Calculation of the rafter design online. Calculation of the rafting system - we make a roof reliable. Calculate snow load

The roof is an important constructive part of the house that performs a number of the most important functions. It protects against atmospheric attacks and takes precipitation, provides insulation and make a solid contribution to the formation of the eigen-style structure. In order for such a significant structure to "excellent" with trusted work, it is necessary to thoroughly think about the project and scrupulously sort out the size.

Careful analysis and calculation of the two-sheet roof is required by independent craftsmen, and country owner owners resorting to the services of construction organizations. Let's figure it out how to do it.

The roof resembling in the context of an inverted Literature V, no accident leads in the list of pitched structures. According to ease of construction and economy, there are almost no rivals from a two-tick roof. Centuries, checked in practice are based on the construction of most roofing structures.

Non-spanning planes do not require complex cutting of coating and other materials, the result of which the impressive amount of waste becomes. Specific triggers do not need to implement intricate configurations. The precipitation is not delayed on inclined surfaces, so there is no need to enhance waterproofing. As a result, the double-wing device is often cheaper than a single one.

The roof with two slopes can be an independent object or part of a complex of structures similar or excellent form. The easiest option does not have built-in auditory windows and canopies over the inlet porch, i.e. There are no additional fractures, ridges and concomitant infants.

The lack of convex and concave angles deprives the wizard of "pleasure" to suffer from a number of difficult operations. Again, the owners will not receive imaginary pleasures from leaks, often appearing in the junctions of the roofs of the roof.

In principle, no one bothers to equip two slides with numerous embedded structures in fans of bizarre architecture. True, there are limitations on climatic features: in areas with a high volume of winter sediments, the construction of roofs with numerous components is undesirable. In the surgery formed, favorable conditions are created to accumulate snow deposits. It will be necessary to consider them as usual, and the extraception in the sphere of snow removal can cause damage to the coating with all the resulting.

However, adherents of simple and clear forms should not relax too. The roof configuration of the angle should be perfectly chosen and is designed, otherwise it will not be able to perfectly fulfill trusted work.

Despite the deceptive elementality, in determining the optimal form of the design there are tricks. To overcome and bypass them is impossible without knowledge of technological subtleties, because all the parameters of the structure are interconnected:

• The width of the two-tie roof depends on the size of the box and the type of coating, which in turn affects the selection of the ridges of the rods.
• The bias of the roof depends on the climatic features of the construction area and on the type of roofing material.
• The set of listed circumstances, width and slope determines the height of the structure, which in the end may not comply with architectural requirements and aesthetic considerations.

At the immaculately designed roof, all proportions are made perfect. The width and height of it determine the rise and the bias needed to remove the precipitation in a particular area. Below, it is impossible for technical reasons, above is expensive and unreasonable if this does not require a unique architecture.

Note that the construction budget is growing with increasing steepness. According to the bias, they choose the roofing material. Focusing on its weight and specificity, design and calculate the rafter frame. The calculation of the rafter frame is made taking into account the listed parameters and taking into account the loads acting from the outside on the design.

The interdependence of the proportions of the roof, the complexity of the device of the rafter frame and the nuances of the selection of the coating causes the best shape through a banal selection. If something is not suitable, replace or strengthen the carrying structures. Fortunately, the range in the construction market is now provisioning, and all sorts of ways have been developed for strengthening the structure.

If you frighten upcoming calculations and shuffle data, it is better to resort to a win-win solution - a typical project. Not in vain abroad, all houses of one settlement are equipped with roofs of equal height and are covered equivalent to the color and characteristics of the material. Typification allows you to withstand the landscape identity and reduce the cost of designing.

However, even a typical design solution is not a panacea from technical dishes and aesthetic shortcomings. We must not forget about the individual dimensions of the box, over which the roof is planned. Compatriots denied the equalization in height and steepness, because it is still desirable to deal with the proportions of roofing facilities.

Step-by-step settlement

The configuration and dimensions of any pitched roof sets the rafter frame. The ribs of the rafter feet are laid out the skates forming a two-way corner. Metropal systems are built from metal and wood, used in the construction of industrial production and lumber construction.

Let's look at the options available for the application of an independent master effort, i.e. The desired method of building a roof frame of lumber.

Stage # 1 - selection of the type of rafter system

The method of the structure of a two-sheet roof is associated with the size of indirectly, but without taking into account the difference in the structure of structures it will be difficult to deal with geometric parameters.

Two traditional technologies are used in the construction of two-sheet roofs:

• CoverAccording to the top and bottom of the rafter there is a durable point of support. The bottom support is the walls of the house equipped with Mauerlat. The top of the removal rafting legs is based on a running beam forming a horse. The running beam is based on the supporting system designed specifically for it, on the inner wall or on the stone frontones of the box, erected to the roof device. The ultimate method is preferably used with the arrangement of large houses with an inner bearing wall or a range of columns.
• HangingAccording to which the tops are resting only to each other. The support for Niza is the walls, as in the previous case. Hanging rafter legs form an equilateral triangle, the base of which is called a tightening. In the aggregate, such a system does not create space, i.e. Does not transfers the pilot load on the walls of the box. Slinge triangles are installed either in finished installation, i.e. assembled on earth form, or built from individual rafalines in place. The lack of top support makes adjustments to the scope of use: the suspension method is used in the arrangement of only small structures with small spans.

The schemes of the rafter systems of both types include a minimum of structural elements when overlapping the boxes of up to 8-10m.

When arranging the spans, the hazard is the danger of deformation of the rafter feet. To eliminate the sagging and deflection of wooden parts from sawn timber, set firming elements: soap, contractions, sidebars, etc.

Additional parts provide stiffness and stability of large facilities, but increase the load. As the total load is determined and produced, we have already disassembled.

Stage # 2 - Width Calculation

Both types of wooden rafting systems are built on the beams of overlapping or by Mauerlat. The basis of the base depends on how the width of the roof is calculated:

• When mounting on the beams of the overlap, it is they form an eaves of the sinks, i.e. The dimensions of the roof are determined.
• When installing the width of the roof on the Mauerlat is determined by adding three quantities. You need to sum up the width of the box and two projections of the width of the cornese swell. However, only the carrier part of the width of the roof is used in the calculations, equal to the width of the box.

The Mauerlat function in frame buildings performs an upper strapping, at the same time connecting the scattered elements into a single frame. In wooden construction, Mauerlat serves the upper crown, folded by a timber or a log.

In the case of the application of the "beam" diagram of the device, the so-called matzits are used - bars or logs, laid under the top of the feet as overlapping.

The roofs of the roofs mounted on the Maurylalat can be formed directly with the plump legs sewn to them with lumps or a brick protrusion. The last option, naturally, is used in the construction of brick walls. The selection of the width of the sink is dictated by the type of roofing and the material from which the walls are folded.

• For slate roof no more than 10 cm;
• For bitumen tiles in the range of 30-40cm;
• For metal tile 40-50cm;
• For professional leaf 50cm;
• For ceramic tiles 50-60cm.

Walls made of logs and timber require reinforced protection against oblique rains, because the sinks are usually increased by 10-15 cm. Upon exceeding the limit value of the width of the sink recommended by the manufacturer, it is necessary to provide measures to strengthen it.

It is possible to install outdoor ducts on walls or support pillars, which will simultaneously play the role of structural elements of the terrace, porch, veranda.

Stage # 3 - definition of slope

The angle of inclination of the skates is permitted to vary in the widest limits, on average from 10º to 60º with permissible deviations in both directions. Traditionally, both planes of a double roof have equal tilt angles.

Even in the asymmetric structures for residential buildings, they are mainly located at an equal corner, and the effect of asymmetry is achieved by the construction of different-dimensional rods. Most often, the differences in the slope of the main parts of the roof are observed during the construction of country houses and household objects.

Three factors have a significant effect on the procedure for determining the optimal steepness of the double roof.

• The type of coating is associated with a weight of the crates intended for him. The type of roofing material defines the installation technology and the method of the base device for its attachment. The more the roof it turns out, the lower a slope can be. The less adhesion and junctions between the elements of the coating, the lower it is allowed to be the roof. And vice versa.
• Weight roofing together with. Located at an angle to the horizon, the heavy coating presses on the basis of only its projection. In short, the higher the slope, the smaller the mass is transmitted to the overlap. Those. Under heavy roof, you need to build a steep roof.
• Climate specificity of the region. The high bias contributes to the rapid relief of snow and water, which is extremely preferably in areas with a significant level of precipitation. However, high races are very sensitive to the impact of winds seeking to overturn them. Therefore, in the regions with characteristic strong winds, it is customary to build a gender structure, and in areas with abundant precipitation - roofs with a high slope.

In the regulatory documentation used in the calculations of the corners for the construction of two-sheet roofs, there are units that are able to confuse inexperienced in the roof business of home builders. The simplest value is expressed in dimensionless units, the most understandable is in degrees.

The second version transmits the ratio of the height of the roof to half its width. To determine it, a line is carried out from the central point of overlapping to the top of the roofing triangle. The real line is carried out on the diagram of the house imagined at the facility. Denotes the value or percentage, or in the form of a mathematical ratio of type 1: 2.5 ... 1: 5, etc., in percent of the wisely and inconvenient.

Stage # 4 - Determination of the height of the skate

At the roof with two skates, at the request of the owner, it may be or not to be an attic. In the attic spaces of two-tie roofs, it is not necessary to arrange useful premises. For this exists. However, the height of the attic applied to the maintenance and inspection of the roof angle is not arbitrary.

According to the prescriptions of the fire service from the vertex to the overlap should be at least 1.6 m. The upper limit is dictated by the aesthetic beliefs of designers. They argue that if the height of the roof is greater than the height of the box, then it seems to "give" to the construction.

The height of the skunk vertex for the hanging roofs arranged on the beams is easiest to determine the drawing method:

• Blacks are black at home.
• We are looking for the middle of the uppermost overlap.
• From the middle up laying the axis of symmetry.
• In any of the sides of the middle, we set half the width of the roof - we get the extreme point of the sink.
• With the help of the vehicle from the extreme point of the sweep, draw the straight at the angle recommended by the roofing manufacturer. The point of its intersection with the axis will be the peak of the roof. We measure the distance from the vertex to the overlap, we get the height.

To get a complete picture, the diagram needs to draw the second slope in the same way. In parallel lines of drawn rods, two more lines should be held at a distance equal to the thickness of the rafter legs on the same scale.

If it does not suit the roof configuration, you can "play" with a height on paper, changing the position of the point of the vertex and the inclusion of the roof in reasonable limits. The same manipulations can be carried out in one of the drawing programs.

When drawing up the Abris of the roof, built on the sleeve technology, should take into account the thickness of the run beam. With an impressive power, it will slightly move the position of the skates.

Folk craftsmen believe that the calculations of the elements of the rafter system for the construction of a two-tie roof can generally be reduced to calculate only the cross section of the run. This is the most loaded element, everyone else has the right to be thinner. For example, if the calculations show that for the skate run, a 100 × 150mm material will be required, then for rafaline, supports, pods are enough 50 × 150mm board.

The process of finding the height of structures with skes formed by lumps, a little differs from the methods described. Just the angle of the slope is drawn not from the extreme point of the sink, but from the lower assembly of the attachment of the rafter to Mauerlat. In any case, variations with the steepness and dimensions planned to build a double roof better pick up on "paper" than on the construction site.

Stage # 5 - calculation of the consumption of material

The normal owner is to think about the construction budget. True, in a preliminary estimate by definition there will be inaccuracies. The process of the construction of a two-tie roof will impose its own adjustments to the initial calculation of the material, but to find out the volume of the main spending will help.

Preliminary estimate should include:

• Bar for the device Mauerlat. In housing construction, a lumber is used with a cross section from 100 × 150mm to 200 × 200mm. The metrah is calculated around the perimeter of the box with a 5% reserve for processing and connections. Similar material is purchased for the Lenzny device, if it is designed.
• Board for the manufacture of rafaline. Most often, material from 25 × 150 mm to 100 × 150mm is used for the manufacture of rafter legs. The metra is determined by multiplying the length of the outer edge by the amount. The material is acquired with a reserve of 15-20%.
• Board or bar for the execution of subposses, tightens and supports with a cross section of 50 × 100, 100 × 100mm depending on the project. Also need a stock of about 10%.
• Material for device cable. It depends on the type of finishing coating. The crate is built either with solid, if it is produced or rarefied under the professional flooring, metal tile, conventional tile, slate, etc.
• Roll waterproofing, which determines the type of roof and steepness. High roofs are covered with a waterproofing carpet along the sinks, skate and in convex or concave corners. The german is covered with a solid carpet.
• Finish coating. Its quantity is calculated, summing up the skate area. If there are embedded hearing windows, then their square is also calculated. Only calculate as a rectangle, and not in fact. The amount of styling stock is recommended by coating manufacturers.
• Material for plating frontones and sols.
• Corners, plates, selflessness, brackets, nails. Need an anchor and studs, their number will tell the project.

Still need the shaped elements for the arrangement of through passages through the roof, endands, sinks, skate. Presented sketch of estimates valid for cold design. For a warmed roof, it will be necessary to purchase a heater and a vapor barrier film, a bar for controlled and the material for plating the roof from the inside.

For buildings of a small altitude, a rafter roof is perfect. It will decorate the facade of the house, and with a sufficient slope, the snow on such a roof does not accumulate, unlike a flat design.

One of the species of the rafter roof - double. This is a fairly simple system that is formed by two slopes. The roofing rod is the entire inclined plane, with which the drainage is provided.

The design is based on two parallel walls. Such a roof forms two triangular side fronts. Fronton is the completion of the facade of the building.

Advantages of a bunk system

1. Easy design.
   The calculation of the bearing capacity and the necessary materials for the device of such a roof is quite simple, since the variants of the types and sizes of the supporting structures are a bit;
2. Easy mounting.
   The duct roof does not have complex structural elements. A small number of sizes allows you to quickly install all elements of the roof;
3. Ease of operation.
   The smaller the different freshers has a roof, the more reliable it protects the dwelling. In the simplest performance, the double roof has only one break - rustle. Such a roof is easier to repair in the event of defects;
4. Free space.
   For the arrangement of the attic preferably a duct roof, since it is less "eats" space. For comparison, consider the house 6x6 m with an attic. In the outer walls, the height of the floor of the room to the roof is 1.5 m, in the skate - 3 m. For a bantal roof, under such conditions, the volume of the room will be 81 m. Cube, and for a holm-having four slope, 72 m. Cube. For large sizes of the loss building in the volume will increase.

Types of structures

There are four main types of bantal roofs:

1. Symmetric.
   Reliable, stable, easy to perform, is based on an equally chaired triangle;
2. Asymmetric.
   Konke is not located in the center, the roofing rates have different slopes;
3. Symmetric broken.
   Roof races have a break. Significantly increases the height of the room;
4. Loars asymmetric.
   An attic or mansard room is less than in the previous case. The roof has a very unusual appearance.

The choice of the type of a duct roof depends on the purpose of the room located directly below it and the architectural appearance of the building.

General principles for calculating the solo system

The most important carrier parts of the rafter system of the two-tie roof of the building are Mauerlat, Rigel and rafters. Maurylalat works for compression, so its section can be taken conditionally.

Rigel and rafting legs feel the bending moment.

The calculation of such structures is made by strength and hardness. For small buildings, you can choose their cross-section approximately, but for serious buildings, in order to security and save material, the calculation of the rafter system must perform a professional.

Load from its own roofing weight

To fulfill the calculation you need to know the load on 1 m.kv. Roof.

To do this, fold the masses of 1 m.kv. All roofing materials:

1. paddle (if it is, most often performed from plasterboard);
2. stropile legs. To calculate how the weight of the rafter falls on a square meter of the roof, you need to find a mass of the rapid meter of the rapid leg and divide this number to the rafted step in meters. To calculate, you can take an approximate section of the rafted, the area of \u200b\u200bthis section must be multiplied by wood density;
3. insulation (if it is). The density of the insulation must be indicated by the manufacturer, it must be multiplied by the thickness;
4. grussol. To ensure a stock into the calculation, you can take a solid incarnation. For example, 1 m.KV Grubes from a glass of 32 mm thick will weigh approximately 25 kilograms;
5. roofing material. Mass 1 m.kv. Coatings are usually indicated by the manufacturer.

Snow load

Snow load for each terrain its own and equals weight of snow cover on the horizontal plane.

In Russia she can take values \u200b\u200bfrom 80 to 560 kilograms per square meter. On the Internet you can easily find a snow load distribution card and choose the desired number based on the construction area.

The angle of inclination of the roof

The roof inclination angle is easy to calculate, knowing the geometry and having an engineering calculator or a standard calculator on a personal computer.

If it is divided into the height of the roof lift to the distance from the skate to the cornice in the plan, the bias of the roof in the shares or tangent of the angle of inclination. In order to calculate the angle, it is enough to find Arctangent.

If the use of an engineering calculator causes difficulties, Arcthangenes can be found using the Calculator online.

Calculation of the step of Stropil

The step of the attic roof rafter should be chosen because of the convenience of mounting the insulation. Mates usually have a width of 60 centimeters, so the step of the rafter should be chosen so that the distance between them clean was 58 or 118 centimeters. Two centimeters will allow installing insulation plates very tightly, which will allow him to keep between rafters and improve thermal insulation.

Length of a rafter foot

The length of the leg is easy to calculate by the formula:
L / COSα.,
Here l is the distance from the roof of the roof to the inner surface of the outer wall in the plan, and Cosα is the causing angle of inclination of the roof. With hard filling, you need to add the size of the loud.

Section of a rafter foot

The cross section of the rafter foot should be selected by a multiple size of boards and a bar.

An example of a simple calculation of the cross section of a rafter foot:

1. we find a load on 1 lineage meter rafters.
   q \u003d. (1.1 * Weight 1 m.kv. Roofing * COSα + 1.4 * Regulatory snow load * COSα2) * Step rafted;
2. find W..
   W \u003d q * 1,25 * flight rafted / 130;
3. we solve the equation:
   W \u003d B * H2 / 6.
   In this equation B - the width of the cross section of the rafting leg, and the H-height.

To solve, you need to set the width and find the height, solving a simple square equation. The width can be prescribed 5 cm, 7.5 cm, 10 cm, 15 cm. With small spans, a width of 15 cm is inexpedient.

To calculate the rafter systems, there are all sorts of tables, programs, online calculators.

The main elements of the roof

The main elements of the bartal, as well as any other rafter roof, are:

Slinge roof with an attic

To fully use the space under the roof, you can design the attic.

Mansard Floor - This is the floor in the attic space. The facade of the attic is completely or partially formed by the roof surfaces. According to regulatory documents, the premises are considered an attic, the crossing line of the roof plane and the outer wall should not be higher than 1.5 m from the floor level. If this requirement is not fulfilled, the space will be considered the usual floor.

The roof of the attic floor is different from the roof of the attic presence in its design of the insulation. Most often, mineral wool plates are used for insulation of the roof roof.

Illumination of the attic space can be carried out in three ways:

1. window Pieces in Frontones;
2. hearing windows;
3. mansard windows.

Hearing window - This is a window structure that has a frame that is mounted simultaneously with the solo system. This frame is made of wood. The auditory window has its own small roof, which can be a duplex or cylindrical. The glazing itself is installed vertically.

Mansard window - This is a window specifically designed for use on a rafting roof. It is installed in the plane of the skate in the oblique position. The mansard window must withstand the estimated snow load. It is better not to use such a type of windows in roofing with a slight bias.

Choosing a roof material

After the appearance of the roof is defined, you can proceed to the choice of material. There are several types of modern coatings. The list below, the variants of the materials are given in the order of decrease in the average market value.

1. Ceramic tile.
   Ceramics, as a roof material, has a long history. The ceramic roof is reliable and durable. The minuses of this material is the price and a large mass. Under the roof from the ceramic tiles will have to make a reinforced rafting system and a doom;
2. Cement-sand tile.
   Possesses almost all the characteristics of ceramic, but it is a little less;
3. Flexible bituminous tile.
   It has good sound insulation characteristics. Thanks to the roofing surface, the tile is capable of not giving snow from the roof. Requires a solid drying, is usually used by a layer of moisture-resistant plywood. You can not use on roofing with big slopes;
4. Metal tile.
   Compared with previous coatings, it has a smaller weight. Easy mounted. The minus of the metal roof is that during the rain it can be too noisy.
5. Folding roofing.
   The most attractive option in terms of cost. Requires special qualifications when installing, as the non-professional will be difficult to fully perform connections. Installation is more time-consuming than a metal and flexible tile. The same "noisy", like a metal tile.

The roof material is completely dependent on the desires and capabilities of the customer. The exceptions are a roof with too large or too small slope, since all materials have limitations on the angle of inclination of the skate.

Types of rafter systems

Constructive systems of the rafter roofing can be three species:

1. Slopils.
   The rafters are based on two sides. From the bottom - to Mauerlat, on top - on the bolt. As intermediate supports can be used racks and saws. Most often used in buildings with a small distance between the ends or if possible, put the rack or wall in the middle of the attic.
   With large spills, rafters (long distances between longitudinal walls) can be additionally used racks, sores or tightening.
   Slot rafters are simple in calculations.
   Usually the most powerful element of such a system is a riglel, which bears half of the load from the entire design of the roof.
2. Hanging rafters.
   In the absence of the possibility of using the riglel as the top support, it is reasonable to use this rafter system.
   Hanging rafters are based only on Mauerlat, and at the top point are connected with the help of the lining.
   This rafter system works under load as a farm. The greatest pressure falls on the outer walls. There is a horizontal force - spacer, which can lead to wall displacement. In the design of the hanging rafters, the spacel force perceives the tightening, which tightens the rafting legs and does not allow them to drive around.
   Hanging rafters are classified depending on the location of the tightening:
   1) Triangular Treated Arch.
   The tightening and rafters form a triangle. The tightening is located in the level of overlapping;
   2) Triangular Three-War Arch with Suspension.
   With a large span, the rafter the tightening may not pass according to the requirements of the deflection. To prevent its sagging, lighten to the skate. But with such a system, as well as under the system of the rafters, the middle of the attic is formed a number of racks;
   3) Triangular three-stroke arch with a raised tightening.
   The tightening is most often in the level of the attic room. Such a scheme is less beneficial in terms of design. The higher the tightening is located, the greater the exposure it perceives.
   Hanging rafters should be considered as a triangular farm, which complicates the calculation.
3. Combined rafters.
   The combined system can include spacer springs. They need both in the installation of Rigel and in the tightening. In contrast to previous options, in which the rafter to Mauerlat is fastened with a hinge, here the rafter foot is attached hard, therefore it raises in the system. For such a system, Mauerlat must be reliably attached to the wall, and the wall itself is durable and thick. An excellent variant of the mill is performed on the perimeter of the reinforced concrete belt.

Installation of the rafter system

Installation occurs in the following order:

1. laying Mauerlat;
2. installing the Rigel (if it is);
3. laying rafters;
4. insulation (if any);
5. doom;
6. roofing material.

Attaching the rafting leg to Mauerlat can be hard and hinge.

Hinged fixing

It makes it possible to compensate for the expansion of wood under the action of humidity and temperature drops.

The mount can be carried out in several ways:

1. with the help of special fasteners, metal "Salace";
2. with the help of a fastener plate;
3. on the rafter foot is done. The junction seat of the rafter foot and the Mauerlat is fixed with nails.

Hard consolidation

The rafter is fastened to Mauerlat with a word and reliably fixed with nails, clogged at an angle in relation to each other. One nail is driven up vertically surface of Maurolalat. Such a connection eliminates the offset in any plane.

The bartal rafter system has undeniable advantages. It can be designed and mounted independently, you just need to respond to this issue and think over everything to the smallest detail.

-\u003e calculation of the rafter system

The main element of the roof, perceiving and opposing all types of loads, is Slinge system. Therefore, in order for your roof to reliably oppose all environmental impacts, it is very important to make the correct calculation of the solo system.

For self-calculation of the characteristics of the materials required for the installation of the rafter system, I cite Simplified formulas calculation. Simplifications are made in the direction of increasing the strength of the structure. This will cause some increase in lumber consumption, but on small roofs of individual buildings it will be insignificant. This formulas can be used when calculating two-tie attic and attic, as well as single-sided roofs.

On the basis of the calculation methods below, the programmer Andrei Mutovkin (Andrei-Mutovkin's business card - Mutovkin.rf) has developed a program for calculating the solo system. At my request, he generously allowed to place it on the site. You can download the program.

The calculation technique was prepared on the basis of SNiP 2.01.07-85 "load and impact", taking into account the "change ..." from 2008, as well as on the basis of the formulas given in other sources. I developed this technique many years ago, and time confirmed its correctness.

To calculate the rafting system, first of all, it is necessary to calculate all loads acting on the roof.

I. Loads acting on the roof.

1. Snow loads.

2. Wind load.

On the rapid system, except the above, the load from the elements of the roof is also available:

3. The weight of the roof.

4. The weight of the draft flooring and doom.

5. The weight of the insulation (in the case of a warmed attic).

6. The weight of the solo system itself.

Consider all these loads.

1. Snow loads.

To calculate snow load, we use the formula:

Where,
S - the desired snow load, kg / m²
μ - coefficient depending on the roof slope.
SG - Regulatory Snow Load, kg / m².

μ is a coefficient depending on the roof slope α. Dimensional value.

It is possible to approximately determine the angle of the liner of the roof α as follows the resulting of the height of H on half of the span - l.
The results are reduced to the table:

Then, if α is less than or equal to 30 °, μ \u003d 1;

if α is greater than or equal to 60 °, μ \u003d 0;

if a 30 ° calculate the formula:

μ \u003d 0.033 · (60-α);

SG - Regulatory Snow Load, kg / m².
For Russia, it is accepted on a card 1 of the mandatory application 5 SNiP 2.01.07-85 "Loads and Impact"

For Belarus, the regulatory SG light load is determined
The technical code of the established practice of Eurocode 1. Impact on the design part 1-3. General impacts. Snow loads. TKP EN1991-1-3-2009 (02250).

For example,

Brest (I) - 120 kg / m²,
Grodno (II) - 140 kg / m²,
Minsk (III) - 160 kg / m²,
Vitebsk (IV) - 180 kg / m².

Find the maximum possible snow load on the roof of 2.5 m high and a long span 7m.
The structure is in the der. Babenki Ivanovo region RF.

On the card 1 of the mandatory application 5 SNiP 2.01.07-85 "load and exposure" define SG - regulatory snow load for the city of Ivanovo (IV district):
SG \u003d 240 kg / m²

Determine the angle of the liner of the roof α.
For this, the height of the roof (H) is divided by half of the span (L): 2.5 / 3,5 \u003d 0.714
And on the table we will find the angle of the slope α \u003d 36 °.

Since 30 °, calculation μ We produce according to the formula μ \u003d 0.033 · (60-α).
Substituting the value α \u003d 36 °, we find: μ \u003d 0.033 · (60-36) \u003d 0.79

Then S \u003d SG · μ \u003d 240 · 0.79 \u003d 189kg / m²;

the maximum possible snow load on our roof will be 189kg / m².

2. Wind load.

If the roof is cool (α\u003e 30 °), then due to its sail, the wind presses one of the rods and strives to overturn it.

If the roof is common (α, then the lifting aerodynamic force arising when it is driving with its wind, as well as turbulence under the sips tend to raise this roof.

According to SNiP 2.01.07-85 "Loads and Impact" (in Belarus - Eurocode 1 Exposure on structures Part 1-4. General impact. Wind exposures), the regulatory value of the medium component of the wind load WM at the height Z above the ground surface should be determined by the formula. :

Where,
Wo is the regulatory value of wind pressure.
K is a coefficient that takes into account the change in wind pressure in height.
C is an aerodynamic coefficient.

K is a coefficient that takes into account the change in wind pressure in height. Its values, depending on the height of the building and the nature of the terrain, are reduced to Table 3.

C - aerodynamic coefficient,
which, depending on the configuration of the building and the roof, can take values \u200b\u200bfrom minus 1.8 (the roof rises) to plus 0.8 (the wind presses on the roof). Since our calculation is simplified in the direction of increasing strength, the value C is taken equal to 0.8.

When building the roof, it is necessary to remember that the wind forces seeking to lift or disrupt the roof can reach significant values, and therefore, the bottom of each rapid leg must be carefully attached to the walls or to the matzam.

This is done by any means, for example, with the help of annealed (for softness) with a steel wire with a diameter of 5 - 6mm. With this wire, each rafter foot is screwed to the matsam or to the ears of the slab overlap. It's obvious that than the roof is harder, the better!

Determine the average wind load on the roof of a single-storey house with the height of the skate from the ground - 6m. , an angle of slope α \u003d 36 ° in the village of Babenki Ivanovo region. RF.

3 applications 5 in "SNiP 2.01.07-85" find that Ivanovo region refers to the second wind area Wo \u003d 30 kg / m²

Since all buildings in the village are below 10m., The coefficient K \u003d 1.0

The value of the aerodynamic coefficient C is taken equal to 0.8

the regulatory value of the average component of the wind load WM \u003d 30 · 1.0 · 0.8 \u003d 24kg / m².

For information: If the wind blows into the end of this roof, it acts on its edge (breaking) force to 33.6 kg / m²

3. The weight of the roof.

Different types of roof have the following weight:

1. Slate 10 - 15 kg / m²;
2. Ondulin (Bituminous Slate) 4 - 6 kg / m²;
3. Ceramic tile 35 - 50 kg / m²;
4. Cement-sand tiling 40 - 50 kg / m²;
5. Bituminous tile 8 - 12 kg / m²;
6. Metal tile 4 - 5 kg / m²;
7. Professional flooring 4 - 5 kg / m²;

4. The weight of the draft flooring, the root and the rafter system.

The weight of the black flooring is 18 - 20 kg / m²;
The weight of the lamb 8 is 10 kg / m²;
The weight of the actual stage system 15 is 20 kg / m²;

When calculating the final load on the solo system, all the above loads are summed up.

Now I will open you a little secret. The sellers of certain types of roofing materials as one of the positive properties note their lightness, which, according to their assurances, will lead to a significant savings of sawnwood in the manufacture of a rafter system.

As a refutation of this statement, I will give the following example.

Calculation of the load on the rapid system when using various roofing materials.

Calculate the load on the rafter system when using the heavyweight (cement-sand tile
50 kg / m²) and the easiest (metal tile 5 kg / m²) of the roofing material for our house in the village of Babenka Ivanovo region. RF.

Cement-sand tile:

Wind Loads - 24kg / m²
Roof Weight - 50 kg / m²
Grub weight weight - 20 kg / m²

TOTAL - 303 kg / m²

Metal tile:
Snow Loads - 189kg / m²
Wind Loads - 24kg / m²
Roof Weight - 5 kg / m²
Grub weight weight - 20 kg / m²
The weight of the solo system itself - 20 kg / m²
TOTAL - 258 kg / m²

It is obvious that the existing difference in settlement loads (only about 15%) will not be able to lead to any tangible savings of lumber.

So, with the calculation of the total load q, acting on the square meter of the roof, we figured out!

I especially pay your attention: when calculating, carefully follow the dimension !!!

II. Calculation of the rafter system.

Slinge system It consists of individual rafters (rafter feet), therefore the calculation is reduced to the definition of the load on each rapid leg separately and the calculation of the cross section of a separate rafting leg.

1. Find a distributed load on the pattern meter of each rapid leg.

Where
QR is a distributed load on a rabbown meter of a rafter foot - kg / m,
A - distance between the rafters (step rafter) - m,
Q is the total load acting on the square meter of the roof - kg / m².

2. Determine the working plot of maximum LMAX length in the rafter foot.

3. Calculate the minimum cross section of the material of the rafter.

When choosing a material for rafters, we are guided by the table of standard lumber sizes (GOST 24454-80 lumber of coniferous rocks. Dimensions), which are reduced to Table 4.

Table 4. Nominal size of thickness and width, mm

Board thickness - Section Width (B)	Board width - section height (H)
16	75	100	125	150
19	75	100	125	150	175
22	75	100	125	150	175	200	225
25	75	100	125	150	175	200	225	250	275
32	75	100	125	150	175	200	225	250	275
40	75	100	125	150	175	200	225	250	275
44	75	100	125	150	175	200	225	250	275
50	75	100	125	150	175	200	225	250	275
60	75	100	125	150	175	200	225	250	275
75	75	100	125	150	175	200	225	250	275
100		100	125	150	175	200	225	250	275
125			125	150	175	200	225	250
150				150	175	200	225	250
175					175	200	225	250
200						200	225	250
250								250

A. Calculate the cross section of the rafter foot.

We specify an arbitrarily width of the section in accordance with the standard dimensions, and the height of the section is determined by the formula:

H ≥ 8,6 · LMAX · SQRT (QR / (B · RIPS)) if the slope of the roof α

H ≥ 9.5 · LMAX · SQRT (QR / (B · RIPS)) if the slope of the roof α\u003e 30 °.

H - the height of the section cm,


B - the width of the section cm,
RiPridge - wood resistance to bending, kg / cm².
For pine and fir riesg is equal to:
1 grade - 140 kg / cm²;
2 grade - 130 kg / cm²;
3 grades - 85 kg / cm²;
SQRT - Square root

B. We check whether the magnitude of the deflection is stacked.

The normalized material deflection under load for all roof elements should not exceed L / 200. Where, L is the length of the work area.

This condition is performed with the faithfulness of the following inequality:

3,125 · QR · (LMAX) ³ / (b · h³) ≤ 1

Where,
QR is a distributed load on a rabbown meter of a rafter foot - kg / m,
LMAX is a working plot of a rafter foot of the maximum length m,
B - the width of the section cm,
H - the height of the section cm,

If the inequality is not respected, then increase B or h.

Condition:
Roof angle α \u003d 36 °;
Step rafted a \u003d 0.8 m;
Working plot of the rafter foot of the maximum length LMAX \u003d 2.8 m;
Material - pine 1 grade (Rizg \u003d 140 kg / cm²);
The roof is a cement-sand tile (the weight of the roof is 50 kg / m²).

As it was calculated, the total load acting on the square meter of the roof is q \u003d 303 kg / m².
1. Find a distributed load on the pattern meter of each rafter foot QR \u003d A · Q;
QR \u003d 0.8 · 303 \u003d 242 kg / m;

2. Choose the thickness of the chalkboard for rafters - 5cm.
Calculate the cross section of the rafting leg with the width of the section 5cm.

Then, H ≥ 9,5 · LMAX · SQRT (QR / B · RIPS)Since the bias of the roof α\u003e 30 °:
H ≥ 9.5 · 2.8 · SQRT (242/5 · 140)
H ≥15.6 cm;

From the table of standard sizes of sawn timber, choose a board with the nearest cross section:
width - 5 cm, height - 17.5 cm.

3. We check whether the magnitude of the deflection is stacked. For this should be observed inequality:
3,125 · QR · (LMAX) ³ / b · h³ ≤ 1
Substituting values, we have: 3,125 · 242 · (2.8) ³ / 5 · (17,5) ³ \u003d 0.61
Value 0.61, which means the cross section of the rafted material is chosen correctly.

The cross section of the rafted, installed in increments of 0.8m, for the roof of our house will be: width - 5 cm, height - 17.5 cm.

All parameters must be specified in millimeters.

B. - Length of the roof.

Y. - Height.

C. - Distance of Sveza.

X. - Width of the roof.

Y2. - Additional height.

X2 - Width extra.

This program will help you to accomplish the exact calculation of building materials for the construction of the roof: the number of rafters and boards of the crate, the underpants material (rubberoid, pergamine), the number of sheet material (metal tile, slate, nulin or ondulin).
Our online calculator will calculate other useful roof sizes.

The presented program performs calculation in two versions: Type 1 - simple bounce roofs, type 2 - duct roofs with 2 side fronts.

If the designed roof is just with one side fronton, then in this case, we perform the calculation by type 1, and after type 2. According to the results of the calculations, you can determine the required volume of materials: subdore, sheet, rafted, and crate board.

Otherwise, you allow an error when calculating the error, since the program when calculating the parameters of the main roof takes into account cutouts for side fronts.

According to the results of the counting, you get the volume and size of the material for one roof scope, and the entire volume and size will be listed in brackets.

When calculating the volume and useful size of an additional roof, you get two parameters in brackets: the volume and size of one or two additional roofs.

Important! It is worth considering that the program performs calculation over the entire area of \u200b\u200bthe roof, when determining the number of sheets of roofing material.

For example, 7.7 sheets take place, and only 2.8 rows. According to the countdown, you will receive 3 real construction series.

In the event that you want to get the exact number of sheets for the future roof you need to reduce their height until you receive an integer number of rows.

Do not forget to put exactly the length of the adolescence.

Important! In Type 2 mode, in the process of calculating the volume of material for a rafted main roofing, the program does not take into account cutouts under the frontal side. This calculation of the sling system of the bone roof is associated with the device of the program itself.

Also, the remaining building material for rafters, you can use to build or repair at home, otherwise you can make corrections in the calculations.

The accurate calculation of the approximate cost of the roof depends on the correct main measurements.

Important! Do not forget, acquire building materials with a reserve of 5-10% for waste.

Dyed row

First of all, we need a diagram (drawing or design) of the bartal roof, according to which we will produce all calculations (indicated above).

The roofing procedure is quite simple, but the sequence of certain steps should be followed.

Before installing beams or translations for future overlap, you need to determine whether the attic will be equipped or just an attic room. As a rule, for a simple attic, it is enough to choose the board 150x150 mm. In the event that you plan to build a attic, then it is the right to choose a bar with the same size. To increase the durability of the frame, you should mount the bars or boards solely on the walls.

The process of fixing the beams is made taking into account the release from the outer edge of approximately 400 mm to prevent sediment or wind to the roof.

We will use a cutting board under 50x150 mm when arranging the mint of the attic, and fixation is carried out with roofing nails. To give a duplex roof of stability, it is necessary to perform all measurements correctly, trying to exclude the error.

Now we go to the assembly of the rafter design, starting the installation with the frontones already described above. At the same time, we spawn the lower parts of the boards, which will give our rafter design additional stability.

When the design is fully erected for a two-sheet roof, we begin to overlap with roofing materials.

The advantages of the duplex roof:

• This design is quite simple in the construction, which allows you to perform all the work independently without expert help;
• The used building materials are affordable;
• A large angle of inclination of the roof is perfectly removing water during precipitation;
• The absence of complex structures and fades, significantly facilitate the construction and facing of the roof.

Design and competent calculations of the elements of the rafter design - the key to success in construction and in the subsequent operation of the roof. It is obliged to resist the aggregate of temporary and permanent loads, while the construction is minimized.

To make calculations, you can use one of the numerous programs laid out on the network, or do it manually. However, in both cases, it is necessary to clearly know how to calculate the roof rafters to thoroughly prepare for construction.

The rapid system determines the configuration and strength characteristics of the pitched roof that performs a number of significant functions. This is a responsible enclosing structure and an important component of the architectural ensemble. Therefore, in the design and calculations of the rafter feet should avoid flaws and try to exclude shortcomings.

As a rule, in project developments, several options are considered, of which the optimal solution is selected. The choice of the best option does not mean that you need to create a certain number of projects, to perform for each accurate calculations and, as a result, preferred the only one.

The course of determining the length, assembly slope, the cross section of Stropilin is in the scrupulous selection of the form of the structure and the size of the material for its structure.

For example, in the formula for calculating the carrying capacity of the rafter leg, the parameters of the cross section of the most suitable material are initially introduced. And if the result does not comply with the technical standards, then the lumber size increases or decrease, until maximum compliance achieves.

Method for finding an angle of inclination

At the definition of an angle of the slope of the scope design there are architectural and technical aspects. In addition to the proportional configuration, the most suitable for the style of the building, the impeccable solution must be considered:

• Snow load indicators. In localities with an abundant precipitation, roofs with a bias from 45 ° and more are erected. Snow departments are not delayed on the ridges of such steepness, so that the total load on the roof is reduced, the total load on the roof is reduced, stodil and construction as a whole.
• Wind load characteristics. In areas with gustful strong winds, coastal, steppe and mountainous areas, low-pitched structures of the streamlined form are built. The steepness of the rods usually does not exceed 30º. In addition, the wind prevent the formation of snow deposits on the roofs.
• Mass and type of roofing. The greater the weight and smaller elements of the roof, the cooler need to build a rafter frame. It is necessary to reduce the likelihood of leakage through compounds and reduce the specific coating weight per unit horizontal roof projection.

In order to choose the optimal angle of inclination of the rafaline, the project must be taken into account all the requirements listed. The steepness of the future roof is obliged to comply with the climatic conditions chosen for the construction of the terrain and the technical data of the roofing coating.

True owner owners in the northern windless areas should be remembered that with increasing angle of inclination of the rafter, the consumption of materials is increasing. The construction and arrangement of the roof of the steepness of 60 - 65º will cost approximately one and a half times more expensive than the construction of an angle of 45º.

Neighborhoods with frequent and strong winds should not be too short enough to save on savings. Necessary gentle roofs lose in architectural terms and do not always help reduce the number of expenses. In such cases, the increase in the insulating layers is most often required, which in counterweight expectations of the economy leads to the rise in the cost of construction.

The sloping slope is expressed in degrees, as a percentage or in the format of dimensionless units displaying the ratio of half of the field of flight to the height of the installation of the skate run. It is clear that degrees outlines the angle between the ceiling overlap line and the line of the skate. Percentages rarely enjoy due to the complexity of their perception.

The most common method for setting the angle of inclination of rafting legs, used both by the designers of low-rise buildings and builders, these are dimensionless units. They in shares transmit the ratio of the length of the overlapping span to the height of the roof. The facility is easiest to find the center of the future frontal wall and will install a vertical rail in it with a rink height mark than to postpone the angles from the edge of the skate.

Calculation of the length of the rafter

The length of the rafylic is determined after the angle of inclination is selected. Both specified values \u200b\u200bcannot be attributed to the number of accurate values, because In the process of calculating the load as a steepness, and after it, the length of the rafting leg can change slightly.

The main parameters affecting the calculation of the length of the rafter include the type of roof of the roof, according to which:

1. The outer edge of the rafter feet is trimmed with a flush with the outer surface of the wall. The rafters in this situation do not form an abuser, protecting the design of precipitation. For the protection of the walls, the drainage is installed, fixed on the rituit to the end edge of the Stropilin of the cornice board.
2. Cropped flush with a wall of rafters are increasing with lumps to form an eaves. Fakes are fixed to rafalines with nails after the construction of a rafter frame.
3. The rafters are initially reproduced taking into account the length of the cornese swell. In the lower segment of the rafter feet choose wrinkles in the form of angle. For the formation of wrinkles, retreat from the lower edge of the rafter to the width of the eaves. Words are needed to increase the reference area of \u200b\u200bthe rafter feet and for the reference node device.

At the stage of calculating the length of the rafter feet, we need to consider the options for fastening the roof frame to Mauerlat, to the crossing or to the top crown of the cut. If the installation of the Stropilin flush with an external contour of the house is designed, then the calculation is carried out along the length of the upper rib rafting, taking into account the size of the tooth, if it is used to form a lower connecting node.

If the rafter legs are rebounded with a carnese removal, then the length is calculated on the upper edge of the rainfall along with the sink. It should be noted that the use of triangular wrists significantly accelerates the rates of the construction of a rafter frame, but weakens the elements of the system. Therefore, a coefficient of 0.8 is used when calculating the bearing capacity of strings with selected angle.

Traditional 55 cm. However, the scatter can be from 10 to 70 and more. The calculations use the projection of the cornese removal on the horizontal plane.

There is a dependence on the strength characteristics of the material, on the basis of which the manufacturer recommends the limit values. For example, the slate manufacturers do not advise the root for the contour of the walls over a distance of more than 10 cm so that the snow mass accumulating along the rumble could not damage the edge of the cornice.

Cool roofs are not accepted to equip wide overlines, regardless of the material of the eaves are not wider than 35 - 45 cm. But structures with a bias up to 30º can perfectly add a wide eaves, which will serve as a peculiar canopy in areas with excess solar lighting. In the case of designing roofs with cornisse, 70 and more cm, they are strengthened with additional support racks.

How to calculate the carrying ability

In the construction of rafal frames, lumber are used made of coniferous wood. The harvested bar or the board must be no lower than the second grade.

The rafting legs of the pitched roofs work according to the principle of compressed, curved and compressed-curved elements. With the tasks of resistance to compression and bending, a second-class wood is perfectly coping. Only if the design element will work on stretching, the first grade is required.

The rafter systems are arranged from a board or timber, pick them up with a margin of strength, focusing on the standard dimensions of the volumetric lumber.

Calculations of the bearing capacity of the rafter feet are carried out in two states, this is:

• Estimated. A condition in which the design is destroyed as a result of the applied load. Calculations are carried out for the total load, which includes the weight of roofing pie, the wind load taking into account the flooding of the construction, the mass of snow, taking into account the linker's slope.
• Regulatory. The state at which the rafter system begins, but the destruction of the system does not occur. It is usually impossible to operate the roof in such a state, but after carrying out repair operations, it is quite suitable for further use.

In the simplified estimated version, the second state is 70% of the first value. Those. To obtain regulatory indicators, the calculated values \u200b\u200bmust be trally multiplied by the coefficient of 0.7.

Loads depending on the climatic data of the construction region are determined by the cards attached to the SP 20.13330.2011. The search for regulatory values \u200b\u200bon the cards is extremely simple - you need to find a place where your city is located, a cottage settlement or another closest settlement, and reflect the readings about the calculated and regulatory value from the card.

The averaged information about snow and wind load should be adjusted according to the architectural specificity of the house. For example, the value taken from the map must be distributed over the skates in accordance with the wind roses composed for the terrain. You can get a printout with it in a local meteorological service.

From the windward side of the construction, the snow mass will be much smaller, therefore the calculated indicator is multiplied by 0.75. From the leeward side, snow deposits will accumulate, so they multiply here at 1.25. Most often to unify material for the construction of the roof, weathered part of the design are built from a paired board, and the implanted part is arranged with rafalines of their single board.

If it is unclear which of the skates will be from a leeward side, and what is the opposite, then it is better to multiply by 1.25. The stock of the strength does not prevent at all, if it does not increase the cost of the sawn timber.

The setting weight of the snow is still adjusted depending on the roof steepness. From the skates installed at an angle of 60º, the snow will immediately slide without the slightest delays. In the calculations for such steep roofs, the correction factor does not apply. However, with a lower slope, the snow will already be able to delay, therefore the additive in the form of a coefficient of 0.33, and for 40º it, but already 0.66 is used for 50º.

Wind load is determined in a similar way according to the corresponding map. Correct value depending on the climatic specificity of the region and from the height of the house.

To calculate the bearing capacity of the main elements of the designed rafter system, it is required to find the maximum load on them, summing up temporary and constant values. No one will strengthen the roofs before the snowy winter, although in the country it would be better to put the safety vertical struts in the attic.

In addition to the mass of snow and the grace of winds, the calculations requires accounting for the weight of all elements of roofing pie: installed on top of the rafaline crate, the roof, insulation, internal binder, if used. Weight of steam and waterproofing films with membranes, it is customary to neglect.

Information about the weight of the materials is indicated by the manufacturer in technical passports. Data on the mass of the bar and boards are taken in approximation. Although the mass of the crate on the meter of the projection can be calculated by taking as a basis the fact that the cubic meter of sawn timber weighs an average of 500 - 550 kg / m 3, but a similar amount of OSP or plywood from 600 to 650 kg / m 3.

The values \u200b\u200bof the loads are denoted in the CB / m 2. However, Stropilina perceives and keeps only the load that directly presses on this linear element. In order to make the calculation of the load specifically on the rafter, the combination of natural tables of loads and the mass of roofing pie is multiplied by a step of installation of the rafter.

The load value given to the linear parameters can be reduced or increased by changing the step - the distances between the rafalines. Correcting the area for collecting the load, the optimal values \u200b\u200bare achieved in the name of a long service of a carcass of the pitched roof.

Determination of the cross section of Stroplin

Stropile legs of roofs of various steepness perform ambiguous operation. On the rafter, gentle structures operates mainly bending moment, another compressive force is added to the analogues of steep systems. Therefore, in the calculations of the cross section, the rafters necessarily takes into account the slope.

Calculations for structures with a bias up to 30º

On the rafting legs of the roofs of the specified steepness acts only bending voltage. They are calculated at the maximum moment of bending with the application of all types of load. Moreover, temporary, i.e. Climatic loads are used in calculations at maximum indicators.

Stropilin, having only supports under both own edges, the point of maximum bending will be in the very center of the rafter foot. If the rafter is laid on three supports and is composed of two simple beams, then the moments of maximum bending will come to the middle of both of the spans.

In solid rafying on three supports, the maximum bending will be in the area of \u200b\u200bthe Central Support, but because Under the bending site is a support, then it will be directed up, and not as the previous cases down.

For normal operation of the rafter legs in the system, two rules must be completed:

• The internal voltage formed in the rafter when bending as a result of the load applied to it, must be less than the calculated resistance of the lumber to bend.
• The deflection of the rafter foot should be less than the normalized deflection value, which is determined by the L / 200 ratio, i.e. It is allowed to progress the element only on one two hundredth of its real length.

Further calculations consist in a sequential selection of the sizes of the rafter foot, which as a result will satisfy the specified conditions. For calculating section there are two formulas. One of them is used to determine the height of the board or bar for an arbitrarily given thickness. The second formula is used to calculate the thickness of an arbitrarily given altitude.

In calculations, it is not necessary to use both formulas, it is enough to apply only one. The result obtained in the end is verified by the first and second limit state. If the calculated value turned out to be an impressive margin by strength introduced into the formula, an arbitrary indicator can be reduced to not overpay for the material.

If the calculated value of the moment of bending will be more than L / 200, then an arbitrary value increases. The selection is carried out in accordance with the standard sizes on sale of sawn timber. So choose the cross section until the moment is calculated and the optimal option is obtained.

Consider a simple example of calculations according to the formula B \u003d 6Wh². Suppose H \u003d 15 cm, and W is the ratio M / R zeal. The value of M is calculated according to the formula G × L 2/8, where G is the total load, vertically directed to the rafter foot, and L is the length of the span, equal to 4 m.

R Izg for lumber from coniferous breeds we take in accordance with the technical standards of 130 kg / cm 2. Suppose, we calculated the total load in advance, and it turned out to be 345 kg / m. Then:

M \u003d 345 kg / m × 16m 2/8 \u003d 690 kg / m

To translate into kg / cm divide the result by 100, we get 0.690 kg / cm.

W \u003d 0.690 kg / cm / 130 kg / cm 2 \u003d 0.00531 cm

B \u003d 6 × 0.00531 cm × 15 2 cm \u003d 7.16 cm

We round the result as it should be on the most side and we obtain that for the device rafters, taking into account the load provided in the exemplary, the ram 150 × 75 mm will be required.

We check the result on both states and make sure that the material is suitable for the cross section calculated. σ \u003d 0.0036; F \u003d 1.39

For rafter systems with a bias over 30º

The rafted roofs of a steepness more than 30º are forced to resist not only bending, but also the strength of compressing them along its own axis. In this case, in addition to checking according to the resistance to the bending described above, and the magnitude of the bend you need to calculate the lines of internal voltage.

Those. Actions are performed in a similar manner, but there are several more verification calculations. The arbitrary height or arbitrary thickness of the lumber is defined, with its help, the second parameter of the section is calculated, and then a check is performed for compliance with the above three technical conditions, including compression resistance.

If necessary, in strengthening the carrying capacity of the rafter, arbitrary values \u200b\u200bentered into formulas increase. If the safety margin is quite large and the regulatory deflection significantly exceeds the calculated value, that is, it makes sense to fulfill the calculations by reducing the height or thickness of the material.

Choosing the initial data for the production of calculations will help the table in which the generally accepted dimensions of the lumber produced with us are reduced. It will help to choose a cross section and the length of the rafter feet for the initial computing.

Video about the calculations of Stropilin

The roller clearly demonstrates the principle of performing calculations for the elements of the rafter system:

Performing the calculations of the bearing capacity and installation angle of the rafter - an important part of the design of the roof frame. The process is not easy, but it is necessary to figure it out in it and those who produce calculations manually, and those who use the calculation program. You need to know where to take table values \u200b\u200band what makes settlement values.