Beam- is a structural element that is horizontal or inclined timber, working mainly on bend. In practice, as a rule, a horizontally located beam perceives a vertical transverse weight load, but in some cases it is necessary to take into account the influence of possible horizontal transverse forces (for example, wind load or taking into account possible earthquakes). The loaded beam, in turn, acts on supports, which can be columns, pendants, walls or other beams (beams). Then the load is transmitted further and, as a result, in most cases, is perceived by structural elements working on compression - supports. A special case can be highlighted truss structure, in which the rods rest on a horizontal beam. The strength qualities of the beam depend on several of its characteristics:
area and shape of its cross section;
beam length;
beam material;
way to secure it.
In modern buildings, as a rule, they are used steel, reinforced concrete or wooden beams. One of the most common types of steel beam cross section is I-beam section. I-beams are used in the construction of building frames and bridges. Also used T-beams, channels, beams with a hollow profile (in particular, pipes), beams with an angular section profile. The beam can be:
26. Determination of design forces in beams using the influence line method. The essence of the method.
Using the influence lines, you can determine the force in a given section from any moving and constant loads.
Stationary load
The force in this section is determined by the lines of influence from the constant load in accordance with Fig. 2.5 according to the formula:
Where J– force in a given section; F i – concentrated load; Y i– ordinate of the line of influence under the load; q i– intensity of distributed load; – square LW the required force within the load limit; M i– concentrated moment; – tangent of the angle of inclination LW at the point of application of the moment.
Rice. 2.5. Definition of effort LW from constant load
Rule of signs
The positive direction of the external load is taken to be:
direction F and q from top to bottom;
direction M clockwise;
Signs ,, taken from the lines of influence with their sign.
Moving load
If in a given section of the structure the greatest force value arises from the movable load system J, then the load position is unfavorable. When the load is in an unfavorable position, one of the loads is necessarily located above the top of the line of influence and is called critical.
Determining the forces along the lines of influence in the case of a moving system of concentrated loads involves finding the critical load and is done in the following order:
one of the weights is installed above one of the vertices of the line of influence, while the largest weight should be installed above the largest ordinates of the line of influence;
The critical load is determined by the trial method, checking whether the criterion for the dangerous load position is satisfied.
Beam types
A beam is a solid element that works primarily on transverse bending and takes up the load located in the span, transferring it to the supports.
Most widespread in steel structures have split beams due to the certainty of their operation, as well as ease of manufacture and installation.
As is known, the cross-sectional shape of a beam most suitable for bending is an I-beam. The possibility of using a channel profile is not excluded, if this is structurally convenient.
Beams can be rolled or composite. If possible, one should strive to use rolled beams as they are less labor-intensive. However, due to the limited range of rolled beams, powerful beams that absorb large moments have to be designed as composite welded or riveted ones.
Welded beams are made up of three sheets: one vertical, called the wall, and two horizontal, called, which are welded to the wall.
Riveted I-beams are made up of a vertical sheet - the wall - and waist corners, which are riveted to the wall. If it is necessary to use powerful riveted beams, then to increase the moment of resistance, horizontal sheets are riveted to the flanges of the corners.
Welded beams are more economical than riveted ones. Therefore, the latter have limited use, mainly in heavy structures, as well as in structures subject to high dynamic or vibration loads.
"Design of steel structures",
K.K. Mukhanov
Flat flooring metal sheet positioned and welded to the beam flanges. The thickness of the flooring is determined by calculation, most often depending on the accepted permissible deflection, since full use of the stresses in the sheet at a given deflection is not always possible. Therefore, the calculation of sheet flooring is carried out according to standard loads. The peculiarity of sheet flooring is that by its nature…
The general dimensions of the beam are its design span and section height. The design span of the beam l is the distance between the centers of the supporting parts; thus, the actual length of the beam lд is always slightly greater than the design span. The distance l0 is called the clear distance; it is usually determined by the operating conditions of the weapon and is justified by economic considerations. General dimensions of beams The section height h is assigned, ...
When designing beam structures As a rule, depending on the purpose of the beams, it is necessary to draw up a diagram of their location, outline the general dimensions and determine the load on the beams. If it is necessary to cover a certain area, the beams supporting the floor are usually placed in two directions. Such a structure, sometimes consisting of an entire system of intersecting beams, is called a beam cage. On a beam cage maybe...
Construction beams various types- these are logs, crossbars, purlins, crossbars, floor beams, roof battens, rafter legs. They carry the structure wooden flooring interfloor ceilings. Wooden ones are used on one- and two-story buildings, and reinforced concrete and metal ones are used on high-rise buildings. The basis of any roof is a beam frame that supports the weight of the entire roof.
Mauerlat
Mauerlat (carpenters call it matitsa) is the most thick timber, which lies parallel to the roof ridge along the axis of the wall. It is needed to distribute the loads from the rafters and the weight of the entire roof along the entire wall of the building, as well as on the internal supports. Do not lay or fasten closer than 5 cm from the outer plane of the wall. The mat is attached using thick wire, embedded into the wall masonry using studs, and if the wall is concrete, it is attached to the concrete with studs. If the house is one-story wooden, you can fasten it with ordinary nails.
Rafter-inclined beam
In most cases it is wooden beam section 7x15 cm. If the roof area is small, you can use 5x15 cm timber, and if the roof is covered clay tiles, then the beam is 8x20 cm. The rafters are located at a distance of 60 cm to 1 m from each other. Where there is a lot of snow, reduce the distance to 60 cm. If the roof slope is more than 45 degrees, you can increase the “step” to 1.2-1.4 meters. And further. When the roof is planned to be insulated, it is calculated in such a way as to eliminate cutting of insulation in order to save money.
Run
An additional support beam for supporting the rafters is located parallel to the matrix and the ridge. According to construction technology optimal distance between the purlin and the matrix (ridge and purlin) - 4-5 meters. If the rafters are extended to 6 meters, then the joint (bow) should be located above the purlin so that both ends of the rafters rest on it. Sometimes it happens that the rafters are composite (6+3) meters, and the width of the run is 4-5 meters. Then the joint is positioned in relation to the purlin in a checkerboard pattern.
The run itself is done like this. Exhibited support posts and the purlin is laid on them, and the rafter will rest on it. The purlin can also be supported on a wall longitudinal to it. Then horizontal expansion beams are laid between the upper purlins. Their purpose is to prevent the roof from folding inward. They are laid so as not to burst the purlin.
I-beams and rafters
The so-called I-beams have an even greater advantage. wooden beams and rafters. Their high specific strength allows them to be used in long spans. They are very straight, so there is no bending moment. Having precise dimensions, they are universal - suitable for the construction of roofs, ceilings and floors. Silent – eliminates creaking floors.
Stable - not subject to deformation. Profitable - save from 40 to 60 percent of materials and labor costs. Eco-friendly - they pollute the environment little. Convenient - can be processed and laid using ordinary carpentry tools. The I-beam is ideal for any roof frame, allowing you to increase the distance between purlins as it can withstand heavy loads.
Bent-laminated wooden beams
Bent-laminated wooden beams have also become very popular recently. They are used if it is necessary to increase the distances between runs. Lightness, reliability and strength are their main advantages. They are resistant to external environment, not subject to biological influence, easy to process. Among the disadvantages, it is worth noting the high cost and the lack of observations of the duration of their service, due to the fact that the material is quite new. It is also necessary to pay very close attention to the quality of such products, since failure to comply with the technology leads to drying out and deformation of the products.
Reinforced concrete beams
Reinforced concrete beams are now widely used in the construction frame structures, in particular, buildings with a height of more than one floor. Structurally, they ensure the ability of the entire structure to withstand large values of bending moments. Beam floors are arranged on spans more than 3 m wide and laid on walls at a distance of at least 130-150 cm from each other. Then they are connected to the reinforcement of the slab floor. The thickness of the support is at least 22 cm. They are widely used in the construction of retail, entertainment and industrial facilities.
Metal beams
Metal beams are the most durable and are mainly used in construction high-rise buildings. They serve as the main load-bearing structures and, due to their rigidity, transfer the load to places of support: columns, walls, partitions. Placed on top of metal beams Various types coatings After installing such a beam in the design position, it is secured in load-bearing structures, arrange formwork and install reinforcement. All tensile loads after pouring concrete are absorbed by this reinforcement.
Beam - is a long element, the length of which is significantly greater than the characteristic size for the cross section. Included building structures the beam works mainly in bending, so it is recommended to make it with thin-walled cross section. The most popular are I-beams, which are an H-shaped profile formed by two parallel flanges and a wall connecting them.
Fig. 1 - I-beams on the rolling mill cooler
Floor beams made of various materials. The most popular option is a welded or rolled I-beam. Calculation of metal floor beams is carried out based on the number of supports, the pattern of support on the walls and attachment to the base, operating conditions and other factors. Based on the calculation, the most economically acceptable beam option is selected.
If necessary, reinforcement of metal floor beams is carried out. Such measures are required if during operation this element is subjected to horizontal loads, which can lead to a decrease in its characteristics and destruction. To avoid this phenomenon, metal beams are reinforced in one of the following ways:
- the use of overlays to increase the cross-section (Fig. 2a, 2b);
- concrete coating (Figure 2c);
- use of a sprengel (Fig. 2d);
- the use of spacer or tension devices to adjust stress (Fig. 2e, 2f);
- use of additional supports (Fig. 2g, 2h).
Rice. 2 - Methods for strengthening beams
Depending on the manufacturing method, the following types of metal floor beams are distinguished:
- hot-rolled I-beams are the cheapest and simplest option, which involves the use of commercially produced rolled products;
- welded, bolted, riveted beams are manufactured by specialized enterprises and allow solving non-standard construction problems.
Hot rolled I-beams metal floor beams
The main volume of I-beams used in construction is manufactured hot rolling from continuously cast billets. Depending on the production technology and geometric characteristics of the product, several groups of beams are distinguished.
I-beams with sloped flange edges according to GOST 8239
This type of product is distinguished by the presence of a slope of the internal edges of the shelves relative to the external ones within the range of 6-12°. Such products have the following characteristics:
- produced profiles - from beam 10 to beam 60 (the number indicates the height in centimeters);
- profile width – from 55 to 190 mm;
- wall thickness – from 4.5 to 12 mm;
- shelf thickness – from 7.2 to 17.8 mm.
Reinforced I-beams with flange slopes in accordance with GOST 19425, which were originally developed for the manufacture of suspended tracks and reinforcement of mine shafts, can be used as floor beams.
Fig. 3 - Beam with sloped flanges
I-beams with parallel edges according to GOST 26020
Recently, in construction, preference has been given to more economical I-beams with parallel flange edges. In addition to the specified standard, such products are also manufactured according to STO ASChM 20-93 (they have minor differences in geometry).
Characteristics of normal I-beams:
- produced profiles - from beam 10B1 to beam 100B4 (the number indicates the height in centimeters, the letter “B” is a normal profile, the last digit is the standard size number in a group with the same height);
- profile width – from 55 to 320 mm;
- wall thickness – from 4.1 to 19.5 mm;
- shelf thickness – from 5.7 to 32.5 mm.
- produced profiles - from beam 20Ш1 to beam 70Ш5 (Ш - wide-flange type);
- profile width – from 150 to 320 mm;
- wall thickness – from 6.0 to 23.0 mm;
- shelf thickness – from 9.0 to 36.5 mm.
- Produced profiles - from beam 20K1 to beam 40K5 (K - column type);
- profile width – from 200 to 400 mm;
- wall thickness – from 6.5 to 23.0 mm;
- shelf thickness – from 10.0 to 35.5 mm.
Fig. 4 - Beam with parallel flanges
Welded, bolted and riveted floor beams
This option is used when the dimensions of the metal floor beams differ from the standard ones or the rolled I-beams do not satisfy the design conditions for overall stability, rigidity or strength. In addition, preference is given to “prefabricated” beams if they are more economical or have a better level of performance characteristics.
The most commonly used is a welded beam, which is made by automatic submerged arc welding. On preliminary stage cutting, cleaning and straightening of metal, cutting edges for welding are carried out, and then, directly, the process of connecting the elements into a single whole. After welding, the finished product is straightened to eliminate thermal deformations (mushroom shape).
In this way, it is possible to obtain not only standard sizes, but also products of variable cross-section, reinforced or bistal I-beams.
I-beam (I-beam) is a type of rolled metal product characterized by high load-bearing capacity. It has a recognizable H-shaped cross-section, which determines specifications products. One of the most popular materials in various industrial fields.
You can always check on our website the current prices for a new I-beam and.
Purpose and scope of application
I-beams are used as load-bearing elements in the construction of metal structures and in large-panel construction. The use of this type of rental makes it possible to simplify design solutions without loss of bearing capacity of structures. Most often, I-beams are used to solve the following technical problems:
It is permissible to use beams of this type in the construction of any structures that have increased load-bearing capacity requirements. It is recommended to place an I-beam in the body concrete structure, during open installation, mandatory anti-corrosion treatment is required.
Product benefits
The specific cross-sectional shape ensures excellent bearing capacity this structural element. Compared to standard rectangular profiles, the I-beam has 7 times increased strength and more than 30 times increased rigidity. According to their own design features the I-beam is close to the channel, but the latter is mainly used in the construction of lighter structures; it will not be able to work effectively under significant loads.
The widespread use of I-beams is determined by the following advantages.
- High resistance to bending and torsion.
- Increased load-bearing capacity.
- Reduced weight compared to other types of rolled metal with similar technical characteristics.
Production Features
In practice, two main methods for manufacturing I-beams are used.
- Hot rolling technology, which allows for the production of products on an industrial scale.
- Production of I-beams using welding technological lines. Welded beams have a more precise geometry, but are inferior to hot-rolled beams in some technical parameters.
Production of this type of carrier structural elements is carried out using high-carbon low-alloy steels, which predetermines mandatory anti-corrosion treatment for open installation.
In accordance with GOST 27772-88, which regulates the production of hot-rolled shaped steel, the following grades of steel should be used for the manufacture of I-beams: C 235, 245, 255, 275, 285, 345, 345K, 375.
Existing classes and corresponding GOSTs
All types of I-beams produced by rolling can be divided into three main classes, the requirements for which are determined by the current standards.
Welded products are produced on the basis technical specifications manufacturer TU U 01412851.001-95. Individual manufacturers use their own specifications to produce one or another type of I-beam.
According to the characteristics of the section, the following product categories are distinguished:
- Beams with normal flange width (B).
- I-beams with increased flange width (W).
- Column I-beams (K).
- Monorail I-beams (M).
- Beams of a special series for especially difficult conditions(WITH).
Manufacturers ship batches with multiple, multiple measured, unmeasured lengths of I-beams. Standard sizes involve the production of products with a length of 4 to 13 meters; the production of beams beyond the specified parameters can be organized by agreement directly with the manufacturer.
Features of demand calculation
When determining the amount needed for various designs material, choosing a transportation method, you need to know the ratio of the sizes and weight of I-beams. The need to convert one value into another also arises when developing design documentation.
Decide this problem possible using online calculators, and in case of their absence, it is recommended to use special tables given in regulatory documents.
So for hot-rolled steel I-beams the ratio is given in the following table.
And to determine the total surface area of I-beams of the same GOST, we recommend using the following table.
Such reference data will significantly simplify the calculation and development of project documentation.
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