The bridge as a construction above the opening, perceiving loads from overlying walls and ceilings, appeared very long ago, as soon as people began to build stone public buildings and housing.
A bit of history
Most of the lintels above the openings were arched, as the upper semicircular contour of the window somewhat weakened the load. They were made of large-sized stones. These stones were carefully woven, adjusted to each other, this work required considerable time and effort.
The construction of the buildings went on for a long time, the slightest inaccuracy in the installation of the jumper stones, especially the central ones, the locks, could lead to distortion and destruction of the structure. But when the magnificent building was built, his life was calculated for centuries.
With the advent of brick as a building material, the lintels were still arched at first. But it was already easier to work, since bricks of the same size, and when the jumper was used, it was possible to make seams of different thickness, due to which the desired radius of the opening
Concrete reinforced concrete lintels
When people built houses from a tree, a lintel over a window or doorway was a thick log, overlapping a window with a large margin.
With the development of science, technology, the discovery of new technologies in construction, in particular with the introduction of reinforced concrete, bridges have appeared reinforced concrete. These jumpers have a rectangular cross-section, their width is not more than 250 mm. They are intended to cover the openings in the brick walls of residential and public buildings. These products are manufactured according to the series 1.038.1-1.
All jumper names consist of five groups of numbers and letters.
For example, the jumper 2 PB 19-3-p.
- 2 denotes a cross-sectional number;
- PB stands for the name - a jumper bar;
- 19 - the length of the product in decimeters;
- 3 - design load in kn / m (kgf / m);
- N means the presence of mounting loops.
The first figures in the marking, from 1 to 5, indicate the dimensions of the cross section of the product.
Those bar jumpers, in the name of which the first digit 1, with transverse dimensions of 120x65 (height) mm, can cover the openings in non-load-bearing brick partitions 120 mm thick.
If the first figure is 2, then the transverse dimensions will be 120x140 (height) mm. These jumpers withstand loads of up to 400 kgf / m and are used in self-supporting walls.
If the first figure is 3, then the transverse dimensions will be 120x220 (height) mm. These jumpers are reinforced, they withstand the load from the overlap.
Each bridge has a certain depth of support on the wall, depending on its bearing capacity. If the load on the jumper does not exceed 400 kgf / m, the depth of support can be 120 mm, if the load is more than 400 kgf / m, then the depth of support will be from 170 mm to 230 mm.
In order to properly choose a jumper, you need to know the width of the opening, the thickness of the wall, where the opening is, and also whether the overlap is based on it.
Depending on the thickness of the wall above the opening, two or three bar bridges are laid, and reinforced on the side of the overlap.
Features of transportation and stowage
Sometimes, especially before transportation, it is necessary to calculate the volume of bridle jumpers. At calculations it is necessary to consider, that the transport stack should have height no more than 2 m, and each crosspiece should be laid on two wooden linings.
The bar jumpers above the apertures are installed after finishing the masonry to the top of the opening, and special attention is paid to the horizontal position of their position. The upper plane of the jumper must be flush with the top of the masonry.
The bridges are installed on a layer of cement-sand mortar M100.
The bridge, located at the outer edge of the wall, is set 65 mm below the others, forming a quarter, necessary for installing the windows, so that the wind does not blow out.