth’s surface) and the depth of the hypocenter.
If you find points on the Earth's surface around the epicenter where an earthquake occurs with the same intensity, and connect them with lines, you will get closed curves - isoseites. Near the epicenter, the shape of the isoseites to a certain extent repeats the shape of the source. As you move away from the epicenter, the intensity of the effect weakens, and the pattern of this weakening depends on the energy of the earthquake, the characteristics of the source and the medium of passage of seismic waves.
During earthquakes, the Earth's surface experiences vertical and horizontal vibrations. Vertical fluctuations are very significant in the epicentral zone, but already at a relatively short distance from the epicenter their significance quickly decreases, and here we mainly have to take into account horizontal influences. Since cases of the epicenter being located within or near settlements are rare, until recently only horizontal vibrations were mainly taken into account in design. As the building density increases, the danger of locating epicenters within populated areas increases accordingly, and therefore vertical fluctuations also have to be taken into account.
Depending on the effect of an earthquake on the Earth's surface, they are classified according to intensity in points, which is determined on various scales. In total, about 50 such scales were proposed. Among the first are the Rossi-Forel (1883) and Mercalli-Cancani-Sieberg (1917) scales. The latter scale is still used in some European countries. In the USA, since 1931, a modified 12-point Mercalli scale (MM for short) has been used. The Japanese have their own 7-point scale.
Everyone is familiar with the Richter scale. But it has nothing to do with classification by intensity points. It was proposed in 1935 by the American seismologist Charles Richter and theoretically substantiated together with B. Gutenberg. This is a magnitude scale - a conditional characteristic of the deformation energy released by the earthquake source. Magnitude is found using the formula
where is the maximum displacement amplitude in the seismic wave, measured during the earthquake under consideration at some distance (km) from the epicenter, μm (10 -6 m);
The maximum displacement amplitude in a seismic wave, measured during some very weak (“zero” earthquake) at some distance (km) from the epicenter, µm (10 -6 m).
When used to determine displacement amplitudes superficial waves recorded by observation stations are received
This formula makes it possible to find the value from , measured by just one station, knowing . If, for example, 0.1 m = 10 5 µm and 200 km, 2.3, then
The C. Richter scale (classification of earthquakes by magnitude) can be presented in the form of a table:
Thus, the magnitude only characterizes well the phenomenon that occurred at the source of the earthquake, but does not provide information about its destructive effect on the Earth’s surface. This is the “prerogative” of the other already mentioned scales. Therefore, the statement of the Chairman of the USSR Council of Ministers N.I. Ryzhkov after the Spitak earthquake that “the strength of the earthquake was 10 points on the Richter scale" makes no sense. Yes, the intensity of the earthquake was indeed equal to 10 points, but on the MSK-64 scale.
International scale of the Institute of Physics of the Earth named after. O.Yu. Schmidt Academy of Sciences of the USSR MSK-64 was created within the framework of the Unified Energy System S.V. Medvedev (USSR), Sponheuer (GDR) and Karnik (Czechoslovakia). It is named after the first letters of the authors' surnames - MSK. The year of creation, as the name suggests, is 1964. In 1981, the scale was modified and it became known as MSK-64 *.
The scale contains instrumental and descriptive parts.
The instrumental part is decisive for assessing the intensity of earthquakes. It is based on the readings of a seismometer - a device that uses a spherical elastic pendulum to record the maximum relative displacements in a seismic wave. The period of natural oscillations of the pendulum is selected so that it is approximately equal to the period of natural oscillations of low-rise buildings - 0.25 s.
Classification of earthquakes according to the instrumental part of the scale:
The table shows that the ground acceleration at 9 points is 480 cm/s 2, which is almost half = 9.81 m/s 2. Each point corresponds to a twofold increase in ground acceleration; with 10 points it would be equal to .
The descriptive part of the scale consists of three sections. In the first, the intensity is classified according to the degree of damage to buildings and structures carried out without anti-seismic measures. The second section describes residual phenomena in soils, changes in the regime of groundwater and groundwater. The third section is called “other signs,” which includes, for example, people’s reactions to an earthquake.
The damage assessment is given for three types of buildings erected without anti-seismic reinforcements:
Damage degree classification:
| Damage level | Name of damage | Characteristics of damage |
| Minor damage | Small cracks in the walls, small pieces of plaster breaking off. | |
| Moderate damage | Small cracks in the walls, small cracks in the joints between panels, fairly large pieces of plaster breaking off; falling tiles from roofs, cracks in chimneys, falling parts of chimneys (meaning building chimneys). | |
| Severe damage | Large deep and through cracks in the walls, significant cracks in the joints between panels, falling chimneys. | |
| Destruction | Collapse of internal walls and frame filling walls, breaks in walls, collapse of parts of buildings, destruction of connections (communications) between individual parts of the building. | |
| Collapses | Complete destruction of the building. |
If the building structures have anti-seismic reinforcements corresponding to the intensity of earthquakes, their damage should not exceed degree 2.
Damage to buildings and structures erected without anti-seismic measures:
| Scale, points | Damage characteristics of different types of buildings |
| 1st degree in 50% of type A buildings; 1st degree in 5% of type B buildings; Grade 2 in 5% of type A buildings. | |
| 1st degree in 50% of type B buildings; 2nd degree in 5% of type B buildings; 2nd degree in 50% of type B buildings; 3rd degree in 5% of type B buildings; 3rd degree in 50% of type A buildings; Grade 4 in 5% of type A buildings. Cracks in stone walls. | |
| 2nd degree in 50% of type B buildings; 3rd degree in 5% of type B buildings; 3rd degree in 50% of type B buildings; 4th degree in 5% of type B buildings; 4th degree in 50% of type A buildings; Grade 5 in 5% of Type A buildings Monuments and statues move, tombstones are knocked over. Stone fences are being destroyed. | |
| 3rd degree in 50% of type B buildings; 4th degree in 5% of type B buildings; 4th degree in 50% of type B buildings; 5th degree in 5% of type B buildings; Grade 5 in 75% of Type A buildings. Monuments and columns topple. |
Residual phenomena in soils, changes in the regime of groundwater and groundwater:
| Scale, points | Characteristic signs |
| 1-4 | There are no violations. |
| Small waves in flowing bodies of water. | |
| In some cases, landslides; visible cracks up to 1 cm wide are possible on damp soils; in mountainous areas there are isolated landslides, changes in the flow of sources and the water level in wells are possible. | |
| In some cases, landslides of roadways on steep slopes and cracks on roads. Violation of pipeline joints. In some cases, changes in the flow rate of sources and water levels in wells. In few cases, existing water sources appear or disappear. Isolated cases of landslides on sandy and gravelly river banks. | |
| Small landslides on steep slopes of road cuts and embankments, cracks in the soil reach several centimeters. New reservoirs may emerge. In many cases, the flow rate of sources and the water level in wells change. Sometimes dry wells fill with water or existing ones dry up. | |
| Significant damage to the banks of artificial reservoirs, ruptures of parts of underground pipelines. In some cases, rails are bent and roadways are damaged. On flood plains, deposits of sand and silt are often noticeable. Cracks in the soil are up to 10 cm, and on the slopes and banks - more than 10 cm. In addition, there are many thin cracks in the soil. Frequent landslides and soil shedding, rock falls. |
Other signs:
| Scale, points | Characteristic signs |
| It is not felt by people. | |
| Celebrated by some very sensitive people who are at peace. | |
| Few people notice very slight swaying of hanging objects. | |
| Slight rocking of hanging objects and stationary vehicles. The faint clink of dishes. Recognized by all people inside buildings. | |
| There is a noticeable swaying of hanging objects, the pendulum clock stops. Unstable dishes tip over. It is felt by all people, everyone wakes up. Animals are worried. | |
| Books fall from shelves, paintings and light furniture move. Dishes fall. Many people are running out of the premises, the movement of people is unstable. | |
| All signs are 6 points. All the people run out of the premises, sometimes jumping out of the windows. It is difficult to move without support. | |
| Some of the hanging lamps are damaged. Furniture moves and often topples. Light objects bounce and fall. People have difficulty staying on their feet. Everyone runs out of the premises. | |
| Furniture tips over and breaks. Great concern for animals. |
The correspondence between the C. Richter and MSK-64 * scales (the magnitude of the earthquake and its destructive consequences on the Earth’s surface) can be displayed as a first approximation in the following form:
Every year, from 1 to 10 million plate collisions (earthquakes) occur, many of which are not even felt by humans; the consequences of others are comparable to the horrors of war. Worldwide seismicity statistics for the 20th century show that the number of earthquakes with magnitude 7 and above ranged from 8 in 1902 and 1920 to 39 in 1950. The average number of earthquakes with magnitude 7 and above was 20 per year, with magnitude 8 and higher – 2 per year.
The record of earthquakes indicates that geographically they are concentrated mainly along the so-called seismic belts, which practically coincide with faults and adjacent to them.
75% of earthquakes occur in the Pacific seismic belt, which covers almost the entire perimeter of the Pacific Ocean. Near our Far Eastern borders, it passes through the Japanese and Kuril Islands, Sakhalin Island, the Kamchatka Peninsula, the Aleutian Islands to the Gulf of Alaska and then extends along the entire western coast of North and South America, including British Columbia in Canada, the states of Washington, Oregon and California in the USA, Mexico, Guatemala, El Salvador, Nicaragua, Costa Rica, Panama, Colombia, Ecuador, Peru and Chile. Chile is already an inconvenient country, stretching in a narrow strip for 4300 km, and it also stretches along the fault between the Nazca plate and the South American plate; and the type of joint here is the most dangerous - the second.
23% of earthquakes occur in the Alpine-Himalayan (another name is the Mediterranean-Trans-Asian) seismic belt, which in particular includes the Caucasus and the Anatolian Fault closest to it. The Arabian plate, moving in a northeast direction, “rams” the Eurasian plate. Seismologists are recording a gradual migration of potential earthquake epicenters from Turkey towards the Caucasus.
There is a theory that the harbinger of earthquakes is an increase in the stressed state of the earth's crust, which, compressing like a sponge, pushes water out of itself. At the same time, hydrogeologists record an increase in groundwater levels. Before the Spitak earthquake, the groundwater level in Kuban and Adygea rose by 5-6 m and has remained virtually unchanged since then; the reason for this was attributed to the Krasnodar reservoir, but seismologists think otherwise.
Only about 2% of earthquakes occur in the rest of the Earth.
The strongest earthquakes since 1900: Chile, May 22, 1960 - magnitude 9.5; Alaska Peninsula, March 28, 1964 - 9.2; near the island. Sumatra, December 26, 2004 - 9.2, tsunami; Aleutian Islands, March 9, 1957 - 9.1; Kamchatka Peninsula, November 4, 1952 – 9.0. The top ten strongest also includes earthquakes on the Kamchatka Peninsula on February 3, 1923 – 8.5 and on the Kuril Islands on October 13, 1963 – 8.5.
The maximum intensity expected for each region is called seismicity. There is a seismic zoning scheme and a list of seismicity in populated areas in Russia.
You and I live in the Krasnodar region.
In the 70s, most of it, according to the seismic zoning map of the USSR territory according to SNiP II-A.12-69, did not belong to zones with high seismicity; only a narrow strip of the Black Sea coast from Tuapse to Adler was considered seismically hazardous.
In 1982, according to SNiP II-7-81, the zone of increased seismicity was extended by including the cities of Gelendzhik, Novorossiysk, Anapa, and part of the Taman Peninsula; it also expanded inland - to the city of Abinsk.
On May 23, 1995, Deputy Minister of Construction of the Russian Federation S.M. Poltavtsev sent a List of populated areas of the North Caucasus to all heads of republics, heads of administrations of territories and regions of the North Caucasus, research institutes, design and construction organizations, indicating the new seismicity scores adopted for them and the repeatability of seismic impacts. This List was approved by the Russian Academy of Sciences on April 25, 1995 in accordance with the Temporary Seismic Zoning Scheme for the North Caucasus (VSSR-93), compiled at the Institute of Physics of the Earth on behalf of the government after the catastrophic Spitak earthquake on December 7, 1988.
According to VSSR-93, now most of the territory of the Krasnodar Territory, with the exception of its northern regions, has fallen into a seismically active zone. For Krasnodar, the intensity of earthquakes began to be 8 3 (indices 1, 2 and 3 corresponded to the average frequency of earthquakes once every 100, 1000 and 10,000 years or the probability of 0.5; 0.05; 0.005 in the next 50 years).
There are still different points of view on the advisability or inexpediency of such a drastic change in the assessment of potential seismic hazard in the region.
An interesting analysis is of maps that show the locations of the last 100 earthquakes in the region since 1991 (an average of 8 earthquakes per year) and the last 50 earthquakes since 1998 (also an average of 8 earthquakes per year). Most earthquakes still occurred in the Black Sea, but they were also observed to “deepen” onto land. The three strongest earthquakes were observed in the area of Lazarevskoye, on the Krasnodar-Novorossiysk highway and on the border of the Krasnodar and Stavropol territories.
In general, earthquakes in our region can be characterized as quite frequent, but not very strong. Their specific energy per unit area (10 10 J/km 2) is less than 0.1. For comparison: in Turkey -1...2, in Transcaucasia - 0.1...0.5, in Kamchatka and the Kuril Islands - 16, in Japan - 14...15.9.
Since 1997, the intensity of seismic impacts in points for construction areas began to be taken on the basis of a set of maps of general seismic zoning of the territory of the Russian Federation (OSR-97), approved by the Russian Academy of Sciences. This set of maps provides for the implementation of anti-seismic measures during the construction of facilities and reflects the 10% (map A), 5% (map B) and 1% (map C) probability of possible exceedance (or, respectively, 90%, 95% and 99% probability of not exceeding) within 50 years the values of seismic activity indicated on the maps. The same estimates reflect a 90% probability of not exceeding the intensity values within 50 (map A), 100 (map B) and 500 (map C) years. The same estimates correspond to the frequency of occurrence of such earthquakes on average once every 500 (map A), 1000 (map B) and 5000 (map C) years. According to OSR-97, for Krasnodar the intensity of seismic impacts is 7, 8, 9.
The set of maps OSR-97 (A, B, C) allows you to assess the degree of seismic hazard at three levels and provides for the implementation of anti-seismic measures during the construction of objects of three categories, taking into account the responsibility of the structures:
map A – mass construction;
cards B and C – objects of increased responsibility and especially critical objects.
Here is a selection from the list of settlements in the Krasnodar Territory located in seismic areas, indicating the estimated seismic intensity in MSK-64 scale points *:
| Names of settlements | OSR-97 cards | ||
| A | IN | WITH | |
| Abinsk | |||
| Abrau-Durso | |||
| Adler | |||
| Anapa | |||
| Armavir | |||
| Akhtyrsky | |||
| Belorechensk | |||
| Vityazevo | |||
| Vyselki | |||
| Gaiduk | |||
| Gelendzhik | |||
| Dagomys | |||
| Dzhubga | |||
| Divnomorskoe | |||
| Dinskaya | |||
| Yeisk | |||
| Ilsky | |||
| Kabardinka | |||
| Korenovsk | |||
| Krasnodar | |||
| Krinitsa | |||
| Kropotkin | |||
| Kurganinsk | |||
| Kushchevskaya | |||
| Labinsk | |||
| Ladoga | |||
| Lazarevskoe | |||
| Leningradskaya | |||
| Loo | |||
| Magri | |||
| Matsesta | |||
| Mezmay | |||
| Mostovskoy | |||
| Neftegorsk | |||
| Novorossiysk | |||
| Temryuk | |||
| Timashevsk | |||
| Tuapse | |||
| Khosta |
According to OSR-97, for the city of Krasnodar the intensity of seismic impacts is 7, 8, 9. That is, there was a decrease in seismicity by 1 point compared to VSSR-93. It is interesting that the border between the 7- and 8-point zones, as if on purpose, “bent” beyond the city of Krasnodar, beyond the river. Kuban. The border bent similarly near the city of Sochi (8 points).
The seismic intensity indicated on the maps and in the list of settlements refers to areas with some average mining and geological conditions (category II of soils according to seismic properties). Under conditions different from average, the seismicity of a specific construction site is clarified based on microzoning data. In the same city, but in different areas, seismicity can be significantly different. In the absence of seismic microzoning materials, a simplified determination of the seismicity of the site is allowed according to table SNiP II-7-81 * (permafrost soils are omitted):
| Soil category according to seismic properties | Soils | Seismicity of the construction site with seismicity of the region, points | ||
| I | Rocky soils of all types are unweathered and slightly weathered, coarse clastic soils are dense, low-moisture from igneous rocks, containing up to 30% sand-clay aggregate. | |||
| II | Rocky soils are weathered and highly weathered; coarse soils, with the exception of those classified as category I; gravelly sands, large and medium-sized dense and medium-density low-moisture and wet sands, fine and dusty sands dense and medium-density low-moisture, clay soils with a consistency index with a porosity coefficient - for clays and loams and - for sandy loams. | |||
| III | Sands are loose, regardless of the degree of humidity and size; sands, gravelly, large and medium-sized, dense and medium-density, water-saturated; fine and dusty sands, dense and medium density, moist and water-saturated; clayey soils with a consistency index with a porosity coefficient - for clays and loams and - for sandy loams. | > 9 |
The zone where an earthquake causes significant damage to buildings and structures is called meisoseismic or pleistoseismic. It is limited to 6-point isoseism. At an intensity of 6 points and less, the damage to ordinary buildings and structures is low, and therefore, for such conditions, design is carried out without taking into account seismic hazard. The exception is some special industries, for which 6-point and sometimes less intense earthquakes can be taken into account when designing.
The design of buildings and structures taking into account the requirements of anti-seismic construction is carried out for conditions of 7-, 8- and 9-point intensity.
As for magnitude 10 or more intense earthquakes, for such cases any seismic protection measures are insufficient.
Here are the statistics of material losses from earthquakes in buildings and structures designed and constructed without and taking into account anti-seismic measures:
Here are statistics on damage to buildings of various types:
Proportion of buildings damaged during earthquakes
Predicting earthquakes is a thankless task.
The following story can be cited as a truly bloody example.
In 1975, Chinese scientists predicted the time of occurrence of an earthquake in Liao Lini (formerly Port Arthur). Indeed, the earthquake occurred at the predicted time, killing only 10 people. In 1976, at an international conference, a Chinese report on this matter caused a furor. And in the same 1976, the Chinese were unable to predict the Tanshan (not Tien Shan, as journalists misrepresented, namely the Tanshan - from the name of the large industrial center Tanshan with a population of 1.6 million people) earthquake. The Chinese agreed on the number of victims of 250 thousand, but according to average estimates, the number of deaths during this earthquake was 650 thousand, and according to pessimistic estimates - about 1 million people.
Predicting the intensity of earthquakes also often makes God laugh.
In Spitak, according to the SNiP II-7-81 map, an earthquake with an intensity higher than 7 points should not have occurred, but it “shook” with an intensity of 9...10 points. In Gazli they also “wrong” by 2 points. The same “mistake” occurred in Neftegorsk on Sakhalin Island, which was completely destroyed.
How to curb this natural element, how to make buildings and structures located practically on vibration platforms, any of which is ready to “launch” at any moment, seismically resistant? These problems are solved by the science of earthquake-resistant construction, perhaps the most complex science for modern technical civilization; its difficulty lies in the fact that we must take action “in advance” against an event whose destructive power cannot be predicted. Many earthquakes occurred, many buildings with a variety of structural designs collapsed, but many buildings and structures were able to survive. A wealth of, mostly sad, literally bloody experience has been accumulated. And much of this experience was included in SNiP II-7-81 * “Construction in seismic areas.”
Let us present samples from SNiP, territorial SN of the Krasnodar Territory SNKK 22-301-99 “Construction in seismic areas of the Krasnodar Territory”, the currently discussed draft of new norms and other literary sources relating to buildings with load-bearing walls made of brick or masonry.
Masonry is a heterogeneous body consisting of stone materials and joints filled with mortar. By introducing reinforcement into the masonry, one obtains reinforced stone structures. Reinforcement can be transverse (grids are located in horizontal joints), longitudinal (reinforcement is located outside under a layer of cement mortar or in grooves left in the masonry), reinforcement by including reinforced concrete in the masonry (complex structures) and reinforcement by enclosing the masonry in a reinforced concrete or metal frame from the corners.
As stone materials in conditions of high seismicity, artificial and natural materials are used in the form of bricks, stones, small and large blocks:
a) solid or hollow brick with 13, 19, 28 and 32 holes with a diameter of up to 14 mm, grade not lower than 75 (grade characterizes the compressive strength); size of solid brick is 250x120x65 mm, hollow brick - 250x120x65(88) mm;
b) with a calculated seismicity of 7 points, hollow ceramic stones with 7, 18, 21 and 28 holes of a grade not lower than 75 are allowed; stone size 250x120x138 mm;
c) concrete stones measuring 390x90(190)x188 mm, solid and hollow concrete blocks with a volumetric mass of at least 1200 kg/m3 grade 50 and above;
d) stones or blocks made of shell rocks, limestones of grade no less than 35, tuffs, sandstones and other natural materials of grade 50 and higher.
Stone materials for masonry must meet the requirements of the relevant GOSTs.
It is not allowed to use stones and blocks with large voids and thin walls, masonry with backfills and others, the presence of large voids in which leads to concentration of stress in the walls between the voids.
The construction of residential buildings made of mud brick, adobe and soil blocks in areas with high seismicity is prohibited. In rural areas, with seismicity up to 8 points, the construction of one-story buildings from these materials is permitted provided that the walls are reinforced with a wooden antiseptic frame with diagonal braces, while the construction of parapets from raw and soil materials is not allowed.
Masonry mortar Usually a simple one is used (on one type of binder). The grade of the solution characterizes its compressive strength. The mortar must meet the requirements of GOST 28013-98 “Building mortars. General technical conditions".
The strength limits of stone and mortar “dictate” the strength limits of the masonry as a whole. There is a formula by Prof. L.I. Onishchik to determine the tensile strength of all types of masonry under short-term loading. The limit of long-term (unlimited time) resistance of masonry is about (0.7...0.8).
Stone and reinforced stone structures work well, mainly in compression: central, eccentric, oblique eccentric, local (crumple). They perceive bending, central stretching and shearing much worse. SNiP II-21-81 “Stone and reinforced masonry structures” provides the corresponding methods for calculating structures based on the limit states of the first and second groups.
These techniques are not discussed here. After becoming familiar with reinforced concrete structures, the student is able to master them independently (if necessary). This section of the course outlines only constructive anti-seismic measures that must be carried out during the construction of stone buildings in areas with high design seismicity.
So, first about stone materials.
Their adhesion to the mortar in the masonry is influenced by:
- design of stones (already discussed);
· the condition of their surface (before laying, stones must be thoroughly cleaned of deposits obtained during transportation and storage, as well as deposits associated with deficiencies in stone production technology, dust, ice; after a break in masonry work, the top row of masonry should also be cleaned);
ability to absorb water (brick, light rocks (< 1800 кг/м3), а также крупные блоки с целью уменьшения поглощения воды из раствора должны перед укладкой смачиваться. Однако степень увлажнения не должна быть чрезмерной, чтобы не получалось разжижение раствора, поскольку как обезвоживание, так и разжижение раствора снижают сцепление.
The construction laboratory must determine the optimal relationship between the amount of pre-wetting of the stone and the water content of the mortar mixture.
Research shows that porous natural stones, as well as dry baked bricks made from loess-like loams, which have high water absorption (up to 12...14%), must be immersed in water for at least 1 minute (at the same time they are moistened up to 4... 8 %). When delivering bricks to the workplace in containers, soaking can be done by lowering the container into water for 1.5 minutes and placing it in the “case” as quickly as possible, reducing the time spent in the open air to a minimum. After a break in masonry work, the top row of masonry should also be soaked.)
Now - about the solution.
Piece-by-piece hand masonry should be carried out using mixed cement mortars of a grade not lower than 25 in summer conditions and not lower than 50 in winter conditions. When constructing walls from vibrated brick or stone panels or blocks, mortars of a grade of at least 50 must be used.
To ensure good adhesion of stones to the mortar in the masonry, the latter must have high adhesion (adhesive ability) and ensure complete contact area with the stone.
The following factors influence the amount of normal adhesion:
we have already listed those that depend on stones (their design, surface condition, ability to absorb water);
but those that depend on the solution. This:
- its composition;
- tensile strength;
- mobility and water holding capacity;
- hardening mode (humidity and temperature);
- age.
In purely cement-sand mortars, large shrinkage occurs, accompanied by partial separation of the mortar from the surface of the stone and thereby reducing the effect of the high adhesive ability of such mortars. As the content of lime (or clay) in cement-lime mortars increases, its water-holding capacity increases and shrinkage deformations in the joints decrease, but at the same time the adhesive ability of the mortar deteriorates. Therefore, to ensure good adhesion, the construction laboratory must determine the optimal content of sand, cement and plasticizer (clay or lime) in the solution. Various polymer compositions are recommended as special additives that increase adhesion: divinylstyrene latex SKS-65GP(B) according to TU 38-103-41-76; copolymer vinyl chloride latex VHVD-65 PTs according to TU 6-01-2-467-76; PVA polyvinyl acetate emulsion according to GOST 18992-73.
Polymers are introduced into the solution in an amount of 15% of the weight of cement, calculated as the dry residue of the polymer.
If the calculated seismicity is 7 points, special additives may not be used.
To prepare a solution for earthquake-resistant masonry, sand with a high content of clay and dust particles cannot be used. Slag Portland cement and pozzolanic Portland cement cannot be used. When choosing cements for mortars, it is necessary to take into account the influence of air temperature on the setting time.
The following data on stones and mortar must be recorded in the work log:
- brand of stones and solutions used
· composition of the mortar (according to passports and invoices) and the results of its tests by a construction laboratory;
- place and time of preparation of the solution;
- delivery time and condition of the solution after transportation at
- centralized preparation and delivery of the solution;
- consistency of the mortar when laying walls;
· measures to increase the adhesion strength carried out when laying walls (wetting the brick, cleaning it from dust, ice, laying “under the flood”, etc.);
- caring for masonry after construction (watering, covering with mats, etc.);
- temperature and humidity conditions during the construction and maturation of masonry.
So, we looked at the starting materials for masonry - stones and mortar.
Now let’s formulate the requirements for their joint work in laying the walls of an earthquake-resistant building:
· the masonry should, as a rule, be single-row (chain). It is allowed (preferably if the calculated seismicity is no higher than 7 points) of multi-row masonry with repetition of bonded rows at least every three spooned rows;
· bonded rows, including backfill rows, should be laid only from whole stone and brick;
· only whole bricks should be used to lay brick pillars and partitions with a width of 2.5 bricks or less, with the exception of cases where incomplete bricks are needed for bandaging masonry seams;
- It is not allowed to lay masonry in a wasteland;
· horizontal, vertical, transverse and longitudinal joints must be completely filled with mortar. The thickness of horizontal joints must be at least 10 and no more than 15 mm, the average within the floor is 12 mm; vertical - no less than 8 and no more than 15 mm, average - 10 mm;
· masonry should be carried out over the entire thickness of the wall in each row. In this case, the milepost rows must be laid using the “pressing” or “end-to-end with cutting” methods (the “end-to-end” method is not allowed). To thoroughly fill the vertical and horizontal joints of the masonry, it is recommended to do it “under the fill” with a mobility of the solution of 14...15 cm.
The solution is poured over the row using a scoop.
To avoid loss of mortar, masonry is carried out using inventory frames protruding above the row mark to a height of 1 cm.
Leveling the solution is done using a lath, for which a frame serves as a guide. The speed of movement of the slats when leveling the solution poured along the row should ensure that it gets into the vertical seams. The consistency of the mortar is controlled by the mason using an inclined plane located to the horizon at an angle of approximately 22.50; the mixture should drain from this plane. When laying a brick, the mason must press it and tap it, making sure that the distances for vertical joints do not exceed 1 cm. Any damage to the mortar bed during the process of laying bricks (sampling mortar for sticking, moving bricks along the wall) is not allowed.
When work is temporarily stopped, do not fill the top row of masonry with mortar. Continuation of work, as already noted, must begin with watering the surface of the masonry;
· vertical surfaces of grooves and channels for monolithic reinforced concrete inclusions (they will be discussed below) should be made with the mortar trimmed by 10...15 mm;
· masonry of walls in places where they are mutually adjacent should be erected only simultaneously;
· pairing thin walls of 1/2 and 1 brick with walls of greater thickness when erecting them at different times by installing grooves is not allowed;
· temporary (assembly) breaks in the masonry being erected should end only with an inclined groove and be located outside the places of structural reinforcement of the walls (reinforcement will be discussed below).
Constructed in this way (taking into account the requirements for stones, mortar and their joint work), the masonry must acquire the normal adhesion necessary to absorb seismic influences (temporary resistance to axial tension along untied seams). Depending on the value of this value, the masonry is divided into category I masonry with 180 kPa and category II masonry with 180 kPa >120 kPa.
If it is impossible to obtain a cohesion value equal to or exceeding 120 kPa at the construction site (including with mortars with additives), the use of brick and stone masonry is not allowed. And only with a calculated seismicity of 7 points is it possible to use natural stone masonry at less than 120 kPa, but not less than 60 kPa. In this case, the height of the building is limited to three floors, the width of the walls is taken to be no less than 0.9 m, the width of the openings is no more than 2 m and the distance between the axes of the walls is no more than 12 m.
The value is determined from laboratory test results, and the designs indicate how to monitor actual adhesion on site.
Monitoring the strength of normal adhesion of the mortar to brick or stone should be carried out in accordance with GOST 24992-81 "Stone structures. Method for determining the adhesion strength in masonry."
Sections of walls for inspection are selected according to the instructions of the technical supervision representative. Each building must have at least one plot per floor with a separation of 5 stones (bricks) on each plot.
Tests are carried out 7 or 14 days after the completion of masonry.
In the selected section of the wall, the top row of masonry is removed, then around the stone (brick) being tested, with the help of scrapers, avoiding shocks and impacts, the vertical seams are cleared into which the grips of the testing installation are inserted.
During testing, the load shall be increased continuously at a constant rate of 0.06 kg/cm2 per second.
The axial tensile strength is calculated with an error of 0.1 kg/cm2 as the arithmetic mean of the results of 5 tests. The average normal adhesive strength is determined from the results of all tests in the building and must be at least 90% of that required by the project. In this case, the subsequent increase in the strength of normal adhesion from 7 or 14 days to 28 days is determined using a correction factor taking into account the age of the masonry.
Simultaneously with testing the masonry, the compressive strength of the mortar is determined, taken from the masonry in the form of plates with a thickness equal to the thickness of the seam. The strength of the solution is determined by a compression test on cubes with ribs 30...40 mm, made of two plates glued together using a thin layer of gypsum dough 1..2 mm.
Strength is determined as the arithmetic mean of tests of 5 samples.
When carrying out work, it is necessary to strive to ensure that the normal adhesion and compressive strength of the mortar in all walls and especially along the height of the building are the same. Otherwise, various deformations of the walls are observed, accompanied by horizontal and oblique cracks in the walls.
Based on the results of monitoring the strength of normal adhesion of the mortar to brick or stone, a report is drawn up in a special form (GOST 24992-81).
So, in earthquake-resistant construction masonry of two categories can be used. In addition, according to their resistance to seismic influences, masonry is divided into 4 types:
1. Complex masonry design.
2. Masonry with vertical and horizontal reinforcement.
3. Masonry with horizontal reinforcement.
4. Masonry with reinforcement of only wall joints.
The complex design of the masonry is carried out by introducing vertical reinforced concrete cores into the body of the masonry (including at the intersection and junction of walls), anchored in anti-seismic belts and foundations.
Brick (stone) masonry in complex structures must be done with a mortar grade of at least 50.
Cores can be monolithic or prefabricated. Concrete of monolithic reinforced concrete cores must be at least class B10, prefabricated - B15.
Monolithic reinforced concrete cores must be arranged open on at least one side to control the quality of concreting.
Prefabricated reinforced concrete cores have a surface grooved on three sides, and on the fourth - an unsmoothed concrete texture; Moreover, the third surface should have a corrugated shape, shifted relative to the corrugation of the first two surfaces so that its cutouts fall on the protrusions of adjacent faces.
The cross-sectional dimensions of the cores are usually at least 250x250 mm.
Remember that the vertical surfaces of the channels in the masonry for monolithic cores should be made with the joint solution trimmed by 10...15 mm or even done with dowels.
First, the cores are placed - the frames of the openings (monolithic - directly at the edges of the openings, prefabricated - with a retreat of 1/2 brick from the edges), and then ordinary - symmetrically relative to the middle of the width of the wall or pier.
The pitch of the cores should be no more than eight wall thicknesses and not exceed the height of the floor.
Monolithic frame cores must be connected to the masonry walls by means of steel mesh of 3...4 smooth (class A240) rods with a diameter of 6 mm, covering the cross-section of the core and launched into the masonry at least 700 mm on both sides of the core in horizontal seams through 9 rows of bricks (700 mm) in height with a calculated seismicity of 7-8 points and through 6 rows of bricks (500 mm) with a calculated seismicity of 9 points. The longitudinal reinforcement of these meshes must be securely connected with clamps.
From monolithic ordinary cores, closed clamps from d 6 A-I are produced into the pier: when the ratio of the height of the pier to its width is more than 1 (even better - 0.7), i.e. when the pier is narrow, the clamps extend across the entire width of the pier on both sides of the core, with the specified ratio being less than 1 (preferably 0.7) - at a distance of at least 500 mm on both sides of the core; The height spacing of the clamps is 650 mm (through 8 rows of bricks) with a calculated seismicity of 7-8 points and 400 mm (through 5 rows of bricks) with a calculated seismicity of 9 points.
The longitudinal reinforcement of the core is symmetrical. The amount of longitudinal reinforcement is at least 0.1% of the cross-sectional area of the wall per core, while the amount of reinforcement should not exceed 0.8% of the cross-sectional area of the concrete core. The diameter of the reinforcement is at least 8 mm.
To allow prefabricated cores to work together with masonry, brackets d 6 A240 are clamped in the corrugated cutouts in each row of masonry, extending into the seams on both sides of the core by 60...80 mm. Therefore, the horizontal seams must coincide with the recesses on two opposite faces of the core.
There are walls of a complex structure that form and do not form a “clear” frame.
A fuzzy frame of inclusions is obtained when reinforcement of only part of the walls is required. In this case, inclusions on different floors may be located differently in plan.
6, 5, 4 for masonry of category I and
5, 4, 3 for masonry of category II.
In addition to the maximum number of storeys, the maximum height of the building is also regulated.
The maximum permitted building height is easy to remember like this:
n x 3 m + 2 m (up to 8 floors) and
n x 3 m + 3 m (9 or more floors), i.e. 6th floor (20 m); 5th floor (17 m); 4th floor (14 m); 3 floor (11 m).
Let me note that the height of the building is taken to be the difference between the elevations of the lowest level of the blind area or the planned surface of the earth adjacent to the building and the top of the external walls.
It is important to know that the height of hospital and school buildings with a calculated seismicity of 8 and 9 points is limited to three above-ground floors.
You may ask: if, for example, with a calculated seismicity of 8 points, n max = 4, then with H fl max = 5 m, the maximum height of the building should be 4x5 = 20 m, and I give 14 m.
There is no contradiction here: it is required that the building have no more than 4 floors, and that at the same time the height of the building does not exceed 14 m (which is possible with a floor height in a 4-story building of no more than 14/4 = 3.5 m). If the height of the floor exceeds 3.5 m (for example, reaches H fl max = 5 m), then there can only be 14/5 = 2.8 such floors, i.e. 2. Thus, three parameters are regulated simultaneously - the number of floors, their height and the height of the building as a whole.
In brick and stone buildings, in addition to external longitudinal walls, there must be at least one internal longitudinal wall.
The distance between the axes of the transverse walls with a calculated seismicity of 7, 8 and 9 points should not exceed 18.15 and 12 m for masonry of the first category, respectively, and 15, 12 and 9 m for masonry of the second category - 15, 12 and 9 m. The distance between the walls of a complex structure (i.e. type 1) can be increased by 30.
When designing complex structures with a clear frame, reinforced concrete cores and anti-seismic belts are calculated and designed as frame structures (columns and crossbars). Brickwork is considered as the filling of the frame, participating in the work on horizontal impacts. In this case, the grooves for concreting monolithic cores must be open on at least two sides.
We have already talked about the cross-sectional dimensions of the cores and the distances between them (pitch). When the core spacing is more than 3 m, as well as in all cases when the thickness of the infill masonry is more than 18 cm, the upper part of the masonry must be connected to the anti-seismic belt by shorts with a diameter of 10 mm coming out of it in increments of 1 m, running into the masonry to a depth of 40 cm.
The number of floors with such a complex wall design is taken to be no more than with a calculated seismicity of 7, 8 and 9 points, respectively:
9, 7, 5 for masonry of category I and
7, 6, 4 for masonry of category II.
In addition to the maximum number of storeys, the maximum height of the building is also regulated:
9th floor (30 m); 8th floor (26 m); 7th floor (23 m);
6th floor (20 m); 5th floor (17 m); 4th floor (14 m).
The height of the floors with such a complex wall design should be no more than 6, 5 and 4.5 m with a calculated seismicity of 7, 8 and 9 points, respectively.
Here, all our discussions about the “inconsistency” between the limit values of the number of floors and the height of the building, which we conducted about buildings with a complex wall structure with a “vaguely” defined frame, remain valid: for example, with a calculated seismicity of 8 points, n max = 6,
H fl max = 5 m, the maximum height of the building should be 6x5 = 30 m, and the Standards limit this height to 20 m, i.e. in a 6-story building, the floor height should be no more than 20/6 = 3.3 m, and if the floor height is 5 m, then the building can only be 4-story.
The distance between the axes of the transverse walls with a calculated seismicity of 7, 8 and 9 points should not exceed 18, 15 and 12 m, respectively.
Masonry with vertical and horizontal reinforcement.
Vertical reinforcement is taken according to calculations for seismic impacts and is installed in increments of no more than 1200 mm (every 4...4.5 bricks).
Regardless of the calculation results, in walls with a height of more than 12 m with a calculated seismicity of 7 points, 9 m with a calculated seismicity of 8 points and 6 m with a calculated seismicity of 9 points, vertical reinforcement must have an area of at least 0.1% of the masonry area.
Vertical reinforcement must be anchored in anti-seismic belts and foundations.
The horizontal mesh spacing is no more than 600 mm (through 7 rows of bricks).
BUILDING REGULATIONS
CONSTRUCTION IN SEISMIC AREAS
SNiP II-7-81*
MINISTRY OF CONSTRUCTION OF Russia
Moscow 1995
Developed by TsNIISK im. Kucherenko NIIOSP named after. Gersevanov, NIISK, Kazakh Promstroyniproekt, TsNNIpromzdanii of the USSR State Construction Committee, TbilZNIIEP Gosgrazhdanstroy Institute of Physics of the Earth of the USSR Academy of Sciences, Institute of Structural Mechanics and Seismic Stability of the Academy of Sciences of the Georgian SSR, Institute of Mechanics and Seismic Stability of Structures of the Academy of Sciences of the Uzbek SSR, TsNNIS Ministry of Transport, VNIIG named after. Vedeneev Ministry of Energy of the USSR, Krasnoyarsk Industrial Construction Project of the Ministry of Heavy Construction of the USSR, TsNIIEPselstroy of the Ministry of Agriculture of the USSR with the participation of the Hydroproject named after. Zhuk and GruzNIIEGS Ministry of Energy of the USSR.
The new map of seismic zoning of the territory of the USSR was compiled by scientific institutions of the USSR Academy of Sciences and the academies of sciences of the Union republics (leading - the Institute of Earth Physics of the USSR Academy of Sciences) and approved by the Interdepartmental Council on Seismology and Earthquake-Resistant Construction under the Presidium of the USSR Academy of Sciences.
With the entry into force of SNiP II-7-81 from January 1, 1982, the following become invalid: chapter SNiP II-A.12-69*. “Construction in seismic areas. Design standards":
Decree of the USSR State Construction Committee dated July 3, 1976 No. 81 “On the addition of Appendix 2 of Chapter SNiP II-A.12-69”;
Decree of the USSR State Construction Committee dated August 24, 1976 No. 140 “On additions and amendments to Appendix 2 of Chapter SNiP II-A.12-69”;
Resolution of the USSR State Construction Committee dated July 28, 1980 No. 116 “On additions and amendments to Appendix 2 of Chapter SNiP II-A.12-69.”
These building codes and regulations have been amended by resolutions of the USSR State Construction Committee dated June 3, 1987 No. 106, August 16, 1989 No. 127, and the Russian Ministry of Construction dated July 26, 1995 No. 18-76.
Items, tables and appendices to which changes have been made are marked in these building codes and regulations with an asterisk.
Editors - Eng. F.M.Shlemin, Ph.D. tech. sciences F.V.Bobrov(Gosstroy USSR), Doctor of Engineering. sciences S.V.Polyakov, Eng. V.I. Oizerman(TsNIISK named after Kucherenko), Doctor of Physics and Mathematics. sciences V.I.Bune(IPZ AS USSR), Doctor of Engineering. sciences O.A. Savinov, Ph.D. tech. sciences N.D. Krasnikov(VNIIG), Ph.D. tech. sciences Ya.I.Natarius(Hydroproject), Ph.D. tech. sciences G.S. Shestoperov(TsNIIS) .
ATTENTION READERS!
It is necessary to take into account approved changes to building codes and regulations and state standards published in the journal “Bulletin of Construction Equipment” and the information index “State Standards”.
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Gosstroy USSR |
Building regulations |
SNiP II-7-8l * |
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Construction in seismic areas |
Instead of chapter SNiP II-A.12-69* |
1. BASIC PROVISIONS
1.1. These standards must be observed when designing buildings and structures erected in areas with seismicity of 7, 8 and 9 points.
1.2. When designing buildings and structures for construction in the specified seismic areas, the following must be done:
use materials, structures and design schemes that ensure the lowest values of seismic loads;
accept, as a rule, symmetrical structural designs, uniform distribution of structural rigidities and their masses, as well as loads on the floors;
in buildings and structures made of prefabricated elements, place joints outside the zone of maximum forces, ensure solidity and homogeneity of structures using enlarged prefabricated elements;
provide conditions that facilitate the development of plastic deformations in structural elements and their connections, while ensuring the stability of the structure.
1.3. When designing buildings and structures for construction in seismic areas, the following should be taken into account:
a) intensity of seismic impact in points (seismicity);
b) repeatability of seismic impact.
Intensity and frequency should be taken from seismic zoning maps of the territory of the USSR (Appendices 1* and 2 *), adopted by the USSR Academy of Sciences, with amendments approved by the Russian Academy of Sciences.
Specified in the appendix. 1* and 2* seismicity refers to areas with soils with average seismic properties (category II according to Table 1*).
1.4. The seismicity of a construction site should be determined on the basis of seismic microzoning.
In areas for which there are no seismic microzoning maps, it is allowed to determine the seismicity of the construction site according to Table. 1*.
1.5. Construction sites with slopes steeper than 15 ° , proximity to fault planes, severe disturbance of rocks by physical and geological processes, soil subsidence, landslides, landslides, quicksand, landslides, karst, mine workings, and mudflows are unfavorable in seismic terms.
If it is necessary to construct buildings and structures on such sites, additional measures should be taken to strengthen their foundations and strengthen the structures.
1.6.* On sites where seismicity exceeds 9 points, the construction of buildings and structures is, as a rule, not allowed. If necessary, construction on such sites is permitted in agreement with the Russian Ministry of Construction.
Table 1*
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Seismicity of the construction site with seismicity of the area, points |
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Rocky soils of all types (including permafrost and permafrost thawed) unweathered and slightly weathered: coarse, dense, low-moisture soils from igneous rocks, containing up to 30% sand-clay aggregate: weathered and highly weathered rocky and non-rocky hard-frozen (permafrost) soils at minus temperatures 2 ° C and below during construction and operation according to principle I (preservation of foundation soils in a frozen state) |
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Weathered and highly weathered rocky soils, including permafrost, except those classified as category I; coarse soils, with the exception of those classified as category I; sands are gravelly, coarse and medium-sized, dense and medium-density, low-moisture and wet; sands are fine and dusty, dense and of medium density, low-moisture; clay soils with consistency index I L 0.5 at porosity coefficient e< 0.9 for clays and loams and e< 0,7 - для супесей; вечномерзлые нескальные грунты пластичномерзлые или сыпучемерзлые, а также твердо-мерзлые при температуре выше минус 2°С при строительстве и эксплуатации по принципу I |
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Sands are loose, regardless of humidity and size: sands are gravelly, large and medium-sized, dense and medium-density, water-saturated; fine and dusty sands, dense and medium density, moist and water-saturated; clay soils with consistency index I L>0.5; clayey soils with consistency index I L<0,5 при коэффициенте пористости е>0.9 for clays and loams and e>0.7 for sandy loams; permafrost non-rocky soils during construction and operation according to principle II (thawing of foundation soils is allowed) |
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Notes: 1*. Classification of a site to category I for seismic properties is allowed if the thickness of the layer corresponding to category I is more than 30 m from the black mark in the case of an embankment or the planning mark in the case of an excavation. In the case of a heterogeneous soil composition, the construction site is classified in a more unfavorable category in terms of seismic properties if, within a 10-meter layer of soil (counting from the planning mark), the layer belonging to this category has a total thickness of more than 5 m.
2. When predicting the rise of groundwater levels and watering of soils (including subsidence) during the operation of a building and structure, soil categories should be determined depending on the properties of the soil (humidity, consistency) in the soaked state.
3. When building on permafrost non-rocky soils according to principle II, if the thawing zone extends to the underlying thawed soil, the foundation soils should be considered as non-permafrost (according to their actual state after thawing).
4. For especially critical buildings and structures being built in areas with a seismicity of 6 points on construction sites with soils of category III for seismic properties, the calculated seismicity should be taken equal to 7 points.
5. When determining the seismicity of construction sites for transport and hydraulic structures, the additional requirements set out in sections 4 and 5 should be taken into account.
6. In the absence of data on consistency or moisture, clay and sandy soils with a groundwater level above 5 m are classified as category III in terms of seismic properties.
2. DESIGN LOADS
2.1. Calculation of structures and foundations of buildings and structures designed for construction in seismic areas must be carried out for basic and special combinations of loads, taking into account seismic influences.
When calculating buildings and structures (except for transport and hydraulic structures) for a special combination of loads, the values of the design loads should be multiplied by the combination coefficients taken according to Table. 2.
Horizontal loads from masses on flexible suspensions, temperature climatic effects, wind loads, dynamic effects from equipment and vehicles, braking and lateral forces from the movement of cranes are not taken into account.
table 2
|
Types of loads |
Combination coefficient value p s |
|
Permanent |
|
|
Temporary long-term |
|
|
Short-term (for floors and coverings) |
When determining the design vertical seismic load, the weight of the crane bridge, the weight of the trolley, and the weight of the load equal to the crane's lifting capacity should be taken into account with a factor of 0.3.
The calculated horizontal seismic load from the weight of crane bridges should be taken into account in the direction perpendicular to the axis of the crane beams. The reduction in crane loads provided for by SNiP for loads and impacts is not taken into account.
2.2. Calculations of buildings and structures for special combinations of loads taking into account seismic effects should be performed:
a) for loads determined in accordance with the instructions of clause 2.5;
b) using instrumental records of foundation accelerations during an earthquake, the most dangerous for a given building or structure, as well as synthesized accelerograms. In this case, the maximum amplitudes of foundation accelerations should be taken to be no less than 100, 200 or 400 cm/s 2 when the seismicity of construction sites is 7, 8 and 9 points, respectively.
When calculating according to point “b”, the possibility of the development of inelastic deformations of structures should be taken into account.
Growing according to item “a” should be carried out for all buildings and structures.
The calculation according to point “b” should be performed when designing especially critical structures and high (more than 16 floors) buildings.
2.3. Seismic impacts can have any direction in space.
For buildings and structures of simple geometric shape, the design seismic loads should be assumed to act horizontally in the direction of their longitudinal and transverse axes. The effect of seismic loads in the indicated directions should be taken into account separately.
When calculating structures of complex geometric shapes, the most dangerous directions of action of seismic loads for a given structure or its elements should be taken into account.
2.4. Vertical seismic load must be taken into account when calculating:
horizontal and inclined cantilever structures;
bridge spans;
frames, arches, trusses, spatial coverings of buildings and structures with a span of 24 meters or more;
structures for stability against overturning or sliding;
stone structures (according to clause 3.37).
2.5 . Design seismic load Sik in the selected direction, applied to the point k and corresponding i the th tone of natural vibrations of buildings or structures is determined by the formula
S ik = K 1 K 2 S 0ik ,(1)
Where TO 1 - coefficient taking into account permissible damage to buildings and structures, taken according to table. 3;
k 2 - coefficient taking into account design solutions of buildings and structures, taken according to table. 4 or the instructions of section. 5;
S 0ik - seismic load value for i th tone of natural vibrations of a building or structure, determined under the assumption of elastic deformation of structures according to the formula
S oik =Q k Ab iKwnik, (2)
Where Q k - k, determined taking into account the design loads on structures in accordance with clause 2.1 (Fig. 1);
A - coefficient, the values of which should be taken equal to 0.1; 0.2; 0.4, respectively, for calculated seismicity 7, 8, 9 points;
b i - dynamic coefficient corresponding i-th tone of natural vibrations of buildings or structures, adopted in accordance with clause 2.6;
TOw- coefficient accepted according to the table. 6 or in accordance with the instructions of section. 5;
Pik- coefficient depending on the form of deformation of a building or structure during its own vibrations along i-th tone and from the location of the load, determined according to clause 2.7.
Note: Design seismicity of buildings and structures, as well as coefficient values K 1, accepted in agreement with the organization approving the project in accordance with table. 3 and 5.
2.6. * Dynamic coefficient b i depending on the calculated period of natural oscillations Ti buildings or structures according to i when determining seismic loads, the th tone should be taken according to formulas (3, 4, 5) or Fig. 2.
at Ti £ 0.08 s b i = 1+15 Ti
at 0.08 s<Ti £0.318c b i = 2,2 (3)
at Ti > 0.318 s b i = 0,7/Ti
For soils of categories II and III with a layer thickness equal to or less than 30 m (curve 2)
at Ti £ 0.1 s b i = 1+15 Ti
at 0.1 s<Ti £0.4c b i = 2,5 (4)
at Ti > 0.4 s b i = 1/Ti
For soils of categories II and III with a layer thickness of more than 30 m (curve 3)
at Ti £ 0.2 s b i = 1+7,5 Ti
at 0.2 s<Ti £0.76c b i = 2,5 (5)
at Ti > 0.76 s b i = 1,9/Ti
In all cases the values b i, must be taken at least 0.8.
Note*. When calculating transport and hydraulic structures, the choice of dependencies b i(T i) provided for in this paragraph should be carried out in accordance with the instructions in sections 4 and 5.
Regional dependencies are allowed b i(T i), approved by the Ministry of Construction of Russia.
2.7. For buildings and structures calculated using a cantilever scheme, the value n ik should be determined by the formula
n ik =(6)
Where Xi(Xk) And Xi(Xj) - displacement of a building or structure during natural vibrations along i-th tone at the point in question k and at all points j, where, in accordance with the calculation scheme, its weight is assumed to be concentrated;
Q j - weight of a building or structure referred to a point j, determined taking into account the design loads on the structure in accordance with clause 2.1.
2.8. For buildings up to 5 floors high, inclusive, with slightly varying height masses and floor rigidities at T 1 less than 0.4 s coefficient n k can be determined using a simplified formula
Where Xk And x j, - distances from points k And j to the top edge of the foundations.
2.9. Efforts in the structures of buildings and structures designed for construction in seismic areas, as well as in their elements, should be determined taking into account at least three modes of natural vibrations, if the periods of the first (lowest) tone of natural vibrations T 1 more than 0.4 s, and taking into account only the first form, if T 1 equal to or less than 0.4 s.
Number of modes and coefficients n ik for hydraulic structures should be taken in accordance with the instructions in Section 5.
2.10. Calculated values of transverse and longitudinal forces, bending and overturning moments, normal and tangential stresses Np in structures from seismic load under the condition of its static action on the structure should be determined by the formula
Np = (8)
Where N i- values of forces or stresses in the section under consideration, caused by seismic loads corresponding i th form of vibration;
P - the number of vibration modes taken into account in the calculation.
2.11. The vertical seismic load in the cases provided for in clause 2.4 (except for masonry structures) should be determined using formulas (1) and (2), while the coefficients TOw And TO 2 , are taken equal to unity.
Cantilever structures, the weight of which is insignificant compared to the weight of the building (balconies, canopies, consoles for curtain walls, etc. and their fastenings), should be calculated for a vertical seismic load with a value b n = 5.
2.12. Structures that rise above a building or structure and have insignificant cross-sections and weight in comparison with it (parapets, pediments, etc.), as well as fastenings of monuments, heavy equipment installed on the ground floor, should be calculated taking into account the horizontal seismic load calculated according to formulas (1) and (2) at b n = 5.
2.13. Walls, panels, partitions, connections between individual structures, as well as fastenings of technological equipment should be calculated for horizontal seismic load according to formulas (1) and (2) at b n corresponding to the elevation of the structure in question, but not less than 2. Friction forces are taken into account only when calculating horizontal butt joints in large-panel buildings.
2.14. When calculating structures for strength and stability, in addition to the operating conditions coefficients adopted in accordance with other SNiP Part II, an additional operating conditions coefficient should be introduced m kp, determined according to table. 7.
2.15. When calculating buildings and structures (except hydraulic structures) with a length or width of more than 30 m, in addition to the seismic load determined in accordance with clause 2.5, it is necessary to take into account the torque relative to the vertical axis of the building or structure passing through its center of rigidity. The value of the calculated eccentricity between the centers of rigidity and mass of buildings or structures at the level under consideration should be taken to be at least 0.1 V, where B is the size of the building or structure in plan in the direction perpendicular to the action of the force Sik.
2.16. When calculating retaining walls, it is necessary to take into account seismic soil pressure.
2.17. Calculation of buildings and structures taking into account seismic impact, as a rule, is carried out according to the limit states of the first group. In cases justified by technological requirements, it is allowed to carry out calculations using the second group of limit states.
Table 3
|
Buildings and constructions |
Coefficient value K 1 |
|
1. Structures in which residual deformations and local damage (settlements, cracks, etc.) are not allowed* |
|
|
2. Buildings and structures in the structures of which there may be residual deformations, cracks, damage to individual elements, etc., complicating normal operation, while ensuring the safety of people and the safety of equipment (residential, public, industrial, agricultural buildings and structures; hydraulic engineering and transport structures; energy and water supply systems, fire stations, fire extinguishing systems, some communication structures, etc.) |
|
|
3. Buildings and structures in the structures of which significant residual deformations, cracks, damage to individual elements, their displacement, etc. may be allowed, temporarily suspending normal operation, while ensuring the safety of people (one-story industrial and agricultural buildings that do not contain valuable equipment ) |
*List of structures by item. 1 is agreed with the customer.
Table 4
|
Structural solutions for buildings |
Coefficient value K 2 |
|
1. Frame buildings, large-block, with walls of complex design and number P floors over 5 |
K 2 = 1+0,1 (n-5) |
|
2. Large-panel buildings or with walls made of monolithic reinforced concrete and the number of floors up to 5 |
|
|
3. The same, and with the number of floors over 5 |
TO 2 = 0.9+0.075 (n-5) |
|
4. Buildings with one or more framed lower floors and overlying floors with load-bearing walls, diaphragms or frame with infill, if infill in the lower floors is absent or has little effect on their rigidity |
|
|
5. Buildings with load-bearing walls made of brick or stone masonry, made by hand without adhesion additives |
|
|
6. Frame one-story buildings, the height of which to the bottom of the beams or trusses is no more than 8 m and with spans of no more than 18 m |
|
|
7. Agricultural buildings on column piles, erected on category III soils (according to Table 1*) |
|
|
8. Buildings not listed in positions 1-7 |
Notes: 1. Values K 1 should not exceed 1.5.
2. By agreement with the Ministry of Construction of Russia, the values of K 2 can be clarified based on the results of experimental studies.
Table 5
|
Characteristics of buildings and structures |
Estimated seismicity for seismicity of the construction site, points |
|||
|
1. Residential, public and industrial buildings and structures, with the exception of those specified in paragraphs. 2-5 |
||||
|
2. Particularly important buildings and structures * |
||||
|
3. Buildings and structures whose damage is associated with particularly severe consequences (large and medium-sized stations, indoor stadiums, etc.) |
7 ** |
8 ** |
9 *** |
|
|
4. Buildings and structures, the functioning of which is necessary during the liquidation of the consequences of earthquakes (energy and water supply systems, fire fighting, fire extinguishing systems, some communication structures, etc.) |
7 *** |
8 *** |
9 *** |
|
|
5. Buildings and structures, the destruction of which is not associated with loss of life, damage to valuable equipment and does not cause the cessation of continuous production processes (warehouses, crane or repair racks, small workshops, etc.), as well as temporary buildings and structures |
Without taking into account seismic impacts |
|||
* The assignment of buildings and structures to clause 2 is made by the customer.
**Buildings and structures are designed for a load corresponding to the calculated seismicity, multiplied by an additional factor of 1.5.
*** The same with a coefficient of 1.2.
Table 6
|
Constructive solutions of knowledge and structures |
Coefficient value TO w |
|
1. Tall structures of small dimensions in plan (towers, masts, chimneys, free-standing elevator shafts, etc. structures) |
|
|
2. Frame knowledge, the wall filling of which does not affect its deformability in relation to the height of the racks h to the transverse dimension b in the direction of action of the calculated seismic load, equal to or more than 25 |
|
|
3. The same as in paragraph 2. but with respect h/b equal to or less than 15 |
|
|
4. Buildings and structures not specified in paragraphs. 13 |
Notes: 1. For intermediate values h/b meaning TOw is accepted by interpolation.
2. For different floor heights, the value TOw taken according to average values h/b.
Table 7
|
Constructions |
Coefficient value T cr |
|
When calculating strength |
|
|
1. Steel and wood |
|
|
2. Reinforced concrete with rod and wire reinforcement (except for checking the strength of inclined sections): |
|
|
a) made of heavy concrete with reinforcement of classes A-I, A-II, A-III, BP-I |
|
|
b) the same, with fittings of other classes |
|
|
c) made of lightweight concrete |
|
|
d) from cellular concrete with reinforcement of all classes |
|
|
3. Reinforced concrete, tested for the strength of inclined sections: |
|
|
a) columns of multi-story buildings |
|
|
b) other elements |
|
|
4. Stone, reinforced stone and concrete: |
|
|
a) when calculating for eccentric compression |
|
|
b) when calculating shear and tension |
|
|
5. Welded joints |
|
|
6. Bolted (including those connected with high-strength bolts) and rivet connections |
|
|
When calculating stability |
|
|
7. Steel elements with flexibility over 100 |
|
|
8. The same, flexibility up to 20 |
|
|
9. The same, flexibility from 20 to 100 |
From 1.2 to 1 (by interpolation) |
Notes: 1. For the indicated positions. 1-4 structures of buildings and structures (except for transport and hydraulic engineering), erected in areas with frequency of 1, 2, 3, value T kr should be multiplied by 0.85; 1 or 1.5 respectively.
2. When calculating steel and reinforced concrete load-bearing structures to be used in unheated rooms or outdoors at a design temperature below minus 40 ° C, should be taken T kr = 1, in cases of checking the strength of inclined sections of columns T cr = 0.9 .
3. RESIDENTIAL, PUBLIC, INDUSTRIAL BUILDINGS AND STRUCTURES
GENERAL PROVISIONS
3.1. Buildings and structures should be separated with anti-seismic joints in cases where:
the building or structure has a complex plan shape;
adjacent sections of a building or structure have height differences of 5 m or more. In one-story buildings up to 10 m high with a calculated seismicity of 7 points, anti-seismic joints may not be installed.
3.2. Anti-seismic joints must separate buildings and structures along their entire height. It is allowed not to create a seam in the foundation, except in cases where the anti-seismic seam coincides with the sedimentary one.
3.3 . The distances between anti-seismic joints and the height of buildings should not exceed the dimensions indicated in the table. 8.
3.4*. Staircases should be closed, with window openings in the outer walls. The location and number of staircases should be determined based on the results of calculations performed in accordance with SNiP for fire safety standards for the design of buildings and structures, but at least one should be taken between anti-seismic joints in buildings with a height of more than three floors.
3.5. Anti-seismic joints should be made by constructing paired walls or frames, as well as constructing a frame and a wall.
The width of the anti-seismic joint should be determined based on the loads determined according to clause 25.
When the height of a building or structure is up to 5 m, the width of such a seam must be at least 30 mm. The width of the anti-seismic joint of a building or structure of greater height should be increased by 20 mm for every 5 m of height.
Table 8
|
Size by length (width), m |
Height, m (number of floors) |
|||||
|
Load-bearing structures of buildings |
Estimated seismicity, points |
|||||
|
1.Metal or reinforced concrete frame or monolithic reinforced concrete walls |
According to the requirements for non-seismic areas, but not more than 150 m |
According to requirements for non-seismic areas |
||||
|
2. Large-panel walls |
||||||
|
3. Walls of complex construction, in which: |
||||||
|
a) reinforced concrete inclusions and reinforced concrete belts form a clear frame system: |
||||||
|
b) vertical reinforced concrete inclusions reinforcing walls or piers do not form a clear frame |
||||||
|
4. Walls made of vibrated brick panels or blocks; concrete block walls |
||||||
|
5. Walls made of brick or stone masonry, except those indicated in pos. 3 and 4: |
||||||
Notes: 1. The height of the building is taken to be the difference between the elevations of the lowest level of the blind area or the planned surface of the earth adjacent to the building and the top of the external walls.
2. The height of hospital and school buildings with seismicity of the construction site of 8 and 9 points is limited to three above-ground floors.
3. In small settlements located in seismic areas, the construction of low-rise, mainly two-story residential buildings should be provided.
Filling anti-seismic joints should not interfere with mutual horizontal movements of compartments of a building or structure.
3.6. In cities and towns, the construction of residential buildings with walls made of mud brick, adobe and soil blocks is prohibited. In rural settlements located in areas with seismicity of 8 points, the construction of one-story buildings from these materials is allowed provided that the walls are reinforced with a wooden antiseptic frame with diagonal braces.
3.7. The rigidity of the walls of frame wooden houses must be ensured by braces. Cobblestone and log walls should be assembled on dowels. Wooden panel houses should be designed one floor high.
3.8. When designing buildings and structures, it is necessary to provide for and check by calculation the fastening of tall and heavy equipment to the supporting structures of buildings and structures, and also take into account the seismic forces that arise in the supporting structures.
3.9. Prefabricated reinforced concrete slabs and roofs of buildings must be monolithic, rigid in the horizontal plane and connected to vertical load-bearing structures.
3.10. The rigidity of prefabricated reinforced concrete floors and coverings should be ensured by:
connecting panels (slabs) of floors and coverings and filling the joints between panels (slabs) with cement mortar;
connection devices between panels (slabs) and frame elements or walls that absorb tensile and shear forces arising in the seams.
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.
3.11*. In brick and stone buildings, the length of part of the floor panels (coverings) resting on load-bearing walls made by hand must be at least 120 mm, and on vibrating brick panels and blocks - at least 90 mm.
In one-story stone buildings with distances between walls of no more than 6 m, the installation of wooden floors (coverings) is allowed, while the floor beams should be anchored in an anti-seismic belt and a diagonal flooring should be installed along them.
3.12. Non-load-bearing elements such as partitions and frame fillings should 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 higher than five floors, the use of hand-made brickwork partitions is not permitted.
The strength of non-load-bearing elements and their fastenings must be confirmed in accordance with clause 2.13 by calculations for the action of design seismic loads from the plane (in all cases) and in the plane of the element (in cases where these elements work together with the load-bearing structures of the building). Partitions made of brick or stone should be reinforced over their entire length, at least every 700 mm in height, with rods with a total cross-section in the seam of at least 0.2 cm. It is allowed to make partitions suspended with limiters for moving out of the plane of the panels.
3.13. Balcony structures and their connections to floors must be designed as cantilever beams or slabs.
The extension of balconies in buildings with stone walls should not exceed 1.5 m.
3.14. The design of the foundations of buildings and structures for construction in seismic areas should be carried out in accordance with the requirements of SNiP for the design of foundations of buildings and structures.
3. I5. When building in seismic areas, a layer of grade 100 mortar with a thickness of at least 40 mm and longitudinal reinforcement with a diameter of 10 mm in the amount of three, four and six rods should be laid on top of prefabricated strip foundations with a calculated seismicity of 7, 8 and 9 points, respectively. Every 300-400 mm, the longitudinal rods must be connected by transverse rods with a diameter of 6 mm.
In the case of making basement walls from prefabricated panels, structurally connected to strip foundations, laying the specified layer of mortar is not required.
3.16. In foundations and basement walls made of large blocks, masonry bonding must be ensured in each row, as well as in all corners and intersections to a depth of at least 1/3 of the height of the block; foundation blocks should be laid in a continuous strip.
To fill the joints between blocks, a solution of a grade of at least 25 should be used.
In buildings with a design seismicity of 9 points, provision should be made for laying reinforcement mesh 2 m long with longitudinal reinforcement with a total cross-sectional area of at least 1 cm in horizontal joints in the corners and intersections of basement walls.
In buildings up to three floors inclusive and structures of the corresponding height with a calculated seismicity of 7 and 8 points, it is allowed to use blocks with a hollowness of up to 50% for laying basement walls.
3.17. Waterproofing layers in buildings should be made of cement mortar.
FRAME BUILDINGS
3.18. In frame buildings, the structure that absorbs horizontal seismic load can be: a frame, a frame with filling, a frame with vertical braces, diaphragms or stiffeners.
3.19. For frame buildings with a calculated seismicity of 7-8 points, the use of external stone walls and internal reinforced concrete or methodological frames (racks) is allowed, and the requirements established for stone buildings must be met. The height of such buildings should not exceed 7 m.
3.20. Rigid components of reinforced concrete building frames must be reinforced using welded mesh, spirals or closed clamps.
Sections of crossbars and columns adjacent to rigid frame units at a distance equal to one and a half height of their section must be reinforced with closed transverse reinforcement (clamps), installed according to calculation, but at least every 100 mm, and for frame systems with load-bearing diaphragms - at least than after 200 mm.
3.21. Diaphragms, connections and stiffeners that carry horizontal loads must be continuous along the entire height of the building and located in both directions evenly and symmetrically relative to the center of gravity of the building.
3.22. Light curtain panels should be used as enclosing wall structures of frame buildings. It is allowed to install brick or stone filling that meets the requirements of clause 3.35.
3.23. The use of self-supporting masonry walls is permitted:
when the pitch of wall columns of the frame is no more than 6 m;
when the height of the walls of buildings erected on sites with seismicity 7, 8 and 9 points, respectively, is not more than 18, 16 and 9 m.
3.24. The masonry of self-supporting walls in frame buildings must be of category I or II (according to clause 3.39), have flexible connections with the frame that do not prevent horizontal displacements of the frame along the walls.
A gap of at least 20 mm must be provided between the surfaces of the walls and columns of the frame. Anti-seismic belts connected to the building frame should be installed along the entire length of the wall at the level of the covering slabs and the top of the window openings.
At the intersections of end and transverse walls with longitudinal walls, anti-seismic joints must be installed to the entire height of the walls.
3.25. Staircase and elevator shafts of frame buildings should be constructed as built-in structures with floor-to-floor sections that do not affect the rigidity of the frame, or as a rigid core that absorbs seismic loads.
For frame buildings up to 5 floors high with a calculated seismicity of 7 and 8 points, it is allowed to arrange staircases and elevator shafts within the building plan in the form of structures separated from the building frame. The construction of staircases in the form of separate structures is not permitted.
3.26. For load-bearing structures of tall buildings (more than 16 floors), frames with diaphragms, bracing or stiffening cores should be used.
When choosing structural schemes, preference should be given to schemes in which plastic zones appear primarily in horizontal frame elements (crossbars, lintels, strapping beams, etc.).
3.27. When designing high ranks, in addition to bending and shear deformations in the frame struts, it is necessary to take into account axial deformations, as well as the compliance of the foundations, and carry out calculations for stability against overturning.
3.28. On sites composed of category III soils (according to Table 1*), the construction of high knowledge, as well as buildings indicated in pos. 4 tables 4. not allowed.
3.29. The foundations of tall buildings on non-rocky soils should, as a rule, be made of piles or in the form of a continuous foundation slab.
LARGE PANEL BUILDINGS
3.30 . Large-panel buildings should be designed with longitudinal and transverse walls, combined with each other and with floors and coverings into a single spatial system that can withstand seismic loads.
When designing large-panel buildings it is necessary:
Wall and ceiling panels should, as a rule, be room sized;
provide for the connection of wall and ceiling panels by welding reinforcement outlets, anchor rods and embedded parts and embedding vertical wells and joint areas along horizontal seams with fine-grained concrete with reduced shrinkage;
when supporting the floors on the external walls of the building and on the walls at expansion joints, provide welded connections between the reinforcement outlets from the floor panels and the vertical reinforcement of the wall panels.
3.31. Reinforcement of wall panels should be done in the form of spatial frames or welded reinforcing mesh. In the case of using three-layer external wall panels, the thickness of the internal load-bearing concrete layer should be at least 100 mm.
3.32. The constructive solution of horizontal butt joints must ensure the perception of the calculated values of forces in the seams. The required cross-section of metal connections in the seams between the panels is determined by calculation, but it should not be less than 1 cm 2 per 1 m of seam length, and for buildings with a height of 5 floors or less, with a site seismicity of 7 and 8 points, not less than 0.5 cm 2 per 1 m seam length. It is allowed to place no more than 65% of the vertical design reinforcement at the intersections of the walls.
3.33. Walls along the entire length and width of the building should, as a rule, be continuous.
3.34. Loggias should, as a rule, be built-in, with a length equal to the distance between adjacent walls. Where loggias are located in the plane of external walls, reinforced concrete frames should be installed.
The installation of bay windows is not allowed.
BUILDINGS WITH LOAD-LOADING WALLS MADE OF BRICK OR MASONRY
3.35. Load-bearing brick and stone walls should be constructed, as a rule, from brick or stone panels or 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.
With a calculated seismicity of 7 points, it is allowed to construct load-bearing walls of masonry buildings using mortars with plasticizers without the use of special additives that increase the adhesion strength of the mortar to brick or stone.
3.36. Carrying out brick and stone masonry manually at sub-zero temperatures for load-bearing and self-supporting walls (including those reinforced with reinforcement or reinforced concrete inclusions) with a calculated seismicity of 9 points or more is prohibited.
If the calculated seismicity is 8 points or less, winter masonry may be done manually with the obligatory inclusion of additives in the solution that ensure hardening of the solution at subzero temperatures.
3.37. Calculations of stone structures must be made for the simultaneous action of horizontally and vertically directed seismic forces.
The value of the vertical seismic load at a calculated seismicity of 7-8 points should be taken equal to 15%, and at a seismicity of 9 points - 30% of the corresponding vertical static load.
The direction of action of the vertical seismic load (up or down) should be taken as more unfavorable for the stress state of the element in question.
3.38. For laying load-bearing and self-supporting walls or filling the frame, the following products and materials should be used:
a) solid or hollow brick of grade no lower than 75 with holes up to 14 mm in size; with a calculated seismicity of 7 points, the use of ceramic stones of a grade not lower than 75 is allowed;
b) concrete stones, solid and hollow blocks (including those made of lightweight concrete with a density of at least 1200 kg/m3) grade 50 and higher;
a) stones or blocks made of shell rocks, limestones of grade no less than 35 or tuffs (except felsic) grade 50 and higher.
Piece masonry of walls should be carried out using mixed cement mortars of a grade not lower than 25 in summer conditions and not lower than 50 in winter conditions. For laying blocks and panels, a solution of a grade of at least 50 should be used.
3.39. Masonry is divided into categories depending on its resistance to seismic influences.
Category of brick or stone masonry made from materials provided for in clause 3.38. is determined by the temporary resistance to axial tension along untied seams (normal adhesion), the value of which should be within the limits:
Less than 120 kPa (1.2 kgf/cm2), but not less than 60 kPa (0.6 kgf/cm2). In this case, the height of the building should be no more than three floors, the width of the walls should be at least 0.9 m, the width of the openings is no more than 2 m, and the distance between the axes of the walls is no more than 12 m.
The masonry project must include special measures for the care of hardening masonry, taking into account the climatic characteristics of the construction area. These measures should ensure that the required strength indicators of the masonry are obtained.
3.40. Design resistance values for masonry R R, R Wed, R ch for untied seams should be taken according to SNiP for the design of stone and reinforced masonry structures, and for untied seams - determined according to formulas (9) - (11) depending on the value obtained as a result of tests carried out in the construction area:
R R = 0,45 (9)
R Wed = 0,7 (10)
R hl = 0.8 (11)
Values R R, R Wed and R hl should not exceed the corresponding values when destroying brick or stone masonry.
3.41. The height of the floor of buildings with load-bearing walls made of brick or stone masonry, not reinforced with reinforcement or reinforced concrete inclusions, should not exceed 5, 4 and 3.5 m with a calculated seismicity of 7, 8 and 9 points, respectively.
When strengthening the masonry with reinforcement or reinforced concrete inclusions, the floor height can be taken equal to 6, 5 and 4.5 m, respectively.
In this case, the ratio of the floor height to the wall thickness should be no more than 12.
3.42. In buildings with load-bearing walls, in addition to external longitudinal walls, as a rule, there must be at least one internal longitudinal wall. The distances between the axes of transverse walls or frames replacing them must be checked by calculation and be no more than those given in Table 9.
FEATURES OF CONSTRUCTION OF STONE STRUCTURES IN EARTHQUICK AREAS
Buildings and structures erected in seismically hazardous (earthquake-prone) areas must be able to withstand seismic impacts without loss of performance, i.e., be seismic resistant. Seismic resistance of buildings and structures is ensured by the use of design solutions, structures and materials corresponding to the seismicity (intensity of seismic impact in points) of the construction site, as well as strict compliance with the rules and requirements for the construction of structures and work in seismic areas.
Constructive anti-seismic measures include: the use of earthquake-resistant structural systems; division of buildings and structures in plan into parts using anti-seismic joints; limiting the height of buildings; regulation of the conditions and scope of use of materials by their types; use of anti-seismic belts in structural schemes; reinforcement of elements of stone structures and a number of other measures provided for by design and construction standards.
These activities are specified by calculations and reflected in projects. For example, in buildings with walls made of brick or masonry at the level of floors and coverings, it is necessary to install anti-seismic belts along all longitudinal and transverse walls, made of monolithic reinforced concrete, or prefabricated with monolithic joints and continuous reinforcement. In this case, the chords of the upper floor must be connected to the masonry by vertical outlets of reinforcement. Constructive solutions of the belts and their reinforcement are indicated in the projects.
At wall junctions, reinforcing mesh 1.5 m long is placed in the masonry with a cross-section of longitudinal reinforcement in the mesh of at least 1 cm2. The grids are laid every 700 mm along the height of the masonry with seismicity - 7...8 points and after 500 mm - with 9 points. The masonry of self-supporting walls is fastened to the frame structures with flexible connections that do not prevent horizontal displacements of the frame.
Gaps of at least 20 mm are provided between the walls and columns of the frame. Along the entire length of the walls at the level of the top of the window openings, at the level of the covering, anti-seismic belts are installed, connected to the frame. The support of floor panels on masonry walls must be at least 120 mm in length, and on vibrating brick panels and blocks - at least 90 mm. Beams, purlins and floor slabs, wooden floor beams are anchored in anti-seismic belts (specific solutions are given in the projects). Ordinary lintels are not used in earthquake-prone areas. Reinforced concrete lintels are installed, as a rule, across the entire width of the walls and are embedded in the masonry to a depth of at least 350 mm; with an opening width of 1.5 m, lintels are allowed to be embedded at a depth of 250 mm.
Seismic resistance of stone buildings is also ensured by many other design techniques, for example, fastening flights of stairs and landings with floors, installing reinforced concrete frames in window and door openings of staircases, etc. All design decisions on anti-seismic measures should be strictly followed during the construction of buildings.
When using materials, the standards also provide for a number of measures. For example, in seismic areas in cities and towns, the construction of residential buildings with walls made of adobe (unfired) brick, adobe and soil blocks is prohibited. In rural villages, construction from these materials is allowed only in areas with seismicity up to 8 points, and only one-story buildings, provided that the wooden walls are reinforced with an antiseptic frame with diagonal braces. For laying walls or filling the frame in seismic zones, it is allowed to use solid or hollow bricks (with holes up to 15 mm in size) of grade no lower than 75; concrete stones, solid and hollow blocks of lightweight concrete of grade no lower than 50; stones or blocks from shell rocks and limestones of a grade of at least 35 and from tuffs (except for felsite) of a grade of at least 50.
Walls are laid using mixed cement mortars of grade no lower than 25 in summer conditions and no lower than 50 in winter, with special additives that increase the adhesion of the mortar to brick or stone. With a calculated seismicity of 7 points, it is allowed to use ceramic stones of a grade of at least 75, as well as the construction of masonry building walls using mortars with plasticizers without the use of special additives that increase the adhesion strength of the mortar to brick or stone.
The most important requirement for masonry in seismic areas is the strength of adhesion to the mortar. According to their resistance to seismic influences, which is determined by the temporary resistance to axial tension along untied seams (the force of separation of a brick laid on mortar from the masonry), masonry used in seismic zones is divided into two categories.
Masonry of the first category, in which the value of normal adhesion between the stone (brick) and the mortar must be at least 180 kPa (1.8 kg/cm2). Masonry of the second category must have an adhesive strength of at least 120 kPa (1.2 kg/cm2). Masonry with an adhesion strength of mortar to brick (stone) of less than 120 kPa in earthquake-prone areas is not allowed. In some cases, with a seismicity of 7 points, when special measures are used in the project, it may be allowed (by decision of the design organization) to reduce the adhesion strength in the masonry to 60 kPa (0.6 kg/cm2).
When erecting stone structures in seismic areas, it is necessary to strictly comply with the special requirements for the work to ensure the seismic resistance of the masonry:
masonry is carried out over the entire thickness of the structure in each row; masonry is performed using single-row (chain) dressing; all masonry joints (horizontal, vertical, transverse and longitudinal) are filled completely with mortar with trimming of the mortar on the outer sides of the masonry; temporary breaks in the masonry being erected should be terminated only with an inclined groove and located outside the areas of structural reinforcement of the walls;
Before laying, the surfaces of bricks (stones, blocks) must be cleaned of dust and dirt: for laying with conventional mortars in areas with a hot climate - with a stream of water, for laying with polymer-cement mortars - with brushes or compressed air. It is necessary to strictly control the adhesion strength of the mortar to the brick (stone). In 7-day-old masonry, the adhesion value should be approximately 50% of the strength of 28-day-old masonry of the corresponding class. If the strength is lower, it is necessary to stop the work until the issue is resolved by the design organization. Before masonry work begins, the construction laboratory determines the optimal relationship between pre-wetting the local stone wall material and the water content of the mortar mixture. Solutions are used with high water-holding capacity (water separation no more than 2%). The use of cement mortars without plasticizers is not allowed. When laying in the locations of anti-seismic joints dividing the building, it is necessary to ensure that they are not filled with mortar or debris. It is prohibited to reduce their width against the design one. It is necessary to strictly carry out the measures provided for by the project for the maintenance of hardening masonry (moisturizing and preventing rapid drying, etc.). It is necessary to take into account the peculiarities of the climate and ensure that the required strength of the masonry is obtained, including when constructing structures at subzero outside temperatures with the use of antifreeze additives.
Carrying out brick and stone masonry at sub-zero temperatures with a calculated seismicity of 9 points or more is prohibited.
7.87 For laying brick (stone) walls, a single-row chain ligation system should be used. On sites with a seismicity of 7 points, the use of a multi-row ligation system is allowed, while the bonded rows of masonry must be arranged at least after three spoon rows.
7.88 In seismic areas, the use of lightweight masonry with internal heat-insulating layers in load-bearing and self-supporting walls is not allowed.
7.89 For laying load-bearing and self-supporting walls, the following products and materials should be used:
Burnt solid or hollow brick of grade 75 and higher with vertical holes with a diameter of no more than 16 mm and a voidness of no more than 25%;
Ceramic stones of grade no lower than 100 with vertical holes with a diameter of no more than 16 mm and a voidness of no more than 25%;
Solid concrete stones and small blocks of heavy and light concrete of class not lower than B3.5;
If the seismicity of the construction site is 7 points, it is allowed to use ceramic stones of a grade not lower than 75 with vertical slot voids up to 12 mm wide and a voidness of no more than 25%.
The walls must be laid using mixed cement mortars of grade no lower than 50.
7.90 Use in the masonry of load-bearing and self-supporting walls of stones and small blocks of regular shape from natural materials (shell rocks, limestones, tuffs, sandstones), hollow concrete stones and blocks, solid blocks of cellular concrete of class below B3.5, bricks and stones made with the use of non-firing technology must be carried out in accordance with regulatory and instructional documents developed in the development of these standards.
7.91 Carrying out brick (stone) masonry of load-bearing and self-supporting walls (including those reinforced with reinforcement or reinforced concrete inclusions) at negative temperatures when the seismicity of construction sites is 9 and 10 points is prohibited.
If the seismicity of construction sites is 7 and 8 points, winter masonry is allowed with the mandatory inclusion of additives in the mortar that ensure hardening of the mortar at subzero temperatures.
7.92 In seismic areas, the use of baked brick or ceramic stone with horizontal (parallel to the masonry bed) voids is not allowed.
7.93 Value of temporary resistance of brick (stone) masonry to axial tension along untied seams (normal adhesion - Rnt) for load-bearing and self-supporting walls must be at least 120 kPa (1.2 kgf/cm2).
To increase the normal adhesion of masonry, solutions with special additives should be used.
7.94 The values of the design resistance of masonry (axial tension), (shear) and (flexural tension) along tied seams should be taken in accordance with the instructions of building codes for the design of masonry and reinforced masonry structures, and for untied seams - determined using formulas (7.1-7.3) depending on the value obtained during tests carried out in the construction area:
The values of , and should not exceed the corresponding values obtained when destroying brick or stone masonry.
7.95 The required value should be assigned depending on the test results of brick (stone) masonry in the construction area and indicated in the project.
If it is impossible to obtain the value at the construction site , equal to or exceeding 120 kPa (1.2 kgf/cm2), the use of brick or stone masonry for the construction of load-bearing and self-supporting walls is not allowed.
7.96 When constructing buildings in seismic areas, control tests should be carried out to determine the actual value of the normal adhesion of the masonry. The construction of buildings with load-bearing and self-supporting brick (stone) walls without carrying out control tests of the masonry is not allowed.
7.97 In the levels of floors and coverings of brick buildings, anti-seismic belts made of monolithic reinforced concrete with continuous reinforcement should be installed along all longitudinal and transverse load-bearing walls.
In buildings with monolithic reinforced concrete floors embedded along the contour into the walls, it is allowed not to install anti-seismic belts at the floor level. In this case, the length of the part of monolithic reinforced concrete floors and coverings resting on brick walls must be at least 250 mm.
7.98 Anti-seismic belts and monolithic reinforced concrete floors of the upper floor of the building must be connected to the masonry by vertical reinforcement outlets or reinforced concrete connections.
7.99 The anti-seismic belt must have an area for supporting the ceiling and be installed across the entire width of the wall. In external walls with a thickness of 510 mm or more, the width of the belt can be less than the thickness of the wall by up to 150 mm. The height of the belt must be at least 150 mm, concrete class not lower than B12.5. Anti-seismic belts are reinforced with spatial frames with longitudinal reinforcement of at least 4Ø10 when the seismicity of construction sites is 7 and 8 points and at least 4Ø12 when the seismicity of construction sites is 9 and 10 points.
7.100 At the junctions of load-bearing walls, reinforcing mesh with a total cross-sectional area of longitudinal reinforcement of at least 1 cm 2, a length of at least 150 cm must be placed in the masonry every 700 mm in height when the seismicity of the construction site is 7 and 8 points and every 500 mm when the seismicity of the construction sites is 9 and 10 points.
7.101 The seismic resistance of brick (stone) walls of buildings should be increased:
Reinforcement meshes laid in horizontal masonry joints;
Creating a complex structure by reinforcing walls with vertical meshes of reinforcement in a layer of shotcrete of a class not lower than B7.5 or in a layer of cement-sand mortar of a grade not lower than 100;
Creating a complex structure by including monolithic vertical and horizontal reinforced concrete elements into the masonry;
The installation of an internal reinforced concrete layer in the masonry (three-layer monolithic stone masonry).
To increase the seismic resistance of brick walls, it is allowed to use other experimentally proven methods.
7.102 When designing complex structures in the form of walls reinforced with mesh reinforcement in a layer of shotcrete or in a layer of cement-sand mortar:
Grids are usually installed on both sides of the walls;
The thickness of the layers of concrete or mortar must be at least 40 mm on each side of the wall;
Fastening of reinforcing mesh to the walls is carried out with anchors made of reinforcement with a diameter of at least 6 mm, which are installed in a checkerboard pattern with a pitch of no more than 600 mm.
When reinforcing walls using this method, technological measures should be taken to ensure reliable adhesion of layers of concrete or mortar to the masonry.
7.103 Reinforced concrete inclusions in masonry of a complex structure must be open on at least one side.
Vertical reinforced concrete inclusions (cores) must be connected to anti-seismic belts. Horizontal reinforcement of walls and anti-seismic belts should be passed through vertical reinforced concrete inclusions.
Cores should be installed in places where walls meet, along the edges of window and door openings, on blind sections of walls with a step not exceeding the height of the floor. Concrete cores must be at least class B15.
7.104 The internal reinforced concrete layer of three-layer monolithic masonry must be made of concrete of class not lower than B10 and have a thickness of at least 100 mm.
The outer layers of monolithic masonry (brick) must be connected to each other by horizontal reinforcement, installed in increments of no more than 600 mm and passed through the inner layer of concrete.
Floors and coverings must rest on the internal reinforced concrete layer of monolithic masonry or on an anti-seismic belt.
7.105 The height of the floor of buildings with load-bearing walls made of brickwork, not reinforced with reinforcement or reinforced only with horizontal reinforcing mesh, should not exceed 5.0 for seismicity of 7, 8 and 9 points, respectively; 4.0 and 3.5 m. In this case, the ratio of the floor height to the wall thickness should be no more than 12.
The height of the floor of buildings with walls of a complex structure or of monolithic masonry can be taken with seismicity of 7, 8, 9 and 10 points, respectively 6.0; 5.0; 4.5 and 4.0 m.
7.106 In buildings with load-bearing brick walls, in addition to external longitudinal walls, as a rule, there must be at least one internal longitudinal wall connected to the end external and internal transverse walls. The transverse load-bearing walls of staircases must extend across the entire width of the building.
7.107 The distances between the axes of transverse walls or frames replacing them must be checked by calculation and be no more than the values given in Table 7.4.
Table 7.4
7.108 The dimensions of brick wall elements should be determined by calculation. For brickwork without reinforcement or with reinforcement in the form of horizontal reinforcement in the joints, the requirements given in Table 7.5 must also be met.
Table 7.5
| Wall element | Size of the wall element, m, with seismicity of the site in points | Notes | ||
| Partitions with a width of at least | 0,77 | 1,16 | 1,55 | The width of the corner walls should be taken 250 mm larger than the value indicated in the table |
| Openings no wider than | 3,5 | 3,0 | 2,5 | Openings of larger width must be reinforced with a closed reinforced concrete frame along the contour of the opening |
| The ratio of the width of the wall to the width of the opening is not less than | 0,33 | 0,50 | 0,75 | |
| Removal of cornices no more, when they are made: - from wall material (brick, stone); - from reinforced concrete elements associated with anti-seismic belts; - wooden, plastered over metal mesh | 0,2 0,4 0,75 | 0,2 0,4 0,75 | 0,2 0,4 0,75 | Removal of wooden unplastered cornices is allowed up to 1 m |
7.109 Door and window openings in the brick walls of staircases with a seismicity of 8 or more points must have a reinforced concrete frame.
7.110 Staircase landings and landing beams should be embedded in the masonry to a depth of at least 250 mm and anchored. Elements of prefabricated stairs (steps, stringers, prefabricated flights) must be secured.
The installation of cantilever steps embedded in the masonry of staircase walls is not permitted.
7.111 The removal of balconies in buildings with stone walls and prefabricated floors should not exceed 1.5 m.
7.112 Sections of walls and pillars above the attic floor, having a height of more than 400 mm, must be reinforced or strengthened with monolithic reinforced concrete inclusions anchored in an anti-seismic belt.
7.113 Lintels should, as a rule, be installed over the entire thickness of the wall and embedded in the masonry to a depth of at least 350 mm. With an opening width of up to 1.5 m, sealing of lintels is allowed at 250 mm.
In seismic areas, the use of prefabricated timber lintels is not allowed.
7.114 Load-bearing walls in which ventilation ducts and chimneys are located should be designed as a complex structure.
Within the building plan or compartment, it is not allowed to change the direction of layout of reinforced concrete slabs of prefabricated floors (coverings) made in accordance with 7.23 (1, 2).
7.115 Self-supporting walls must have connections with the frame that do not prevent horizontal displacements of the frame along the walls. A gap of at least 20 mm must be provided between the surface of the walls and the columns of the frame.
Along the entire length of a self-supporting wall made of brick (stone) masonry, at the level of floor slabs (coverings) or the top of window openings, anti-seismic belts must be installed, connected by flexible connections to the building frame. At the intersection of end and longitudinal walls, anti-seismic joints should be installed along the entire height of the walls.
7.116 The strength of self-supporting wall structures and their fastenings should be checked by calculations performed in accordance with 5.21. Seismic forces acting in the plane of self-supporting walls must be absorbed by the walls themselves.
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