●Constructive solutions for solid foundations are similar to solutions for monolithic reinforced concrete floors and can be designed as ribbed or beamless slabs, loaded from below with soil pressure, and from above - 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.
When you plan to build your own home, you want everything to be perfect, starting from the foundation. Since this is the most important part of any construction, it is important to know how to properly make the foundation for a house in order to prevent subsidence or, conversely, heaving. A well-made and correctly selected foundation for a house, taking into account the type of soil, is the key to its long service life and comfort.
The choice of foundation depends on many factors. The design can be simple and labor-intensive, or take into account many factors. The following foundations are distinguished and widely used:
- pile;
- monolithic or slab;
- tape;
- columnar.
The following criteria will help you choose the right type of foundation:
- weight and structural features of the future house;
- soil type;
- the nature of the terrain;
- depth of groundwater.
Depending on the set of specific characteristics of the site, one or another design is chosen, each of which has its own application features.
Tape
This type of base is suitable for houses with medium to high mass. For example, for buildings made of brick or cinder block, as well as monolithic ones made of reinforced concrete. The strip foundation is characterized by:
- high strength;
- uniform distribution of force on the ground;
- Allows for varying thicknesses to compensate for mass.
The technology for constructing and pouring a strip foundation can be considered classical, since it uses all the techniques and approaches involved in creating other types of foundations. The answer to the question of how to properly make a strip foundation can be extensive, since different solutions can be used for insulation, ventilation, and drainage.
Strip foundations can be used on all types of soils in average climates. If the ground freezes, as well as loose soil, you should not choose a strip foundation structure for a large house.
Columnar
For houses with low mass, for example, those assembled using modern technologies of frame-panel and wooden housing construction, a columnar foundation is perfect. There is no single answer on how to properly make a columnar foundation, since there can be many engineering solutions. From brick pillars laid on a waterproofed sand and gravel bed to reinforced concrete pillars cast in formwork.
The columnar foundation is characterized by the following features:
- relatively low material consumption;
- ease of construction;
- the ability to carry out work quickly and immediately begin installation of the house.
The columnar foundation works well on stable soils with deep groundwater and is suitable for buildings with low mass. In some cases, with flat terrain, you can replace the columnar one by laying concrete blocks on a cushion.
Pile
In conditions of deeply frozen soil or unstable outer layer, a pile foundation is used. The design is simple and reliable. Piles are driven into the ground, located at a distance of one to two meters, depending on the load capacity of the soil. The upper parts of the piles are tied together with beams or a solid slab is poured on which the structure is directly located.
Such a foundation correctly and evenly distributes the load of the house over a large volume of soil, while simultaneously providing the opportunity to erect buildings of large mass and get rid of problems that arise when soil characteristics change with climate or groundwater levels.
Pile-type foundation structure for a private house
Solid or block
It is the simplest design and at the same time the most resource-intensive. A solid foundation can represent various solutions:
- a solid block poured into a relatively large pit;
- space lined with reinforced concrete blocks;
- vaults and box structures;
- beam structures;
- slab, it is possible to use a unified building slab of constant thickness with support columns built on it.
A solid foundation is used in the most difficult cases - unstable soils, soils with low load capacity. Block guarantees the absence of uneven settlement of the house.
The option to make a solid foundation for the house has its advantages
The load from the mass of the building is distributed evenly over the ground, so even unstable soil can show good results. Where stable areas are located, the force is distributed to a greater extent, on unstable areas - to a lesser extent.
It is correct to use a solid foundation when constructing large or massive structures, since its final cost is such that in a private or low-rise building such an approach is not justified.
Methods for building a good foundation
For any work, there is a mandatory and additional list of actions that will ensure the correct microclimate of the foundation, prevent its destruction, as well as negative factors such as penetration of dampness or swelling of the soil. Briefly about the operating procedure:
- pillow construction;
- preparatory work;
- horizontal waterproofing;
- fill;
- vertical waterproofing;
- insulation.
The structure will help to make the foundation for the house correctly and reliably
Waterproofing
To answer the question of how to properly waterproof a foundation in a country house, you need to describe the evaluation criteria on which the selected types of protection depend. With any method, a number of factors must be taken into account:
- Approximate groundwater level. To do this, you need to dig a vertical hole a meter or more deep. If it does not fill with water over time, it means that the groundwater lies deep.
- When constructing a foundation, especially a strip type, the risk of flooding and flooding should be taken into account.
The house must be protected from moisture
- If the soils on which buildings are erected are characterized by high humidity, it would be correct to take into account the rise of the soil due to the fact that water freezes in winter and expands.
- Depending on the type of house, different types of water insulation must be used. For example, for an unheated warehouse space, you need to ensure a minimum level of humidity.
Waterproofing can be divided into direct - by methods of treating the surface of the foundation - and additional, which includes drainage and a ventilation system.
Drainage system design
In cases where groundwater comes close to the surface or there is a danger of light flooding, a system for draining water from the foundation is constructed.
There is an optimal answer to the question of how to properly drain the foundation. To do this, a depression is dug around the perimeter with an inclination to one point, from which water is drained. The depth of the ditch should be below the level of groundwater rise, and it should be located at a distance of 70-100 cm from the foundation.
Drainage is properly arranged as follows:
- the bottom of the ditch is located 20-30 cm below the base of the foundation;
- the surface is covered with polymer textiles, which are applied to the walls and around by 50 cm;
- a small layer of gravel is poured and a drainage pipe is placed;
- It is recommended to make the pipe slope 5 mm per linear meter; to change the slope, you can add gravel from below;
- gravel is poured almost to the top of the ditch, wrapped in textiles and everything is covered with a layer of earth.
Don't forget to drain properly
If done correctly, the result is a long-lasting system because the gravel easily carries water to the pipe without causing it to become clogged. Excess water is discharged into a convenient drain.
Bottom waterproofing
A mandatory measure is the bottom layer of moisture protection. A thin concrete screed is poured onto a sand-gravel cushion or clay layer. After it hardens, it is treated with bitumen and a layer of roofing felt or roofing felt is laid. It is coated with mastic and another layer is applied. At the end, another concrete screed is poured.
After it has dried, you can begin the main work of pouring the foundation. Similar insulation can be carried out for the top surface, since this guarantees the absence of moisture, which is very important for a wooden house.
Vertical waterproofing
Complete protection of the foundation from water penetration is carried out by treating its vertical surfaces. It can be done:
- Bitumen mastic, which is heated and applied in 2-4 layers. The method is simple, cheap and accessible, but the effectiveness of protection lasts approximately 5-10 years.
- Ruberoid. It is done in the same way as covering a roof using bitumen mastic and applying roofing material heated by a burner.
- Insulated with special plaster. The method can be used to solve two problems at once - waterproofing and surface leveling.
- Liquid rubber. The foundation is treated with a penetrating primer, then a special composition is sprayed onto it. The method is expensive, but the coating is very durable.
- Penetrating compounds. Using a sprayer, a special composition is applied that penetrates to a depth of more than 10 cm. This insulation is the most effective, but the method is the most expensive.
There are different ways to waterproof the base of a house.
One of the classic methods of waterproofing is a clay castle. This is a layer of gravel poured around the perimeter and clay laid on it in several layers. As a result, water cannot penetrate into the base.
Today you can also find clay mats that can be attached to the vertical surface of the foundation. The method is cheap, but the least effective. However, with a combination of techniques, a clay castle can be an excellent addition to the main waterproofing.
Insulation
To achieve good conditions in the basement or to ensure a warmer floor in cold climates, the foundation is insulated. For this, mineral wool mats, various types of insulation, even polyurethane foam and boards can be used in some cases (convenient when insulating a columnar type base).
But the leader in the role of insulation is polystyrene foam. The insulation process can be briefly described as follows:
- Dig a trench around the perimeter of the future house.
- Clean the surfaces and waterproof them.
- Lay polystyrene foam close to the foundation.
The house must be insulated
Vertical sheets can be supplemented with horizontal insulation. To do this, a layer of soil is removed along the perimeter to a depth of approximately 50 cm, sheets of foam plastic are laid and a sand cushion is poured almost to ground level. After this, a concrete blind area with a width of 700 to 1000 millimeters is formed, inclined outward from the foundation. Make a drainage ditch along the edge of the blind area to drain water.
How to make a pillow
The foundation cushion is used in the construction of any type of structure, except for piles with beam connections. To do this, sand is poured into the bottom of a ditch, pit or pit under the post and compacted. It is best to use special settings for this purpose. Crushed stone is poured into the second layer and compacted in the same way. The total thickness of the pillow is 20-25 cm.
How to make a specific type of base correctly is shown in the diagram
Now that we have considered all types of work separately, we will describe how to properly make a foundation for a house using the example of creating a strip-type structure (as the most complex), as they say, from scratch.
- Carefully mark the location of the building.
- Mark the lines along which the foundation will go.
- Remove a layer of fertile soil.
- Determine the lowest point in the area. The depth of the foundation will be measured from it.
- Dig ditches to the required depth.
- Make a sand and gravel bed.
- Make a layer of horizontal waterproofing.
- Install formwork.
- Pour a layer of concrete approximately 10 cm thick.
- Install fittings.
- Pour the base layer.
After the composition has hardened, if necessary, an upper horizontal layer of waterproofing is made, the formwork is removed and all the necessary work is carried out on the construction of a drainage system, vertical waterproofing and insulation.
The construction of a pile foundation, in addition to driving, digging or screwing in piles, also includes work on marking the territory, determining the lowest point, removing soil, and filling a cushion. After which a flat foundation slab is poured and waterproofed.
Making a quality foundation for a house is a top priority
A columnar foundation can be constructed either by a simple method of casting pillars in formwork (in this case, the procedure is similar to the previous one), or by laying out columns from bricks or blocks. In this case, the cushion is filled and waterproofed, and also, depending on the size of the pillars, vertical waterproofing and insulation can be done.
As you can see, making a foundation correctly is a labor-intensive job that requires many operations. However, a responsible approach to each of them guarantees that the house will last a long time, without defects.
Foundations for low-rise construction are made from local building materials (natural stone, rubble concrete, red brick, etc.), and they also use monolithic concrete or prefabricated concrete and reinforced concrete blocks.
The plane of the lower part of the foundation is called sole(Fig. 3.1), its broadening is pillow, and the horizontal plane of the upper part of the foundation is with a sawn-off shotgun. In the absence of basements and large pits, shallow foundations are usually designed, the base of which is located at a depth of at least 0.5 m from the ground level. On soils that swell when frozen, the depth of the base of the foundation of the external walls is taken to be at least 0.2 m below the thickness of the freezing layer.
There is a certain relationship between the architectural and planning solution of a low-rise building, the design of the foundation and the condition of the soil. For example, if an architect envisions a basement, large pit, or basement in a house design, then the foundation must be of a strip structure in order to successfully serve as a basement wall. The condition of the soil can influence the choice of architectural solution for the underground part of the house. For example, if a house is placed on soils with a high level of groundwater, then the thickness of the walls of the strip foundation increases due to additional waterproofing elements, which leads to a slight reduction in the area of the underground premises. In addition, there may be a threat of the basement part along with the house or part of the house with the pit rising (“floating up”) under the influence of groundwater pressure. In this case, it is usually necessary to abandon the design of underground premises or to design an expensive foundation structure with anchors in the ground or a weighted floor of the underground premises.
The most important parameter on which the shape and volume of foundations depend is foundation depth.Foundation depth- Thisdistance from the ground surface to the base of the foundation.
The depth of foundations depends on many factors: the purpose of the building; its space-planning and design solutions; magnitude and nature of loads; quality of the base; surrounding buildings; relief; accepted foundation designs and methods of construction work. However, first of all, the depth will determine the quality of the foundation soil, groundwater level and soil freezing.
The minimum foundation depth for heated buildings is usually 0.7 m for external walls and 0.5 m for internal walls.
The practice of operating low-rise residential buildings with shallow foundations has shown that soils that swell when frozen gradually push such foundations out of the ground. Over the course of several years, a house can rise above ground level by tens of centimeters, while different sections of the building usually rise by different amounts, which leads to skewing of windows, doors and even breaking of walls. This phenomenon occurs from the action of lateral friction forces of swelling soil on the surfaces of foundations, which exceed the resistance of the relatively small mass of the house. To neutralize the undesirable effect of swelling when the soil freezes, it is necessary to design houses without basements on shallow foundations with a base in the form of a sand cushion. When installing a sand cushion, the soil is removed to a depth below freezing of at least 0.2 m and the excavation is filled with coarse sand, poured with water and compacted layer by layer. Backfilling is carried out to a level of 0.5 m from the site planning level. Shallow foundations are installed on the artificial foundation obtained in this way. This technique allows you to achieve significant savings in materials and costs. For example, in the Kyiv region, the depth of soil freezing is 0.9 m, therefore, a shallow foundation will be 1.1 m high, and with a sand cushion - 0.5 m, i.e. with a sand cushion on soils that swell from freezing, about 50% of the material for constructing the foundation is saved.
According to the method of construction, foundations can be industrial or non-industrial. In mass construction, industrial foundations are used, which are made from prefabricated large-sized concrete or reinforced concrete elements. These foundations allow work to be carried out without seasonal restrictions and reduce labor costs on the construction site. Non-industrial foundations can be made of monolithic concrete or reinforced concrete, as well as small-sized elements (brick, rubble stone, etc.). Foundations of this kind are used, as a rule, for non-standard buildings.
By the nature of their work, foundation structures can be rigid, working only in compression, and flexible, which are designed to absorb tensile forces. The first type includes all foundations, with the exception of reinforced concrete ones. The use of flexible reinforced concrete foundations that can withstand bending moments can dramatically reduce the cost of concrete, but sharply increases the consumption of metal.
According to the structural design, foundations are divided into strip, columnar, pile and solid.
Install under all load-bearing walls of the building strip foundations in the form of solid walls. They can serve not only as a load-bearing structure that transfers permanent and temporary loads from the building to the foundation, but also as an enclosing structure for basement premises.
Strip foundations they are installed under all main (load-bearing and self-supporting) walls, and in some cases under columns. They are strip-walls sunk into the ground with a rectangular or stepped cross-section.
Strip foundations have become widespread in residential construction for buildings up to 12 floors, built using a frameless design.
The shape in plan and section, as well as the dimensions of the strip foundation, are set so as to ensure the most even distribution of the load on the base. The size of the foundation base is determined by calculation depending on the mass of the above-ground part, the foundation material and the bearing capacity of the soil. The thickness of its wall is determined by calculating strength and depending on the technological features of the material, for example, a wall made of rubble concrete is made at least 0.35 m thick, depending on the size of the filling stones. It is necessary to ensure that the resultant of all loads from the building passes in the middle third of the width of the base of the foundation, i.e. e< 1/3 (рис.3.3). Этим самым исключается появление в фундаменте растягивающих усилий.
Depending on the magnitude and direction of the design loads, strip foundations can be symmetrical or asymmetrical (Fig. 7.3).
Fig.7.3. Strip foundations: a – plan and section of a strip foundation made of prefabricated concrete blocks for a building with a basement; b, c – options without a basement made of solid and hollow blocks; d, e, f – design of a rigid foundation with a minimal, normal and maximally widened base; g – asymmetrical foundation; and – transition from one foundation depth to another; k, l, m, - options for strip foundations made of monolithic concrete, rubble concrete and rubble; 1 – basement wall blocks; 2 - hollow wall blocks of basements; 3 - foundation pillows; 4 – walls; 5 – floors; 6 – basement floors; 7 – blind area; 8 – concrete foundation; 9 – rubble concrete foundation; 10 – rubble foundation; 11 – floor of the first floor.
For the manufacture of strip foundations, any building materials except wood are used. On rocky soils, monolithic concrete with the inclusion of rock fragments (rub concrete) is more often used. This material better fills uneven surfaces of the rock base. Rubble stone foundation strips are characterized by lower cement consumption, but are more labor and material intensive. Due to the size of the stones, according to the standard, the minimum width of the strips is taken to be no less than 0.5 m. As a rule, the walls of strip foundations made of these materials for low-rise buildings do not have widening in the area of the soles. Strip foundations made of red brick are designed for dry, strong soils with a thickness of 0.25 - 0.51 m. It is better to make the brick foundation pad from monolithic reinforced concrete with a thickness of at least 0.1 m, which increases the durability of the structure.
In mass construction conditions, strip foundations are usually erected from prefabricated concrete or reinforced concrete elements. Prefabricated strip foundations are assembled from two types of blocks (Fig. 7.4) - foundation pillow blocks (FBP) and wall blocks (FSB). The latter are made solid from lightweight concrete (γ ≤ 1600 kg/m 3) or hollow from heavy concrete (γ > 1600 kg/m 3), which can be used for internal walls and for external ones in soils not saturated with water. Wall blocks are used in the following sizes: height 0.6 m, length up to 2.4 m and width 0.3, 0.4, 0.5 and 0.6 m.
Fig.7.4. Prefabricated strip foundations: a – foundation design for weak soils; b – laying foundation blocks with dense soils and low loads; c, d - foundations of large-panel buildings; d – elements of prefabricated large-block concrete foundations; f, g – elements of large-panel foundations.
Installation of prefabricated concrete foundations is carried out using cement mortar and bandaging the seams. In case of weak soils, reinforced distribution belts are laid along the foundation pads and along the edge of the foundation (Fig. 7.4 a). For dense soils and light loads, foundation pads can be laid at intervals (Figure 7.4 b). The gaps should be filled with soil.
For low-rise buildings with low loads and strong foundations, when strip foundations are irrational, they are used columnar foundations. They are installed under all load-bearing and self-supporting walls, as well as under individual pillars and columns.
Columnar foundations are foundations consisting of pillars sunk into the ground and foundation beams resting on them, which take the load from the walls and transfer it to the pillars.
The pillars are installed at the intersections of the walls and in the spaces between them with a certain pitch, which is determined by calculation depending on the mass of the building and the bearing capacity of the soil. For low-rise buildings, the pitch of the foundation pillars is 2.5 - 3.0 m.
Structural options for foundation beams and their proportions depending on the pitch of the pillars are shown in Fig. 7.5. To eliminate the possibility of displacement of the foundation beam and the wall located on it due to soil heaving, a cushion of sand or slag 0.4 m thick is placed under the foundation beam.
Fig.7.5. Structural diagrams of foundation beams for columnar foundations: a – fragment of a general view of the foundation; 1 – wall; 2 – foundation beam; 3 – pillars; b – f – various types of foundation beams; 4 – prefabricated reinforced concrete; 5 – prefabricated reinforced concrete lintels (reinforced beams); 6 – monolithic reinforced concrete beam; 7 – ordinary reinforced brick beam; 8 – reinforced brick beam with steel frames in the vertical joints of the masonry.
Pillars with a square cross-section in diameter are made from prefabricated concrete blocks, monolithic concrete, red brick, and natural stone. The dimensions of the pillars are taken based on strength calculations (material and soil). For low-rise residential buildings, the size of the pillar cushion does not exceed 1 m, and the horizontal section of the pillar can be equal to the size of the base or be smaller. In the latter case, the height of the pillow is taken to be no more than 0.3 m.
In cases where it is necessary to transfer significant loads to soft soil, pile foundations .
Pile foundations are foundations consisting of reinforced concrete, concrete or metal pile rods immersed in the ground, caps - the upper widened end of the pile, and a grillage that combines the work of all piles
Pile foundations are used on weak compressible soils, with deep occurrence of strong continental rocks, heavy loads, etc. Recently, pile foundations have become widespread for conventional foundations, because... their use provides significant savings in excavation volumes and concrete costs.
According to the material, piles can be wooden, reinforced concrete, concrete, steel and combined. Depending on the method of immersion in the ground, driven, driven, shell piles, drilled and screw piles are distinguished (Fig. 7.6).
Driven piles immersed using pile drivers, vibrating hammers and vibrating pressing units. These piles are most widely used in mass construction. In cross-section, reinforced concrete piles can be square, rectangular or hollow round: ordinary piles with a diameter of up to 800 mm, and shell piles - over 800 mm. The lower ends of the piles can be pointed or flat, with or without widening, and hollow piles can be with a closed or open end and with a camouflage heel (Fig. 7.6 d).
Driven piles arranged by filling pre-drilled, punched or stamped wells with concrete or another mixture. The lower part of the wells can be widened using explosions (piles with a camouflage heel).
Bored piles They differ in that ready-made reinforced concrete piles are installed into the well and the gap between the pile and the walls of the well is filled with cement-sand mortar.
Depending on the nature of the work in the ground, two types of piles are distinguished: rack piles and hanging piles. Rack piles , cutting through the thickness of weak soil, their ends rest on strong soil (rock) and transfer the load from the building to it. They are used when the depth of solid soil does not exceed the possible length of the piles. Foundations on rack piles practically do not give rise to precipitation.
If solid soil is located at a considerable depth, use hanging piles , the bearing capacity of which is determined by the sum of the resistance of friction forces on the side surface and the soil under the tip of the pile. Pile foundations in plan may consist of:
single piles - for individual supports (Fig. 7.6 d);
strips of piles - under the walls of a building, with piles arranged in one, two or more rows;
bushes of piles - under heavily loaded supports;
continuous pile field - for heavy structures with loads evenly distributed throughout the entire building plan.
Fig.7.6. Pile foundations: a – plan and sections; b – types of piles depending on the design scheme – rack piles and hanging piles; c – elements of a pile foundation: 1 – grillage; 2 – criminal; 3 – pile; d – types of piles: 1 – four driven concrete and reinforced concrete piles – square, round, solid and hollow; 5.6 – printed regular and with a widened heel; 7, 8 – camouflage; 9 – with hinged opening stops; 10 – prismatic pile; 11 – pile-shell; 12 – pile in the leader well; 13 – wooden pile; 14 – screw pile; d – arrangement of piles: pile rows, pile bushes, pile field; e – option of a pile foundation without grillage; g, i – options for pile foundations without grillages and caps: 1 – cap; 2 – pile; 3 – base panel; 4 – floors; 5 – column; 6 - crossbar
For low-rise construction, short reinforced concrete driven piles are used, usually with a square section of 150 × 150 mm, 200 × 200 mm, or drilled piles with a diameter of 300, 400 mm or more. The depth of laying short piles is no more than 6 m.
The distance between the piles and their number are determined by calculation. Typically, the distance between hanging piles is taken to be (3 – 8)d, where d is the diameter of a round pile or the side of a square pile. The clear distance between shell piles must be at least 1 m.
Grillage beams have much in common with foundation beams. The same materials are used for their manufacture. There are two types of reinforced concrete grillage - monolithic and prefabricated. Its width is 250 × 250 or 300 × 300 mm, height – 400 – 500 mm.
Pile foundations are 32–34% more economical than strip foundations in terms of cost, 40% in terms of concrete costs and 80% in terms of the volume of excavation work. Such savings make it possible to reduce the cost of the building as a whole by 1–1.5%, labor costs by 2%, and concrete consumption by 3–5%. However, steel costs increase by 1 - 3 kg per m 2.
In cases where the load transferred to the foundation is significant and the foundation soil is weak, arrange solid foundations under the entire building area. They are usually built on heavy heaving and subsidence soils.
Solid foundations are foundations in the form of rigid solid beam or beamless concrete or reinforced concrete slabs, arranged under the entire area of the building.
Such foundations well level all vertical and horizontal movements of the soil.
The ribs of the beam slabs can face up or down. The intersections of the ribs are used to install columns in frame buildings. The space between the ribs in slabs with the ribs up is filled with sand or gravel, and a concrete screed is placed on top. Concrete slabs are not reinforced. Reinforced concrete reinforced according to calculation. If solid foundations are deeply buried and there is a need to ensure their greater rigidity, the foundation slabs can be designed with a box-shaped section and placed between the ribs and ceilings of the boxes of the basement rooms (Fig. 7.7).
Solid foundations are especially appropriate when it is necessary to protect the basement from the penetration of groundwater at a high level, if the basement floor is subjected to high hydrostatic pressure from below.
A solid foundation slab for low-rise buildings is designed only in cases of construction of buildings on soils with uneven settlement or swelling and with a high level of groundwater (in buildings with a basement). The slab is made of monolithic heavy reinforced concrete with a thickness of at least 100 mm. The thickness of the slab is determined by calculation depending on the mass of the building, the strength of the soil and the distance between the walls. For houses without a basement, the foundation slab is installed on a sand cushion, which reduces the uneven settlement of the soil. In buildings with a basement, the foundation slab simultaneously serves as the base of the floor.
Slab foundations are quite expensive due to the large volume of concrete and metal consumption for reinforcement.
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. The construction of monolithic foundations in the construction of country houses and country cottages is constantly used due to its reliability, good load-bearing capacity and long service life. Typically, a monolithic foundation is erected when installing buildings with heavy structures, reinforced concrete floors and difficult soils. This type of foundation shows itself most effectively in the construction of houses and buildings that are still planned to be completed. They have also proven themselves well in the construction of frames for multifunctional buildings (indoor swimming pools, winter gardens and other buildings), which will bear significant loads and in which it is guaranteed to prevent the appearance of cracks in the walls and foundations. The design feature of this structure is the absence of the occurrence and development of dangerous deformation processes in the load-bearing and enclosing structures of the building. In this article we will look at how to properly make a monolithic foundation with your own hands. When starting the construction of a private house or any other structure, you need to pay attention to the soil on the site and the total weight of the future structure. After choosing a construction project and studying the soil, the most suitable type of foundation for the construction of the zero cycle is selected. According to the construction method, there are the following types of monolithic foundations: According to the technology for constructing concrete foundations, before building a monolithic foundation, it is necessary to use removable or permanent formwork (from wooden boards, prefabricated panels or special plywood). If the role of the formwork is performed by the walls of the pit (ground), the outer surfaces of the foundation are first waterproofed from polyvinyl chloride film or roofing felt, otherwise, as a result of the absorption of cement mortar into the ground, the strength of the zero-cycle structure can be significantly reduced. According to production technology, two types of monolithic foundations are distinguished: To construct a concrete foundation, concrete grade 100 and higher is used. To reduce cement consumption and shorten the base, rubble stones are added to the concrete foundation. The resulting rubble concrete foundation has excellent strength characteristics. Reinforced concrete foundations are reinforced with meshes, which are knitted or connected into frames with rods. This type of foundation for any building is considered the most reliable and durable structure, resistant to moisture, and can easily withstand lateral and vertical loads. According to technical and economic indicators, monolithic reinforced concrete foundations are used for multi-story construction or the construction of heavy private houses, for example, for a country house made of brick. The construction of monolithic foundations is characterized by a long construction period due to significant volumes of preparatory and excavation work, massive construction and high labor intensity, as well as high consumption of materials. However, based on modern requirements and standards for the construction of buildings and structures for various purposes, monolithic foundations have priority advantages - maximum reliability and durability. Typically, in the past, the construction of a monolithic foundation was carried out in the spring and summer. Currently, if there is a need to carry out work at sub-zero temperatures, a number of measures are carried out that make it possible to build a zero cycle of this type year-round. You can learn how to choose the type of foundation and make all the necessary calculations from this video:
