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Calculator for calculating the height of a gable roof. Calculation of rafters. Types of gable roof truss system

Beautiful and reliable.

And what is the basis of any roof?

From how correctly the calculation of the parameters of the elements of the rafter system will be carried out, how strong and reliable the roof will be will depend.

Therefore, even at the stage of drawing up a building project, a separate calculation of the rafter system is performed.

Factors taken into account when calculating rafters

It is impossible to perform the calculation correctly if you do not take into account the intensity of the various loads that will affect the roof of the house at different periods.

Factors affecting the roof are usually classified into:

  1. Constant loads. This category includes those loads that are constantly acting on the elements of the rafter system, regardless of the season. These loads include the weight of the roof, lathing, waterproofing, heat and vapor barrier and all other roof elements that have a fixed weight and constantly load the rafter system. antenna Internet, smoke exhaust and ventilation systems, etc.), then the weight of such equipment must be added to the constant loads.
  2. Variable loads. These loads are called variable due to the fact that they load the rafter system only in a certain period of time, and at other times this load is minimal or not at all. Such loads include the weight of the snow cover, the load from the blowing winds, the load from people that will serve the roof, etc.
  3. A special type of load. This group includes loads that arise in areas where hurricanes or seismic impacts are very frequent. In this case, the load is taken into account in order to lay an additional safety factor in the structure.

The calculation of the parameters of the rafter system is quite complicated.

And it is difficult for a beginner to do it, since there are a lot of factors that affect the roof, it is necessary to take into account.

Indeed, in addition to the above factors, it is also necessary to take into account the weight of all elements of the rafter system and fasteners.

Therefore, special calculation programs come to the aid of calculators.

Determination of the load on the rafters

Roofing cake weight

To find out the load on the rafters of our house, we must first calculate the weight of the roofing cake.

Such a calculation is easy to do if you know the total area of ​​the roof and the materials that are used to create this very pie.

First, the weight of one square meter pirogue.

The mass of each layer is added up and multiplied by the correction factor.

This coefficient is equal to 1.1.

Here typical example calculating the weight of the roofing cake.

Let's say you made a decision as roofing material use ondulin.

And this is true!

After all, ondulin is reliable and inexpensive material... It is for these reasons that it is so popular with developers.

So:

  1. Ondulin: its weight is 3 kg per 1 square meter.
  2. Waterproofing. Polymer-bitumen material is used. One square meter weighs 5 kg.
  3. Insulation layer. Mineral wool is used. The weight of one square is 10 kg.
  4. Lathing, boards 2.5 cm thick. Weight 15 kg.

Let's summarize the obtained data: 3 + 5 + 10 + 15 = 33 kg.

Now the result obtained must be multiplied by 1.1.

Our correction factor.

The final figure is 34.1 kg.

This is the weight of one square meter of roofing cake.

The total roof area, for example, 100 sq. meters.

This means that it will weigh 341 kg.

This is very small.

This is one of the advantages of ondulin.

We calculate the snow load

The moment is very important.

Because in many areas of our winter there is a fairly decent amount of snow.

And this is a very large weight, which must be taken into account!

The snow load map is used to calculate the snow load.

Define your region and calculate the snow load using the formula

In this formula:

- S is the required snow load;

- Sg is the mass of the snow cover.

The weight of snow per 1 square meter is taken into account. meter.

This indicator is different in each region.

It all depends on the location of the house.

The map is used to determine the mass.

- µ is the correction factor.

The indicator of this coefficient depends on the angle of inclination of the roof.

If the slope of the slopes is less than 25 degrees, then the coefficient is 1.

At an angle of inclination of 25 - 60 degrees, the coefficient is 0.7.

If the angle of inclination is greater than 60 degrees, then the coefficient is not taken into account.

For example, a house was built in the Moscow region.

The slopes have an angle of inclination of 30 degrees.

The map shows us that the house is located in the 3rd district.

Snow mass per 1 sq. meter is 180 kg.

We carry out the calculation, not forgetting about the correction factor:

180 x 0.7 = 126 kilograms per 1 sq. meter of the roof.

Determination of wind loads

To calculate wind loads, a special map with a breakdown by zones is also used.

Use the following formula:

Wo is a normative indicator determined from a table.

Each region has its own wind tables.

And the indicator k is a correction factor that depends on the height of the house and the type of terrain.

We count wooden rafters

Rafter length

The calculation of the length of the rafter leg is one of the simplest geometric calculations.

Since you only need two dimensions: width and height, as well as the Pythagorean theorem.

To make the calculation clearer, look at the figure below.

We know two distances:

- a is the height from the bottom to the top point of the inside of the rafters.

First leg;

- b is a value equal to half the width of the roof.

Second leg.

- c is the hypotenuse of the triangle.

c² = (2 x 2) + (3 x 3).

Total c² = 4 + 9 = 13.

Now we need to get the square root of 13.

You can, of course, take Bradis tables, but it's more convenient on a calculator.

We get 3.6 meters.

Now you need to add the extension length d to this number to get the desired rafter length.

We calculate and select the cross-section of the elements of the rafter system

The section of the boards that we will use for the manufacture of rafters and other elements of the rafter system depends on how long the rafters have, with what step they will be installed and on the values ​​of snow and wind loads that exist in a particular region.

For simple designs use the table typical sizes and sections of the board.

If the design is very complex, then it is better to use special programs.

We calculate the step and the number of rafter legs

The distance between their bases is called.

Experts believe that the minimum distance should be 60 cm.

And the optimal distance is 1 meter.

We calculate the distance between the rafters:

  • we measure the length of the slope along the cornice;
  • then the resulting figure should be divided by the estimated pitch of the rafters. If the step is planned to be 60 cm, then it should be divided by 0.6. If 1 meter - then divided by 1. The preliminary selection of the step will be further;
  • then 1 should be added to the obtained result and the resulting value should be rounded up. Thus, we get the number of rafters that can be installed on the roof of your house;
  • the total length of the ramp must be divided by the number of rafters to get the rafter pitch.

For example, the length of the roof slope is 12 meters.

Pre-select the pitch of the rafters 0.8 meters.

12 / 0.8 = 15 meters.

Add one unit 15 + 1 = 16 rafters.

If we got a fractional number, then we would round it up.

Now from 12 meters should be divided by 16.

As a result, 1216 = 0.75 meters.

Here is the optimal distance between the rafters on one ramp.

The table mentioned earlier can also be used.

We calculate wooden floor beams

For wooden beams the optimum span is 2.5 to 4 meters.

The optimal section is rectangular.

The ratio of height to width is 1.4: 1.

The beam should go into the wall by at least 12 cm.

Ideally, the beams are attached to anchors that are pre-installed in the wall.

The waterproofing of the beams is carried out "in a circle".

When calculating the cross-section of the beams, the load from its own weight (as a rule, 200 kg / sq. Meter) and the operational live load are taken into account.

Its value is equal to a constant load - 200 kg / sq. meter.

Knowing the size of the span and the step of installing the beams, their cross section is calculated from the table:

Span (m) / Installation step (m) 2.0 2.5 3.0 4.0 4.5 5.0 6.0
0.6 75x10075x15075x200100x200100x200125x200150x225
1 75x150100x150100x175125x200150x200150x200175x250

If a more accurate calculation is required, then use the Romanov calculator.

Calculation of shed roof rafters

A pitched roof is the simplest roof option.

But this option is not suitable for every building.

And the calculation of the rafters is required in any case.

Calculations pitched roof start by defining the angle of inclination.

And it depends on, first of all, what material you plan to use for the roof.

For example, for corrugated board the minimum angle is 8 degrees.

And the optimal one is 20 degrees.

Calculation programs

If online calculators perform simple calculations, then special software can calculate everything you need.

And there are quite a few such programs!

The most famous of them are 3D Max and AutoCAD.

Such programs have only two drawbacks:

  • to use them, you must have certain knowledge and experience;
  • such programs are paid.

There are a number of free programs available.

Most of the programs can be downloaded to your computer.

Or use them online.

Video about the calculation of rafters.

This article provides a simplified method for calculating the rafter system. You will learn how to quickly and correctly make a decision on the cross-section of the rafters and the width of the span. The adapted mathematical calculation contains a minimum of formulas and leads to fairly accurate results.

There is a standard calculation method roof structure, brought in accordance with SNiP 2.01.07-85 "Loads and Impacts". It includes many rather complex calculations and reference values. A popular service of sites - online calculation of the gable roof rafter system - will allow you to determine the amount of material very accurately.

Note. The article discusses the methodology for calculating the rafter system of a gable roof with a hip, half-hip or pediment without additional structural elements- canopies, birdhouses, towers, etc. and a slope angle of at least 45 °.

Where to begin

The traditional technique assumes the following approach: the roof structure and the cross-section of the beams are selected for the design load. This does not fully meet the requirements of today and the initial data in our case will be the following indicators:

  1. Requirements (wishes) for the roof structure. First of all, this means the presence of an attic (residential) floor, the location roof windows or the presence of an attic technical room.
  2. The existing dimensions of the house, or the boundaries of the building. 70% of private houses are located in relatively dense buildings, and this should also be taken into account when designing a roof. The limited area of ​​the site and the possible requirements of neighbors in relation to sunlight can make their own adjustments.
  3. Unification. The rafter system is a multi-piece structure. It is reasonable to try to bring the maximum number of elements to one standard - the section of the board or timber.

The most difficult, oddly enough, is the first point. However, after you have obtained a complete understanding of what functions the rafter system should perform (direct or combined), you can proceed to the design stage.

How to create a sketch

This stage is one of the decisive ones, since in it we find out the approximate sizes of the elements. The main one - the truss truss - will become the basis for further calculations. The drawing itself will be based on two initial parameters:

  1. Span between load-bearing walls. It is highly desirable that the support points of the rafter system, which transmit vertical loads, are located along the axes load-bearing walls or supports. The distance from the projection of the ridge to the wall is called a half span.
  2. Ridge height from floor. This parameter is made up of the functional features of the design - the height of the attic ceiling, an accessible attic or a "blank" attic space.

As you know, 75% of simple rafter systems are roofs with a straight and "broken" slope. This significantly affects the calculations, so we will immediately separate these types. Since any standard roof is based on a triangular structure, we will try to limit ourselves to one formula (the Pythagorean theorem):

  • c 2 = a 2 + b 2

At this stage, you can fairly accurately calculate the area of ​​\ u200b \ u200bthe slopes and the consumption of roofing material along with the crate. To do this, it is enough to use the calculation of the gable roof rafter system online, which is provided by many sites.

Straight equilateral slope

We transfer to the sketch the dimensions of the floor or the location of the load-bearing walls (the structure does not always imply the presence of a wooden floor) to scale. Then we mark the ridge point and draw straight lines to the walls, taking into account the accepted roof overhang. These straight lines can already be measured and multiplied by the scale - we get the length of the rafter leg.

In accordance with the chosen structure of the organization of the internal space (combined or divided), we place the rafter tie (crossbar) and determine its length. We place stops, slopes and vertical posts on the drawing, observing the requirements that the portal site gave in the article "Do-it-yourself gable roof rafter system." The spans should not be more than 2 m, and the rafters must have an intermediate brace. In this case, it is enough to adhere to the approximate tolerance limits.

Using the formula for the ratio of the sides of a right-angled triangle, you can calculate any of the dimensions of the truss truss. The rest of the dimensions can be removed from the drawing through the scale. The main task is to get the dimensions of each of the elements.

"Broken" slope

This type of roof is always taken in connection with the construction of the attic or the superstructure of the residential floor. It has one characteristic feature - a row of vertical posts at the intersection of the slopes and a rafter beam, which can be located both at the level of the top of these posts, and under the ridge. Rows of uprights and crossbars form the walls and ceiling of the attic room.

In a similar way, we transfer the main elements to the drawing - first the walls and the ceiling, then a series of racks and crossbars (at the ceiling level), then we connect them with lines that will fairly accurately show the shape of the slope fracture.

After measurements and calculations, the lengths of all elements of the truss truss should be added up and 10% added to the resulting number. This will be the total length of the structure of one truss (ODK 1).

Selection of rafter section and unification

Cross-section of system elements, especially rafter legs, directly depends on the span between the supports in the central part. Of all the lumber, timber and board are suitable for the rafter system (not counting the factory glued trusses). At the same time, the board has a much better indicator of the ratio of section to bending strength. In our case, we are talking about the reliability of the rafters, for which the board is used, because there is a margin of depth of the bosom for laying the insulation.

Table of dependence of span width and rafter thickness

Arrange roof truss spans more than 6 meters without intermediate supports Not recommended.

Advice. When splicing two boards to create a vertical support, lay 25 mm ("bosses") between them at the points of attachment of trimming boards with a step of 300-400 mm. This will increase the strength of the support compared to direct splicing.

After determining the sufficient section of the board, you can calculate the volume of one truss. To do this, we multiply the ODK-1 by the sectional area of ​​the board. The resulting volume of one farm (OF 1) will be used to calculate the total volume.

Calculation of the pitch of roof trusses

The pitch of the rafters of the attic rafter system depends on the thickness and design of the trusses.

Pitch versus thickness table

Dividing the length of the longitudinal (parallel to the ridge) wall by the selected step, we get the number of trusses (N). Accordingly, we can calculate the length of the board for the trusses:

  • ODK 1 x N

truss board volume:

  • OF 1 x N or ODK 1 x S section of the board x N

Mauerlat calculation

If the rafter system is arranged on wooden floor, then the entire horizontal strapping refers to it. We will consider the option with a Mauerlat on a stone wall.

Since the uprights, struts, and purlins are included in the truss design, it remains for us to calculate the horizontal strapping. There is a simple rule here - it must be at least a double rafter leg thick. If the total weight of the roof (including battens and roofing material and snow) is noticeably high, three plank layers should be used.

The volume of the board for the Mauerlat will be equal to the length of the bearing walls multiplied by the section of the board and the number of layers. A Mauerlat made of several layers will bond better in corners.

Total count

We put all the volumes obtained together and add 20% for waste and trimming. The number of metal products and fasteners is determined individually. It is only known for certain that the more, the better.

Note. All the given values ​​and proportions of dependence are taken from the reference literature.

Despite the apparent simplicity, this adapted calculation can compete exactly with online rafter system calculators. However, the decisive word always remains with whoever will carry out the project.

Related Videos

rmnt.ru, Igor Maksimov

We offer a professional free calculation of the gable roof truss system using online calculator a website, 3D visualization and detailed drawings. Detailed calculations of the roof and roof, all materials, lathing, rafters, Mauerlat. Try calculating a gable roof now!

Our online calculator rafter system will calculate the gable roof:

  • calculation of the length of the gable roof rafters
  • number of rafters and step
  • calculation of the gable roof area and the angle of inclination
  • calculation of the roof lathing
  • the number of sheet roofing materials (for example, corrugated board, metal tiles, slate)
  • parameters of vapor barrier and insulation

To form the calculation of the gable roof calculator, you need to measure and enter the following dimensions in the appropriate windows:

The cross-section (thickness x width) and the pitch of the rafters depend on the angle of inclination of the roof, its type, the length of the rafter leg, the maximum withstand basic loads, as well as on the type and weight of the roof covering, and even to some extent on the width of the insulation. If you don't know where to get the standard parameters of rafters and battens, our article will help you " Optimal cross-section, pitch of the lathing and rafter legs, depending on the type of roof ».

The calculator calculates the materials for the roof, starting from the dimensions of the roofing sheet you entered and from the calculated value of the roof area. We advise you to buy the amount of roofing materials for the roof, boards and beams for the rafter system with a small margin, it is always better to hand over the leftovers to a hardware store than pay a lot of money for the delivery of a missing pair of boards.

Be careful! From how accurate the values ​​you enter, the online calculator will be able to calculate the gable roof so reliably.

Simplify your calculations and save time, the program will draw itself rafter plangable roof and will display the results of calculating a gable roof according to the data you entered in the form of a drawing of a gable roof in different angles review, and its interactive 3d model.

On the tab “ 3 D- View»You can better see your future gable roof in 3D. In our opinion, visualization in construction is a very necessary feature.

If you have a gable roof with different slopes in your project, you should calculate with the calculator twice - for each slope separately.

The online calculator for a gable roof, also called a gable roof, will help you calculate the desired angle of inclination of the slopes, determine the cross-section and number of rafters, the amount of materials for the crate, the consumption of insulating materials, and at the same time it will take into account the existing norms for wind and snow loads. You do not have to perform unnecessary additional calculations, because this calculator contains most of the existing roofing materials.

You can easily calculate the consumption and weight of common materials such as bituminous shingles, cement-sand and ceramic tiles, metal tiles, bituminous and asbestos-cement slate, ondulin and others. If you use non-standard material, or want to get more accurate calculations, you can specify the weight of your own roofing material by selecting the appropriate item in the drop-down list of materials. The calculator makes calculations in accordance with the current SNiP "Loads and Impacts" and TKP 45-5.05-146-2009.

Please indicate the roofing material:

Select material from the list - Slate (corrugated asbestos-cement sheets): Medium profile (11 kg / m2) Slate (corrugated asbestos-cement sheets): Reinforced profile (13 kg / m2) Corrugated cellulose-bitumen sheets (6 kg / m2) Bituminous (soft , flexible) roof tiles (15 kg / m2) Galvanized sheet (6.5 kg / m2) Sheet steel (8 kg / m2) Ceramic roof tiles(50 kg / m2) Cement-sand tile (70 kg / m2) Metal tile, corrugated board (5 kg / m2) Keramoplast (5.5 kg / m2) Seam roof (6 kg / m2) Polymer-sand tile (25 kg / m2) Ondulin (euro slate) (4 kg / m2) Composite tile (7 kg / m2) Natural slate (40 kg / m2) Indicate the weight of 1 square meter of coverage (? kg / m2)

kg / m 2

Enter roof parameters:

Base width A (cm)

Base length D (cm)

Lift height B (cm)

Side overhang length C (cm)

Front and rear overhang length E (cm)

Rafters:

Rafter pitch (cm)

Wood grade for rafters (cm)

Side rafter working area (optional) (cm)

Crate calculation:

Sheathing board width (cm)

Sheathing board thickness (cm)

The distance between the boards of the crate
F (cm)

Calculation results

Roof angle: 0 degrees.

The angle of inclination is suitable for the given material.

It is advisable to increase the angle of inclination for this material!

It is desirable to reduce the angle of inclination for this material!

Roof surface area: 0 m 2.

Approximate weight of roofing material: 0 kg.

Number of rolls insulating material with 10% overlap (1x15 m): 0 rolls.

Rafters:

Load on the rafter system: 0 kg / m 2.

Rafters length: 0 cm.

Number of rafters: 0 pcs.

Lathing:

Number of rows of battens (for the entire roof): 0 rows.

Uniform distance between battens: 0 cm.

The number of battens with a standard length of 6 meters: 0 pcs.

Volume of lathing boards: 0 m 3.

Approximate weight of crate boards: 0 kg.

General information about the gable roof

A gable roof (there are variants of the name “gable roof” and “gable roof”) is the most common type of roof, in which there are two inclined slopes from the ridge to the outer walls of the structure. The popularity of this type of roof is due to their moderate cost, ease of construction, good performance and attractive appearance.

In this design, the rafters of different slopes lean on each other in pairs and are sheathed with sheathing boards. The end of the building with gable roof has a triangular shape and is called a pediment (the name "tong" is also found). Usually, an attic space is located under the roof slopes, naturally illuminated with the help of small window openings located in the upper part of the gables.

Additional information on the calculation results

Roof angle- the slope and rafters are inclined at this angle to the base of the roof. Roofing materials have individual maximum roof slope angles, therefore, for some materials, the angle may be outside acceptable standards... Whether your angle satisfies the selected material or not, you will find out in the calculation results. In any case, it is always possible to adjust the height of the roof rise (B) or the width of the base (A), or choose a different roofing material.

Roof surface area- the area of ​​the entire roof surface, including overhangs. To determine the area of ​​one slope, it is enough to divide the obtained value by two.

Approximate weight of roofing material- the weight of the selected roofing material based on the total roof area (including overhangs).

Number of rolls of insulation material- the amount of insulating material required for the construction of the roof. The number of rolls indicated is required for the entire roof area. It is based on the standard roll - 15 meters long, 1 meter wide. The calculation also takes into account an overlap of 10% at the joints.

- the maximum weight per rafter system. Wind and snow loads, the angle of inclination of the roof, as well as the weight of the entire structure are taken into account.

Rafter length- the full length of the rafters from the roof ridge to the edge of the ramp.

Number of rafters- the total number of rafters required for the rafter system at a given step.

Minimum cross-section of rafters / Weight of rafters / Volume of timber

  1. The first column shows the cross-sections of the rafters along GOST 24454-80 Softwood lumber... Here are the sections that can be used to build a given structure. The calculator proceeds from the total loads that can affect the structure of a given roof and selects the section options that satisfy them.
  2. The second column shows the total weight of all rafters with the specified section, if they are used to build a given roof.
  3. The third column shows the total volume of this bar in cubic meters... This volume will be useful to you when calculating the cost.

Number of rows of crate- the number of rows of lathing that will be needed for the entire roof with the given parameters. To calculate the number of rows of the sheathing of one slope, you need to divide the resulting value by two.

Uniform distance between battens- the distance that it is recommended to maintain between the battens in order to optimize material consumption and avoid cutting it.

The volume of lathing boards- the total volume of the lathing for a given roof. This value helps you calculate your lumber costs.

Approximate weight of crate boards- the total weight of the entire lathing.

Before proceeding with the construction of the roof, it is of course desirable that it be designed for strength. Immediately after the publication of the last article "", I began to receive questions in the mail regarding the choice of the section of rafters and floor beams.

Yes, it is really quite difficult to understand this issue on the vastness of our beloved Internet. There is a lot of information on this topic, but, as always, it is so scattered and sometimes even contradictory that an inexperienced person, who in his life may not even have encountered such a subject as "Strength" (someone was lucky), can easily get confused in these wilds.

I, in turn, will now try to draw up a step-by-step algorithm that will help you independently calculate the rafter system of your future roof and finally get rid of constant doubts - and suddenly it will not stand, but suddenly it will fall apart. I must say right away that I will not delve into the terms and various formulas. Well, why? There are so many useful and interesting things in the world that you can fill your head with. We just need to build a roof and forget about it.

The whole calculation will be described using the example of a gable roof, which I wrote about in

So Step # 1:

Determine the snow load on the roof. For this we need a map of snow loads of the Russian Federation. To enlarge the picture, click on it with the mouse. Below I will give a link where you can download it to your computer.

Using this map, we determine the number of the snow region in which we are building the house and from the following table we select the snow load corresponding to this region (S, kg / m²):

If your city is on the border of regions, choose a higher load value. It is not necessary to correct the resulting figure depending on the angle of inclination of the slopes of our roof. The program we are going to use will do it itself.

Let's say in our example we are building a house in the suburbs. Moscow is located in the 3rd snow region. The load for it is 180 kg / m².

Step # 2:

Determine the wind load on the roof. For this we need a map of the RF wind loads. It can also be downloaded from the link below.

Using this map, we also select the corresponding region number and determine the value of the wind load for it (the values ​​are shown in the lower left corner):

Here, column A - open coasts of seas, lakes and reservoirs, deserts, steppes, forest-steppe and tundra; Column B - urban areas, forests and other areas evenly covered with obstacles. It should be noted that in some cases the type of terrain may differ in different directions (for example, the house is located on the outskirts of a settlement). Then we select values ​​from column "A".

Let's go back to our example. Moscow is located in the 1st wind region. The height of our house is 6.5 meters. Suppose that it is being built in a settlement. Thus, we take the value of the correction factor k = 0.65. Those. the wind load in this case will be equal to: 32x0.65 = 21 kg / m².

Step # 3:

You need to download to your computer a calculation program made in the form of an Excel table. Further we will work in it. Here is the download link: “. It also contains maps of snow and wind loads of the Russian Federation.

So, download and unpack the archive. Open the file "Calculation of the rafter system", while we get into the first window - "Loads":

Here we need to change some values ​​in the filled cells in blue... All calculations are done automatically. Let's continue with our example:

In the plate "Initial data" we change the angle of inclination by 36 ° (what angle you will have, write this, well, I think everyone understands this);

We change the pitch of the rafters to the one we chose. In our case, this is 0.6 meters;

Load roof (load from the own weight of the roofing material) - we select this value from the table:

For our example, we select a metal tile with a weight of 5 kg / m².

Snow. region - here we enter the sum of the values ​​of snow and wind loads that we received earlier, i.e. 180 + 21 = 201 kg / m²;

Insulation (mans.) - we leave this value unchanged if we lay insulation between the rafters. If we do cold attic without insulation - change the value to 0;

Enter the required dimensions of the lathing in the "Crate" plate. In our case, for metal tiles, we will change the pitch of the lathing by 0.35 m and the width by 10 cm. Leave the height unchanged.

All other loads (from the own weight of the rafters and lathing) are automatically taken into account by the program. Now let's see what we got:

We see the inscription "The load-bearing capacity of the crate is provided!" We do not touch anything else in this window, there is even no need to understand what the numbers are in other cells. If, for example, we choose another step of the rafters (more), it may turn out that the bearing capacity of the lathing will not be provided. Then it will be necessary to select other dimensions of the crate, for example, to increase its width, etc. In general, I think you will figure it out.

Step # 4:

Lanyard 1»And go to the rafter calculation window with two support points. Here, all the input data we entered earlier have already been substituted by the program automatically (this will be the case in all other windows).

In our example from the article "Do-it-yourself gable roof of a house", the rafters have three points of support. But let's imagine that there are no intermediate racks and let's make a calculation:

Change the length of its horizontal projection on the rafter diagram (the cell is filled with blue). In our example, it is 4.4 meters.

In the plate "Calculation of rafters" we change the value of the thickness of the rafters B (given) to our choice. We put 5 cm.This value must necessarily be greater than that indicated in the cell Tue (steady);

Now the line “ Accept H»We need to enter the selected rafter width in centimeters. It must be greater than the values ​​specified in the lines " Ntr., (Durable)" and " Ntr., (Deflection)". If this condition is met, all the inscriptions at the bottom under the rafter scheme will look like "Condition met". In the line “ H, (by grade)"The value that the program itself suggests to us is indicated. We can take this figure, or we can take another. Usually we select the sections available in the store.

So, what we got is shown in the figure:

In our example, in order to comply with all strength conditions, it is necessary to choose rafters with a section of 5x20 cm. But the roof scheme shown by me in the last article has rafters with three support points. Therefore, to calculate it, we proceed to the next step.

Step # 5:

Click at the bottom of the working screen on the tab " Lanyard 2"Or" Lanyard. 3 ″... This opens a window for calculating rafters with 3 support points. The choice of the tab we need is made depending on the location of the middle support (rack). If it is located to the right of the middle of the rafter, i.e. L / L1<2, то пользуемся вкладкой "Lanyard 2"... If the post is located to the left of the middle of the rafter, i.e. L / L1> 2, then we use the tab "Lanyard 3"... If the rack is exactly in the middle, you can use any tab, the results will be the same.

In the rafter diagram, we forward the dimensions in the cells filled with blue (except for Ru);

By the same principle as described above, we select the dimensions of the rafter section. For our example, I took the dimensions 5x15 cm. Although it could have been 5x10 cm. I'm just used to working with such boards, and the margin of safety will be more.

Now it is important: from the figure obtained during the calculation, we will need to write down the value of the vertical load acting on the rack (in our example (see the figure above) it is equal to 343.40 kg) and the bending moment acting on the rack (Mop. = 78.57 kghm). We will need these figures further when calculating the racks and floor beams.

Further, if you go to the tab " Arch“, The window for calculating the rafter system will open, which is a ridge arch (two rafters and a tightening). I will not consider it, it will not fit our roof. We have too large a span between the supports and a small angle of inclination of the slopes. There you will get rafters with a section of about 10x25 cm, which is certainly unacceptable for us. For smaller spans, such a scheme can be used. I am sure whoever understood what I wrote about above will figure it out on their own with this calculation. If you still have questions, write in the comments. And we move on to the next step.

Step 6:

Go to the "Rack" tab. Well, everything is simple here.

The previously determined values ​​of the vertical load on the rack and the bending moment are entered in the figure, respectively, in the cells "N =" and "M =". We have them written in kilograms, we enter them in tons, while the values ​​are automatically rounded;

Also, in the figure, we change the height of the rack (in our example, it is 167 cm) and set the dimensions of the section we have chosen. I chose a 5x15 cm board. Below, in the center, we see the inscription "Central provided!" and "Vnecenter. provided. " So everything is in order. The safety factors "Kz" are very large, so you can safely reduce the cross-section of the racks. But we will leave it as it is. The calculation result in the figure:

Step # 7:

Go to the tab "Beam". A distributed load and a concentrated load act on the floor beams at the same time. We need to consider both. In our example, beams of the same cross-section cover spans of different widths. We of course make calculations for a wider span:

- in the plate "Distributed load" we indicate the step and span of the beams (from the example we take 0.6 m and 4 m, respectively);

- we take the values ​​Load (normal) = 350 kg / m² and Load (calculated) = 450 kg / m². The values ​​of these loads in accordance with SNiP are averaged and taken with a good margin of safety. They include the load from the own weight of the floors and the operating load (furniture, people, etc.);

- to the line “ B given»Enter the selected width of the section of the beams (in our example, it is 10 cm);

In the lines “ H, strength" and " H, deflection»The minimum possible cross-section heights of the beams will be indicated at which it will not break and its deflection will be acceptable. We are interested in the largest of these numbers. We take the height of the section of the beam proceeding from it. In our example, a 10x20 cm beam is suitable:

So, if we did not have racks resting on floor beams, the calculation would be over at this point. But there are racks in our example. They then create a concentrated load, so we continue to fill in the plates "" and " Distribution + concent.«:

In both plates we enter the dimensions of our spans (here I think everything is clear);

In the plate "" we change the values ​​of Load (normal) and Load (calculated) by the figure that we received above when calculating rafters with three support points - this is the vertical load on the rack (in our example, 343.40 kg);

In both plates we enter the accepted width of the beam section (10 cm);

The height of the section of the beam is determined by the plate " Distribution + focus. " ... Focusing on a higher value again. For our roof, we take 20 cm (see the picture above).

This completes the calculation of the rafter system.

I almost forgot to say: the calculation program we use is applicable for roof systems made of pine (except for Weymouth), spruce, European and Japanese larch. All used wood is of the 2nd grade. When using other woods, some changes will need to be made to the program. Since other types of wood are rarely used in our country, I will not describe now what needs to be changed.

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