As you already know, most of the city's residents live in three main types of houses: small-block, large-block, large-panel. Frame-panel buildings are, as a rule, public and administrative. Let's try to imagine an earthquake situation for each of these houses.
So, you are in a small block house. The lack of seismicity of such an unfortified house is 1.5-2 points. We only note that cracks in the internal and external walls can be from hairline to 3-4 centimeter. Cracks of such dimensions, through which the street was visible, were observed by a commission of specialists in similar houses in the city of Leninakan after the Spitak earthquake. You should not panic at the sight of such violations, because the house is designed for this. You should be especially careful if the destruction will be very different from those that we have described. For example, there will be a shift of floors from the walls by 3 or more centimeters. rice. 5 What elements of the house best resist the elements?
Let's turn to Figure 5, which shows the most typical layout of a residential 2-5-storey small-block house. Bearing (on which the floors are supported) main walls 1.2 are less damaged than transverse 3.4.5. The latter are easier to move (cut off) by horizontal seismic forces, since they are less loaded. Particularly dangerous is the end wall 4, which is connected to the other walls only on one side. Sometimes the ends of buildings even break away from the building and fall out, which has been repeatedly observed in the village of Gazli, the cities of Spitak and Neftegorsk. The most dangerous corner of the building 6, which is the least connected with the building and is most susceptible to "loosening" during an earthquake. Already with a 7-8 magnitude earthquake, the corners of buildings on the top floor, as a rule, are damaged, and with a magnitude 9 earthquake they can fall out. It is not recommended to be at the outer longitudinal walls (1) during an earthquake, since glass can “shoot out” here, windows fall out in and out (this remark is true not only for small-block houses), and even come off in especially weak houses (longitudinal walls from transverse ). The most secure during an earthquake are the intersections of the internal load-bearing longitudinal walls (2) with internal transverse ones. The figure shows the most typical "safety islands": at the exits from the apartments to the stairwell and at the intersection wall 5. In these places, due to the cross-shaped intersection of load-bearing and non-bearing walls, a core of increased strength is created, which can withstand even when the remaining walls collapse. This core is stronger, the fewer doorways it has. So, for example, the most reliable place will be at the right three-room apartment in the area of the intersection of internal walls 2 and 5. Also, the island in the two-room apartment at the intersection of blind sections of walls of type 3 and 2 seems to be reliable. As for the one-room and left three-room apartments, they have cores they have one or two openings and are therefore considered less durable than cores with blank walls. Therefore, if necessary, here you can move along wall 2. In such houses built in the 70-80s. the doorways leading to the staircase are framed with reinforced concrete frames, which guarantees their strength. However, in houses of earlier construction, frames are not everywhere, so these exits cannot be considered completely safe. A few general tips for behavior. As soon as the earthquake starts, you should open the doors leading to the landing and go to the safety island. It is worth trying to run out of the building if you are on the first or second floors. From a higher floor, you may not have time to do this before serious destruction begins. You need to run out of the house especially quickly and carefully so that you are not “covered” by bricks flying from the roof from destroyed pipes, or crushed by a heavy visor. If you did not have time to get to the island of safety, then you should remember that partitions made of small-block masonry are very dangerous. They are among the first to be destroyed, up to the collapse. Wooden shield partitions are less dangerous, but rather large pieces of plaster can fall off from them, which are especially dangerous for young children. It is easy to distinguish a stone partition from a shield one by a deaf, very short, non-vibrating sound when you hit the wall with your fist. When arranging furniture in the apartment, pay attention to the fact that bulky furniture cannot fall into the territory of the island of safety or into the path of a possible evacuation from the apartment.
Many residents of large block houses know that their houses withstand an earthquake quite well. Their real seismic resistance is estimated by experts at 7.7 points.
On fig. 6 shows a typical layout of a large-block house. The position of the capital load-bearing and non-bearing walls is the same as in a small-block house. A large-block house loses its bearing capacity mainly due to the stratification of the walls into separate blocks, which, unfortunately, do not have a good connection with each other in old houses. The outer walls consist of two blocks according to the height of the floor: a wall block with a height of 2.2 m and a lintel with a height of 0.6 m. The internal walls consist of blocks with a floor height, i.e. 2.8 m. on the lintel blocks of the outer walls and directly on the blocks of the inner walls. With an earthquake of more than 7 points, the blocks begin to shift from the plane of the wall. The greatest cracks and destruction of joints (11) should be expected in non-bearing transverse walls less loaded with slabs, especially in the end wall (4) and the walls of the staircase (3). In the last walls there is a small connection of the blocks with each other with the help of not very strong metal plates, which already during an earthquake of 7.5-8 points will begin to loosen greatly, breaking off pieces of concrete and plaster around them. This debris can injure people running up the stairs, so it is necessary to move by clinging closer to the railing. rice. 6. As in small block buildings, the corners of the building (6) are very dangerous, especially on the upper floors. The displacement of blocks from the plane of the wall can lead to partial collapse of the end wall (4) and floor slabs. Partitions in these houses, as a rule, are wooden, panel, plastered, and one should not be afraid of their collapse. Injury, especially to a small child, can be caused by pieces of plaster falling off the partitions and pieces of cement mortar falling out of the joints between the floor slabs. Such damage occurs during an earthquake of 7.5 points. The figure shows the safest places in a large-block house. Unlike small-block buildings, here all the doors leading to the landing are reinforced with reinforced concrete frames (9), so the probability of door jamming due to skew is low and the exit from the apartment is quite reliable. To the general advice - do not hang heavy shelves in the safety island area and fix furniture, it should be added that this is especially important to do in the storage closet (7) and in the corridor (8), otherwise there will simply be no place for you on the safety island.
In old large-panel five-story residential buildings, the typical layout of which is shown in Fig. 7, the area of safety islands is already much larger. Despite the fact that these houses were designed for 7-8 points, practice has shown that their real seismic resistance is close to 9 points. No such building anywhere during earthquakes on the territory of the former Soviet Union was not destroyed. All external and internal walls in such houses are reinforced concrete large panels, well connected at the nodes using monolithic and welding (node 5). Internal walls and partitions are connected to each other on welded outlets. The floor panels are the size of a room, rest on the walls on four sides and are also welded to the walls. It turns out a reliable honeycomb structure. Calculations of the behavior of a large-panel house during a 9-point earthquake showed that the greatest damage is expected in the corners of the building (6), and in the junctions of the end panels (4), where large vertical cracks of 1-2 cm can open up. The first cracks may already appear with L-7.5 points. The same cracks can appear at expansion joints between buildings. But these cracks do not affect the overall stability of the building. Unpleasant factors include the possible appearance of oblique cracks up to 1 cm wide in reinforced concrete lintels above the entrance doors to apartments, which can lead to door jamming. Therefore, they must be closed immediately at the beginning of oscillations with a force of 6 points or more. Since large-panel buildings are quite reliable, you should not run out of them during an earthquake. But it is recommended to stay during an earthquake in the zone of safety islands, away from the outer walls, where window panes can “shoot out”, and from the end wall, in the nodes of which extended frightening cracks can open. You should not run out also because in the old houses of this series there are very heavy dangerous peaks over the entrances to the entrances. Embedded metal parts with which these visors were attached to the building. due to aging, they are heavily rusted and may not hold them in case of strong seismic shocks.
During an earthquake on In Shikotan, in 1994, several canopies fell near similar large-panel three-story houses, which crushed two residents who ran out of one house. However, not a single person who remained in the house was injured. The house itself was not seriously damaged. Later large-panel houses, the so-called "improved" series, with bay windows, as well as houses of a "new" layout with large glazed balconies, were originally designed for 9 points and it is practically safe to be in them during an earthquake of this magnitude. You need to beware of falling from above, especially from balconies, broken glass, which can scatter over long distances - up to 15 meters. Therefore, it is not recommended to run out of these houses, just as it is not recommended to be on the street next to them. Fig.7 Experience shows that even with strong 8-9 magnitude earthquakes, 1-2-storey wooden houses practically do not collapse before a collapse. One of the authors of the book, observed the behavior of panel and block houses during a 9-point earthquake on about. Shikotan. Of the almost fifty two-story houses surveyed, there was not a single house where at least one wall collapsed or the ceiling failed. There were cases when the foundation "pulled out" from under the house and was carried away by a landslide by 1-1.5 meters, and the house, bowed, stood! There were breaks in the walls in the corners up to 20 cm and subsidence of the soil under the building up to 0.5 m, but the houses survived. Therefore, one should not run out of such houses anywhere, especially since the danger is represented by bricks falling on running out from collapsing chimneys. In wooden houses, floors sway more strongly than others and walls “crack” which causes discomfort. Pieces of plaster can fall out of the walls and from the ceiling. Therefore, in such houses it makes sense to choose a place where the plaster fits snugly against the wall, ceiling, i.e., it “does not coil” in advance when tapped. Children are better off hiding under the table. And, of course, you need to stay away from the outer walls with windows, from heavy cabinets and shelves, especially if they are not specifically fixed. This is general rule for any building.
Home training. Let's do a thought experiment. Close your eyes and imagine that you are lying on your own bed. Imagine that in this moment the first strong seismic shock occurred. Now mentally try to get to the door as quickly as possible, open it and take a place in the doorway. At the same time, bend your fingers on your hand in each case when, in your mental progress, you come across obstacles that really exist. Now count. Each obstacle is at least 3 lost seconds. Estimate net movement time and door lock opening time. Add seconds to grab a backpack with documents and products (no doubt, it hangs next to the door, as recommended). And if you get more than 20 seconds, then give yourself a fat FAILURE, and let's get down to reorganization. Make a list of obstacles found during the experiment. This is the minimum to be done. Let's start moving in reverse order. Evaluate the door lock in terms of the ability to quickly open the door. Is it easy for you to find the lock itself and its opening device even in the dark? How many actions are required to unlock the lock and the door? Try to arrange everything in such a way that the lock opens with a minimum of movements, and bring these movements to automatism .. Inspect the space near the front door. Are there objects nearby that, at the first push, can fall and block your path? If there are any, either strengthen them, or determine a more suitable place for them in the apartment. The corridor should be as free as possible. Very often, the passage is cluttered with things that have only recently been brought into the apartment and have not yet found their permanent place. Everyone knows that there is nothing more permanent than temporary. Therefore, without postponing "for later", clear your way to salvation. Pay attention to the fact that there are no objects along the walls that you can catch on. Look under your feet to see if shoes that are not currently in use have been removed from the corridor and if they create obstacles for movement. Now let's pay attention to the door from the corridor to the room. It is desirable that it be constantly open. Think about how you can fix it in the open position, and equip the latch. If there is carpet on the floor or there are tracks, then check how tightly they fit to the floor, if there are any gathers, folds, scuffs. Does the track slip on the main floor covering? Pay special attention to the joints of carpets and paths. Eliminate all flaws, let the path be "silk". AT last years mobile interior elements have firmly entered our everyday life: tables on wheels, mobile cabinets for TV, video and audio equipment. Make it a rule not to leave them in the evening on a possible escape route. Leave them in such a position that their spontaneous movement in the event of seismic shocks cannot occur in the direction of this escape route and does not cause objects or furniture to fall along this route. If you use extension cords to connect electrical equipment, then make sure that the wires do not cross the path of your movement to the exit. The pride of almost every family is the home library. Check for books on open shelves, from which, at the first seismic shock, they can fall under your feet or fall on your head when you run to the door. Evaluate from the same positions objects standing on open shelves, especially if these shelves are above the doors. Make sure the shelves themselves are securely fastened. Bedside tables should also be securely fastened so as not to be the first insurmountable barrier to salvation. It is advisable to fix the table lamps standing on these cabinets. If the drawers in these bedside tables easily fall out or open with slight pressure on the door, then make sure that they are securely fixed. Clothing periodically accumulating next to the bed can be a serious obstacle to fast movement. Make it a rule to put things away that you won't be wearing that day. (It turns out that a possible strong earthquake is an important reason to keep the house in order!)
Recall the thought experiment you did again and note which obstacle came first in your path. If it is resolved, then check if there are any unresolved barriers in your post-experimental list and take appropriate measures. Check now the exit path for each family member. If there are small children in the family and you will first move towards them, then pay attention to those sections that you will have to cross twice in different directions. Find out if you will create obstacles for the way back with your first movement. Similarly, inspect and tidy up the escape route from the living room and kitchen. Please note that several people, including children, can move from these rooms at the same time. When you watch athletics competitions, then, watching a steeplechase race, you often have a desire to make the path easier for athletes and remove obstacles and a hole with water. How easily and beautifully they would have reached the finish line. But the rules of the game don't allow it. The rules of seismic safety, on the contrary, tell us - do not bring things to a home steeplechase, otherwise you will not be able to safely reach the finish line. Therefore, we advise you to remove barriers from the road and not take unnecessary risks.
An excerpt from the work of V.N. Andreeva, V.N. Medvedev "PROBLEMS OF SEISMIC RISK IN THE REPUBLIC OF SAKHA (YAKUTIA)" without author's illustrations.
Killer houses on the disaster map
An alarming trend has been revealed by the latest Maps of the general seismic zoning of the territory of the Russian Federation: in comparison with previous calculations, the number of regions with increased seismic hazard has increased significantly.
The planet continues to show its violent nature. Earthquakes occur with surprising regularity. In just two weeks there were 15 of them - in Turkey and Mexico, Sakhalin and Kamchatka, Los Angeles and Alaska, the Caucasus and Taiwan, the Ionian Sea and Japan. Fortunately, this time the tremors were not the strongest - their maximum intensity did not exceed 6.2 points, but they also led to destruction and death. But a strong earthquake can become an economic and social catastrophe for the whole country, just remember the tragedy in India on January 26 last year.
In recent decades, the danger of seismic disasters has increased dramatically, which is primarily due to human economic activity, man-made impacts on the earth's crust - the creation of reservoirs, the extraction of oil, gas, solid minerals, the injection of liquid industrial waste and a number of other factors. And the possible destruction of large engineering structures built on the surface (nuclear power plants, chemical plants, high-rise dams, etc.) can lead to environmental disasters. An example of such a potential hazard is the Balakovo NPP, which will withstand an earthquake no stronger than 6 points, despite the fact that the Saratov region today is classified as a seven-point seismicity zone.
Practically not a single strong tremor passes without a trace: after each, the expected seismic hazard in the affected and adjacent regions increases. For example, the earthquake in Neftegorsk in 1995 was estimated by experts as 9-10 points. But back in the 60s, this and the adjacent territories were not considered seismically dangerous at all, and the possibility of earthquakes was not taken into account when designing buildings. The same underestimated seismic activity forecasts were made in Japan, China, Greece and other countries. Unfortunately, similar errors are not ruled out in the future.
So the sad list of regions where the earth can suddenly stand on end is constantly growing. The latest Maps of the general seismic zoning of the territory of the Russian Federation clearly demonstrate this. Until recently, two regions of Russia - Sakhalin, Kamchatka, the Kuriles and other regions of the Far East, as well as territories Eastern Siberia adjoining the Baikal and Transbaikal regions, including the Altai Mountains. Catastrophic earthquakes with an intensity of 9 or more points (up to 8.5 on the Richter scale) are possible there. By the way, the territory of the Sakhalin region is one of the most seismically dangerous not only in Russia, but also in the world.
Now, on the latest maps, the threat of earthquakes of magnitude 9 or more has spread to a significant part of the North Caucasus, where about 7 million people live. And this despite the fact that the construction of residential buildings and industrial buildings until recently was carried out here, taking into account the seismicity of 7 points. The greatest concern is Krasnodar region with a population of five million. In the summer months, on a narrow strip of the Black Sea coast, the number of people increases many times over.
Another very important difference between the new maps is that for the first time zones of 10-magnitude earthquakes appeared on them. They are located on Sakhalin, Kamchatka and Altai. Previously, there were no such areas in our country.
But the exact location, strength and time of an earthquake cannot be predicted. There are no ways to prevent the cataclysm. The main task is to minimize the destruction and loss of life. Latest strong earthquakes in Neftegorsk (1995), in Turkey and Taiwan (1999) showed that fundamentally new approaches are needed in the regulation and design of engineering structures.
In the meantime, experts come to shocking results: the main "killers" of people during earthquakes are buildings of two types. And the most common. First of all - houses with walls made of low-strength materials. The second type is reinforced concrete frame buildings, the massive destruction of which turned out to be completely unexpected, since until recently they were in one of the first places in terms of seismic resistance. So, during the earthquake in Leninakan, 98 percent of the reinforced concrete frame houses folded like an accordion, more than 10 thousand people died in them.
Unlike frame buildings, large-panel buildings and houses with walls made of monolithic reinforced concrete, which have maximum rigidity in all directions, have proven themselves very well.
Of course, the cardinal solution to the current situation: the demolition of all dangerous houses and the construction of new ones in their place is unrealistic today. Therefore, the most difficult and urgent task is to strengthen buildings built without taking into account possible seismic effects or designed for minor earthquakes. Unfortunately, in Russia this problem is extremely acute. It is not for nothing that the Federal Target Program “Seismic Safety of the Territory of Russia”, which began operating this year, contains a terrible phrase: “In the entire history of the USSR and the Russian Federation, nationwide programs on seismic safety have not been implemented in the country, as a result of which tens of millions of people live in seismically hazardous territories. in houses characterized by a seismic resistance deficit of 2-3 points. At the same time, in a number of constituent entities of the Russian Federation, even according to rough estimates, from 60 to 90 percent of buildings and other structures should be classified as non-seismic.
According to the Program, more than half of the territory of Russia may be affected by earthquakes of medium magnitude, which can lead to severe consequences in densely populated areas, and “about 25 percent of the territory of the Russian Federation with a population of more than 20 million people may be subject to earthquakes of magnitude 7 or more.
Taking into account the high seismic hazard, population density, the degree of actual seismic vulnerability of development, the subjects of the Russian Federation were classified depending on the seismic risk index and divided into 2 groups.
The first group (see table) included 11 constituent entities of the Russian Federation, the regions with the highest seismic risk. Many cities and large settlements in these regions are located in areas with seismicity of 9 and 10 points.
The second group includes Altai, Krasnoyarsk, Primorsky, Stavropol and Khabarovsk Territories, Amur, Kemerovo, Magadan, Chita Regions, Jewish Autonomous Region, Ust-Ordynsky Buryat, Chukotsky and Koryaksky autonomous regions, the republics of Sakha (Yakutia), Adygea, Khakassia, Altai and the Chechen Republic. In these regions, the predicted seismic activity is 7-8 points and lower.
Moscow and the Moscow region, according to Russian Academy Sciences, are not a seismically hazardous area. The maximum possible fluctuations here will not exceed 5 points.
Alexander Kolotilkin
High risk area
| Region | Seismic risk index * | Large cities (number of facilities requiring priority strengthening) |
|---|---|---|
| Krasnodar region | 9 | Novorossiysk, Tuapse, Sochi, Anapa, Gelendzhik (1600) |
| Kamchatka region | 8 | Petropavlovsk-Kamchatsky, Yelizovo, Keys (270) |
| Sakhalin region | 8 | Yuzhno-Sakhalinsk, Nevelsk, Uglegorsk, Kurilsk, Aleksandrovsk-Sakhalinsky, Kholmsk, Poronaysk, Krasnogorsk, Okha, Makarov, Severo-Kurilsk, Chekhov (460). |
| The Republic of Dagestan | 7 | Makhachkala, Buynaksk, Derbent, Kizlyar, Khasavyurt, Dagestan Lights, Izberbash, Kaspiysk (690) |
| The Republic of Buryatia | 5 | Ulan-Ude, Severobaikalsk, Babushkin (485) |
| Republic of North Ossetia - Alania | 3,5 | Vladikavkaz, Alagir, Ardon, Digora, Beslan (400) |
| Irkutsk region | 2,5 | Irkutsk, Shelekhov, Tulun, Usolye-Sibirskoe, Cheremkhovo, Angarsk, Slyudyanka (860) |
| Kabardino-Balkarian Republic | 2 | Nalchik, Prokhladny, Terek, Nartkala, Tyrnyauz (330) |
| Ingush Republic | 1,8 | Nazran, Malgobek, Karabulak (125) |
| Karachay-Cherkess Republic | 1,8 | Cherkessk, Teberda (20) |
| Tyva Republic | 1,8 | Kyzyl, Ak-Dovurak, Chadan, Shagonar (145) |
_______
*Seismic risk index characterizes the required volume of anti-seismic reinforcements, takes into account seismic hazard, seismic risk and population in large settlements.
|
Conventional name event magnitude |
Approximate ratio of values M and I for shallow earthquakes |
|
|---|---|---|
|
Magnitude interval M, according to Richter, units IN THE HEART |
Intensity I, on a scale MSK-64, points ON A SURFACE |
|
| Weak | 2.8 - 4.3 | 3 - 6 |
| Moderate | 4.3 - 4.8 | 6- 7 |
| Strong | 4.8 - 6.2 | 7 - 8 |
| Very strong | 6.2 - 7.3 | 9 - 10 |
| catastrophic | 7.3 - 9.0 | 11 - 12 |
FADE-OFF OF THE SEISMIC EFFECT WITH REMOVAL FROM THE EPICENTER
The magnitude of an earthquake characterizes the energy of seismic waves emitted by its source, and the intensity of seismic shaking on the earth's surface depends both on the magnitude of the epicentral distance and on the depth of the source.The presented decay curves characterize the decrease in the intensity of seismic shaking with distance from the epicenter of earthquakes of different magnitudes with a "normal" depth of sources, the upper edge of which is located close enough to the earth's surface. The deeper the source, the weaker the seismic effect at the epicenter and the slower it decays with distance.
// This effect can be compared to the intensity of illumination of the surface with a regular flashlight. The closer he is to it, the brighter the illumination at the shortest distance from him, but the faster it decreases with the distance from the flashlight. When the flashlight itself moves away from the illuminated surface, the illumination in the center becomes dimmer, but this "less dangerous twilight" covers a fairly large area. //
POTENTIAL SCENARIO EARTHQUAKES
In construction practice, along with probabilistic assessments of seismic hazard, determined on the basis of normative maps of seismic zoning of the territory of the Russian Federation - OSR-97, deterministic methods for calculating the expected seismic impacts from the so-called scenario earthquakes are often also used, regardless of when they occur. In this case, the decisive role is played by an adequate choice of potential earthquake sources that pose the greatest danger to given areas and specific construction projects.
An indispensable condition for the identification and seismological parameterization of potential earthquake sources (PES), considered as scenario ones, is the reliance on the seismogeodynamic model of earthquake source zones (POZs), on the basis of which a set of official OSR-97 maps of federal significance was created.
When calculating the theoretical (synthetic) accelerograms and the dynamic response of buildings and structures to seismic impacts, a number of geological and geophysical parameters of the ESP and the environment in which seismic waves propagate (the location of the source, its size and orientation in space, magnitude, seismic moment, attenuation of seismic waves of different lengths with distance, spectral influence of real soils and other factors).
Since the deterministic estimates of the seismic effect obtained from scenario earthquakes are conservative, they often significantly overestimate the value of seismic intensity obtained by probabilistic methods. At the same time, such extreme seismic events can be extremely rare events, which can often be neglected. In this regard, it is allowed to convert deterministic estimates into probabilistic ones that meet the regulatory requirements of OSR-97 maps.
Volumetric model of earthquake sources and potential sources, representing the greatest danger to the conditional city. 1 – lineaments, 2 – domains, 3 – sources of large earthquakes with magnitude M=6.8 or more, 4 – sources of earthquakes with M=6.7 or less, 5 – trajectories of seismic waves propagation from potential sources Z1 and Z2 of earthquakes towards the city. This figure shows an example of the propagation of seismic waves from two potential sources of earthquakes - from a relatively small source Z1, located in the domain directly under the city, and from the largest source Z2, which belongs to the lineament and is located at a considerable distance from the city. In the first case, the scenario earthquake is characterized by a moderate magnitude (no more than M=5.5) and a small depth of the source (no more than 10 km). In the second case, the source belongs to the lineament of high rank (magnitude M=7.5) and has a fairly large extent (about 100 km). Center Z1 generates a high-frequency spectrum of radiated waves with a short duration and sufficiently large accelerations, which are dangerous mainly for low buildings. And vice versa, low-frequency dynamic impacts from the Z2 source, which are characterized by relatively small accelerations, compared to the Z1 event, pose a significant danger to high-rise building objects due to their very long duration (possibly also large oscillation velocities and ground displacements) at low acceleration values.
Traditional methods and means of protecting buildings and structures from seismic impacts include a large range of various measures aimed at increasing the bearing capacity of building structures, the design of which is carried out on the basis of standards and rules developed by domestic and foreign construction experience that guarantee the seismic resistance of buildings and structures in areas with seismicity 7 , 8 and 9 points.
The design of buildings and structures in seismically hazardous areas begins with the observance of the generally accepted principles of seismic construction, according to which all building materials, structures and structural schemes used must ensure the lowest value of seismic loads. When designing, it is recommended to adopt, as a rule, symmetrical structural schemes and to achieve a uniform distribution of structural rigidities and masses. In buildings and structures made of prefabricated elements, it is recommended to locate joints outside the zone of maximum effort; it is necessary to ensure the uniformity and solidity of structures through the use of reinforced prefabricated elements.
The choice of space-planning schemes, their shape and dimensions has a significant impact on the seismic resistance of buildings. The most preferred forms of structures in the plan are a circle, a polygon, a square and outlines similar to them in shape. However, such shapes do not always meet the planning requirements, therefore, a rectangular shape is most often used with parallel spans, without height differences between adjacent spans and without reentrant corners. If there is a need to create complex shapes in terms of the building, then it should be cut along the entire height into separate closed compartments of a simple shape. The design solutions of the compartments during an earthquake should ensure the independent operation of each of them. This is achieved by the device of anti-seismic seams, which can be combined with temperature or sedimentary seams. Anti-seismic seams are carried out by installing paired walls, paired columns or frames, as well as by erecting a frame and a wall.
With a building height of up to 5 m, the width of such a seam should be at least 3 cm. For buildings of greater height, the width of the seam is increased by 2 cm for every 5 m of height.
In multi-storey buildings, an important role in their seismic resistance is played by the structures of interfloor ceilings and coatings, which act as stiffening diaphragms, ensuring the distribution of seismic load between vertical bearing elements. Prefabricated reinforced concrete floors and roofs of buildings must be monolithic, rigid in the horizontal plane and connected to vertical load-bearing structures.
The side faces of panels (plates) of ceilings and coverings must have a keyed or corrugated surface. For connection with an anti-seismic belt or for connection with frame elements in panels (slabs), reinforcement outlets or embedded parts should be provided.
The mass of the structure has a significant influence on the values of seismic loads. Therefore, under the action of seismic forces, it is necessary to strive for the maximum possible reduction in the weight of structures and the resulting loads.
Non-bearing elements such as partitions and frame fillings are recommended to be made light, as a rule, of a large-panel or frame structure and connected to walls, columns, and with a length of more than 3 m - to ceilings. In buildings with more than five floors, the use of hand-made brickwork partitions is not allowed. Partitions made of brick or stone should be reinforced for the entire length at least every 700 mm in height with rods with a total cross section in the seam of at least 0.2 sq. see. It is allowed to carry out suspended partitions with movement limiters from the plane of the panels.
Stone buildings receive the most damage during earthquakes compared to other types of buildings of modern construction.
The seismic resistance of stone buildings is determined by the strength of brick and stone, and also depends on the strength of their adhesion to the mortar. According to current regulations, it is recommended to build load-bearing brick and stone walls, as a rule, from brick or stone panels, blocks manufactured in the factory using vibration, or from brick or stone masonry on mortars with special additives that increase the adhesion of the mortar to brick or stone .
To ensure seismic resistance, the choice of a construction site is important - close proximity to fault lines should be avoided. Changes are also being made to the foundations of structures - “pillows” are created from concrete or polymeric materials, thanks to which buildings slide or “float” during an earthquake and do not break along those lines where the greatest stress is created.
The most promising direction for improving seismic resistance is seismic isolation of buildings. Seismic isolation means detuning the frequencies of vibrations of the building from the prevailing frequencies of the impact. This is what ensures the reduction of the mechanical energy received by the structure from the base.
Russian specialists and foreign countries various devices for seismic isolation systems and vibration dampers of structures, as well as systems using alloys that store the volumetric state, and other "intelligent" systems have been proposed.
The following trends are observed in the world: the first is the use of seismic insulation of buildings in its pure form, which is usually arranged in the lower floors: rubber-metal supports of various modifications, with low and high damping, with and without a lead core, using various materials . There are also pendulum-type friction sliding bearings. Both those and other supports are used in the world very widely.
(Construction (Moscow), 30.03.2009)
The second direction is the use of damping (oscillation damping), which has been known for a very long time and is constantly being improved. For high-rise construction, as a rule, a combination is used: seismic isolation is located in the lower floor, and damping is installed along the height of the building. Now manufacturers offer a variety of dampers: metal, liquid, there are special alloys with memory, special damping walls, the latest devices, although relatively expensive, are quite effective.
The material was prepared on the basis of information from open sources
Unfortunately, a copy of the work on the topic "Earthquakes and houses" without illustrations has been preserved on the Internet. But, there was no other similar material on this very topical topic. Therefore, I publish an excerpt from the work of V.N. Andreeva, V.N. Medvedev "PROBLEMS OF SEISMIC RISK IN THE REPUBLIC OF SAKHA (Ya)" without author's illustrations.
As you already know, most of the city's residents live in three main types of houses: small-block, large-block, large-panel. Frame-panel buildings are, as a rule, public and administrative. Let's try to imagine an earthquake situation for each of these houses.
So, you are in a small block house. The lack of seismicity of such an unfortified house is 1.5-2 points. We only note that cracks in the internal and external walls can be from hairline to 3-4 centimeter. Cracks of such dimensions, through which the street was visible, were observed by a commission of specialists in similar houses in the city of Leninakan after the Spitak earthquake. You should not panic at the sight of such violations, because the house is designed for this. You should be especially careful if the destruction will be very different from those that we have described. For example, there will be a shift of floors from the walls by 3 or more centimeters. rice. 5 What elements of the house best resist the elements?
Let's turn to Figure 5, which shows the most typical layout of a residential 2-5-storey small-block house. Bearing (on which the floors are supported) main walls 1.2 are less damaged than transverse 3.4.5. The latter are easier to move (cut off) by horizontal seismic forces, since they are less loaded. Particularly dangerous is the end wall 4, which is connected to the other walls only on one side. Sometimes the ends of buildings even break away from the building and fall out, which has been repeatedly observed in the village of Gazli, the cities of Spitak and Neftegorsk. The most dangerous corner of the building 6, which is the least connected with the building and is most susceptible to "loosening" during an earthquake. Already with a 7-8 magnitude earthquake, the corners of buildings on the top floor, as a rule, are damaged, and with a magnitude 9 earthquake they can fall out. It is not recommended to be at the outer longitudinal walls (1) during an earthquake, since glass can “shoot out” here, windows fall out in and out (this remark is true not only for small-block houses), and even come off in especially weak houses (longitudinal walls from transverse ). The most secure during an earthquake are the intersections of the internal load-bearing longitudinal walls (2) with internal transverse ones. The figure shows the most characteristic "safety islands": at the exits from the apartments to the stairwell and at the intersection wall 5. In these places, due to the cross-shaped intersection of load-bearing and non-bearing walls, a core of increased strength is created, which can withstand even when the remaining walls collapse. This core is stronger, the fewer doorways it has. So, for example, the most reliable place will be at the right three-room apartment in the area of the intersection of internal walls 2 and 5. Also, the island in the two-room apartment at the intersection of blind sections of walls of type 3 and 2 seems to be reliable. As for the one-room and left three-room apartments, they have cores they have one or two openings and are therefore considered less durable than cores with blank walls. Therefore, if necessary, here you can move along wall 2. In such houses built in the 70-80s. the doorways leading to the staircase are framed with reinforced concrete frames, which guarantees their strength. However, in houses of earlier construction, frames are not everywhere, so these exits cannot be considered completely safe. A few general tips for behavior. As soon as the earthquake starts, you should open the doors leading to the landing and go to the safety island. It is worth trying to run out of the building if you are on the first or second floors. From a higher floor, you may not have time to do this before serious destruction begins. You need to run out of the house especially quickly and carefully so that you are not "covered" by bricks flying from the roof from the destroyed pipes, or crushed by a heavy visor. If you did not have time to get to the island of safety, then you should remember that partitions made of small-block masonry are very dangerous. They are among the first to be destroyed, up to the collapse. Wooden shield partitions are less dangerous, but rather large pieces of plaster can fall off from them, which are especially dangerous for young children. It is easy to distinguish a stone partition from a shield one by a deaf, very short, non-vibrating sound when you hit the wall with your fist. When arranging furniture in the apartment, pay attention to the fact that bulky furniture cannot fall into the territory of the island of safety or into the path of a possible evacuation from the apartment.
Many residents of large block houses know that their houses withstand an earthquake quite well. Their real seismic resistance is estimated by experts at 7.7 points. On fig. 6 shows a typical layout of a large-block house. The position of the capital load-bearing and non-bearing walls is the same as in a small-block house. A large-block house loses its bearing capacity mainly due to the stratification of the walls into separate blocks, which, unfortunately, do not have a good connection with each other in old houses. The outer walls consist of two blocks according to the height of the floor: a wall block with a height of 2.2 m and a lintel with a height of 0.6 m. The internal walls consist of blocks with a floor height, i.e. 2.8 m. on the lintel blocks of the outer walls and directly on the blocks of the inner walls. With an earthquake of more than 7 points, the blocks begin to shift from the plane of the wall. The greatest cracks and destruction of joints (11) should be expected in non-bearing transverse walls less loaded with slabs, especially in the end wall (4) and the walls of the staircase (3). In the last walls there is a small connection of the blocks with each other with the help of not very strong metal plates, which already during an earthquake of 7.5-8 points will begin to loosen greatly, breaking off pieces of concrete and plaster around them. This debris can injure people running up the stairs, so it is necessary to move by clinging closer to the railing. rice. 6. As in small block buildings, the corners of the building (6) are very dangerous, especially on the upper floors. The displacement of blocks from the plane of the wall can lead to partial collapse of the end wall (4) and floor slabs. Partitions in these houses, as a rule, are wooden, panel, plastered, and one should not be afraid of their collapse. Injury, especially to a small child, can be caused by pieces of plaster falling off the partitions and pieces of cement mortar falling out of the joints between the floor slabs. Such damage occurs during an earthquake of 7.5 points. The figure shows the safest places in a large-block house. Unlike small-block buildings, here all the doors leading to the landing are reinforced with reinforced concrete frames (9), so the probability of door jamming due to skew is low and the exit from the apartment is quite reliable. To the general advice - do not hang heavy shelves in the safety island area and fix furniture, it should be added that this is especially important to do in the storage closet (7) and in the corridor (8), otherwise there will simply be no place for you on the safety island.
In old large-panel five-story residential buildings, the typical layout of which is shown in Fig. 7, the area of safety islands is already much larger. Despite the fact that these houses were designed for 7-8 points, practice has shown that their real seismic resistance is close to 9 points. Not a single building of this kind was destroyed anywhere during earthquakes in the territory of the former Soviet Union. All external and internal walls in such houses are reinforced concrete large panels, well connected at the nodes using monolithic and welding (node 5). Internal walls and partitions are connected to each other on welded outlets. The floor panels are the size of a room, rest on the walls on four sides and are also welded to the walls. It turns out a reliable honeycomb structure. Calculations of the behavior of a large-panel house during a 9-point earthquake showed that the greatest damage is expected in the corners of the building (6), and in the junctions of the end panels (4), where large vertical cracks of 1-2 cm can open up. The first cracks may already appear with L-7.5 points. The same cracks can appear at expansion joints between buildings. But these cracks do not affect the overall stability of the building. Unpleasant factors include the possible appearance of oblique cracks up to 1 cm wide in reinforced concrete lintels above the entrance doors to apartments, which can lead to door jamming. Therefore, they must be closed immediately at the beginning of oscillations with a force of 6 points or more. Since large-panel buildings are quite reliable, you should not run out of them during an earthquake. But it is recommended to stay during an earthquake in the zone of safety islands, away from the outer walls, where window panes can “shoot out”, and from the end wall, in the nodes of which extended frightening cracks can open. You should not run out also because in the old houses of this series there are very heavy dangerous peaks over the entrances to the entrances. Embedded metal parts with which these visors were attached to the building. due to aging, they are heavily rusted and may not hold them in case of strong seismic shocks.
During an earthquake on In Shikotan, in 1994, several canopies fell near similar large-panel three-story houses, which crushed two residents who ran out of one house. However, not a single person who remained in the house was injured. The house itself was not seriously damaged. Later large-panel houses, the so-called "improved" series, with bay windows, as well as houses of a "new" layout with large glazed balconies, were originally designed for 9 points and it is practically safe to be in them during an earthquake of this magnitude. You need to beware of broken glass falling from above, especially from balconies, which can scatter over long distances - up to 15 meters. Therefore, it is not recommended to run out of these houses, just as it is not recommended to be on the street next to them. Fig.7 Experience shows that even with strong 8-9 magnitude earthquakes, 1-2-storey wooden houses practically do not collapse before a collapse. One of the authors of the book, observed the behavior of panel and block houses during a 9-point earthquake on about. Shikotan. Of the almost fifty two-story houses surveyed, there was not a single house where at least one wall collapsed or the ceiling failed. There were cases when the foundation "pulled out" from under the house and was carried away by a landslide by 1-1.5 meters, and the house, bowed, stood! There were breaks in the walls in the corners up to 20 cm and subsidence of the soil under the building up to 0.5 m, but the houses survived. Therefore, one should not run out of such houses anywhere, especially since the danger is represented by bricks falling on running out from collapsing chimneys. In wooden houses, ceilings sway more strongly than others and walls “crack” which causes discomfort. Pieces of plaster can fall out of the walls and from the ceiling. Therefore, in such houses it makes sense to choose a place where the plaster fits snugly against the wall, ceiling, i.e., it does not “buff” beforehand when tapped. Children are better off hiding under the table. And, of course, you need to stay away from the outer walls with windows, from heavy cabinets and shelves, especially if they are not specifically fixed. This is a general rule for any buildings.
Home training. Let's do a thought experiment. Close your eyes and imagine that you are lying on your own bed. Imagine that at this moment the first strong seismic shock has occurred. Now mentally try to get to the door as quickly as possible, open it and take a place in the doorway. At the same time, bend your fingers on your hand in each case when, in your mental progress, you come across obstacles that really exist. Now count. Each obstacle is a minimum of 3 lost seconds. Estimate net movement time and door lock opening time. Add seconds to grab a backpack with documents and products (no doubt, it hangs next to the door, as recommended). And if you get more than 20 seconds, then give yourself a fat FAILURE, and let's get down to reorganization. Make a list of obstacles found during the experiment. This is the minimum to be done. Let's start moving in reverse order. Evaluate the door lock in terms of the ability to quickly open the door. Is it easy for you to find the lock itself and its opening device even in the dark? How many actions are required to unlock the lock and the door? Try to arrange everything in such a way that the lock opens with a minimum of movements, and bring these movements to automatism .. Inspect the space near the front door. Are there objects nearby that, at the first push, can fall and block your path? If there are any, either strengthen them, or determine a more suitable place for them in the apartment. The corridor should be as free as possible. Very often, the passage is cluttered with things that have only recently been brought into the apartment and have not yet found their permanent place. Everyone knows that there is nothing more permanent than temporary. Therefore, without postponing "for later", clear your way to salvation. Pay attention to the fact that there are no objects along the walls that you can catch on. Look under your feet to see if shoes that are not currently in use have been removed from the corridor and if they create obstacles for movement. Now let's pay attention to the door from the corridor to the room. It is desirable that it be constantly open. Think about how you can fix it in the open position, and equip the latch. If there is carpet on the floor or there are tracks, then check how tightly they fit to the floor, if there are any gathers, folds, scuffs. Does the track slip on the main floor covering? Pay special attention to the joints of carpets and paths. Eliminate all flaws, let the path be "silk". In recent years, mobile interior elements have firmly entered our everyday life: tables on wheels, mobile cabinets for TV, video and audio equipment. Make it a rule not to leave them in the evening on a possible escape route. Leave them in such a position that their spontaneous movement in the event of seismic shocks cannot occur in the direction of this escape route and does not cause objects or furniture to fall along this route. If you use extension cords to connect electrical equipment, then make sure that the wires do not cross the path of your movement to the exit. The pride of almost every family is the home library. Check for books on open shelves, from which, at the first seismic shock, they can fall under your feet or fall on your head when you run to the door. Evaluate from the same positions objects standing on open shelves, especially if these shelves are above the doors. Make sure the shelves themselves are securely fastened. Bedside tables should also be securely fastened so as not to be the first insurmountable barrier to salvation. It is advisable to fix the table lamps standing on these cabinets. If the drawers in these bedside tables easily fall out or open with slight pressure on the door, then make sure that they are securely fixed. Clothing periodically accumulating next to the bed can be a serious obstacle to fast movement. Make it a rule to put things away that you won't be wearing that day. (It turns out that a possible strong earthquake is an important reason to keep the house in order!)
Recall the thought experiment you did again and note which obstacle came first in your path. If it is resolved, then check if there are any unresolved barriers in your post-experimental list and take appropriate measures. Check now the exit path for each family member. If there are small children in the family and you will first move towards them, then pay attention to those sections that you will have to cross twice in different directions. Find out if you will create obstacles for the way back with your first movement. Similarly, inspect and tidy up the escape route from the living room and kitchen. Please note that several people, including children, can move from these rooms at the same time. When you watch athletics competitions, then, watching a steeplechase race, you often have a desire to make the path easier for athletes and remove obstacles and a hole with water. How easily and beautifully they would have reached the finish line. But the rules of the game don't allow it. The rules of seismic safety, on the contrary, tell us - do not bring things to a home steeple chase, otherwise you will not be able to safely reach the finish line. Therefore, we advise you to remove barriers from the road and not take unnecessary risks.
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Earthquake on demand
Earthquake scientists at the University of Nevada on Wednesday tested new vehicular bridge designs that were designed with innovative connectors that should better withstand dangerous ground tremors and prevent structures from falling, burying thousands of tons of concrete and rebar.
was placed on a special stand to simulate the movements of the earth's crust. The structure weighs 100 tons and is 21 meters long.
The tests were carried out a day after the devastating earthquake that hit Mexico. The shaking of the model lasted for 30 seconds, during which time the seismic sensors located on the columns and beam joints of the bridge recorded the movement of the structure and monitored the behavior of the new connecting elements.
Graduates of local technical universities were present at the experiment and put into practice the knowledge gained by measuring the effects of the bridge crash test. As stated in the preliminary conclusion, during the initial inspection of the structure, no serious structural damage was noted.
"The bridge survived the experiment better than we expected" said Said Sayidi, a professor of civil and environmental engineering who led the project. He has been conducting such research for more than 30 years, so he has considerable experience in such cases.
Already designed to withstand earthquakes, but often unsafe to move around after big jolts. According to him, in the tested designs, special types of connectors were used to connect parts of prefabricated bridges, including ultra-high performance concrete.
"Earthquakes don't kill people, they kill structures" Sayidi said.
The elements have previously been tested individually, but never before combined into a bridge model subjected to realistic substrate motions. The model and amplitude of the shocks was taken from the 1994 earthquake in California, this corresponded to 7.5 points, which is quite a serious test for the design.
Among other things, innovative connectors allow concrete and other elements to be attached to the existing bridge structure to expedite repair and reconstruction after a cataclysm.