Elements of a precast reinforced concrete frame: a unified version

Precast reinforced concrete frames are a common option for building sturdy and long-lasting structures. These frames are perfect for a variety of construction projects because they offer strength and flexibility. What precisely is contained in a precast reinforced concrete frame, though? Gaining an understanding of its components can help you better understand how these frames support modern buildings and demystify the process.

A precast reinforced concrete frame is made up of a number of essential parts, each of which is vital to the structure. Every component, including slabs, connectors, beams, and columns, is expertly crafted and produced to fit together flawlessly. The overall stability and safety of the structure are enhanced by this cohesive approach, which guarantees that the frame can withstand a variety of loads and stresses.

We’ll dissect these components and examine how they work within the overall construction project in this post. Whether you’re a builder brushing up on your skills or a homeowner planning an addition, knowing these elements will help you gain important insights into the durability and performance of precast reinforced concrete frames.

Element	Description
Column	Vertical support that carries the load from the beams and slabs above. Typically made from reinforced concrete.
Beam	Horizontal support that spans between columns and supports slabs or other loads.
Slab	Flat horizontal surface, often used as flooring or ceilings, supported by beams and columns.
Footing	Base of a column that spreads the load to the ground. It ensures stability and prevents settling.
Joint	Connection point between different elements like columns, beams, and slabs. Designed to handle movement and stress.
Reinforcement	Steel bars or mesh embedded within the concrete to improve strength and durability.

The strength and stability of a precast reinforced concrete frame are dependent on a number of essential components. Columns, beams, and slabs that are produced off-site and assembled on-site are all part of this unified version. Standardized components allow for faster and more efficient construction without sacrificing strength or quality. This method not only expedites the construction process but also guarantees that every component fits together perfectly, producing a sturdy and dependable structure.

By what principle is the frame assembled

I want to clarify right away that the construction of the building frame is not some sort of utterly archaic operation carried out using pre-made plans and identical planning solutions. Each object has its own set of options for how the frame components are arranged, and each project has a specification for the elements made of precast reinforced concrete.

They merely use a particular static scheme known as unified as a basis:

• The task of designers is to create such a rigid system that will allow it to withstand everything horizontally affecting the load building.
• They are perceived not by separate vertical elements, but by vertically connected by diaphragms, which convey efforts to the foundation.
• Along with them, horizontal structures provide stability, which are the overlap.
• Their joint work is designed to give the frame stability, avoiding its loss when twisting and exposure to bending loads.

Speaking of which, There are at least three flat, stiff diaphragms with non-overstraining horizontal axes provided by the building’s dependability in each block. The core is closed and resists attempts to twist. The best choice is this one.

• As for vertical diaphragms, they are usually placed so that their common center of bending can coincide with the center of influence of the building"s weight, as well as with the point of influence of the wind load.

Nevertheless, flat diaphragms are not sufficient on their own. In order to join them, spatial diaphragms are made, which result in a monolithic and prefabricated rigidity core. Our additional instructions explain how all of this comes together and functions.

Components of a unified frame

It is evident that the rigidity of the entire frame is guaranteed by the rigidity of a single reinforced concrete element. As a result, there are numerous modifications for every kind of product. Depending on where it is located within the frame’s structure and, of course, the loads it must support, one option or another is chosen.

Each product is therefore calculated for these specific loads. However, we will first bring to your notice a list of components that make up a cohesive frame.

The components are thus a frame made of reinforced concrete:

• The length corresponds to the height of one or two floors, which creates convenience in designing buildings with both even and odd storeys.
• In this case, the size is taken into account the possibility of organizing special-purpose premises – for example, a technical floor.
• Their section is standard – 400 * 400 mm. A single standard size in this case is justified by the fact that this makes it possible to reduce the nomenclature – and not only the columns themselves, but also all the structures adjacent to them.

With this kind of design, the portion of the beam that projects into the space can be made smaller.

The undercuts at the ends of the beam, which are caused by the beam resting on the columns, match the vertical support console’s dimensions in depth.

• Together with stiffening diaphragms, the floors form a spatially unchangeable integral frame system of the building. Their layout is carried out taking into account the need for technological openings for installing stairs or elevators, passing utility pipes, etc. d.
• The floor elements are reinforced concrete panels: hollow 220 mm thick (for light frames), and ribbed 400 mm thick (for heavy frames).

They fall into the following categories:

• Ordinary;
• Facade (laid in rows of columns from the facade side);
• Internal;
• Additional (they are usually mounted on stiffening diaphragms, around stair spans);
• Plumbing (with openings for utilities)
• For balconies and loggias.

• They can have a variety of shapes: from a steel channel welded in the form of a rectangle to a reinforced concrete product in the form of a flat wall.
• The latter are 180 mm thick and one floor high.
• The dimensions of the diaphragm, which can be solid or have an opening, are 2.15 m * 1.21 m.
• The product can be also flat, or have a console on which the overlap is based.
• The consoles are designed for two types of loads – depending on the thickness of the flooring.

• Когда лестничная клетка располагается внутри здания, её со всех сторон ограждают диафрагмами жёсткости. If this is an external option, then the diaphragms will be located on three sides.
• The march on the private or facade crossbar is based on how the enclosing structures are mounted. Inside the building, the staircase is based on the console of the diaphragm of stiffness.
• As in the case of columns, the supply of stairs can be targeted – that is, for a specific object. The difference with typical marches is only in the set of embedded parts.

The developers were initially presented with two options: lightweight concrete single-layer panels, like the one we are talking about, or heavy reinforced concrete three-layer products.

However, some challenges emerged in their manufacturing process due to the requirement to hang panels on a frame and create products with a complex configuration. Manufacturing a single-layer panel doesn’t require as much labor.

Kindly take note! A variety of concrete types with different fillers fall under the category of lightweight concrete. Expanded clay concrete, on the other hand, was preferred when building a unified frame because it was the strongest material and still maintained the necessary thermal efficiency indicators.

We will then go over the selection criteria for elements in more detail when we design a frame.

Optimal solutions for selecting connecting elements

Using a sixteen-story building as an example, the structure of its frame may have up to five different concrete column types with varying strengths. Additionally, high-grade concrete (roughly M800 B60) is the ideal surface for reinforced concrete compressed elements to function best on.

How efficiency is achieved

Concrete and the reinforcement it contains are both essential to columns’ effectiveness. Class At-V steel, which is thermomechanically strengthened and has a high strength, is typically used.

Kindly take note! The key to optimization is the ability to modify a product’s bearing capacity while maintaining its existing configurations by arranging different reinforcement options and choosing concrete, rather than increasing the number of possible forms. Naturally, in this situation, not only do the strength indicators of the structures change, but so does their cost.

• The same bearing capacity can be obtained on concrete of different strengths, varying only their grades and the amount of reinforcement. However, given that reinforcement is always more expensive, it is more economically feasible to give preference to the option where there is less of it.
• To maintain balance, concrete of a higher grade should be used, which allows to reduce the cost of structures by a third. It is by this principle that designers optimize the nomenclature of columns – comparing different options for consumption and cost of materials.
• The columns are connected to the diaphragms of rigidity by means of embedded parts – and this is also expensive steel. The project can provide for up to four such abutments (on all sides).
• Accordingly, the nomenclature is optimized not only for internal working reinforcement, but also for embedded parts. Therefore, the entire system of columns is divided into:

1. Non-addressable (have a standard set of embedded parts);
2. Addressable (intended for specific objects).

• Particular attention is paid to the joints of columns when choosing design solutions, which have to work under increased loads. The development of a unified frame took place in stages.
• Some solutions – in particular, the method of joining columns – were finalized taking into account the inconvenience of their implementation in practice and high cost. Additional tests were carried out on samples, measuring concrete deformations, recording the occurrence of cracks.
• In particular, it was confirmed that the concrete with which the column joint is monolithic is almost simultaneously included in the work with the concrete of the column itself. And the higher its strength grade, the more efficiently this work occurs. Therefore, concrete of at least M600 (B45) is used here. In this regard, the calculations also take into account the area of ​​monolithic sections.
• It was also found that the joint performance is significantly improved by installing a twelve-millimeter diameter clamp that ties the joint reinforcement. It is clear that the reliability of the joint depends on the method of its implementation.

The unified frame’s list of columns also includes the following additions:

1. Option with a console enlarged to support the horizontal elements of the façade.
2. Models with long consoles, which, protruding beyond the front part of the facade, form loggias or balconies.
3. Column with a hole in the console – heating risers pass through them.
4. Models with increased height for supporting heavy crossbars.

The deflection of the bent reinforced concrete element is determined by the choice of each individually installed column at the site. When designing, every effort is evaluated against the frame’s vertical supports’ ability to support weight as well as potential displacements and refractions of their axes at the joints.

Everything functions comprehensively in a rigidly connected frame. For instance, the bending moments in the crossbars are determined by the vertical loads sensed by the column consoles.

In unified frames, there is free support in the plane that is perpendicular to them, which is the ceiling. Since the spans are loaded unevenly in this instance, the interaction between bending moments and longitudinal forces is calculated when calculating eccentrically compressed elements for columns.

Unification of beams

The beams in a single lightweight frame are engineered to withstand loads of either 72 or 110 kilonewtons per meter. These numbers serve as the foundation for figuring out how supported floors with 1.2 or 1.8 m of width are distributed and concentrated. The floor width in heavy frames is 1.5 meters.

• Beams are made of concrete grades M300; 400; 500, they are reinforced with flat frames and meshes, joined by contact or arc welding. Products are delivered from the factory only after reaching seventy percent strength, however, in accordance with GOST requirements, they must be guaranteed conditions for recruiting the remaining 30%.
• As in the case of columns, to calculate the crossbars, the general provisions of design standards were initially used, which did not fully take into account the specifics of the product’s operation.
• In particular, the problems were related to the loads acting along the height of the section, and the results of calculating the shelf of the product for concrete spalling were not entirely reliable. Therefore, the relevant organizations, headed by the Research Institute of Reinforced Concrete, conducted research and the existing methods of reinforcement were replaced with more rational ones.

• In short, it looked like this. It was found that as a result of the impact of the load on the shelf, on both sides of its rib, in the stretched zone not only normal cracks appear on the shelf itself, but also inclined ones – in the rib above it. This is essentially normal, since it is caused by the general bending of the product. However, when the load increased, cracks appeared at the place of application of the load, or the shelf completely broke off.
• The fact is that the calculation of reinforced concrete bending elements along an inclined section – or rather, its methodology, presented in SNiP, does not take into account some factors. Namely, the load position relative to the beam height.
• To strengthen the structure, it was necessary to increase the number of transversely located reinforcement bars, and to determine it correctly, a method developed by the Institute of Reinforced Concrete (NIIZhB) was used.
• We will not go into its essence now, we will only say that its use allows you to make an accurate calculation based on the tear-off section and take into account all the transverse reinforcement used.
• This helps to establish the tear-off zone and include it in the calculation, which is very important, since the beam load is concentrated on a limited area, and then transferred to the edge. This, in fact, is the peculiarity of this product. Accordingly, it was important to determine the most rational dimensions of the beam shelves.
• After the design was improved, the consumption of reinforcement per cubic meter of reinforced concrete was about 20 kg, which provides significant savings for any manufacturing plant. In the process of developing the frame design of a unified type, crossbars of greater height were developed (4 types in total).

Similar to columns, crossbars are intended for light frames with braced schemes and can be employed in low-rise building construction. However, frame-type frames are often designed for industrial buildings.

Their flat frames with flexible (elastic-plastic) nodes form the basis of their structural design. These units are made possible by special steel components known as fish, which are used to attach the crossbar to the column console. This option is displayed in the preceding diagram.

Features of enclosing structures

As was previously mentioned, single-layer expanded clay concrete panels are used in the unified version of the reinforced concrete frame. The optimal product geometry and precise dimensioning are guaranteed by the use of conductors.

They create front surfaces that are decorated and include enclosed structural elements with built-in, even glazed window frames. In other words, these products are at least 90% factory ready.

• Depending on the architectural solution of the building"s facade, its enclosing structures can have a strip horizontal or vertical cut. To ensure aesthetic individuality, the panels can have a wide variety of finishes.
• This can be glass or marble (granite) chips, gunite, ceramic or glass tiles, and even thin slabs of natural stone – most often travertine. There are also more complex options – such as stemalite (colored tempered glass in an aluminum frame).
• Note that all types of cladding are performed only due to adhesion, without the use of any mechanical fasteners. This applies to exterior decoration. On the inside, the surface of the panels is simply plastered with a thin layer of cement mortar.
• The wall elements are attached to the frame by welding to embedded parts, but sometimes steel half-timbering can be used. Accordingly, all the mounting parts required for connection are included in the kit, and their nomenclature is specified in the specification.
• The panels are reinforced with a spatial frame consisting of several flat welded meshes and rods that unite them into a spatial frame.

After installation, the panel joints are monolithic, and the proper end edge configuration guarantees that the panels are positioned correctly. Gaskets made of polyurethane foam, gernit, synthetic rubber, or natural rubber are used to seal the joints.

In conclusion, knowing the components of a precast reinforced concrete frame enables us to recognize the part that each one plays in building a stable, dependable structure. Through the combination of different standardized elements, such as beams, slabs, and columns, we can achieve durability and efficiency in construction.

The frame’s seamless integration of its components guarantees that the system functions as a whole. This unification expedites construction time, lowers expenses, and streamlines the building process without compromising quality.

In the end, a cohesive precast concrete frame provides a workable answer for contemporary building requirements. Its standardized procedure not only makes the process run more smoothly, but it also increases the structure’s longevity and general safety.

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