As the name suggests, this is the external pressure that will be exerted on the hangar through snow and wind. Calculations are made in order to lay in the future building materials with characteristics that will withstand all the loads in the aggregate.
Calculation snow load produced according to SNiP 2.01.07-85* or according to SP 20.13330.2016. At the moment, SNiP is mandatory, and joint venture It is advisory in nature, but in general, the same is written in both documents.
The SNIP indicates 2 types of loads - Normative and Design, let's figure out what their differences are and when they are applied: - this is the largest load that meets normal operating conditions, taken into account in calculations for the 2nd limit state (by deformation). The normative load is taken into account when calculating beam deflections, and tent sagging when calculating crack opening in reinforced concrete. beams (when the requirement for watertightness does not apply), as well as rupture of the awning fabric.
is the product of the standard load and the load safety factor. This coefficient takes into account the possible deviation of the standard load in the direction of increase in an unfavorable set of circumstances. For a snow load, the load safety factor is 1.4 i.e. the calculated load is 40% more than the normative one. The design load is taken into account in calculations for the 1st limit state (for strength). In the calculation programs, as a rule, it is the calculated load that is taken into account.
A big advantage of frame-tent construction technology in this situation is its ability to "exclude" this load. An exception implies that precipitation does not accumulate on the roof of the hangar, due to its shape, as well as the characteristics of the covering material.
covering material
The hangar is equipped with an awning fabric with a certain density (an indicator that affects strength) and the characteristics you need.
Roof forms
All frame-tent buildings have a sloping roof shape. It is the sloping shape of the roof that allows you to remove the load from precipitation from the roof of the hangar.
In addition to this, it should be noted that the awning material is covered with a protective layer of PVC. Polyvinyl protects the fabric from chemical and physical influences, and also has good anti-adhesion, which contributes to
snow rolling under its own weight.
Snow load.
There are 2 options to determine the snow load of a specific location.Option I- see your locality in the table
II Option- determine on the map the number of the snowy area, the location you are interested in and convert them to kilograms, according to the table below.
- Find the number of your snow region on the map
- match the number with the number in the table
Hard to see? Download all maps in one archive in good resolution (TIFF format).
| wind region |
Ia | I | II | III |
IV |
V | VI | VII |
| Wo (kgf/m2) | 17 | 23 | 30 | 38 | 48 | 60 | 73 |
85 |
The calculated value of the average component of the wind load at a height z above the ground is determined by the formula:
W=Wo*k
Wo- standard value of the wind load, taken according to the table of the wind region of the Russian Federation.
k- coefficient that takes into account the change in wind pressure with height, is determined from the table, depending on the type of terrain.
- A- open coasts of the seas, lakes and reservoirs, deserts, steppes, forest-steppes and tundras.
- B- urban areas, forests and other areas evenly covered with obstacles more than 10 m.
*When determining the wind load, terrain types can be different for different calculated wind directions.
- 5 m. - 0.75 A / 0.5 V.
- 10 m - 1 A / 0.65 B°.
- 20 m - 1.25 A / 0.85 V
Snow and wind loads in Russian cities.
| City | snow area | wind region |
| Angarsk |
2 |
3 |
| Arzamas |
3 |
1 |
| Artem |
2 |
4 |
| Arkhangelsk |
4 |
2 |
| Astrakhan |
1 |
3 |
| Achinsk |
3 |
3 |
| Balakovo |
3 |
3 |
| Balashikha |
3 |
1 |
| Barnaul |
3 |
3 |
| Bataysk |
2 |
3 |
| Belgorod |
3 |
2 |
| Biysk |
4 |
3 |
| Blagoveshchensk |
1 |
2 |
| Bratsk |
3 |
2 |
| Bryansk |
3 |
1 |
| Velikiye Luki |
2 |
1 |
| Velikiy Novgorod |
3 |
1 |
| Vladivostok |
2 |
4 |
| Vladimir |
4 |
1 |
| Vladikavkaz |
1 |
4 |
| Volgograd |
2 |
3 |
| Volzhsky Volgograd. Region |
3 |
3 |
| Volzhsky Samarsk. Region |
4 |
3 |
| Volgodonsk |
2 |
3 |
| Vologda |
4 |
1 |
| Voronezh |
3 |
2 |
| Grozny |
1 |
4 |
| Derbent |
1 |
5 |
| Dzerzhinsk |
4 |
1 |
| Dimitrovgrad |
4 |
2 |
| Ekaterinburg |
3 |
1 |
| Dace |
3 |
2 |
| Railway |
3 |
1 |
| Zhukovsky |
3 |
1 |
| Chrysostom |
3 |
2 |
| Ivanovo |
4 |
1 |
| Izhevsk |
5 |
1 |
| Yoshkar-Ola |
4 |
1 |
| Irkutsk |
2 |
3 |
| Kazan |
4 |
2 |
| Kaliningrad |
2 |
2 |
| Kamensk-Uralsky |
3 |
2 |
| Kaluga |
3 |
1 |
| Kamyshin | 3 | 3 |
| Kemerovo |
4 |
3 |
| Kirov |
5 |
1 |
| Kiselevsk |
4 |
3 |
| Kovrov |
4 |
1 |
| Kolomna |
3 |
1 |
| Komsomolsk-on-Amur |
3 |
4 |
| Kopeysk |
3 |
2 |
| Krasnogorsk |
3 |
1 |
| Krasnodar |
3 |
4 |
| Krasnoyarsk |
2 |
3 |
| Mound |
3 |
2 |
| Kursk |
3 |
2 |
| Kyzyl |
1 |
3 |
| Leninsk-Kuznetsky |
3 |
3 |
| Lipetsk |
3 |
2 |
| Lyubertsy |
3 |
1 |
| Magadan |
5 |
4 |
| Magnitogorsk |
3 |
2 |
| Maykop |
2 |
4 |
| Makhachkala |
1 |
5 |
| Miass |
3 |
2 |
| Moscow |
3 |
1 |
| Murmansk |
4 |
4 |
| Murom |
3 |
1 |
| Mytishchi |
1 |
3 |
| Naberezhnye Chelny |
4 |
2 |
| Nakhodka |
2 |
5 |
| Nevinnomyssk |
2 |
4 |
| Neftekamsk |
4 |
2 |
| Nefteyugansk |
4 |
1 |
| Nizhnevartovsk |
1 |
5 |
| Nizhnekamsk |
5 |
2 |
| Nizhny Novgorod |
4 |
1 |
| Nizhny Tagil |
3 |
1 |
| Novokuznetsk |
4 |
3 |
| Novokuibyshevsk |
4 |
3 |
| Novomoskovsk |
3 |
1 |
| Novorossiysk |
6 |
2 |
| Novosibirsk |
3 |
3 |
| Novocheboksarsk |
4 |
1 |
| Novocherkassk |
2 |
4 |
| Novoshakhtinsk |
2 |
3 |
| New Urengoy |
5 |
3 |
| Noginsk |
3 |
1 |
| Norilsk |
4 |
4 |
| Noyabrsk |
5 |
1 |
| Obnisk | 3 | 1 |
| Odintsovo |
3 |
1 |
| Omsk |
3 |
2 |
| Eagle |
3 |
2 |
| Orenburg |
3 |
3 |
| Orekhovo-Zuevo |
3 |
1 |
| Orsk |
3 |
3 |
| Penza |
3 |
2 |
| Pervouralsk |
3 |
1 |
| Permian |
5 |
1 |
| Petrozavodsk | 4 | 2 |
| Petropavlovsk-Kamchatsky |
8 |
7 |
| Podolsk |
3 |
1 |
| Prokopyevsk |
4 |
3 |
| Pskov |
3 |
1 |
| Rostov-on-Don |
2 |
3 |
| Rubtsovsk |
2 |
3 |
| Rybinsk |
1 |
4 |
| Ryazan |
3 |
1 |
| Salavat |
4 |
3 |
| Samara |
4 |
3 |
| Saint Petersburg |
3 |
2 |
| Saransk |
4 |
2 |
| Saratov |
3 |
3 |
| Severodvinsk |
4 |
2 |
| Serpukhov |
3 |
1 |
| Smolensk |
3 |
1 |
| Sochi |
2 |
3 |
| Stavropol |
2 |
4 |
| Stary Oskol |
3 |
2 |
| Sterlitamak |
4 |
3 |
| Surgut |
4 |
1 |
| Sizran |
3 |
3 |
| Syktyvkar |
5 |
1 |
| Taganrog |
2 |
3 |
| Tambov |
3 |
2 |
| Tver |
3 |
1 |
| Tobolsk |
4 |
1 |
| Tolyatti |
4 |
3 |
| Tomsk |
4 |
3 |
| Tula |
3 |
1 |
| Tyumen |
3 |
1 |
| Ulan-Ude |
2 |
3 |
| Ulyanovsk |
4 |
2 |
| Ussuriysk |
2 |
4 |
| Ufa |
5 |
2 |
| Ukhta |
5 |
2 |
| Khabarovsk |
2 |
3 |
| Khasavyurt |
1 |
4 |
| Khimki |
3 |
1 |
| Cheboksary |
4 |
1 |
| Chelyabinsk |
3 |
2 |
| Chita |
1 |
2 |
| Cherepovets |
4 |
1 |
| Mines |
2 |
3 |
| Schelkovo |
3 |
1 |
| Elektrostal |
3 |
1 |
| Engels |
3 |
3 |
| Elista |
2 |
3 |
| Yuzhno-Sakhalinsk |
8 |
6 |
| Yaroslavl |
4 |
1 |
| Yakutsk |
2 |
1 |
The strength and durability of roof structures are significantly affected by snow, wind, rain, temperature changes and other physical and mechanical factors affecting the building.
The calculation of the load-bearing structures of buildings and structures is carried out according to the method of limit states, in which the structures lose their ability to resist external influences, or receive unacceptable deformations or local damage.
There can be two limit states, according to which the roof load-bearing structures are calculated:
- The first limit state is reached when building structure the bearing capacity (strength, stability, endurance) is exhausted, but simply, the structure is destroyed. The calculation of load-bearing structures is carried out for the maximum possible loads. This condition is written by the formulas: σ ≤ R or τ ≤ R, meaning that the stresses developing in the structure when the load is applied should not exceed the maximum allowable;
- The second limit state is characterized by the development of excessive deformations from static or dynamic loads. Unacceptable deflections occur in the structure, the joints of the joints open. However, in general, the structure is not destroyed, but its further operation without repair is impossible. This condition is written by the formula: f ≤ f norm, which means that the deflection that appears in the structure when a load is applied should not exceed the maximum allowable. The normalized beam deflection for all roof elements (rafters, girders and battens) is L / 200 (1/200 of the length of the checked beam span L), see Fig.
Calculation truss system pitched roofs is carried out over both limit states. The purpose of the calculation: to prevent the destruction of structures or their deflection above the permissible limit. For snow loads acting on the roof, the supporting frame of the roof is calculated according to the first group of states - for the estimated weight of the snow cover S. This value is commonly called the design load, it can be denoted as S race. For the calculation for the second group of limit states: the weight of snow is taken into account according to the standard load - this value can be denoted as S norm. . The normative snow load differs from the calculated one by the reliability factor γ f = 1.4. That is, the design load should be 1.4 times higher than the standard:
S races = γ f × S norm. \u003d 1.4 × S norm.
The exact load from the weight of the snow cover required to calculate the bearing capacity of the truss systems at a particular construction site must be clarified at the district construction organizations or established using the maps of SP 20.13330.2016 "Loads and Impacts" enclosed in this Code of Rules.
On fig. 3 and table 1 show the loads from the weight of the snow cover for the calculation for the first and second groups of limit states.
Table 1
rice. 3. Zoning of the territory Russian Federation by weight of snow coverInfluence of the angle of inclination of the roof, valleys and dormer windows on the snow load
Depending on the slope of the roof and the direction of the prevailing winds, there can be significantly less snow on the roof and, oddly enough, more than on a flat surface. When phenomena such as a snowstorm or snowstorm occur in the atmosphere, snowflakes picked up by the wind are transferred to the leeward side. After passing the obstacle in the form of a roof ridge, the speed of movement of the lower air flows decreases in relation to the upper ones and snowflakes settle on the roof. As a result, on one side of the roof there is less than the norm, and on the other side there is more (Fig. 4).
rice. 4. The formation of snow "bags" on roofs with slopes of slopes from 15 to 40 ° The decrease and increase in snow loads, depending on the direction of the wind and the angle of inclination of the slopes, is changed by the coefficient µ, which takes into account the transition from the weight of the snow cover on the ground to the snow load on the roof. For example, on gable roofs with a slope angle above 15 ° and less than 40 °, 75% will lie on the windward side, and 125% on the leeward side of the amount of snow that lies on the flat surface of the earth (Fig. 5).
rice. 5. Schemes of standard snow loads and coefficients µ (the value of the coefficients µ taking into account more complex geometry of roofs is given in SNiP 2.01.07-85) A thick layer of snow that accumulates on the roof and exceeds the average thickness is called a snow bag. They accumulate in valleys - places where two roofs intersect and in places with close dormer windows. In all places where there is a high probability of a snow "bag", paired rafter legs and perform a continuous crate. Also here they make a subroofing substrate, most often from galvanized steel, regardless of the material of the main roofing.
The snow "bag", formed on the leeward side, gradually slides and puts pressure on the roof overhang, trying to break it off, therefore the roof overhang should not exceed the dimensions recommended by the manufacturer roofing. For example, for a conventional slate roof, it is taken equal to 10 cm.
The direction of the prevailing wind is determined by the wind rose for the given region of construction. Thus, after the calculation, single rafters will be installed on the windward side, and paired rafters on the leeward side. If data on the wind rose are not available, it is necessary to consider patterns of evenly distributed and unevenly distributed snow loads in their most unfavorable combinations.
With an increase in the angle of inclination of the slopes, there is less snow on the roof, it slides under its own weight. At slope angles equal to or greater than 60 °, there is no snow left on the roof at all. The coefficient µ in this case is equal to zero. For intermediate values of slope angles, µ is found by direct interpolation (averaging). So, for example, for slopes with an angle of inclination of 40 °, the coefficient µ will be equal to 0.66, for 45 ° - 0.5, and for 50 ° - 0.33.
Thus, the required for the selection of the section of the rafters and the step of their installation, the calculated and standard loads from the weight of the snow, taking into account the angles of inclination of the slopes (Q µ.ras and Q µ.nor), must be multiplied by the coefficient µ:
S µ.ras = S ras ×µ
S
µ.nor = S nor ×µ .
Effect of wind on snow load
On flat roofs with slopes up to 12% (up to about 7°), designed on terrain types A or B, partial snow removal from the roof occurs. In this case, the calculated value of the load from the weight of the snow must be reduced by applying the coefficient c e, but not less than c e= 0.5. Coefficient c e calculated by the formula:
c e \u003d (1.2-0.4√k) × (0.8 + 0.002 lc),
Where lc- estimated size taken according to the formula l c \u003d 2b - b 2 / l, but not more than 100 m; k- taken according to table 3 for terrain types A or B; b And l- the smallest dimensions of the width and length of the coating in the plan.
On buildings with roofs with a slope of 12 to 20% (approximately 7 to 12°) located on type A or B terrain, the value of the coefficient c e= 0.85. Snow load reduction factor c e= 0.85 does not apply:
- on the roofs of buildings in areas with an average monthly air temperature in January above -5°C, since periodically formed ice prevents the snow from being blown away by the wind (Fig. 6);
- at height differences of buildings and parapets (details in SP 20.13330.2016), since parapets and multi-level roofs adjacent to each other prevent snow from blowing off.
rice. 6. Zoning of the territory of the Russian Federation according to the average monthly air temperature, °С, in January In all other cases, for pitched roofs, the coefficient c e= 1. The formulas for determining the design and standard load from the weight of snow, taking into account wind drift of snow, will look like this:
S s.ras. = S race. × c e- for the first limit state;
S
s.nor. = S norm. × c e- for the second limit state
Influence temperature regime buildings for snow load
In buildings with increased heat dissipation (with a heat transfer coefficient of more than 1 W/(m²×°C)) the snow load is reduced due to snow melting. When determining snow loads for non-insulated coatings of buildings with increased heat emissions leading to snow melting, with roof slopes of more than 3% and ensuring proper removal of melt water, a thermal coefficient should be entered c t= 0.8. In other cases c t = 1,0.
Formulas for determining the design and standard load from the weight of snow, taking into account the thermal coefficient:
S t.rac. = S race. × c t- for the first limit state;
S
t.nor. = S norm. × c t- for the second limit state
Determination of snow load taking into account all factors
The snow load is determined by the product of the standard and design load taken from the map (Fig. 3) and Table 1 and all the influencing coefficients:
S snow race = S race. ×µ × c e× c t- for the first limit state (strength calculation);
S snow. = S norm. ×µ × c e× c t- for the second limit state (calculation for deflection)
The roof provides permanent protection of the building from all weather and climatic manifestations, excluding the contact of all materials with atmospheric or rain water and being a boundary layer that cuts off the impact of frosty air on the attic.
These are the main and most important functions of the roof in the view of an unprepared person, they are quite true, but do not reflect full list functional loads and test stresses.
At the same time, the reality is much harsher than it seems at first glance, and the impact on the roof is not limited to a certain wear of the material.
It is passed on to almost everyone. load-bearing elements buildings - first of all, the walls of the building, on which the entire roof directly rests, and ultimately the foundation.
It is impossible to neglect all the loads that are created, this will lead to an early (sometimes sudden) destruction of the building.
The main and most dangerous impacts on the roof and on the entire structure as a whole are:
- Snow loads.
- Wind loads.
At the same time, snow is active during certain winter months, being absent during the warm season, while the wind creates an impact all year round. Wind loads, having seasonal fluctuations in strength and direction, are constantly present to one degree or another and are dangerous by periodically occurring squall amplifications.
In addition, the intensity of these loads has a different character:
- Snow creates constant static pressure, which can be adjusted by cleaning the roof and removing accumulations. The direction of the active efforts is constant and never changes.
- The wind acts inconstantly, in jerks, suddenly intensifying or subsiding. The direction can change, which makes all roof structures have a solid margin of safety.
Large masses of snow falling off a roof suddenly can cause damage to property or people caught in the fall. Besides, intermittent but extremely destructive atmospheric phenomena occur periodically- hurricane winds, heavy snowfalls, especially dangerous in the presence of wet snow, which is an order of magnitude heavier than usual. It is almost impossible to predict the date of such events, and as protective measures, one can only increase the strength and reliability of the roof and truss system.
Collection of roof loads
Dependence of loads on the angle of inclination of the roof
The angle of the roof determines the area and power of the roof's contact with wind and snow. At the same time, the snow mass has a vertically directed force vector, and the wind pressure, regardless of direction, is horizontal.
Therefore, taking a steeper angle of inclination, you can reduce the pressure snow masses, and sometimes completely eliminate the occurrence of accumulations of snow, but, at the same time, the "sail" of the roof increases, wind stresses increase.
It's obvious that a flat roof would be ideal to reduce wind loads, while it is she who will not allow masses of snow to roll down and will contribute to the formation of large snowdrifts, which, when melted, can wet the entire building. The way out of the situation is to choose such an angle of inclination at which the requirements for both snow and wind loads are met as much as possible, and they are in different regions have individual meanings.
Dependence of the load on the angle of the roof
Snow weight per square meter of roof depending on the region
Precipitation is an indicator that directly depends on geography region. The more southern regions hardly see snow, the more northern ones have a constant seasonal amount of snow masses.
At the same time, high-mountain regions, regardless of geographic latitude, have high rates of snowfall, which, combined with frequent and strong winds, creates a lot of problems.
Building Norms and Rules (SNiP), compliance with the provisions of which is mandatory, contain special tables, displaying normative indicators of the amount of snow per unit of surface in different regions.
NOTE!
The usual state of snow masses in the area should be taken into account. Wet snow is several times heavier than dry snow.
These data are the basis for calculating snow loads, since they are quite reliable, and are also given not in average, but in limit values that provide an adequate margin of safety during roof construction.
However, one should take into account the device of the roof, its material, as well as the presence additional elements, causing accumulations of snow, since they can significantly exceed the normative indicators.
The weight of the snow square meter roofs depending on the region in the diagram below.
Snow load region
Calculation of snow load on a flat roof
The calculation of load-bearing structures is carried out according to the method of limit states, that is, those when the experienced forces cause irreversible deformations or destruction. Therefore, the strength of a flat roof must exceed the amount of snow load for a given region.
There are two types of limit states for roof elements:
- The structure is destroyed.
- The design is deformed, fails without complete destruction.
Calculations are carried out for both states, with the aim of obtaining robust design, guaranteed to withstand the load without consequences, but without unnecessary costs building materials and labor. For flat roofs, the snow load values will be maximum, i.e. the slope correction factor is 1.
Thus, according to the tables of SNiP, the total weight of snow on flat roof will be the value of the standard multiplied by the area of \u200b\u200bthe roof. Values can reach tens of tons, so buildings with flat roofs are practically not built in our country, especially in regions with high precipitation rates in winter.
Calculation of snow load on the roof online
An example of calculating the snow load will help to clearly demonstrate the procedure, and also show the possible amount of snow pressure on the structure of the house.
The snow load on the roof is calculated using the following formula:
S = Sg * µ;
Where S- snow pressure per square meter of roof.
Sg— normative value of snow load for the given region.
µ - a correction factor that takes into account the change in load at different angles of inclination of the roof. From 0° to 25°, the value of µ is taken equal to 1, from 25° to 60° - 0.7. At angles of inclination of the roof over 60°, the snow load is not taken into account, although in reality there are accumulations of wet snow on steeper surfaces.
Let's calculate the load on the roof with an area of 50 sq.m, the angle of inclination is 28 ° (µ = 0.7), the region is the Moscow region.
Then the standard load is (according to SNiP) 180 kg / sq.m.
We multiply 180 by 0.7 - we get a real load of 126 kg / sq.m.
The total snow pressure on the roof will be: 126 times the roof area - 50 sq.m. Result - 6300 kg. This is the estimated weight of snow on the roof.
Snow impact on the roof
The wind load is calculated in a similar way. The standard value of the wind load in force in the given region is taken as the basis, which is multiplied by the correction factor for the height of the building:
W= Wo*k;
Wo— normative value for the region.
k- a correction factor that takes into account the height above the ground.
Rose of Wind
There are three groups of values:
- For open areas of the earth's surface.
- For forest areas or urban areas with obstacle heights from 10 m.
- For urban settlements or areas with difficult terrain with an obstacle height of 25 m or more.
All standard values, as well as correction factors, are contained in the SNiP tables and must be taken into account when calculating loads.
CAREFULLY!
When carrying out calculations, one should take into account the independence of snow and wind loads from each other, as well as the simultaneity of their impact. The total roof load is the sum of both values.
In conclusion, it is necessary to emphasize the large magnitude and uneven loads created by snow and winds. Values comparable to the own weight of the roof cannot be ignored, such values are too serious. The inability to regulate or exclude their presence forces them to react by increasing strength and right choice tilt angle.
All calculations should be based on SNiP; to clarify or verify the results, it is recommended to use online calculators, which are many on the network. the best way will be the use of several calculators with the subsequent comparison of the obtained values. Proper calculation is the basis for a long-term and reliable service of the roof and the entire building.
Useful video
You can learn more about roofing loads from this video:
In contact with
When calculating the foundation
First of all, the snow load is taken into account when calculating the maximum weight of the entire house. And the mass of the house, in turn, is necessary in order to correctly calculate the foundation for the house.
Naturally, the snow load does not directly affect the foundation, but is transmitted through the walls of the house, but it is impossible not to take it into account when calculating the foundation, especially on soft soils.
When calculating the roof itself
The snow load affects the roof in the most direct way, and if it is distributed more or less evenly on the foundation, then it is difficult to guess where there will be more snow on the roof and where there will be less, as it depends on the direction of the wind, the slope of the slopes and many other factors.
Therefore, when calculating the roof, the snow load should be taken into account as the main impact.
How to correctly calculate the snow load on the roof
For a full calculation, we will need to calculate the roof area of a private house. How this is done - I have described in detail in previous articles, so we will not dwell on it.
So, the formula for calculating the snow load Q on the roof is as follows:
Q=G*s, Where
G- the weight of the snow cover on a flat roof, which is taken from the table (kg / m2)
s- correction factor depending on the slope of the roof
The correction factor s, as already mentioned, depends on the slope of the roof:
- slope less than 25 degrees s taken equal to 1
- slope 25 - 60 degrees - s will be equal 0,7
- a slope of more than 60 degrees - the snow load is not taken into account at all, since snow will practically not linger on such a roof
But what to do with G?
The weight of snow cover on a flat roof can be found using the table and map of the snow cover zone in Russia:
As can be seen from the table, the mass of snow on the roof, especially in the snowy regions of Russia, can exceed the weight of the roof itself, so the snow load in the winter cannot be ignored.
A real example of calculating the snow load on the roof
Let's calculate the snow load using the example of my house. Let's define Weight Limit snow per 1 square meter, as well as calculate the total mass of snow on the roof in winter, to calculate the load on the foundation.
So, my house is located in the RF area No. 3, so we take Q equal to 180 kg/m2 .
The slope of the roof of the house is about 40 degrees, so it is necessary 180 * 0.7 \u003d 126 kg / m 2 .
Thus, the maximum possible snow load on the roof of my house is 126 kg/m2 .
To calculate the foundation, we need the entire mass of snow on the roof, and for this we must first calculate the area of \u200b\u200bthe roof of the house. In my case, the roof area is approximately 150 square meters.
M = 126 * 150 = 18,900 kg
Thus, snow adds another 19 tons to the total mass of the house. And how can such a mass be ignored?
ATTENTION! When calculating in construction, it is always necessary to take a margin of safety, so it is advisable to multiply the obtained values by 1.2.
During the construction of the roof, one of the important technical solutions is the calculation of the maximum snow load, which determines the design of the truss system, the thickness of the elements of the supporting structure. For Russia, the standard value of the snow load is found according to a special formula, taking into account the area where the house is located and the norms of SNiP. To reduce the likelihood of consequences from the excessive weight of the snow mass, when designing the roof, it is imperative to calculate the load value. Particular attention is paid to the need to install snow retainers that prevent snow from falling off the roof overhang.
In addition to putting an excessive load on the roof, the snow mass, sometimes, is the cause of leaks in the roof. So, with the formation of a strip of ice, the free flow of water becomes impossible and melted snow will most likely fall into the under-roof space. The heaviest snowfalls occur in mountainous regions, where the snow cover reaches several meters in height. But, the most negative consequences of the load occur during periodic thawing, ice and freezing. In this case, deformations of roofing materials are possible, incorrect operation drainage system and an avalanche-like flow of snow from the roof of the house.
Snow load influence factors
When calculating the load from snow masses on pitched roof one should take into account the fact that up to 5% of the mass of snow evaporates during the day. At this time, it can slide, blown away by the wind, covered with infusion. As a result of these transformations, the following negative consequences arise:
Methods for cleaning the roof of snow
A reasonable way out of the situation is manual cleaning. But, based on human safety, performing such work is extremely dangerous. For this reason, the load calculation has a significant impact on the design of the roof, truss system and other roof elements. It has long been known that the steeper the slopes, the less snow will linger on the roof. In regions with a high amount of precipitation in the winter season, the angle of inclination of the roof is from 45 ° to 60 °. In this case, the calculation shows that a large number of junctions and complex connections provides an uneven load.
Cable heating systems are used to prevent the formation of icicles and ice. The heating element is installed along the perimeter of the roof directly in front of the gutter. Used to control the heating system automatic system controls or manually control the entire process.
Calculation of snow mass and load according to SNiP
During snowfall, the load can deform the elements of the supporting structure of the house, the truss system, roofing materials. In order to prevent this, at the design stage, a design calculation is performed depending on the impact of the load. On average, snow weighs about 100 kg / m 3, and when wet, its mass reaches 300 kg / m 3. Knowing these values, it is quite easy to calculate the load on the entire area, guided only by the thickness of the snow layer.
The thickness of the cover should be measured at open area, after which this value is multiplied by the safety factor - 1.5. To take into account regional features of the terrain in Russia, a special snow load map is used. On its basis, the requirements of SNiP and other rules are built. The total snow load on the roof is calculated using the formula:
S=S calc. ×μ;
S calc. - the calculated value of the weight of snow per 1 m 2 of the horizontal surface of the earth;
μ - design coefficient, taking into account the slope of the roof.
On the territory of Russia, the calculated value of the weight of snow per 1 m 2 in accordance with SNiP is taken on a special map, which is presented below.
SNiP stipulates the following values coefficient μ:
- with a roof slope of less than 25 °, its value is equal to one;
- with a slope of 25° to 60°, it has a value of 0.7;
- if the slope is more than 60°, the design factor is not taken into account in the load calculation.
Friends, U-ra, it happened and we are glad to present you an online calculator for calculating snow and wind loads, now you don’t need to figure anything out on a piece of paper or in your mind, you just indicated your parameters and immediately received the load. In addition, the calculator can calculate the depth of soil freezing if you know its type. Here is a link to the calculator -> Online Snow and Wind Load Calculator. In addition, we have many other construction calculators You can see a list of all on this page:
An illustrative example of calculation
Let's take the roof of the house, which is located in the Moscow region and has a slope of 30 °. In this case, SNiP stipulates the following procedure for calculating the load:
- According to the map of regions of Russia, we determine that the Moscow region is located in the 3rd climatic region, where the standard value of the snow load is 180 kg / m 2.
- According to the formula from SNiP, we determine the total load: 180 × 0.7 = 126 kg / m 2.
- Knowing the load from the snow mass, we calculate the truss system, which is selected based on the maximum loads.
Installation of snow guards
If the calculation is performed correctly, then the snow from the roof surface can not be removed. And to combat its sliding from the eaves, snow retainers are used. They are very easy to use and eliminate the need to remove snow from the roof of the house. In the standard version, tubular structures are used that are able to work if the standard snow load does not exceed 180 kg / m 2. With a denser weight, the installation of snow retainers in several rows is used. SNiP stipulates the use of snow retainers:
- with a slope of 5% or more with an external drain;
- snow retainers are installed at a distance of 0.6-1.0 meters from the edge of the roof;
- when using tubular snow retainers, a continuous roof sheathing should be provided under them.
Also, SNiP describes the main structures and geometric dimensions of snow retainers, their installation locations and the principle of operation.
flat roofs
The maximum possible amount of snow accumulates on a flat horizontal surface. The calculation of loads in this case should provide the necessary margin of safety for the supporting structure. Flat horizontal roofs are practically not built in regions of Russia with a large amount of precipitation. Snow can accumulate on their surface and create an excessively large load, which was not taken into account in the calculation. When organizing a drainage system from a horizontal surface, they resort to installing heating, which ensures that water drains from the roof.
The slope towards the drain funnel must be at least 2 °, which will make it possible to collect water from the entire roof.
During the construction of a canopy for a gazebo, parking, country house Special attention given to the calculation of the load. The canopy in most cases has a budget design, which does not provide for the influence of large loads. In order to increase the reliability of the operation of the canopy, a continuous crate, reinforced rafters and other structural elements. Using the results of the calculation, it is possible to obtain a known value of the load and use materials of the required rigidity for the construction of the canopy.
The calculation of the main loads makes it possible to optimally approach the issue of choosing the design of the truss system. This will provide long service roofing, increase its reliability and safety of operation. Installing snow retainers near the eaves allows you to protect people from sliding dangerous snow masses. In addition, there is no need for manual cleaning. An integrated approach to roof design also includes the option of installing a cable heating system that will ensure stable operation of the gutter system in any weather.
