Reinforced concrete bridges: dimensions, GOST, marking. Reinforced concrete products

Reinforced concrete found widespread use in modern construction. The material is characterized by high strength, resistance to external influences, durability. When building buildings from piece materials (brick, cinder block, aerated concrete blocks), it becomes necessary to block the door and window openings. For these purposes, a special type of reinforced concrete products is used - jumper.

Appointment

The lintels are reinforced concrete beams resting on the masonry of the walls and transferring to them the load of masonry and overlapping above the opening. Constructively, the jumper consists of reinforcing cage and heavy concrete. In practice, prefabricated reinforced concrete products of factory production or monolithic, manufactured on site are used. In this case, the marks of the used products and the area of their support should be determined by calculation taking into account the collected loads.

Standards

The main parameters of prefabricated products are determined by GOST "Reinforced concrete jumpers for buildings with brick walls". This standard defines the classification, brands, sizes and characteristics. Jumpers are divided into:

• PB - bar, having a width of up to 250 mm.
• PP - plate, with a width of the base from 250 mm.
• PG - girder, a quarter cut in section.
• PF - facade, for apertures with a quarter with a layer of the exposed part of the masonry from 250 mm.

A set of standard working documents - 1.038.1-1, including working drawings was developed for the production of standard products.

Design

The reinforcement frame of the jumper provides its strength. It consists of longitudinal and transverse reinforcement. Norms provide for the use of both prestressed and non-straining fittings. The diameter and pitch of the rods is determined by calculation or by standard designs.

When pouring bridges use heavy concrete with a density of 2200-2500 kg / m3. The required strength of concrete is determined by calculation, the brand for water permeability and frost resistance - taking into account the environment.

For lifting in the construction, stitching holes were made or sang, as required by the GOST. Reinforced ferro-concrete jumpers are allowed to be manufactured with valve outputs for construction in seismic zones.

The range of commercially available jumpers is reflected in the table of GOST 948-84. The standard provides bridged bridge PCBs from 1030 to 5950 mm in length with a straining or non-tensioning armature. Their section is divided into 10 groups - from 125 x 65 (h) mm to 250 x 290 (h) mm.

Plate jumpers PP are available in lengths from 1160 to 2980 mm with tension or non-tensioning reinforcement. Their cross section is represented by 10 groups - from 380 x 65 (h) mm to 510 x 220 (h) mm.

Beams with a quarter of the type of PG are provided only with non-tensioning reinforcement length from 1550 to 5960 mm. There are 8 variants of section - from 250 х 290 (h) mm to 510 х 440 (h) mm.

The facade bridges of the PF are made from 770 mm to 4280 mm in length with a cross section of eight groups - from 90 x 90 (h) mm to 290 x 90 (h) mm.

Designation

Stamps of serial products consist of two or three groups and fully characterize the reinforced concrete bridges: dimensions, bearing capacity, cross-section and so on.
The first group begins with the figure that determines the section (according to the table), the letter name and length, expressed in tens of centimeters. For example, 8PB25 - bridging bridge, section number 8 from the table of GOST 948-84, length - 2460 mm.

The second group shows the average permissible load (kN / m), the class of reinforcement.
For example, 71-AtV: load 70.61 kN / m and AT-V fittings.

The third group of markings contains information about the availability of valve releases, embedded parts, stitching loops, as well as various characteristics that depend on external conditions.

The additional markings use symbols:

• "А" - anchor fittings for the installation of balcony slabs;
• "N" - stitching loops;
• "C" - for seismically dangerous areas over 7 points;
• "P" is concrete of increased density, or "O" is a high-density concrete.

Full marking of reinforced concrete jumpers can look like this:
10PB21-27-up - a bar with a cross-section of 2070 mm, section number 10, an allowable load of 27.26 kN / m, with stitching loops and anchor fittings for the installation of balcony slabs.

Warming

The external walls of the house must provide the level of thermal protection stipulated by the standards. This level is characterized by the value of the heat transfer resistance. The larger it is, the higher the thermal protection of the building and, correspondingly, the lower the heat consumption and the heating fees. Unfortunately, reinforced concrete is an excellent conductor of heat. The bridges form heat-conducting inclusions on the surface of the walls - cold bridges. They lead not only to additional heat losses, but also in a number of cases to the loss of dew. To avoid this negative effect, it is necessary to insulate the jumpers. If the building has additional insulation by the system of a ventilated facade or by "wet technology" - there are no questions. But if the outer walls do not require additional insulation, then the jumpers are set with an indent from the outer surface of the wall. In this indentation install a liner from an effective insulation (for example, stone wool) and cover with plaster or other finishing material under the plane of the wall.

Selecting the jumper mark

For the correct choice of the jumper mark, in addition to the assignment, it is necessary to determine the bearing capacity. The permissible load of the product of each brand is indicated in the State Standard "Ferro-concrete jumpers". After collecting the loads and determining the length of the span, you can use the tables of the series 1.038.1-1, where each brand is compared: the calculated span, the length of support and load. Choosing reinforced concrete bridges, sizes and cross-sections, it is necessary to take into account the seismic hazard of the construction area.

Calculation of a jumper

The bridge is the load-bearing structure of the building, and its calculation should be handled by a specialist with appropriate education and work experience. Nevertheless, for small projects it is possible to choose ferro-concrete jumpers on their own. The dimensions of the products are determined by the SNiP "Stone Constructions". It is necessary to calculate the height of the masonry over the jumper and compare it with the calculated span of the jumper. If the height of the masonry is greater than the calculated span, then a supporting bridge is not needed. It's easy to explain: at a certain height, the wall above the opening has enough of its own bearing capacity, then a jumper does not need help from it. Knowing the specific weight of the masonry, it is easy to determine the brand of the lintel. The specific gravity of the most popular masonry materials is given below:

• Brickwork - 1400-1900 kg / m3;
• Foam blocks - 900-1400 kg / m3;
• Aerated concrete blocks - 400-1200 kg / m3.

It is necessary to take into account the density of the masonry material of a particular manufacturer.

Jumper Mounting

Non-carrying lintels of door and window openings with a span of up to two meters are allowed to be laid manually, more than two meters - with the use of lifting mechanisms. Depth of support is adopted for the series, but usually not less than 200 mm in the partitions and at least 250 mm in the walls. The pads are checked by level.

Reinforced concrete jumpers for brick walls should be installed on the masonry, additionally reinforced with grids. To fill the entire thickness of the walls of the jumper set a package of several pieces. The marginal products must not protrude beyond the plane of the walls. When installing jumpers, you must follow their project orientation. You can not adjust the jumpers along the length of the trimming, because their reinforcement is uneven and is calculated for the length of the span indicated in the product brand.

Self-made jumpers

In the case where it is not possible to deliver finished reinforced concrete products to the construction site, they can be manufactured directly on site.
Preliminarily it is necessary to produce timber of the appropriate size from sawn timber. It is convenient if the formwork will be designed for the manufacture of several products at the same time. From the reinforcement, a frame is made, a longitudinal frame is used with a diameter of 12-14 mm, a transverse diameter is 4-6 mm. For longitudinal reinforcement, the rods are installed in two levels, the transverse reinforcement is set in steps of 3/4 the height of the article. At a length of 1/6 of the length of the span from the support zone, the step of the transverse reinforcement is reduced. For large bridges, it is necessary to lay mounting loops. In the manufacture of the frame, welding or binding wire is used.

The assembled frame is installed in the formwork. To create a protective layer of concrete, the reinforcement is lifted using plastic stands of the "rack" or "stool" type. Then the formwork is poured with heavy concrete with subsequent consolidation by vibrating. After pouring the jumper reinforced concrete door and window must be kept for at least 24 days for solidification.

Production of jumpers in the span

In private housing construction, often, reinforced concrete lintels for openings can be made on site. This method is not very technological, but it does not need lifting and installation, which is very convenient in the absence of load-lifting mechanisms. When casting directly on the wall, it is possible to make arched reinforced concrete bridges.

The dimensions of such a design are determined by an individual design. Before casting the jumper, the masonry of the walls is brought to the required mark. The support pads are checked in accordance with the level and leveled by the footing. From the lumber in the opening is installed formwork. The lower part of the formwork is made of a thick enough board and reinforced with supports. The step and cross-section of the supports are selected in accordance with the length of the span and the weight of the bridge, assuming a density of heavy concrete of 2500 kg / m3. The supports are fixed to each other and to the construction of the walls. The reinforced concrete lintels require a quarter of the formwork for the installation of the window unit.

Often in the construction of houses from blocks of suppliers of masonry material produce special U-shaped blocks. They fit into the support in the opening and serve as a fixed formwork. Such elements have a thickness of ordinary blocks in the masonry and do not secrete a bridge on the smooth surface of the wall.

The reinforcement frame is mounted in the formwork, installation loops are not needed in this case. Then the formwork is poured with heavy concrete, compacting it with vibration tampers. The filled jumper is left for 24 days, after which the formwork is dismantled.