Beams подстепильные: kinds, cross-section, installation. Podstropilnaya farm

The basis for the construction of roofs are rafter and trimming elements. Bearing system of roofing - this rafter beams and trusses. The beams are used as support for rafter elements. They are used in the construction of coatings in single-storey multi-span industrial buildings, in apartment houses with the construction of attic floors.

Types of underlay beams and trusses

The reliability of the entire roofing system depends entirely on the strength and solidity of the load-bearing roof and underlay structure. It has a large number of various external loads.

Podstropilnye beams are products from one single element, which takes an external load, distributing it along its entire length. In this case, the greatest stresses occur at the ends of the beam. It is used in beam roof rafter systems.

Podstropilnaya farm - a complex composite structure, which is assembled from individual rods, rigidly connected to each other. Loads occur only in the nodal joints of the rods. Such structures are used in roofing systems with rafter trusses.

Depending on the material of the production, the underlay structures can be divided into:

• Reinforced concrete.
• Steel.
• Wooden.
• Reinforced wooden systems.

Reinforced concrete and steel beams and trusses are most often used in the construction of industrial buildings and structures. Wooden elements reinforced with reinforcement made of wood are actively used for the device not only production roofs, but also for the construction of roofs in residential buildings.

In industrial construction, the 12-meter, 18-meter, 24-meter and 30-meter spans between the columns overlap with the under-roof structures. With a six-meter pitch of rafter structures, the trunnion beam elements and trusses serve as intermediate support elements for them.

By type of cross-section the beams are divided into:

• Rectangular.
• Tavrovye.
• I-beam.
• Box beams.

In individual housing construction, the structures designed to support the truss system are not often used. They are mainly used in the construction of attic rooms.

Reinforced concrete beams

Reinforced concrete products are used for the construction of roofing with a slight slope, as well as pitched roofs. They are produced in the factories of reinforced concrete, where the preliminary tension of beams with steel reinforcement is immediately applied. Kinds of used reinforcement:

• Rods with a periodic profile are strengthened.
• Wire bundles made of extra strong wire.
• Twisted wire strands.
• String armature.

According to the form, the beams are subdivided with parallel and non-parallel belts. Their calculation is made on the basis of the load exerted by the rafter beam, supported pointwise on the middle of the sub-spiral element, and the load from the weight of the beam itself, distributed along its length. The products are manufactured with stitching holes designed for mounting and lifting, sometimes mounting laces are used instead.

They are installed in the middle rows of structures to support rafters and trusses, if the width of their step is 6 meters, and the width of the installation of medium columns is 12 meters. The installation of the underlay beams is performed on the columns, they are fixed by the method of welding the embedded parts. In the middle of the beams of the sub-spiers and at their ends special support areas with embedded sheets and anchor bolts for the installation of rafter structures are made.

They have a T-shaped or I-shaped cross-section with a lower shelf and a trapezium shape. The lower shelf is reinforced in the places where the rafters are supposed to be installed.

By the length of the beams, the sub-spiers are generally 12-meter, sometimes 18-meter or 24-meter items are used. The height in the center is 1.5 meters, in the support points - 0.6 meters. The width of the lower shelf is 0.7 meters. Must have certain I- beam dimensions. GOST 19425-74.

Chain Reinforced Concrete Farm

Reinforced concrete trusses are used in the construction of pitched roofs. They have the form of a trapezoid, in which two belts: the lower one - of the horizontal type and the upper one - of the broken structure. At the moment, the most relevant are the bezracacious farms from prefabricated reinforced concrete.

For the reliability of fastening trusses trusses support areas of the chisel elements are strengthened. For the installation of slabs, supports are provided at the supports. The posts and the lower belt of the truss are pre-tensioned. For production, concrete grades 300-500 are used.

As in the beam version, embedded metal elements are provided in the sub-trusses for fastening to the columns and the support.

Steel underlay beams

Steel systems have a length of 12 meters, 18 meters, 24 meters, can be produced in length of 48 meters. They are structurally similar to the rafters used. Consist of two belts: upper and lower. The upper one rests on the mounting table on the column and is bolted to it. The lower belt of the beam is attached to the column by means of horizontal bars.

Trussed steel truss

Are made with parallel upper and lower belts. The length is unified and is 12 meters, 18 meters, 24 meters. Depending on the type of truss, the height of the trimming structure can be 3.13 meters, 3.27 meters or 3.75 meters.

Fastening to the columns is carried out with the help of suppressing racks on which the trusses are supported.

At present, light steel versions of manufacturing trusses have been used in industrial construction. For example, tubular systems or beams with thin walls. Thanks to this design, the trusses are made lighter, the consumption of steel for their manufacture is reduced, and the period of their installation is shortened.

Wooden Sub-Sling Systems

Designs made of wood, designed to support the truss system, have enough strength and resistance to many aggressive influences. They are durable when used in buildings with normal modes of temperature and humidity. In industrial construction they are used in buildings where there are unfavorable for reinforced concrete and metal environments.

According to the constructive form, the following elements are distinguished:

• Beams.
• Farms.
• Arches.
• Ram.

If the length of spans in the building is up to 18 meters, then a wooden girder is used. In buildings where the spans are large enough - up to 30 meters, it is more expedient to use wooden sub-trusses. Arches and frames made of wood are not often used as trimmings.

Wooden underlay beam

In industrial construction, most often used beams, glued from boards. Such structures are much stronger and durable than whole products, it is possible to produce various forms of under-beams. Products made of structural glued beams are widely used in the installation of roofing systems. Solid round logs can withstand more severe loads, but they are much inferior to the glued beam by the flexural strength.

The junction of the wooden under-beam can be seen in the photo below.

The cross-section of the beam is rectangular or I-beam. The upper and lower belts of the sub-spine can be parallel, or the gable upper belt and the horizontal or broken lower belt. When the span is up to 15 meters, I-beams with walls made of boards or plywood and bar stiffeners are often used .

Wooden truss truss

The main materials for making wooden trusses are wooden blocks, boards or logs. Fastening of elements is possible by means of metal hardware, plates. Glued wooden trusses were widely used. Their belts are made solid in width. With this method of manufacturing, threaded spikes and similar grooves are formed at the ends of the connecting elements. The glue is applied to the entire joint surface, then the design details are pressed.

Reinforced wooden under-truss beam elements and trusses

Wooden trimming elements are reinforced in order to strengthen them. The steel or fiberglass is used as an armature. Mounted reinforcing element inside the wooden with epoxy glue. Sometimes the pre-stress of the reinforcement is used.

Installation

The installation of the underlay beams and trusses is carried out as follows. Reinforced concrete underlay elements and trusses are welded directly to the column headers by means of embedded metal parts. Perhaps fixing them to the bolts. Reinforced concrete consoles or metal tables on the trimmings serve as support platforms for load-bearing truss structures.

Steel trusses are attached to the columns on the side to the metal columnar by the lower belt. Its height is 0.7 m. Each other's farms are fastened with upper belts. Rafting farms rely on the tables of the trunks and on the patella attached to the columns.

Wooden trims in the device roofs look like this (see photo).

Installation of beams for a gable roof

When there are two load-bearing inner walls in the building, the truss system is mounted on the sub-string elements. In this case, they lean on a log, by means of pillars from the beams, as well as internal walls. Typically, these are two sub-sill beams arranged along the roof. This option is used at a height from the ceiling to the roof ridge from 1.4 meters to 2.5 meters. In this case, a sufficiently free space is formed under the roof, which can be used as an attic.

The underlay beam, or the tightening, can be installed directly on the rafters at a distance of one-third the height from the overlap to the ridge. This option allows you to increase the amount of internal space under the roof. The roofing, under-roofing systems and the roof play the role of external walls and coverings.

The rafters and the trunks can be seen in the photo in the article.

First of all, on the Mauerlat the extreme underlay beams are laid on both walls of the house. At the variant of the wooden house instead of the Mauerlat, the upper crown of the log is used. Beams must be strictly parallel to each other, you can check this by measuring the distance between their ends diagonally. The beams lie with a ledge not less than 0.5 meters behind the edges of the perimeter of the house. If the length of the boards is less than what is required for the beam, then the matching of the underlay beams is performed.

Then you need to pull the ropes between the laid beams on both edges, and adjust them to the level. At a distance of one meter from the extreme, the next sub-bolster is installed. The board on the opposite side also lies down. It is necessary to check their horizontality. Thus, the rest of the joists Along the entire length of the wall.

To align the ledges of the boards beyond the walls, measures 0.5 meters on each extreme beam, stretches the rope. On the middle beams marks are made on the rope, the excess ends are cut off. Further on, the underlay system is supported by load-bearing rafters.

GOSTs for underlay structures

The manufacture of reinforced concrete underlay structures is covered by GOST 20372-2015, which was put into effect on January 1, 2017. According to this document, heavy or lightweight structural concrete is used for production. Steel sub-trusses are manufactured in accordance with GOST 27579-88. Has a certain and glued I- beam dimensions. GOST 19425-74.