One of the most popular solutions for the device interfloor ceilings in private homes is the use load-bearing structure from wooden beams. It must withstand the design loads without bending and, especially, without collapsing. Before you start constructing the floor, we recommend using our online calculator and calculating the main parameters beam structure.
Wooden floor beams are often the most economical option during the construction of a private country house. It should be noted that wooden beams are easy to manufacture and simple to install, have low thermal conductivity compared to steel or reinforced concrete structures. The main disadvantage of wooden beams is their low mechanical strength, requiring large sections, as well as low resistance to damage by microorganisms and wood-boring insects and flammability. Therefore, wooden floor beams must be carefully calculated for the required load and treated with antiseptic and fire protective equipment.
Beams are inserted into the wall at least 120 mm deep and waterproofing is installed around the perimeter, except for the end. In addition, it is advisable to secure the beam with an anchor embedded in the wall.
The section of the beam and the pitch of laying the beams are calculated when designing a house, depending on the width of the span to be covered. If there is no such project, then the cross-section of the beam is chosen to be larger, and the step of laying the beams is smaller. The best cross-section for a wooden beam is rectangular with a width-to-height ratio of 1:1.4. So, with a beam width of 150 mm, its height should be about 210 mm. It should be noted that the optimal span for wooden beams is in the range of 2.5-4.0 meters. Floor beams are laid along a short section of the span. Installation step of wooden beams frame structure It is recommended to choose equal to the installation pitch of the frame racks.
When choosing the cross-section of a wooden beam, take into account the dead weight load of the floor, which for interfloor floor beams is usually 190-220 kg/m2, and the temporary (operational) load, the value of which is taken to be 200 kg/m2. Therefore, it is recommended to calculate the cross-section of wooden beams for a floor load of 400 kg/m2.
The cross-section of wooden floor beams under a load of 400 kg/m2 can be determined depending on the span length and installation pitch using Table 1.
Table 1. Optimal sections of wooden floor beams under a load of 400 kg/m 2.
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Installation step |
Span length, m |
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If, when installing an interfloor or attic floor heat and sound insulation are not planned, and also if this is a floor with an unused attic, then for lower load values it can be determined from Table 2 minimum dimensions sections of wooden floor beams.
Table 2. Minimum sections of wooden floor beams for loads from 150 to 350 kg/m 2.
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Section of beams with span length, m |
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In conclusion, it can be noted that the installation step of floor beams for a given structure is optimal, and the cross-section should be determined from the tables.
If the cross-section of the wooden floor beams is not sufficient and the floor does not move enough, additional supports should be installed under the floor beams. This can be in the form of a cross beam supported on walls or columns.
If installing additional support under the floor beams on the lower floor is not desirable, then you can install cross beam on top of the floor beams and fasten it to them, and if possible, then to the central purlin of the rafter system. This will redistribute the load between the beams.
There is another option for eliminating the deflection of beams - reducing the pitch of their installation.
Added: 05/25/2012 09:14
Discussion of the issue on the forum:
They re-roofed the 2nd floor at my dacha. We laid the logs (150*150mm timber, 500mm pitch), and nailed plywood on top = 10mm thick. In some places the ceiling moves up and down. Please tell me if I made the pitch of the beam correctly and how I can strengthen the structure?The main condition for any construction is simplicity and reliability of the design, but in order to achieve this, it is necessary to carry out correct calculations strength of the material. Since for construction wooden houses, attic or attic space used wooden frame its choice must be approached with all responsibility, because the durability, reliability and stability of the built house will directly depend on the load the timber can withstand (100x100, 50x50, 150x150, etc.).
To correctly calculate the load that a beam can withstand, you can use special programs or formulas, but in this case, additional loads that directly affect the strength of the structure will have to be included in the calculations. In order to correctly calculate the load on the beam, you will have to indicate the snow and wind influences present directly in the development region, as well as the characteristics of the materials used (thermal insulator, timber, etc.).
In this article we will look at what load a beam of size 50x50, 100x100, 150x150 in will withstand various designs, such as a log house, wooden floor and rafter system, and as an example we will analyze the latter, because this is the most important and complex work.
In the photo you can see varieties of timber, which differ not only in shape, but also in the load they can withstand.
What will we talk about:
How does the cross-section of a log house affect its reliability?
When creating a roof prerequisite Its reliability is determined by the cross-section of the timber used and the type of wood, which affects durability.
When performing the calculation yourself, you will need to take into account such indicators as:
- what mass do all roofing building materials have;
- weight of attic or attic finishing;
- For rafter supports and beams, the calculated value is taken into account;
- The thermal and sedimentary effects of nature are taken into account.
In addition, you will need to indicate:
- distance between beams;
- length of the gap between the rafter supports;
- the principle of fastening the rafters and the configuration of its truss;
- the severity of precipitation and the impact of winds on the structure;
- other factors that may affect the reliability of the design.
All these calculations can be performed with your own hands using special formulas. But it will be simpler, both in terms of time and quality, to calculate the beam load using special programs, and even better, when these calculations are performed by a professional.
What requirements must the timber meet?
In order for the entire rafter system to be strong and reliable, the quality of building materials will have to be approached with all responsibility. For example, the timber should be free of defects (cracks, knots, etc.), and its humidity should not exceed 20%. In addition, a log house of any size (50x50, 100x100, 150x150, etc.) must be treated with protective agents against shashel and other insects, rotting and fire.
Also, when choosing a material, you will have to take into account that additional loads may be placed on the beam, such as:
- Continuous beam loads. These include the very weight of the entire rafter system, which includes: facing and roofing materials, insulation, etc. The data obtained for each material is summarized.
- Short-term loads can be of several types: especially rare, short-term and long-term exposure. The first type includes incidents that happen very rarely (earthquakes, floods, etc.). Short-term loads are wind and snow impacts, movement of people repairing the roof, etc. Long-term loads are all other impacts occurring within a certain period of time.
We determine the wind and snow load on the timber
To determine what load the beam can withstand (100x100, 150x150, 50x50, etc.) under wind and snow influence, you can use certain tables.
To determine the impact of snow on the rafters different sections apply the formula S=Sg*µ.
- Sg is the estimated weight of snow lying on the ground that affects 1 m².
Important! This value cannot be compared to the roof load.
- µ is the value of the load on the roof surface, which varies from horizontal to inclined. This coefficient can take different meanings, it all depends on the slope of the roof.
When the surface slopes up to 25 degrees, µ takes the value 1.
When the roof slope is in the range of 25-60 degrees, µ is 0.7.
With a slope of 60 degrees or more, the coefficient µ is not taken into account as it has virtually no effect on the rafter system.
In addition to the snow load, before constructing a rafter system, the wind load on a wooden beam of 50 by 50, 100x100, etc. is calculated. If these indicators are not taken into account, as a result, everything can end in disaster. Table values and the formula W=Wo*k are used for calculation.
Wо – is a tabular value of wind load for each individual region.
k is the wind pressure, which has different values as the altitude changes. These indicators are also tabular.
Shown in the photo is a table of timber loads when exposed to the elements, easy to use, you just need to remember that the 1st column shows values for steppe, desert regions, rivers, lakes, forest-steppe, tundra, seashores and reservoirs. The next column contains data related to urban areas and areas with 10 meter obstacles.
Important! In calculations, it is advisable to use information on the direction of wind movement, because this can make an important amendment to the results.
What are the rules for calculating the required cross-section of timber?
The selection of the log section for the rafter system is influenced by several parameters:
- what is the length of the rafter construction;
- the distance between each subsequent beam;
- the obtained results of load calculations for the corresponding area.
Today, for each specific area, there are special tables with already entered data on load values for rafter systems. As an example, we can cite the Moscow region:
- to install the Mauerlat, you can use timber with a cross section of at least 100x100, 150x100 and 150x150;
- timber 200x100 can be used for diagonal valleys and rafter supports (legs);\
- purlins can be created from wood 100x100, 150x100 or 200x100;
- log house 150x50 will become optimal solution for tightening;
- It is best to use a log frame 150x150 or 100x100 as racks;
- rafter 150x50 is suitable for a cornice, struts or filly;
- It is best to install crossbars from rafters 150x100 or 200x100;
- A board of at least 22x100 can be used as cladding or fronting.
The above data are optimal, that is, less than this value the material cannot be used. Also, all dimensions are indicated in millimeters.
Summarize
To create a reliable and durable wooden structure, you need to carefully calculate all possible loads, and then just purchase timber. If you have doubts about the correctness of the calculations, it is best to use the services of a professional or use a special program that will calculate the permissible load on the beam (150x150, 100x100, etc.).
Date of publication: 03/03/2018 00:00
What loads will the beam withstand?
Timber and logs have long been used in Rus' to build houses. Wooden buildings have a number of advantages:
- Ease of building construction.
- High speed of construction;
- Low cost.
- Unique microclimate. Wooden house“breathes”, the air in it is much lighter and more pleasant;
- Excellent performance characteristics;
- A wooden house holds heat well. It's warmer brick buildings 6 times, and buildings made of foam concrete 1.5 times;
- Various types and sizes of this lumber allow you to realize a wide variety of projects and design ideas.
This kind building material is a log rectangular section. It is considered the cheapest lumber and at the same time very convenient for construction.
The timber is made from saw logs and coniferous trees.
- Double-edged - only two opposite sides are processed (cut off the log), while the other two are left rounded.
- Three-edged. Three sides are cut off here.
- Four-edged - 4 sides cut off.
Dimensions:
The standard length of the timber is 6 meters. Glued laminated timber is a prefabricated structure, so the length here can reach 18 meters.
Section dimensions
- Thickness from 100 to 250 mm. The section step size is 25 mm, that is, the thickness is 100, 125.
- Width from 100 mm to 275 mm.
The choice of beam cross-section must be approached with special care. After all, the safety of the building will depend on the load this building material can withstand.
To correctly calculate the load, there are special formulas and programs.
1. Permanent. These are the loads on the timber that are exerted by the entire building structure, the weight of the insulation, finishing materials and roofs.
2. Temporary. These loads can be short-term, infrequent or long-term. This includes ground movements and erosion, wind, snow loads, the weight of people when construction work. Snow loads are different, they depend on the region where the structure is being erected. In the north snow cover more, so the load on the beam will be higher.
In order for the calculation of the load to be correct, both types of loads, the characteristics of the building material, its quality, and humidity must be entered into the formula (it can be found on the Internet). Particular care must be taken to calculate the load on the timber when erecting rafters.
What load can a 150x150 beam withstand? Beam with a section of 15 by 15 cm is widely used in the construction of buildings. It is used for the manufacture of supports, formwork and for the construction of walls, as it can withstand heavy loads. But the size 15 by 15 is better used for building houses in the southern regions; in the north you will need additional insulation walls, since this lumber stores heat only at an air temperature of -15 degrees. But if you use glued laminated timber of this size, then in terms of its heat-saving properties it will be equal to a timber with a cross-section of 25 by 20 cm.
What load can a 100 by 100 mm beam withstand?
This beam is no longer so reliable, it can withstand less load, so its main application - manufacturing rafters and ceilings between floors. It is also necessary when constructing stairs, making supports, arches, decorating attics, and the ceiling of a house. You can also make the frame of a panel one-story house from it.
What load can a 50 by 50 mm beam withstand?
50x50 mm timber is in great demand. You can’t do without this size, as it is auxiliary material. It, of course, is not suitable for erecting walls, since it can withstand a small load, but for erecting sheathing for exterior finishing walls, frames, partitions, this size is required. A wall frame is made from 50 by 50 timber, onto which drywall is then attached. Here you can use a wide variety of fastenings from nails to staples or wire.
Beams in a house usually belong to rafter system or ceiling, and in order to obtain a reliable structure, the operation of which can be carried out without any fear, it is necessary to use beam calculator.
What is the beam calculator based on?
When the walls have already been brought under the second floor or under the roof, it is necessary to make, in the second case smoothly turning into rafter legs. In this case, the materials must be selected so that the load on the brick or log walls does not exceed the permissible value, and the strength of the structure is at the proper level. Therefore, if you are going to use wood, you need to choose the right beams from it, make calculations to find out required thickness and of sufficient length.
The subsidence or partial destruction of the ceiling can be caused by various reasons, for example, too large a step between the lags, deflection of the cross members, too small area their cross sections or defects in the structure. To eliminate possible excesses, you should find out the expected load on the floor, be it basement or interfloor, and then use a beam calculator, taking into account their own weight. The latter can change in concrete lintels, the weight of which depends on the density of the reinforcement; for wood and metal, with a certain geometry, the weight is constant. The exception is damp wood, which is not used in construction work without first drying it.
On beam systems in floors and rafter structures load is exerted by forces acting on section bending, torsion, and deflection along the length. For rafters, it is also necessary to provide for snow and wind loads, which also create certain forces applied to the beams. You also need to accurately determine the required step between the jumpers, since too many crossbars will lead to excess weight of the floor (or roof), and too little, as mentioned above, will weaken the structure.
You may also be interested in the article about calculating the amount of unedged and edged boards cubed:
How to calculate the load on a floor beam
The distance between the walls is called a span, and there are two of them in the room, and one span will necessarily be smaller than the other if the shape of the room is not square. Interfloor or attic floor lintels should be laid along a shorter span, the optimal length of which is from 3 to 4 meters. Larger spacing may require non-standard sized beams, which will result in some unsteadiness of the deck. The best solution in this case would be to use metal crossbars.
Regarding the section wooden beam, there is a certain standard that requires that the sides of the beam be in a ratio of 7:5, that is, the height is divided into 7 parts, and 5 of them must make up the width of the profile. In this case, deformation of the section is excluded, but if you deviate from the above indicators, then if the width exceeds the height, you will get a deflection, or, if the opposite discrepancy occurs, a bend to the side. To prevent this from happening due to the excessive length of the beam, you need to know how to calculate the load on the beam. In particular, the permissible deflection is calculated from the ratio to the length of the lintel as 1:200, that is, it should be 2 centimeters per 4 meters.
To prevent the beam from sagging under the weight of logs and flooring, as well as interior items, you can grind it from below a few centimeters, giving it the shape of an arch; in this case, its height should have an appropriate margin.
Now let's turn to the formulas. The same deflection mentioned earlier is calculated as follows: f nor = L/200, where L– span length, and 200 – permissible distance in centimeters for each unit of timber subsidence. For reinforced concrete beam, distributed load q which is usually equated to 400 kg/m 2, the calculation of the limiting bending moment is performed using the formula M max = (q · L 2)/8. In this case, the amount of reinforcement and its weight is determined according to the following table:
Cross-sectional areas and mass of reinforcing bars
Diameter, mm | Square cross section, cm 2, with the number of rods | Weight 1 linear meter, kg | Diameter, mm |
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Wire and rod reinforcement |
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Seven-wire ropes class K-7 |
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The load on any beam made of a sufficiently homogeneous material is calculated using a number of formulas. To begin with, the moment of resistance W ≥ M/R is calculated. Here M is the maximum bending moment of the applied load, and R – design resistance, which is taken from reference books depending on the material used. Since most often beams have rectangular shape, the moment of resistance can be calculated differently: W z = b h 2 /6, where b is the width of the beam, and h– height.
What else should you know about beam loads?
The ceiling, as a rule, is at the same time the floor of the next floor and the ceiling of the previous one. This means that it needs to be made in such a way that there is no risk of combining the upper and lower rooms by simply overloading the furniture. This probability especially arises when the step between the beams is too large and logs are abandoned (plank floors are laid directly on the timber laid in the spans). In this case, the distance between the crossbars directly depends on the thickness of the boards, for example, if it is 28 millimeters, then the length of the board should not be more than 50 centimeters. If there are lags, the minimum gap between the beams can reach 1 meter.
It is also necessary to take into account the mass used for the floor. For example, if mats are laid from mineral wool, That square meter the basement floor will weigh from 90 to 120 kilograms, depending on the thickness of the thermal insulation. Sawdust concrete will double the mass of the same area. The use of expanded clay will make the flooring even heavier, since the load per square meter will be 3 times greater than when laying mineral wool. Further, we should not forget about the payload, which for interfloor floors is at least 150 kilograms per square meter. In the attic it is enough to take permissible load 75 kilograms per square.
