What is a crossbar in construction and why is it needed?

Crossbar is a word of German origin that translates as transverse beam or crossbar.But in construction, beams and crossbars have different functional purposes.

A crossbar is a purely horizontal element, the main purpose of which is to evenly distribute the loads acting on it onto support posts installed vertically.

What is a crossbar in construction?

The crossbar in construction is used as part of the supporting structure of the structure. Usually it connects two vertical posts of a supporting type. And its task is to increase the stability of these supports, and the entire structure as a whole. A simple example is two pillars of a frame building, on which a horizontal element is laid on top. It is not subjected to serious loads, so it practically does not bend.

If the distance between the support posts is large, which means the length of the crossbar is also large, then additional supports can be installed under it. The latter can be vertical or inclined. Such structures are often used in the construction of roofs.

The crossbar has one more purpose - with its help, the loads acting on the racks from the overlying building elements are evenly distributed over them. The entire structure of the building is loaded evenly, which makes it both stable and durable. This is important in different situations, for example, the most common ones - shrinkage of the house or the appearance of cracks.

Different types of crossbars have always been used in construction. They differ from each other in the material of manufacture, size and shape.

Reinforced concrete crossbar - GOST and dimensions

Reinforced concrete crossbars are produced in accordance with GOST 18990-2015. The title of the document is “Reinforced concrete crossbars for multi-storey buildings.”

Products of this type, manufactured in accordance with GOST, are not always found on the market. Some manufacturers use technology based on technical specifications (TS). But GOST determines that this element for the construction of a building must be made of high quality concrete.

The size of the crossbar for construction is also regulated by GOST. This is convenient both in terms of selection according to loads when a building design is being created, and in construction, because builders purchase exactly the crossbar specified by the designer in accordance with GOST.

If for some reason the designer is not satisfied with the GOST products, then the crossbar is manufactured according to the calculations that he makes. But this must be technically and economically justified. The calculation is carried out on the basis of existing loads, which takes into account the ratio of two parameters: the length of the crossbar and its cross-section. All dimensional parameters can be viewed in the above-mentioned GOST.

The requirements for reinforced concrete options are serious.

They must meet high technical and operational characteristics:

Metal crossbar in construction

This is still the same element for construction, only made of metal profiles. Therefore, it may have a different cross-section:

• T-bar - with one shelf. Used under floor slabs and flights of stairs;
• I-beam - with two. Installed under central spans;
• square.

Metal crossbars, all the above-mentioned varieties, are fastened using electric welding, bolted joints, and hinges. In this case, an expansion joint is provided. Its purpose is to prevent the beam from increasing or decreasing in size when the temperature changes.

Protection from moisture is required. The metal is simply coated with varnish, enamels, or galvanized profiles are used.

Types, shape and markings

The classification of types of crossbars is based on materials of manufacture, cross-sectional (profile) shape, and dimensions. Reinforced concrete and steel analogues are mainly used in construction. In wooden construction - beams. This also applies to wooden roofs.

Profiles

This is the basis for the classification of reinforced concrete products.

Each type has its own letter designation:

• RDP - with two shelves on which hollow floor slabs can be laid;
• RDR - with two shelves on which ribbed slabs can be laid;
• ROP – with one shelf or single-shelf. Used for laying hollow slabs;
• ROP – with one shelf for ribbed slabs;
• RLP – single-shelf. Used as a basis for flights of stairs;
• RPB - without shelves with laying of ribbed slabs;
• R – flangeless rectangular section;
• RCP - cantilever, on which hollow slabs from balconies rest.

Marking

The stamp contains both letters and numbers. They are divided into groups, where the first indicates the type of product, its cross-sectional height and length. Numerical designations are dimensions in decimeters, which are rounded to the nearest whole number.

The second group is characteristics: load-bearing capacity and steel class of the reinforcement used.

The third group is additional information regarding operating conditions. For example, seismic impact, design features (presence of additional parts), resistance to the environment in which the construction element is used.

An example of marking is RDP 6.56 – 110A IV.

First group of notations:

• RDP is a two-shelf element on which hollow slabs can be laid;
• 6 – 600 mm section height;
• 56 – length equal to 5566 cm.

Second group:

• 110 – load-bearing capacity with unit of measurement kN/m;
• A-IV – class of reinforcement used internally as a reinforcing frame.

Advantages of formless forming technology

Formless manufacturing technology was developed in Europe in three countries: Finland, Germany, Spain. In all three states, production differs from the rest. But it is based on the principle of pouring concrete mortar into metal molds of great length - several tens of meters.

Reinforcement is placed inside the form, concrete is poured on top, which is immediately compacted using a pouring machine. It moves on rails along the metal mold.

After all operations are completed, a long crossbar is obtained, which is subsequently cut into pieces of the required length. Large diameter diamond wheels are used for cutting.

There is one advantage of this technology - reducing the cost of concrete products. This is an important factor for construction.

Why is a crossbar with additives in concrete better than a product without additives?

The main task when forming a concrete crossbar is to evenly distribute the concrete solution over the form so that there are no voids left. The latter greatly reduce the quality.Plus - the mixture should tightly envelop the reinforcement so that shells do not form between it and the concrete.

The main requirement for concrete mortar is its high plasticity. This cannot be achieved without additives, namely without plasticizers.

Some reinforced concrete elements in construction are used outdoors, for example, in bridge construction. They are exposed to temperature stress, especially in winter. Therefore, additives are added to the concrete mixture to increase frost resistance.

That is, under the required operational loads, additives are introduced into the concrete that increase one or another characteristic of the reinforced concrete element.

How does a crossbar differ from a beam?

Both elements in construction can be called a beam. There is no mistake in this. Because a beam is a building element whose length exceeds its width. In this case, it rests on two supports with its own ends, but may have additional intermediate posts.

The differences between a beam and a crossbar are in their purpose. The second in construction is an element of the supporting structure. Loads are transferred to it, which it distributes evenly between vertical racks. If the support is horizontal building elements or structures, then it is a beam. It can also be located at an angle, which is impossible for a crossbar.

In this case, the beam bends. And it is not always part of the supporting structure. Can “exist” as a unit of a building structure.

It turns out that the crossbar and the beam have a lot in common, but there are also differences. This is especially true for the installation location.

The beam always has a rectangular cross-section, the crossbar has a complex shape, including a rectangular one.

Applications in construction

Construction crossbars have a wide range of applications:

• construction of buildings;
• bridge construction;
• construction of aqueducts and arched spans;
• are elements of power transmission line supports.

The element performs an important function in a frame house. It is used in the Scandinavian technology of constructing frame houses, where the crossbar serves as a strapping for vertical posts. At the same time, load-bearing floor beams or rafters of the roof structure are laid on it, the load from which it evenly distributes across the racks.

Installation

In construction, this process is simple. A lifting mechanism is used for this.

The ends of the reinforced concrete crossbars are laid on:

• consoles of reinforced concrete columns;
• steel tables that are welded to the embedded columns;
• concrete pads.

The connection to the columns is made by electric welding. The reinforcement protruding from the beam is welded to the reinforcing bars protruding from the column. After which the joint is filled with concrete mortar. The result is a monolithic structure.

Installation of metal crossbars is carried out identically, that is, using a crane. The difference is that the building element is installed on steel consoles, which are pre-attached to metal mortgages using electric welding.

The crossbar itself is attached to the consoles by electric welding or bolts. If the first option is used, then the joints are welded on both sides. Moreover, all work is carried out only by specialized companies that have highly qualified welders on their staff.

How to make it yourself

If you need a construction crossbar for the construction of small buildings, then you can make it yourself right at the site of its installation. The process is almost identical to manufacturing strip foundation.

You need to prepare:

• formwork - this can be boards, sheets of iron and other flat materials;
• fittings;
• knitting wire;
• materials for concrete mortar.

The formwork is installed directly at the location where the crossbar is installed. These are the bottom part and two sides. The distance between the latter determines the width of the crossbar. Their height is the height of the reinforced concrete products. Supports are mounted under the lower element.

A reinforcing frame is placed inside the box. It can be assembled on the ground and transferred to formwork. Or the assembly is carried out directly inside the latter. Pieces of reinforcing bars are connected to each other with knitting wire.

The reinforcing frame is not placed on the bottom of the formwork, but on supports - at a height of at least 5 cm. The frame must be located inside the reinforced concrete product.

The last stage is the production and pouring of concrete. It must be compacted to remove air that got inside the mixture during the mixing of the ingredients. Air bubbles reduce the strength of concrete. In this condition, the building element must stand for 28 days for the concrete to gain its original strength. After which it can be loaded.

It must be added that a homemade reinforced concrete element will be inferior in all respects to one manufactured according to GOST.

Expert advice

The crossbar performs an important function in construction. Therefore, in the design of each building a certain type is used, taking into account the calculations performed. The main goal of the latter is the balance between the ability of the concrete solution to compress and the tensile reinforcement.

If you independently manufacture a product for use in construction, this balance may not be achieved, which will lead to a decrease in the quality of the building frame. Therefore, the advice is to purchase concrete products only from factories that provide a quality certificate.

Before starting welding work, each installed crossbar must be checked for correct location: horizontalness is checked with a water level, alignment with a tape measure. The complexity of installation work depends on the size and weight of the reinforced concrete product.

When installing metal crossbars, you cannot use pads that are not provided for in the project. Any changes, even the most minor ones, must be agreed with the designers.

What is a crossbar: video.

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