Classification of loads. Permanent and temporary loads and their types. Special loads. Regulatory and calculated values \u200b\u200bof loads. Strength of materials. The main tasks of the section. Classification of loads for what features classify loads

Statistical Loads do not change over time or change very slowly. Under the action of statistical loads, it is calculated for strength.

Repeated variables Loads repeatedly change the value or value and sign. The effect of such loads causes metal fatigue.

Dynamicloads change their value in a short period of time, they cause greater acceleration and inertia forces and can lead to sudden destruction of the design.

From theoretical mechanics it is known that by the method of application loads can be focused or distributed on the surface.

Really, the transfer of the load between the parts is not at the point, but at some site, i.e. the load is distributed.

However, if the contact site is negligible compared with the size of the part, the force is considered concentrated.

When calculating the real deformable bodies in the resistance of materials, it should not be replaced by a distributed load.

Axioms of theoretical mechanics in the resistance of materials are used limited.

You can not tolerate a pair of forces to another point of the part, move the focused force along the line of the action, you can not replace the system to replace the resultant when determining movements. All of the above changes the distribution of domestic forces in the design.

In the process of construction and operation, the building is experiencing the action of various loads. External influences can be divided into two types: force and nonalovy or environmental impact.

TO silov The impacts include various types of loads:

permanent- from its own weight (mass) of the elements of the building, the pressure of the soil on its underground elements;

temporary (long) - on the weight of stationary equipment, long-stored cargo, the own weight of the constant elements of the building (for example, partitions);

short-term - on weight (mass) of mobile equipment (for example, cranes in industrial buildings), people, furniture, snow, from wind action;

special - from seismic impacts, effects as a result of equipment accidents, etc.

TO nesilov relate:

temperature effectscausing changes in linear dimensions of materials and structures, which in turn to the occurrence of power influences, as well as affecting the thermal regime of the room;

impact of atmospheric and soil moisture, as well as vaporous moisturethe premises contained in the atmosphere and in the air, causing a change in the properties of materials from which the building structures are made;

air movement causing not only load (under wind), but also its penetration into the construction and premises, the change in their humidity and thermal regime;

impact of radiant energy Sun (solar radiation) caused by local heating a change in the physico-technical properties of surface layers of material, structures, a change in the light and thermal regime of the premises;

impact of aggressive chemical impuritiescontained in the air, which in the presence of moisture can lead to the destruction of the material of the building structures (corrosion phenomenon);

biological impactscaused by microorganisms or insects leading to the destruction of structures from organic building materials;

sound energy exposure (noise) and vibrations from sources inside or outside the building.

At the place of application effort load divided by focused (for example, the weight of the equipment) and uniform distributed (Own weight, snow).

By the nature of the workload can be static. permanent in time and dynamic (shock).

In the direction - horizontal (wind pressure) and vertical (own weight).

So The building has a variety of loads in terms of the size, direction, nature of the action and the place of the application.

Fig. 2.3. Load and exposure to the building.

There may be such a combination of loads, in which they all act in one direction, reinforcing each other. It is on such unfavorable combinations of loads that the building designs are calculated. The regulatory values \u200b\u200bof all efforts acting on the building are shown in DBN or SNiV.

5. Central-stretched steel elements: work scheme, application, strength calculation

Central stretched elements - These are elements, in the normal section of which point of application of longitudinal stretching N. Coincides with the point of the application of the equal effort in the longitudinal reinforcement.

The centrally stretched elements include arches, bottom belts and downlink farms and other elements (Fig. 51).

Centrally stretched elements are designed, as a rule, pre-tense.

Basic principles for the design of centrally stretched elements:

The rod working reinforcement without pre-stress is connected along the welding length;

The junctions of the messenger without welding are allowed only in slab and wall structures;

Stretched pre-stress fittings in linear elements should not have joints;

In cross section, the pre-stressed reinforcement is placed symmetrically (in order to avoid the extracentrate compression of the element);

Essentrenno-stretched elements - these are elements that are simultaneously stretched by the longitudinal force N. And bend moment M.that is equivalent to outcidentren stretching by force N. with eccentricity E O.relative to the longitudinal axis of the element. At the same time distinguish 2 cases: when the longitudinal stretching force N. It is applied between the resultant efforts in the stretched and compressed fittings, and the position is applied outside the distance.

Especially stretched elements include the lower belts of rigorous farms and other designs.

As practice shows, the topic of load collection causes the greatest number of issues in young engineers who begin their professional activities. In this article, I want to consider what constant and temporary loads are more than long-term loads differ from short-term and for which such separation is necessary, etc.

Classification of loads by duration of action.

Depending on the duration of the load and impacts are divided into permanent and temporary . Temporary Load In turn, divided into long, short-term and special.

As follows from the very name, permanent loads Act all over operation. Temporary loadsmanifest themselves in certain periods of construction or operation.

include: Own weight of carrier and enclosing structures, weight and pressure of soils. In the case of applying in the project of structures of factory production (riglels, plates, blocks, etc.), the normative value of their weight is determined on the basis of standards, work drawings or passport data of the manufacturer. In other cases, the weight of structures and soil is determined by project data on the basis of their geometric sizes as a product of their density ρ on the volume V. Taking into account their humidity in the context and operation of structures.

The estimated densities of some major materials are shown in Table. 1. The estimated weights of some rolled and finishing materials are shown in Table. 2.

Table 1

The density of the main building materials

Material	Density, ρ, kg / m3
Concrete: - Heavy - boilers	2400 400-600
Gravel	1800
Wood	500
Reinforced concrete	2500
Ceramzitobeton	1000-1400
Brick laying on a heavy solution: - from full ceramic brick - from the hollow ceramic brick	1800 1300-1400
Marble	2600
Trash construction	1200
River sand	1500-1800
Cement mortar - sandy	1800-2000
Mineral wool insulation plates: - Unfertime load - for thermal insulation of reinforced concrete coatings - in the systems of the ventilated facade - for thermal insulation of exterior walls, followed by plastering	35-45 160-190 90 145-180
Plaster	1200

table 2

Weight of rolled and finishing materials

Material	Weight, kg / m2
Bituminous tile	8-10
Plasterboard sheet 12.5 mm thick	10
Ceramic tile	40-51
Laminate with a thickness of 10 mm	8
Metal tile.	5
Parquet oak: - 15 mm thick - 18 mm thick - 22 mm thick	11 13 15,5
Roll roof (1 layer)	4-5
Sandwich - Roofing panel: - 50 mm thick - 100 mm thick - 150 mm thick - 200 mm thick - 250 mm thick	16 23 29 33 38
Plywood: - 10 mm thick - 15 mm thick - 20 mm thick	7 10,5 14

Temporary loads are divided by long, short-term and special.

relate:

- load from people, furniture, animals, equipment on overlapping residential, public and agricultural buildings with reduced regulatory values;

- loads from vehicles with reduced regulatory values;

- weight of temporary partitions, gravy and sweeping for equipment;

- snow loads with reduced regulatory values;

- the weight of stationary equipment (machines, motors, tanks, pipelines, liquids and solids, filling equipment);

- pressure of gases, liquids and bulk bodies in tanks and pipelines, excessive pressure and air discharge arising from ventilation of mines;

- load on overlapping from stored materials and stele equipment in storage rooms, refrigerators, granaries, books, books, archives of such rooms;

- Temperature technological impacts from stationary equipment;

- weight of the water layer on water-filled plane coatings;

- Vertical loads from bridge and suspended cranes with a reduced regulatory value, determined by multiplying the full normative value of the vertical load from one crane in each span of the building on the coefficient:

0.5 - for groups of operation modes of Cranes 4K-6K;

0.6 - for a group of operation of cranes 7K;

0.7 - for a group of operation of the cranes 8k.

Groups of crane modes are accepted according to GOST 25546.

relate:

- weight of people, repair materials in the maintenance and repair areas of equipment with full regulatory values;

- load from motor vehicles with full regulatory values;

- snow loads with complete regulatory values;

- wind and ice load;

- loads from equipment arising in pumping, transitional and testing modes, as well as during its permutation or replacement;

- temperature climatic effects with full regulatory value;

- loads from mobile lifting - transport equipment (loaders, electrocars, cranes - stackers, telphers, as well as from bridge and suspended cranes with a full regulatory value).

relate:

- seismic effects;

- explosive effects;

- loads caused by sharp impaired technological process, temporary malfunction or equipment breakdown;

- Impact due to deformations of the base, accompanied by a radical change in the structure of the soil (when soaking by the sediments) or sedimentation in areas of mountain workings and in karst.

Competently dosed physical exertion have a beneficial effect on the body. They allow you to achieve an ideal figure, increase muscle tone and even strengthen human immunity. However, in order to get the desired result, you need to create a set of exercises and choose their optimal intensity. What types of physical exertion exist and for what purposes they are most suitable, we will tell us in our article.

Load classification

Sport classes are performed with some kind of definite purpose. It may be support for muscle tone, weight loss, recovery after injury or preparation for sports. In each case, the types of physical exertion and their intensity will differ, so they are accepted to divide in accordance with the following classification:

• aerobic;
• anaerobic;
• interval;
• hypoxic.

Some of these loads, our body is subjected daily, and others can not be completely under the power of a novice athlete. Let's wonder what the differences of each type and for which tasks should choose one or another option.

A group of aerobic loads

Aerobic physical exertion (or cardion loads) are a complex of simple exercises that are aimed at enriching the cells with the necessary amount of oxygen, an increase in the protective forces of the body and the training of its stability.

With these loads, our body is subjected daily: during a hike to the store, in the process of cleaning the apartment, on the road to work and during the walk. Also here can be attributed:

• ride a bike;
• water sports;
• skiing, skating, rollers;
• daily gymnastics;
• walking on the stairs;
• dancing classes, etc.

This group includes almost all versions of active pastime. To support the body in good shape, this is the ideal type of physical exertion.

Aerobic type exercises are considered the most secure. They can be performed by people of different ages, regardless of the level of preparation. Patients who have suffered severe injuries and having chronic diseases are recommended that such loads. However, in this case, the intensity of classes and the reaction of the body should strictly control the attending physician.

Anaerobic exercises and methods of their implementation

Anaerobic exercise group includes types of physical exertion characterized by increased weight and intensity. This includes which are carried out by athletes in order to increase muscle mass, and training the endurance of the body.

Exercises are performed using heavy dumbbells, rods and various simulators. Their main essence is short-term movement of gravity without the movement of the body. The final result is considered a significant increase in muscle tissue and high power indicators. However, it should be known that in the process of rapid increases in the volume of muscles, their elasticity is significantly reduced.

Anaerobic loads have contraindications and are not recommended to people over 40 years old. Nevertheless, you can perform exercises with moderate burdens, allowing you to maintain the body in good physical form: lift dumbbells up to 5 kg, use rubber or spring expander.

Group of interval exercises: What are their features?

During training athletes, various types of physical exertion (and their intensity) can be alternated and combined. In this case, they speak about the interval load when classes include elements of the first and second type.

For example, young and healthy men engaged in a severe sport, it is mandatory to perform aerobic exercises. That is, during their training, heavier exercises alternate and easy run. At the same time, athletes can additionally use heavy loads affecting a certain muscle group. In sports, the types of physical exertion alternate constantly, especially when it comes to professional training.

Hypoxic loads

They are used to train the endurance of professional athletes. Hypoxic loads relate to heavy exercises, since they are performed under conditions of lack of oxygen when a person is at the limit of its capabilities.

The main purpose of this type of training is to minimize the process of acclimatization of the body in an unusual setting. Used to train the respiratory system of climbers, which are often reside in the conditions of highlands, where prevails

Principle of selection of physical exertion (by nature of the impact)

The right choice of optimal exercises is a guarantee of obtaining the desired result. That is why before starting training, you need to clearly designate the final goal. It can be:

• rehabilitation after injuries, operations and chronic diseases;
• improvement and restoration of forces, lifting tension after working day;
• maintaining the body in existing physical form;
• increased endurance and an increase in body forces.

Selecting the load in the second and third version usually does not cause difficulties. But the exercises with therapeutic goal to choose much more difficult to choose. Thinking about what types of physical exertion is most effectively restored, the current state and human opportunity should be taken into account.

The same exercise can be very effective for an athlete in moderate physical form and is absolutely useless for novice athlettes. Therefore, the choice of training programs should be carried out on the principle of threshold loads, and better if the coach is well aware of the status and capabilities of an athlete.

Types of load

In addition to the main classification of training, there is a separation of exercises for several types. Each of them is aimed at the development of concrete quality.

According to the nature of the impact on the body, several main types of physical exertion distinguish:

• power;
• speed;
• on flexibility;
• on the development of agility and coordination abilities.

In order for the workouts to be obtained the maximum benefit, they should be performed in accordance with certain rules that we will talk about.

Power exercises

Claims of power exercises help keep the body in a tone, slow down the process of aging tissues, prevent the development of various cardiovascular diseases. It is important that the load is obtained all because the inactive tissues are deprived of the necessary substances, which leads to their aging.

The positive effect on the power exercises is achieved if the load gradually increases, but it corresponds to the state of human health. The burden of loads and their repetition should also increase gradually. Exercises with an uncontrolled amount of repetitions are absolutely no intended to train endurance and strength.

In recreational exercises, the physical activity (classification and species of which appoints a doctor) is based on an unsaturated burden and a clearly established number of repetitions. This method of selection of loads allows you to achieve results and avoid injury.

At the initial stages of training, the burden should be used by no more than 40% of the maximum possible basis. Next, the load can be chosen so that the maximum number of repetitions of the exercise was about 8-12 times. And for the muscles of the forearm, neck, leg and abdomen would reach 15-20 times (with pauses between approaches for 1-3 minutes).

Speed \u200b\u200bload type

Such training does not require a man of great endurance and strong tension. They have a positive effect on both young and aging organism. In the latter case, high-speed exercises are considered particularly relevant. After all, the main sign of the fading of the body is not only the fussing of its motor functions, but also slowing down movements.

High-speed loads should not be held longer than 10-15 seconds. Long exercises (from 30 to 90 seconds) must be performed with lower power. It is these exercises that alternated with small time intervals for rest to the maximum extent contribute to the slowdown of cell aging processes. In order to support the body in optimal form, high-speed exercises are recommended to perform during each sports.

The benefits of the elasticity of muscles, ligaments, joints

Exercises for flexibility - the most popular types of loads in them include the children of the junior classes in school. Such loads contribute to the preservation of the flexibility and mobility of the joints and the spine. In addition, the positive effects of such loads include:

• prevention of excessive joints of the joints;
• preventing the development of arthritis;
• improving the state of the articular bag;
• prevention of osteochondrosis.

The elasticity of muscles, joints and ligaments significantly reduces the likelihood of injury, contributes to the speedy restoration of muscle tissues after physical exertion. Exercises on flexibility are perfectly relaxing muscles, improve their tone.

The absence of such loads leads to the reaffection of tissues. The energy that could be used for recovery is wasted, and the muscle itself suffers from the lack of oxygen.

What other workouts are needed

Dexterity and coordination abilities are no less important qualities required by man throughout his life. In the absence of systematic training, these skills gradually decrease. What types of physical exertion should be included in training for the development of data of abilities? Everything is easier simple. The best option will be various sports games: tennis, desktop, badminton, etc.

Easy sports perfectly train dexterity and are good prevention of cardiovascular diseases. Age restrictions do not have such loads, but they are very difficult to dose. For this reason, during the training process, you need to control your own breathing and monitor the cardiac rhythm.

Training A dexterity with sports games significantly increase the adaptive abilities of the body, and exercises that require constant attention, well train the mental response. A person begins to make difficult decisions faster and operates faster in unforeseen situations.

As we saw, any type of physical activity is able to positively influence the person. However, to achieve maximum result, training must be systematic and include several types of exercises simultaneously. Thus, it is possible to ensure a high degree of sustainability of the organism to adverse factors, as well as to constantly develop and improve new skills. The main thing is to remember, whatever the type of loads you choose, it is important to always know the measure!

Permanent loads.(q.) Depending on the duration of the load, the load is divided into permanent and temporary. By permanent loads are the weight of carrier and enclosing structures of buildings and structures, weight and pressure of soils, the effects of pre-stress of reinforced concrete structures.

Temporary loads. Long load (P) . These include: the weight of stationary equipment at the floors - machines, devices, engines, tanks, etc.; Pressure of gases, liquids, bulk bodies in tanks; weight of specific content in warehouses, refrigerators, archives, libraries and similar buildings and structures; mounted part of the temporary load in residential buildings, in service and household premises; long temperature technological impacts from stationary equipment; Loads from one suspended or one bridge crane multiplied by coefficients: 0.5, 0.6... depending on the type of crane

Short-term load. (S) These include: the weight of people, parts, materials in the areas of service and repair of equipment - the passages and other areas free of equipment; part of the load on the overlap of residential and public buildings; loads arising from the manufacture, transportation and installation of structural elements; loads from suspended and bridge cranes used in the construction or operation of buildings and structures; Snow and wind loads; Temperature climatic effects.

Special loads. These include: seismic and explosive effects; loads caused by a malfunction or equipment breakdown and a sharp disruption of the process (for example, with a sharp increase or decrease in temperature, etc.); The impact of uneven deformations of the base, accompanied by a radical change in the structure of the soil (for example, the deformation of the sedentary soils during soaking or choresomerous soils during thawing), etc.

Regulatory loads. They are installed by norms or nominal values. Regulatory permanent loads are taken by the design values \u200b\u200bof geometric and structural parameters and on average density values. Regulatory temporary technological and installation loads are installed at the highest values \u200b\u200bprovided for normal operation; Snow and wind - on average of annual adverse values \u200b\u200bor by adverse values \u200b\u200bcorresponding to a specific average period of their repetitions.

Estimated load. Their values \u200b\u200bwhen calculating structures for strength and stability determine the multiplication of the regulatory load on the reliability coefficient by load γfusually more than a unit. Accurateness of reliability in the action of the weight of concrete and reinforced concrete structures γ f -1\u003e 1. The reliability factor in the action of the weight of the structures used in the calculation of the status of the position against ascent, overturning and slipping, as well as in other cases where the mass decreases deteriorates the working conditions of the design, adopted γ f \u003d 0.9. When calculating structures at the embodiment stage, the calculated short-term loads are multiplied by the coefficient of 0.8. When calculating structures on deformations and movements (according to the second group of limit states), the calculated loads take equal regulatory values \u200b\u200bwith the coefficient ΓT \u003d.1.

Combination of loads. The designs should be calculated on various combinations of loads or their corresponding efforts if the calculation is carried out according to the scheme of an inelastic state. Depending on the composition of the taken into account, the loads distinguish: main combinations,include constant, long and short-term loads or efforts from them; special combinations,including constant, long, possible short-term and one of the special loads or efforts from them.

In the main combinations, when taking into account at least two time loads, their calculated values \u200b\u200b(or their corresponding efforts) are multiplied by the coefficients of the combination of equal: for long-term loads F1 \u003d 0.95; For short-term F2 \u003d 0.9. When accounting for one time load F1 \u003d F2 \u003d L. Norms allowed when taking into account three and more short-term loads, their calculation values \u200b\u200bare multiplied by the coefficients of combinations: F 2 \u003d L- for the first to the degree of importance of short-term load; F 2 \u003d 0.8 - for the second; F2 \u003d 0.6 - for the rest.

In special combinations for long-term loads F1 \u003d 0.95, for short-term f 2 \u003d 0.8, except for cases specified in the designations of building and structures in seismic areas.

You decided, for example, make yourself a house. Alone, without attracting architects-designers. And at some point in time, usually almost immediately, there is a need to calculate the weight of this house. And then there begins a series of questions: what is the magnitude of the snow load, which load should withstand overlap which coefficient is used when calculating wooden elements. But before giving specific numbers, it is necessary to understand what the relationship between the length of the impact of the load and its value.
Loads are generally divided into permanent and temporary. And temporary in turn on long-term, short-term and instantaneous. Surely the unprepared reader will have a question: what, in fact, the difference, how to classify the load? Take, for example, the load on the intergenerational overlap. In SNILE, a regulatory value of 150 kgf per square meter is registered. With a careful reading of the document it is easy to see that 150 kgf / m² (complete regulatory value) is used when classifying the load as "short-term", but if we classify it as a "long-term", then the load on the overlap is accepted already only 30 kgf / m²! Why is this happening? The answer lies in the depths of the theory of probability, but for simplicity I will explain on the example. Imagine the weight of everything that you have in the room. Perhaps you are a collector of cast-iron hatches from wells, but statistically, if we consider thousands of rooms of different people, then on average, people are limited to half-bottom all sorts of items on a room at 17 m². Haltone - this is not enough for the room! But by sharing the load on the area we get just 30 kg / m². The digit is statistically confirmed and fixed in SNiP. And now imagine that you (weighing 80 kg) enter the room, sit on the chair (weighing 20 kg) and your wife is satisfied with your knees (weighing 50 kg). It turns out that the load is 150 kg on a sufficiently small area. Of course you can always move around the apartment in such a tandem, or simply weigh all 150 kg on your own, but you cannot sit still motionless 10 years. This means that the load in these 150 kg you create every time in a different place, while there is no such load else. Those. In a long run, you do not exit the average 500 kg per 17 m², or 30 kg / m², but in a short period you can create a load of 150kg / m². And if you are engaged in jumping on a trampoline with a weight of 150 kg - then it will already be "instant" load, and its calculation is carried out on the basis of individual features, because there are simply no statistics for such cases.

So, with the difference between the terms, they figured out a bit, now to the question: What is the difference for us as designers? If you press the board with a small mass for decades - it will drive it, and if you press it up, and then let go of the board will return your original state. That is this effect and take into account the assignment of load classes when calculating the strength of the wood.

All information for the article is given from Snip 2.01.07-85 "Load and Impact" . Since I am a supporter of a wooden house-building, I will also refer to the special case of the classification of loads according to the current 2017, as well as mentioned Eurocode EN 1991.

Load classification 2.01.07-85

Depending on the duration of the load, constant and temporary loads should be distinguished.

​

Permanent loads

weight of parts of structures, including the weight of carriers and enclosing building structures;

weight and pressure of soils (embankments, backfills), mining pressure;

hydrostatic pressure;

structuring in the design or base of pre-voltage, the preliminary voltage should also be taken into account in the calculations as efforts from constant loads.

Temporary loads

Time loads are divided into three classes:

1. Long load

weight of temporary partitions, gravy and sweeping for equipment;

inpatient equipment weight: machine tools, devices, motors, tanks, pipelines with fittings, supporting parts and insulation, belt conveyors, permanent lifting machines with their ropes and guides, as well as the weight of liquids and solids that fill equipment;

pressure of gases, liquids and loose bodies in tanks and pipelines, excess pressure and air loss that occurs when ventilating mines;

loads on overlapping from stored materials and rack equipment in warehouses, refrigerators, granaries, books, archives and similar premises;

temperature technological impacts from stationary equipment;

weight of water layer on water-filled plane coatings;

the weight of the sediments of production dust, if its accumulation is not excluded by the relevant activities;

loads from people with reduced regulatory values;

snow loads with a reduced regulatory value, defined by multiplying the full regulatory value to the coefficient:

• 0.3 - for the III of the Snow Area,

  0.5 - for the IV region;

  0.6 - for V and VI areas;

temperature climatic effects with reduced regulatory values;

impacts due to deformations of the base that are not accompanied by a fundamental change in the structure of the soil, as well as the thawing of the festive soils;

impact due to changes in humidity, shrinkage and creep materials.

2. Short-term loads

loads from equipment arising in pumping, transitional and testing modes, as well as during its permutation or replacement;

weight of people, repair materials in equipment service and repair areas;

loads from people, animals, equipment on the overlap of residential, public and agricultural buildings with full regulatory values;

loads from moving lifting and transport equipment (loaders, electrocarbers, cranes-stackers, telphers, as well as from bridge and suspended cranes with a full regulatory value);

snow load with full regulatory value;

temperature climatic effects with full regulatory value;

wind loads;

looled loads.

3. SPECIAL LOADS

seismic impacts;

explosive effects;

loads caused by sharp impaired technological process, temporary malfunction or equipment breakdown;

the impact due to deformations of the base, accompanied by a radical change in the structure of the soil (when soaking by the sediments) or sedimentation in the areas of mountain workings and in karst.

Regulatory loads mentioned above are shown in the table:

In the current version of this document, the reduced regulatory values \u200b\u200bof uniformly distributed loads are determined by multiplying their complete regulatory values \u200b\u200bto the coefficient of 0.35.
Such a classification was adopted for quite a long time and has already managed to root in the consciousness of the "post-Soviet engineer". However, gradually, after Europe, we go to the so-called Eurocodes.

Classification of Loads for the Eurocode EN 1991

Everything is more diverse in the Eurocode and more difficult. All settlement impacts should be taken in accordance with the relevant sections EN 1991:

EN 1991-1-1 Specific, permanent and temporary loads

EN 1991-1-3. Snow loads

EN 1991-1-4 Wind exposure

EN 1991-1-5 Temperature effects

EN 1991-1-6 Impact in the production of construction work

EN 1991-1-7 Special impact

In accordance with the TCP EN 1990, when considering the impacts apply the following classification:

permanent exposure G.. For example, the effects of their own weight, stationary equipment, internal partitions, finishes and indirect effects as a result of shrinkage and / or precipitation;

variables of influences Q.. For example, the accompanying payloads, wind, snow and temperature loads;

special effects of A.. For example, loads from explosions and shocks.

If with constant influence, everything is more or less clear (just take the volume of the material and multiply it on the average density of this material and so for each material in the design of the house), then variables are required by explanations. I will not consider special impacts in the context of private construction.
According to the euro, the magnitude of the impact is characterized by the categories of using the structure according to Table 6.1:

Despite all the information provided, Eurocode implies the use of national applications developed to each Eurocode section individually in each country that uses this Eurocode. These applications take into account the various climatic, geological, historical and other features of each country, allowing, however, adhere to uniform rules and standards in the calculation of structures. EUROMode EN1991-1-1 The national application has and it is in part of the load values \u200b\u200bentirely and fully refers to SNiP 2.01.07-85, considered in the first part of this article.

Classification of loads in the design of wooden structures according to EN1995-1-1

For 2017, the European Document is in effect in Belarus TKP EN 1995-1-1-2009 "Design of wooden structures" . Since the document refers to Eurocodes, the previous classification according to EN 1991 is fully applicable to wooden structures, but has additional refinement. So, in the calculations on strength and suitability of operation, it is necessary to take into account the duration of the operation of the load and the influence of humidity!

Classes of duration of the loads are characterized by exposure to constant loads acting at a certain period of time during the operation of the structure. For variable exposure, the corresponding class is determined based on the interaction assessment between the type variation of the load and the time.

This is a general classification recommended by Eurocode but, the structure of Eurocoders, as I mentioned, implies the use of national applications developed in each country individually, and, of course, for Belarus, this application also has. It is slightly reduced classification of duration:

This classification is sufficiently correlated with the classification by SNiP 2.01.07-85.

Why do we know all this?

• Effect on the strength of wood

In the context of the design and calculation of the wooden house and any of its element, the classification of loads together with the class of operation is important and can more than twice (!) Change the estimated strength of wood. For example, all calculated wood strength values, among other coefficients, are multiplied by the so-called KMOD modification coefficient:

As can be seen from the table, depending on the class of exposure to the load and operating conditions, the same variety board I can withstand the load, for example, a compression of 16.8 MPa with a short-term exposure in a heated room and only 9.1 MPa at a permanent load in Fifth grade operating conditions.

• Impact on the strength of composite reinforcement

When designing foundations and reinforced concrete beams, the composite reinforcement is sometimes used. And if the length of the load does not have a significant effect on the steel reinforcement, then everything is very different with the composite. The effects of the load duration for ACP are given in Appendix L to SP63,13330:

In the formula for calculating the resistance of the stretch, given in the table, there is a yf coefficient - this is the coefficient of reliability according to the material taken by calculating the limit states of the second group equal to 1, and when calculated on the first group - equal to 1.5. For example, in the outdoor beam, the strength of fiberglass fittings can be 800 * 0.7 * 1/1 \u003d 560 MPa, but with a long load 800 * 0.7 * 0.3 / 1 \u003d 168 MPa.

• Impact on the value of the distributed load

According to SNiP 2.01.07-85, the loads from people, animals, equipment on the overlap of residential, public and agricultural buildings are accepted with a reduced regulatory value if we refer these loads to prolonged. If we classify them as short-term, then we accept full regulatory values \u200b\u200bof loads. Such differences are formed by the theory of probabilities and mathematically calculated, but in the rules of the rules are presented as ready answers and recommendations. There is also the same influence of the classification and snow loads, but I will consider snow loads already in another article.

What should be considered?

We have already figured out a bit with the classification of loads and realized that the load on overlapping and snow loads relate to temporary loads, but it may be as long as long and short-term. Moreover, their value can differ significantly depending on how the class we count them. Is there really a solution to a solution depending on our desire? Of course not!
In TKP EN 1995-1-1-2009 "Designing of wooden structures" there is the following prescription: If the combination of the load consists of the effects that belong to different load classes of the load validity, then the value of the modification coefficients that corresponds to the effect of less duration, for example for Combinations of their own weight and short-term load applies the value of the coefficient corresponding to short-term load.
In the joint venture 22.13330.2011 "The foundations of buildings and structures" indication of this: load on overlappings and snow loads, which, according to SP 20.13330, can relate to both long and short-term, when calculating the bases on the bearing capacity, are considered short-term, and when calculating deformations - Long. Loads from mobile lifting and transport equipment in both cases are considered short-term.