Reinforcement of elements of monolithic reinforced concrete

Monolithic and frame-monolithic construction in recent years has received a marked spread. In addition to apartment buildings, monolithic reinforced concrete structures are increasingly used in the construction of private houses; Often, relevant work is performed on the basis of speculation and intuition, rather than knowledge and experience. This article is addressed to those readers who plan to build their own house with their own hands.

List of monolithic structures

So, what kind of monolithic structures are filled during the construction of the house?

Dавайте двинемся снизу вверх.

• Foundation. We will consider several options for its execution: slab, tape and on bored piles with a monolithic grillage.
• Walls.

To clarify: we are talking about load-bearing walls. Non-loaded partitions, as a rule, are made of porous materials with high heat and noise insulating qualities: gas and foam concrete, shell rock, limestone, etc.

• Overlaps.

AT этом порядке мы их и рассмотрим. Однако вначале нам предстоит познакомиться с типами арматуры и материалами, применяющимися для армирования железобетона.

ATиды арматуры

If we discard the exotic like bamboo stalks, which are used mainly in low-rise construction in Asian countries, in the dry residue we get only two materials.

It is useful: in a wide sale it is possible to meet composite reinforcement of only one type - rod.

What types of fittings are used in low-rise construction?

AT абсолютном большинстве случаев это рифленые стальные стержни. Их цена  делает сталь более чем конкурентоспособной на фоне композитных материалов; рифление обеспечивает хорошее сцепление с бетоном, а толщина (обычно 12-16 мм) - отличную прочность на разрыв. Нагрузки на сжатие воспринимает сам бетон.

Smooth reinforcement and meshes are used less often.

Foundation

Dавайте изучим общие принципы армирования фундаментов наиболее распространенных в частном строительстве типов (узнайте здесь, как происходит армирование газобетона).

Slab

Dля его армирования обычно используется стержневая рифленая арматура диаметром от 12 миллиметров. Изгибающие нагрузки под несущими стенами будут значительными; раз так - хорошее сцепление стали с бетоном играет решающую роль.

What is worth knowing about this type of foundation?

• The thickness of the slab is determined by the height of the house and the material used for construction. It is clear that a log house will create a much lower bending load than a brick or solid concrete structure. As a rule, slab thickness varies from 15 to 30 centimeters.

Nuance: with a small mass of the building, the use of reinforcing mesh with a cross section of rods of 6-10 millimeters is permissible.

• Reinforcement is always double layered. In this case, the lower and upper lattices are not rigidly connected with each other; only the use of props forming a gap of the desired size is permissible.

• Кстати, о зазорах: решетка или сетка нигде не должны выходить на поверхность бетона. По краям между арматурой и опалубкой делается примерно 10-сантиметровый просвет; от нижней и верхней поверхностей плиты решетки отделяются слоем в 1,5 - 3 сантиметра. Dля создания соответствующих просветов используются подпорки из отожженной проволоки.
• The armature is not welded into the lattice, but is knitted with the same annealed wire.
• The optimal step for rod reinforcement in the slab is 20-22 centimeters. If a finished mesh is used, the reduced wire thickness is somewhat compensated by a smaller mesh size (15 cm).

Tape

The instructions for the reinforcement of the strip foundation in some points repeat the recommendations for the slab base:

• The grille must be present at the top and bottom of the concrete strip.

Почему? ATспомните: арматура воспринимает нагрузки на растяжение; сжимающее усилие воспринимает сам бетон. При неравномерной нагрузке и/или морозном пучении лента будет подвергаться изгибающему усилию (то есть в зависимости от его вектора будет растягиваться нижняя или верхняя часть фундамента).

• Welding in this case is undesirable: heating deteriorates the strength properties of steel. The exception is the material in the marking of which the letter C is present (for example, A500C).
• The thickness of the concrete separating the steel from the ground should not be less than five centimeters.

There are differences.

• The maximum distance between the longitudinal reinforcing bars should not be more than twice the cross section of the building structure element (walls or columns) supported by the foundation and not more than 400 millimeters.
• The transverse and vertical elements of the frame are needed with a foundation height of 150 mm or more (that is, almost always). In this case, transverse and vertical reinforcement is often performed not by segments, but by a single bent yoke with a diameter of 6-8 mm.
• The minimum distance between adjacent rods (excluding the splice of segments) must be greater than their diameter and more than 25 millimeters.
• Corners, cross-shaped and T-shaped joints of the basement sections are necessarily strengthened in such a way as to form not a joint of two separate beams, but a single rigid frame.

Tip: the simplest way to understand how the reinforcement cage should look is to imagine the vectors of all forces acting on the foundation (first of all, the masses of the house and the frost heaving). Where the concrete is under tension, and reinforcement is necessary. The location of the reinforcement should be parallel to the force vector.

Pile

How to mount the reinforcement cage of the foundation on bored piles with a monolithic reinforced concrete grillage?

On heaving soils, the optimal distance from the grillage to the ground level is only 100-150 millimeters. Such a small gap will not only simplify the base warming, but also save us time and effort during casting the grillage: under it is simply enclosed a layer of foam plastic that will become the lower part of the formwork and prevent the cement jelly from leaving the soil.

Piles are poured with concrete of grade not lower than M300 directly in the ground, in the wells drilled under them. Formwork, and at the same time, waterproofing is usually served as rolled roofing felt. The reinforcement cage is lowered inside the pipe before pouring.

The pile frame is usually assembled from longitudinal corrugated reinforcement with a cross section of 12-14 millimeters and square, polygonal or round solid-faced clamps with a cross section of 5-8 mm perpendicular to it.

AT идеале и здесь лучше использовать крепление вязальной проволокой; однако есть немалый шанс нарушить расположение элементов каркаса при штыковании, поэтому на использование сварки в этом случае профессиональные строители смотрят сквозь пальцы.

Piles are reinforced to full length. There are exceptions to this rule, but they have nothing to do with low-rise construction. Suffice it to say that partial reinforcement implies a pile diameter of 700 mm.

The minimum diameter of the pile in accordance with applicable building codes is 400 mm. The cross section of the reinforcement cage should be 100-120 mm less; for the minimum diameter and a two-story house, in practice, 4 rods of longitudinal reinforcement with a cross section of 14 mm are sufficient.

The longitudinal rods of the frame are tied with reinforcement of the grillage. Significant loads in the transverse direction, the joint of the pile and the grillage is not experiencing; however, frost heaving may create a situation where the joint will be loaded to break. That is why this connection is also enhanced; gain circuit resembles the solutions used for strip foundations.

And what about the reinforcement of the grillage itself? He is experiencing exactly the same load as a strip foundation; if so, all the recommendations will be identical.

Walls

How is the reinforcement of reinforced concrete walls?

• The reinforcement cage in this case should also be double-layered, preventing the wall from bending under load in any direction.
• Основные нагрузки будут сжимающими, поэтому допустим минимальный диаметр продольной арматуры в 8 миллиметров. AT малоэтажном строительстве допускается использование сеток из 8-миллиметровой проволоки.
• The maximum pitch of the longitudinal reinforcement is 20 centimeters. Transverse (horizontal) - 35 centimeters.

• Поперечная арматура должна иметь площадь сечения не менее 25% от площади сечения продольной. Dля диаметра продольных стержней в 8 мм площадь сечения поперечного армирования составит 0,25х3,14х(8/2)^2=12,56 мм2.
• The ends of the reinforcement anchors in the concrete (of course, without going on its surface). How it's done?

Overlaps

Характер нагрузок, испытываемых монолитными перекрытиями, сродни описанному выше случаю монолитного плитного фундамента (читайте также статью «Железнение бетона: способы, материалы, последующая обработка»).

Hence the similarity of the reinforcement scheme.

• Frame - two-layer, in the lower and upper parts of the ceiling.
• Минимальная толщина перекрытия - 150 миллиметров. AT общем случае она берется равной 1/30 ширине пролета. Так, для пролета в 5,5 метра плита перекрытия должна иметь толщину 5,5/30=0,183 метра, или 18,3 сантиметра.

Nuance: with a span of 6 meters or more, the plate should be reinforced with bolts.

• Dиаметр арматуры определяется расчетными нагрузками; минимум и в этом случае составляет 8 миллиметров. Шаг между стержнями - не более 20 сантиметров; допускается использование готовой сетки с ячеей в 15-20 см.

• The protective layer of concrete between the surface and the reinforcement is 15-20 mm.
• Wherever possible, whole rods are used across the full span. If this is not possible, they are built up with an overlap of 40 diameters. So, for a rod with a cross section of 10 mm, the overlap at splicing will be at least 40 cm.

ATнимание: сращивания смежных стержней располагаются вразбежку, со смещением друг относительно друга.

• On the edges of the slab, the upper and lower grids are connected by a U-shaped reinforcement. In the same way, the edges of the openings are enhanced.
• If it is assumed that after a set of overlap strength will be made additional openings and holes that require breaking the reinforcement, only corrugated rods are used exclusively.

Useful: diamond drilling of holes in concrete gives much more even holes than drilling with a crown using a hammer drill. With a large opening size, it is permissible to cut reinforced concrete with diamond circles, and reinforcement with ordinary abrasive ones, which have a smaller thickness.

Conclusion

AT рамках небольшой статьи нами затронуты лишь основные моменты армирования железобетонных конструкций и самые простые сценарии.  Dополнительную информацию читателю предложит видео в этой статье. Успехов!