Solid foundations in the form of monolithic reinforced concrete ribbed or beamless slabs are installed under the entire building in cases where a significant load is applied to the foundation, and the foundation soils are very weak, with uneven subsidence, or when it is necessary to protect the basement from penetration groundwater at their high level.
To transfer significant loads from buildings or structures during weak soils arrange pile foundations. Pile foundations allow increasing the level of industrialization construction work. In recent years, they have found increasing use in construction on natural foundations.
According to the manufacturing method, a distinction is made between piles driven into the ground by impact, vibration, screwing, and in the form of a monolithic structure, concreted on site in specially prepared wells (cast-in-place piles). Depending on the nature of the work, a distinction is made between hanging piles and continental piles (rack piles).
Hanging piles are appropriate when the depth of solid (continental) soil is significant, and the soil resistance at the side surface of the piles and under the lower ends is sufficient to withstand the transmitted load (Fig. 1. a).
If the depth of solid soil does not exceed the possible length of the piles, rack piles are used, which with their ends enter the continental soil and transfer the load to it (Fig. 1. b).
Rice. 1. Pile foundations a - hanging pile; b-pile-rack; c-reinforced concrete piles; g-rammed concrete; d-metal screw-on; 1 - reinforced concrete pile; 2 - prefabricated reinforced concrete grillage; 3 - concrete filling; 4 - wall panel; 5 - weak soil; 6 - dense (continental) soil; 7 - blade. 8 - joint
Depending on the material, piles can be wooden, reinforced concrete, concrete, steel or combined (Fig. 1. c-d).
Piles under the base of the foundation are usually placed in groups or rows. Single piles are those placed in isolation or at a distance of more than 1/4 of their length.
A group of piles located under the foundation is called a pile bush, and piles located in one or more rows form a pile strip. The upper ends of the piles are combined into a single structure using a concrete or reinforced concrete slab - a grillage (Fig. 1. a, b).
Blind areas or sidewalks are used to remove precipitation from the foundation and plinth.
With all the modern variety of types of foundations and their advantages, many bathhouse builders still prefer monolithic ones. After all, what is whole is always stronger than prefabricated structures. And the construction process in this case is somewhat simpler. And the most popular foundation is a monolithic slab, which is so reliable that skyscrapers are even built on it.
What is good about this type of foundation?
Monolithic foundations are always strong and can withstand heavy loads. They are not afraid of uneven soil movements, constant heavy rainfall, or severe freezing and thawing. The bathhouse will simply rise and fall along with the foundation, without destroying any supports. After all, it is known that concrete works only for compression - and not for expansion. That is why a foundation in the form of a monolithic slab is practically irreplaceable for heaving and sandy soils where the groundwater level is high.
Yes, for timber, frame and log bathhouses such a foundation in some cases is a luxury - if the soil is normal, then it is easier to make a shallow strip foundation. But the Russian bathhouse itself has long ceased to be just a hut - its own dimensional ones are becoming fashionable bath complexes with swimming pools and entire billiard rooms. And for a massive steam room, a slab monolithic foundation is what you need.
Types of monolithic foundation designs
There are several types of monolithic foundation. The most popular is the slab type, which is also divided into just a slab and a slab on a tape, similar to an inverted bowl, which is becoming more and more popular abroad day by day.
But in terms of building a bathhouse, this type of monolithic foundation has proven itself to be the best so far - a monolithic slab of a simple design. Its main advantage is that there is no need to install it below the freezing depth of the soil - and this is a significant reduction in costs Construction Materials and reliability during sudden changes in air temperature.
A slab monolithic foundation is essentially a solid reinforced concrete slab that is buried in the ground. Both the external and internal walls of the bathhouse are built directly on this slab. And thanks to the uniform distribution of the entire load over the slab area, the pressure on the ground is minimized - the same physical law applies here when a person in boots falls into the snow, but not on skis, because the pressure area is already larger. The design of the slab is so versatile that it is suitable even for open peat bogs and even swamps. And most importantly, any errors are practically excluded in the construction of such a foundation, and therefore it is ideally suited for private construction. Including for a bathhouse, because the volume of excavation work in this regard is minimal, and ground floor the steam room is not really needed.
Another type of monolithic foundation is a columnar monolithic foundation, which is built for light baths. In fact, this is a single structure made of a grillage and the pillars connected to it.
But a strip monolithic foundation with a basement is capable of withstanding quite large loads and feels good in the most unfavorable climatic conditions due to the fact that it copes well with subsidence, thawing and ground vibrations. Essentially, this is a reinforced concrete strip that runs along the entire perimeter of the building. It can be shallow or recessed. The first option is suitable for a bathhouse made of logs and timber, but the second is for two-story brick steam rooms, which have considerable weight.
Stages of construction of a reinforced concrete slab
The process of constructing a monolithic foundation is much simpler than constructing prefabricated ones. But there is an important point: all materials used must be the same High Quality, because more serious requirements are imposed on a monolithic foundation. But there is no need to use construction equipment!
Stage I. Site preparation
The first thing you need to do is clear the area well: remove the top layer of soil with vegetation, for which you can hire a bulldozer.
The thickness of such a foundation, or rather, a monolithic slab, can vary from 15 to 40 cm. This depends on the characteristics of the soil, the weight of the future bathhouse and what it will be filled with.
Stage II. Digging a pit
Typically, a pit for such a foundation is dug to a depth of 1.5 meters, clay is pulled out from there and replaced with gravel or sand. The surface should be leveled according to construction level– there can be no talk of any slopes, otherwise deformation and complete destruction of the future foundation cannot be avoided.
Stage III. Installation of formwork
Sometimes such foundations are built from ready-made monolithic reinforced concrete slabs, which can be seen during construction in a panel house. They already have a clearly calculated quality, but to install them you will have to call a crane and still make a concrete screed on top of everything. And such a structure will no longer be as rigid as an absolutely monolithic slab.
But for something built with your own hands, you initially need formwork. It will require boards with a thickness of at least 25 mm plus bevels. The formwork itself must be installed with supports - and it is advisable to initially check the rigidity of the entire structure. This can be done with a simple kick - if the formwork breaks, it is better at this stage, and not during concreting.
Stage IV. Insulation and waterproofing
Here it is worth mentioning the Swedish technology for constructing such a foundation - it involves the use of modern heat and waterproofing materials. Such a base is called an insulated slab, which has amazing energy-saving properties with short construction times and low costs. Just right for a Russian bath!
Stage V. Reinforcement
The next step is to install the fittings. Sometimes a floor heating system is additionally attached to a special mesh.
It is best to take 16 mm reinforcement - in extreme cases, of course, you can use 14 mm. But calculating it is not so easy - it is better to do it in advance.
The reinforcement must be laid crosswise, in two rows. This will result in two grids - one from below, 5 cm from the surface of the sand cushion, and the second from above, 5 cm from the surface of the foundation slab. There should be exactly 20 cm between the bars in the mesh. You need to knit the reinforcement with regular steel wire.
Stage VI. Pouring the foundation
It needs to be poured in one step, and it itself must only be of a high strength class - from M300 by brand, with a water resistance coefficient greater than W8 and frost resistance from F200 and a mobility index of P3. There is an important point here - all materials used must be of the highest quality, because more serious requirements are imposed on a monolithic foundation. In total, at least 20 cubic meters of concrete will be needed.
As soon as the slab is dry, the concrete floors in the bathhouse will be completely ready for finishing. This is the biggest advantage of a monolithic foundation – minimum hassle, maximum result!
●Constructive solutions solid foundations similar to monolithic solutions reinforced concrete floors and can be designed as ribbed or beamless slabs, loaded from below by soil pressure, and from above by concentrated or distributed loads from columns or walls.
In ribbed slabs, the ribs are placed on the top or bottom of the slab. The latter solution is preferable, especially in buildings with a basement, since in this case no formwork is required for the ribs (concrete can be placed in trenches) and the construction of the basement floor is simplified. Beamless slabs are suitable for column grids close to square (see Fig. 10.1, c). Box-shaped (frame) foundations are also used for multi-story buildings and some other tall structures. They consist of upper and lower plates and a system of longitudinal and transverse vertical ribs (diaphragms).
Features of the calculation of solid foundations are set out in.
Pile foundations
●Pile foundations are used in the construction of buildings and structures on soils with insufficient bearing capacity. They consist of a group of piles united on top by a grillage - a reinforced concrete slab (beam). Compared to foundations on natural foundations, the use of pile foundations reduces the volume of excavation work, reduces the labor intensity of the zero cycle, and facilitates work in winter.
Rice. 10.6. Pile foundation diagram:
a - on rack piles, b - on hanging piles;
1 - hard ground; 2 - piles; 3 - loose soil; 4 - grillage
●By the nature of the work, a distinction is made between rack piles, resting on solid soil, and hanging piles, the load on which is perceived by the soil both over the cross-sectional area of the pile and by friction forces along its lateral surface (Fig. 10.6). In domestic practice, more than 150 types of piles are known, differing in material, construction method, etc., but reinforced concrete piles are most widespread.
●Based on the cross-sectional shape, reinforced concrete piles are distinguished between solid and hollow (hollow and shell piles). With a cross-sectional diameter of up to 800 mm and the presence of an internal cavity, piles are called hollow piles, with a diameter of more than 800 mm - shell piles.
For light loads, piles of square solid cross-section (solid and composite) with dimensions from 200×200 mm to 400×400 mm, length 3...16 m without prestressing longitudinal reinforcement and 3...20 m with prestressing are widely used. Piles without prestressing are made of class B15 concrete, reinforcement of classes A-II, A-III, with a diameter of at least 12 mm. In the upper part of the pile, which directly receives the hammer blow, 3...5 meshes of reinforcing wire are installed at a distance of 5 cm from each other. In the middle part there are two sling loops. The pitch of the transverse (spiral) reinforcement is 50 mm at the ends of the pile, and 100...150 mm in the middle part (Fig. 10.7). Piles with prestressed longitudinal reinforcement are made of B20...B25 concrete; Compared to piles without prestressing reinforcement, they are more economical (in terms of reinforcement consumption) and therefore preferable. Hollow round piles and shell piles are used for heavy loads. They are made in links 2...6 m long. The joints of the links can be bolted, welded or on liners.
The bearing capacity of foundations on rack piles (for any arrangement in plan) is equal to the sum of the bearing capacities of individual piles, and the bearing capacity of pile foundations on hanging piles depends on the number of piles, their arrangement in plan, shape, cross-sectional dimensions and length.
Piles and pile foundations are calculated based on limit states. Using the limit states of the first group, the load-bearing capacity of piles on the ground, the strength of the material of piles and grillages are determined; Using the limit states of the second group, settlements of pile foundations, the formation and opening of cracks in reinforced concrete foundations and grillages are calculated. In addition, the piles are calculated based on their strength to withstand the forces arising during installation, transportation, as well as when removing the piles from the steaming chambers.
They are divided into: separate - under each column; strip - under rows of columns in one or two directions, as well as under load-bearing walls; solid - under the entire structure. Foundations are most often erected on natural foundations (they are mainly discussed here), but in some cases they are also built on piles. In the latter case, the foundation is a group of piles united on top by a distribution reinforced concrete slab - a grillage.
Individual foundations are constructed with relatively light loads and relatively sparse placement of columns. Strip foundations under rows of columns are made when the bases of individual foundations come close to each other, which usually happens with weak soils and heavy loads. It is advisable to use strip foundations for heterogeneous soils and external loads of varying magnitude, since they level out uneven settlements of the foundation. If the bearing capacity of strip foundations is insufficient or the deformation of the foundation under them is greater than permissible, then solid foundations are installed. They even out the foundation sediments to an even greater extent. These foundations are used for weak, heterogeneous soils, as well as for significant and unevenly distributed loads.
Based on the manufacturing method, foundations can be prefabricated or monolithic.
28. Shallow reinforced concrete foundations. Calculation of centrally loaded foundations.
Depending on the size, prefabricated column foundations are made prefabricated or monolithic. They are made from heavy concrete of classes B15...B25, installed on compacted sand and gravel preparation with a thickness of 100 mm. The foundations include reinforcement placed along the base in the form of welded mesh. The minimum thickness of the protective layer of reinforcement is 35 mm. If there is no preparation under the foundation, then the protective layer is made at least 70 mm.
Required area of the base of a centrally loaded foundation upon preliminary calculation
A=ab=(1.2…1.6)Ncol/(R-γ m d) R – design pressure on the ground; γ m average load from the weight of the foundation and soil on its steps; D – foundation depth
The minimum height of a foundation with a square base is determined by conditionally calculating its punching strength on the assumption that it can occur along the surface of a pyramid, the sides of which begin at the columns and are inclined at an angle of 45°. This condition is expressed by the formula (for heavy concrete)
P<=Rbt ho u m
The punching force is taken according to the calculation for the first group of limit states at the level of the top of the foundation minus the soil pressure over the area of the base of the punching pyramid: P=N-A1 p.
P=N/A1; A1=(hc+2ho)(b c +2h 0)
29. Shallow reinforced concrete foundations. Features of the calculation of eccentrically loaded individual foundations.
Eccentrically loaded foundations. It is advisable to perform them with a rectangular sole, elongated in the plane of action of the moment.
Aspect ratio b/a=0.6…0.8. Moreover, we round the dimensions of the sides up to a multiple of 30 cm when using metal inventory formwork and 10 cm when using non-inventory formwork.
The maximum and minimum pressure under the edge of the sole is determined from the assumption of a linear distribution of stresses in the soil:
Pmax min=Ntot/A+-Mtot/W=Ntot/ab(1+-b*eo/a)
Ntot Mtot – normal force and bending moment at gamma f = 1 at the level of the base of the foundation.
Ntot=Ncol+A gamma m N
Mtot=Mcol+Qcol H
Eo is the eccentricity of the longitudinal force relative to the center of gravity of the foundation base. Eo= Mtot/ Ntot
The maximum edge pressure on the ground should not exceed 1.2R and the average pressure - R.
In industrial buildings with Q overhead cranes<75 т принимают pmin>0, separation of the foundation from the ground is not allowed.
The height of an eccentrically loaded foundation is determined from the condition:
Ho=-hcol/2+0.5(Ncol/Rbt+P)^0.5
And design requirements
Hsoc=>(1-1.5)hcol+0.05
Hsoc=>lan+0.05
Hsoc – glass depth
Lan – anchorage length of the column reinforcement in the foundation glass
Having determined the height of the foundation based on punching force and design requirements, the larger one is accepted.
At h<450
мм фундамент выполняют одноступенчатым,
при 450 Then the bottom of the glass is checked for punching, the height of the step is checked for the action of transverse force along the inclined section and the reinforcement is selected. 30. Classification of one-story industrial buildings according to design characteristics. Layout of the structural diagram of the building, linking elements to alignment axes. Construction of temperature expansion joints. One-story industrial buildings are divided into: By the number of spans - single-span and multi-span; By the presence of crane equipment: buildings without crane equipment, buildings with overhead cranes, buildings with overhead cranes; Lantern and lanternless buildings; Buildings with pitched roofs, buildings with low-slope roofs. Modern one-story industrial buildings are in most cases constructed using a frame design. The frame can be formed from flat elements working according to a beam scheme (truss structures), or include a spatial structure of the covering (in the form of shells supported on columns). The spatial frame is conventionally divided into transverse and longitudinal frames, each of which absorbs horizontal and vertical loads. The main element of the frame is a transverse frame, consisting of columns clamped in the foundations, crossbars (truss beam arch), and a covering above them in the form of slabs. The transverse frame absorbs the load from the mass of snow, cranes, walls, wind and ensures the rigidity of the building in the transverse direction. The longitudinal frame includes one row of columns within the temperature block and longitudinal structures, such as crane beams, vertical braces, column struts, and covering structures. The longitudinal frame provides rigidity to the building in the longitudinal direction and absorbs loads from the longitudinal braking of the cranes and the wind acting at the end of the building. The task of constructing a structural diagram includes: Selecting a grid of columns and internal dimensions of the building Coverage layout Dividing the building into temperature blocks Selecting a connection scheme that ensures the spatial rigidity of the building In order to ensure maximum typification of frame elements, the following references to the longitudinal and transverse coordination alignment axes have been adopted: 1. The outer edges of the columns and the inner surfaces of the walls are aligned with the longitudinal alignment axes (zero reference) in buildings without overhead cranes and in buildings equipped with overhead cranes with a lifting capacity of up to 30 tons inclusive, with a column spacing of 6 m and a height from the floor to the bottom of the load-bearing structures of the coating less than 16.2 m. 2. The outer edges of the columns and the inner surfaces of the walls are shifted from the longitudinal alignment axes to the outside of the building by 250 mm in buildings equipped with overhead cranes with a lifting capacity of up to 50 tons inclusive, with a column spacing of 6 m and a height from the floor to the bottom of the load-bearing structures of the coating of 16.2 and 18 m , as well as with a column pitch of 12 m and a height from 8.4 to 18 m. 3. Columns of the middle rows (with the exception of columns adjacent to the longitudinal expansion joint, columns installed in places where the heights of spans in one direction differ, as well as columns with transverse expansion joints and columns adjacent to the ends of buildings) are positioned so that the crane section axes parts of the column coincided with the longitudinal and transverse alignment axes. 4. The geometric axes of the end columns of the main frame are shifted from the transverse alignment axes into the building by 500 mm, and the internal surfaces of the end walls coincide with the transverse alignment axes (zero alignment). 5. Height differences between spans of the same direction and longitudinal expansion joints in buildings with a reinforced concrete frame should, as a rule, be carried out on two columns with an insert. 6. Transverse expansion joints are carried out on paired columns. In this case, the axis of the expansion joint is aligned with the transverse alignment axis, and the geometric axes of paired columns are shifted from the alignment axis by 500 mm. 7. In buildings equipped with electric overhead cranes with a lifting capacity of up to 50 tons inclusive, the distance from the longitudinal alignment axis to the axis of the crane rail is taken to be 750 mm. 8. The junction of two mutually perpendicular spans should be carried out on two columns with an insert measuring 500 and 1000 mm. The height of the building is determined by technological conditions and is assigned based on the top of the crane rail. With changes in temperature, reinforced concrete structures are deformed - shortened or lengthened; due to concrete shrinkage, they are shortened. When the foundation settles unevenly, parts of the structures are mutually displaced in the vertical direction. In most cases, reinforced concrete structures are statically indeterminate systems and therefore, due to temperature changes, shrinkage of concrete, as well as uneven settlement of foundations, additional forces arise in them, which can lead to the appearance of cracks or destruction of part of the structure. To reduce the forces caused by temperature and shrinkage, reinforced concrete structures are divided along the length and width by temperature-shrinkage joints into separate parts - deformation blocks. Temperature-shrinkage joints are made in the ground part of the building - from the roof to the top of the foundation, while separating the floors and walls. The width of the temperature-shrinkable seam is 20-30 mm. Settlement joints, which also serve as temperature-shrinkable joints, are installed between parts of buildings of different heights or in buildings erected on a site with heterogeneous soils; foundations are also divided with such seams. Sedimentary joints are made using an inlay span of slabs and beams. The maximum permissible distance between temperature-shrinkage joints in reinforced concrete structures is standardized and is 72 m in heated one-story buildings made of precast reinforced concrete, and 48 m in unheated ones. They are a type of shallow, or rather, non-buried foundations, the depth of which is 40 - 50 cm. Unlike shallow strip and column foundations, they have rigid spatial reinforcement along the entire load-bearing plane, which allows them to withstand alternating loads that arise during uneven movement without internal deformation soil. Foundations that, together with the soil, move seasonally are called floating. Their design is a solid or lattice slab made of cast-in-place reinforced concrete, precast cross-beams or precast slabs with a monolithic cover (Fig. 1). The construction of a slab foundation is associated with the consumption of concrete and reinforcement and may be advisable when constructing small and compact houses or other buildings when a high base is not required and the slab itself is used as a floor. For higher-class houses, foundations are often installed in the form of ribbed slabs or reinforced cross strips. The large support area of the slabs makes it possible to reduce the pressure on the ground to 10 kPa (0.1 kgf/cm2), and the cross stiffening ribs create a structure that is sufficiently resistant to alternating loads that occur during freezing, thawing and subsidence of the soil. For their construction, high-strength concrete (not lower than class B12.5) and reinforcing bars with a diameter of at least 12 - 16 mm are used. The relatively large consumption of concrete and reinforcing steel can be considered justified if all other technical solutions for foundations under these conditions cannot guarantee their reliable operation. In buildings where the floors are located low above the ground level, such foundations can be even more economical than columnar foundations (there is no need to install a basement floor and grillage). A solid, non-buried slab as part of the spatial system “slab - superfoundation structure” ensures the perception of external force influences and possible deformations of the soil foundation and eliminates the need for various kinds of measures to prevent uneven deformations of the soil, which usually require significant resources in conditions of weak, sandy and heaving soils. The use of non-buried foundation slabs allows reducing concrete consumption by up to 30%, labor costs by up to 40% and the cost of the underground part by up to 50% compared to buried foundations. To protect such foundations from freezing, they must be insulated. Frost-resistant shallow foundations are a practical alternative to more expensive deep foundations in cold regions with seasonal ground freezing and potential for frost heave. Shallow laying of frost-resistant foundations is achieved by installing thermal insulation placed in the most important places - practically around the house. Thus, it becomes possible to carry out foundations with a laying depth of 40 - 50 cm even in very harsh climates. The technology of frost-resistant shallow foundations has gained wide recognition in the Scandinavian countries. Frost-resistant foundations are made in the form of a monolithic reinforced concrete slab 25 - 20 cm thick with thickened edges - contour ribs, and foam insulation (foam plastic) is used to protect against frost (Fig. 2). Fig.2. Scheme of an insulated monolithic foundation slab with thickened ribs: 1 - continental soil; 2 - compacted sand cushion; 3 - monolithic reinforced concrete slab; 4 - insulation with waterproofing; 5 - concrete blind area Rice. 3. Scheme of reinforcement of a monolithic slab: 1 - reinforcing bars AIII, d 12-16 mm; pitch 200 mm; 2 - reinforcing bars AIII, d 8 mm, pitch 400*400 mm; 3 - protective layer of concrete 35 mm thick Heat escaping from the house into the ground through the foundation slab, plus geothermal heat, causes the frost line to rise up along the perimeter of the foundation. Experts know that heat from a building actually reduces the depth of freezing around the perimeter of the foundation. In other words, the frost line rises near any foundation if the building is heated or insulated at ground level. Foundation perimeter insulation prevents heat loss and transfers heat through the foundation slab into the soil beneath the building's foundation. At the same time, geothermal heat sources radiate heat towards the foundation, which reduces the frost depth around the building. When building houses using frost-resistant foundations, one of the problems that builders face is that polypropylene decomposes under the influence of ultraviolet radiation and has insufficient impact resistance. Vinyl chloride plastic in the form of a roll 610 mm wide, 15 m long is well suited for these purposes. The upper outer edge of the foundation is wrapped with film, starting from the inner edge of the slab. The plastic is easily bonded to the edge of concrete and polypropylene foam with a mastic compatible with the foam. Flexible vinyl chloride plastic is glued in place. It is important to note the cost savings when constructing frost-resistant foundations in comparison with traditional ones. It accounts for approximately 3% of the total mandatory costs of building a house. Solid slab foundations are also installed buried in the form of a monolithic slab under the entire building (Fig. 3). Such structures ensure the most uniform distribution of the load on the foundation and, as a result, uniform settlement of the building, and also protect basements well from groundwater backing up. Solid foundations are erected on weak or heterogeneous soils when it is necessary to transfer significant loads to them. Such structures have proven themselves well in low-rise construction, especially if it is necessary to organize a basement or semi-basement under the building. The construction of basement or semi-basement premises affects another important aspect of design and construction - waterproofing (waterproofing, etc.) of foundations from groundwater and moisture. A competent assessment of the hydrological situation at the construction site, the correct choice of water protection scheme and high-quality work are the main conditions, the fulfillment of which largely determines the trouble-free operation of both the underground and above-ground parts of buildings. Violation or destruction of the structure of a building is almost always associated with violations or destruction of its foundation. This may occur due to errors made during design or construction. Only with a responsible approach to the entire range of work - from design to practical implementation - can you build a reliable house that will last for many decades. Options for installing non-buried slab foundations are shown in Fig. 1.
