Installation of reinforced concrete structures: regulatory

The subject of this article is reinforced concrete bearing and enclosing structures. We have to deal with their classifications and get acquainted with the requirements for installation, as set out in the current regulatory documents.

Classification

What types of reinforced concrete structures are used in construction?

• Monolithic. The most obvious example is modern frame-monolithic apartment buildings. The bearing frame of the building is cast on site in a removable formwork; after a set of strength by concrete, enclosing walls and partitions of light porous materials are erected.
• Prefabricated. A sample of this design is a panel house: it is built from prefabricated elements. Installation of precast concrete structures, as a rule, is reduced to the unification of the reinforcing structural elements of the frame by welding and concreting joints.

Useful: this technology, among other things, allows the use of structural elements with pre-stressed reinforcement. The reinforcing rods heated by high currents, cooling down, stretch and thereby increase the strength of the product for bending. The production method of reinforced concrete with reinforcement voltage implies industrial conditions.

• Prefabricated - monolithic. This type of construction includes, for example, the overlap of plates laid on monolithic girders.

In addition, the construction of buildings and industrial facilities in a single structure can combine dissimilar elements. Joint installation of reinforced concrete and steel structures is used, for example, when creating open warehouses adjacent to a building: beams or trusses of a canopy are cooked to embedded parts in concrete or anchored to a monolith.

Regulations

What documents regulate the installation of products from reinforced concrete?

We have to get acquainted mainly with the content of the last document: it contains the most complete information on the installation work.

SNiP 3.03.01-87

The document covers the following list of works:

• Construction of monolithic concrete and reinforced concrete walls, beams, columns, floors and other supporting and enclosing structures.

• Installation of reinforced concrete and prefabricated metal structures in a construction site.
• Welding of assembly joints of metal structures, welding of reinforcement joints of reinforced concrete products and embedded parts in them.
• Construction of stone, ceramic, silicate and concrete blocks.

Work begins with the preparation of the PPR (project work). The project, among other things, should include a statement of the order of the main operations, taking into account the safety and manufacturability of the construction.

All materials used must comply with applicable standards and / or specifications.

Let's examine the basic requirements of SNiP.

Warehousing and relocation

When storing the structural elements should be based on gaskets of rectangular cross section with a thickness of at least 30 millimeters. In case of stacked storage, gaskets must be placed on the same vertical line.

Reinforcement releases are protected from damage. Protection requires and surface, equipped with an invoice to ensure better adhesion to concrete.

Storage is carried out taking into account the order of installation. At the same time, the factory marking must remain visible.

Metal fasteners (bolts, nuts, etc.) are stored exclusively in enclosed spaces; they must be sorted by size, strength class, and in the case of high-strength products - by batch.

Moving any products with fiber is prohibited. For movement or giving to the place of works the lifting equipment is used. Slinging is carried out for mounting hinges or in the places indicated in the working drawings.

Specify: ENiR for installation and construction work (a document containing uniform standards and rates) is based on the movement of goods weighing up to 50 kg at a distance of up to 30 meters with your own hands, without using loading equipment.

The method of slinging should exclude displacement of the sling and damage to the reinforcement. Hang off products for the issue of valves is prohibited. The position of the element when lifting should be as close as possible to the design one (that is, for example, the wall panel is fed to the work site in a vertical position, and the floor panel is horizontal).

Elements rise without jerking and swinging; the desired orientation in space is achieved by using braces (one for vertically oriented elements and at least two for horizontal parts of the structure).

The rise is carried out in two steps:

1. The product rises to 20-30 cm to check the quality of slinging.
2. After the check is carried out further rise.

The method of fixing elements should exclude their displacement at any stage of installation. Until reliable fixation (permanent or temporary), the product cannot be used as a support for other structural elements.

Concrete works

According to SNiP, for them should be used mixtures prepared in accordance with the following requirements:

Dosing of components of concrete produced by weight. By volume of water for mixing, only modifying additives can be dosed (plasticizers, antifreeze, etc.).

The ratio of components is determined separately for each batch of cement and aggregate with mandatory testing of samples for mobility and strength.

It is forbidden to increase the mobility of concrete by introducing water into it.

Before concreting, the surfaces of working joints should be cleaned from dirt, dust, debris, grease stains, cement film, snow and ice. Immediately before laying concrete surface is washed with water and dried with a stream of air. The instruction is associated with a decrease in the adhesion of cement to the base when the surface is contaminated.

Concrete is laid horizontal layers of the same thickness.

When vibropacking vibrator should not rely on reinforcement, embedded parts or formwork. The deep vibrator should sink 5-10 cm into the previously laid layer and move in increments of no more than one and a half radii of action; surface moves with a 10-centimeter overlapping vibrated area.

Laying the next layer of concrete is permissible either prior to the setting of the previous layer, or after gaining a strength of at least 1.5 MPa. The same strength is necessary so that you can walk on the concrete or install formwork for the overlying part of the structure.

Concrete processing

It may include the cutting of expansion joints, openings and technological holes.

What does the document recommend?

• For all work, SNiP provides for the use of diamond tools. It is quite natural: in spite of the fact that its price is quite high, cutting reinforced concrete with diamond circles is cheaper than the same work done with conventional abrasive ones. The reason is a huge difference in wear rates.

It is useful: in addition, diamond drilling of holes in concrete, in contrast to the use of borehole drills and crowns, makes the edges of the holes perfectly flat.

• The tool is cooled with water with the addition of surfactants that reduce energy loss to overcome friction.
• The strength of concrete at the time of processing should reach at least 50% of the design.

Reinforcement

Welded rebar connections are made using annealed knitting wire. Crimped sleeves and screw couplings are allowed for butt joints.

Preferably the use of large-block reinforcing products or prefabricated nets.

When installing reinforcement, it is necessary to withstand the thickness of the protective layer of concrete, preventing contact of the reinforcement with atmospheric air and water.

Prefabricated конструкции

How the document regulates the installation of concrete and reinforced concrete structures of precast type?

• In the general case, the next tier of the multi-tiered structure is erected not only after the reinforcement cages are joined by welding, but also after the monolithing of the seams and the concrete has been specified in PPR strength. Exceptions are specifically mentioned in the draft.

• To fix the structural element during assembly, temporary assembly connections can be used. Their number, type and order of application is again stipulated in the CPD.
• For concreting seams it is not allowed to use the mortar that has begun to set. The consequence of violating this rule is a catastrophic decrease in the compressive strength of the assembly seam.
• Crossbars, supporting trusses, annular plates and roof beams are placed on the supporting surfaces of the columns dry, without solution. Floor slabs are stacked on the mortar; the thickness of its layer should not exceed 20 mm. Surfaces of adjacent plates are aligned on the side of the ceiling.
• At installation of ventilating blocks it is necessary to control filling of horizontal seams with solution. Clearances should not remain.
• Sanitary cabins are exposed on gaskets with the combination of the vertical axis of the risers. Holes for risers are sealed after crimping hot and cold water systems.

• For cementing seams of precast concrete structures, concrete is used on quick-hardening portland cement (M400 grade and above). The use of hardening accelerators is allowed and even recommended. The maximum grain size of aggregate in concrete should not exceed 1/3 of the minimum cross-section of the joint and 3/4 of the minimum distance between reinforcement elements.
• At the time of removal of the formwork, the concrete must reach the minimum strength specified in the project.

Note: in the absence of specific instructions, the stripping is performed after reaching 50% of the nominal strength.

• During installation of welded steel structural elements, impact on them is prohibited at low temperatures. To be precise, for steels with a yield strength of 390 MPa and less, the lower limit of temperature is -25 ° C, and for steels with a yield strength of more than 390 MPa, 0 degrees.

Conclusion

We hope that the information offered to the reader will be useful. The video in this article, as usual, contains additional materials on the subject under discussion. Successes in construction!