Building construction requires the use of strip foundations, which evenly distribute the weight of the structure to the ground below, giving vital support. This kind of foundation, which resembles a continuous strip around the outside of the building, is long and narrow and is frequently used for load-bearing walls.
A thorough examination of the soil conditions at the construction site and the structural requirements of the building is the first step in the design of a strip foundation. Based on variables like the building’s weight, the kind of soil, and regional building codes, engineers determine the foundation’s size and depth. The foundation will be able to sustain expected loads and environmental conditions over time thanks to this careful planning.
Strip foundation construction entails a few crucial processes. First, in accordance with the design specifications, trenches are dug along the building’s intended perimeter. After that, the trenches are meticulously leveled and compacted to create a solid foundation base. The base of the foundation is then formed by pouring a layer of concrete into the trenches. Concrete has reinforcement bars embedded in it to increase its strength and durability; these bars are usually made of steel.
Depending on the needs of the design, more layers may be added after the concrete has dried and strengthened sufficiently. Waterproofing materials to shield the foundation from moisture and other environmental elements might be included in these layers. Ultimately, the finished strip foundation ensures longevity and structural integrity by providing a strong and stable base upon which the remaining building structure can be erected.
- Regulatory framework and features of drafting a project
- Methods for calculating belt technological dimensions
- The concept of bearing capacity of a site
- Basic information about shallow LFs
- Sequence of design work
- Video on the topic
- nanoCAD Structures – Foundations. Lesson No. 3 – Calculation and design of a monolithic strip foundation
- Foundation plan
- HOW IS THE FOUNDATION DESIGNED?
Regulatory framework and features of drafting a project
The design engineer’s job is to figure out the conditions on the land that has to be developed and the foundation for a particular structure. One of the design tasks is to remove the potential for the building and foundation to deform and collapse.
The requirements for the design and construction of foundations are outlined in detail in SP 50-101-2004, which also includes references to relevant acts.
In order to assess the site’s bearing capacity, data regarding the area’s geology, seismic activity, building design, and operating circumstances must be gathered.
To choose the most logical and dependable construction option, evaluate the technical and financial aspects of potential engineering solutions. It is necessary to take precautions that will guarantee the structure’s strength and durability both during construction and during use.
The project is designed with consideration for the design duties outlined in GOST 27751:
- I degree of responsibility – petroleum product storage facilities, industrial facilities with large spans, unique houses.
- II degree – residential and public buildings, agricultural buildings.
- III degree – temporary buildings (summer sheds, gazebos, pavilions, storage buildings.
A technical specification containing preliminary data, drawings of the base options and their sections, and plan layout diagrams are created prior to construction. This data is required to support installation and construction activities. The project has the necessary regulatory documentation attached.
Methods for calculating belt technological dimensions
The foundation’s depth, as well as the tape’s height and width, are calculated during the design phase. The earth’s bearing capacity dictates the technological dimensions. The frost line, heave tendency, and groundwater level will be ascertained by geological research.
Select a recessed foundation, which is poured into a trench 0.4–0.6 meters below the frost line, for unstable soils. It is possible to dig a trench for tape down to a depth of just 0.5 meters for lightweight structures like bath houses or frame homes.
Because the soil is strong, uniform, and has low levels of clay and moisture, it can withstand stress and the belt’s depth can be as little as 0.5 meters. The table below illustrates the connection between the site’s geological features and the belt’s depth:
| Freezing limit, m | Belt depth, m | |
| Average degree of heaving | Less susceptible to heaving | |
| From 2.5 | — | 1.5 |
| 1.5 – 2.5 | more than 3.0 | 1.0 |
| 1.0 – 1.5 | 2.0 – 3.0 | 0.8 |
| up to 1.0 | up to 2.0 | 0.5 |
The level of soil freezing must be multiplied by a correction factor related to the structure’s thermal regime in order to determine the depth of a reinforced concrete foundation (you can rely on the set of rules for construction and design SP 50-101-2004). The width of the base (D) is taken to be equal to or greater than the thickness of the structure’s load-bearing walls.
The formula D = (q/R), where: is the foundation of the applied method for computing the indicator D.
- q is the total load on the reinforced concrete strip, which takes into account the mass of the structure, payload, and the weight of equipment that will be located in the building;
- R – section resistance.
The concept of bearing capacity of a site
A property that expresses the earth’s resistance to vertical loads in units of (kg/cm2) or (t/m2). The stronger the foundation for the construction, the lower this indicator is.
The following variables have an impact on the site’s bearing capacity:
- Type of soil;
- moisture saturation;
- The seal of soil masses.
When designing structures I and II degree of responsibility, you should get in touch with a geological research organization to learn more about the local geology.
It is possible to determine the type of soil independently when designing structures with a III degree of responsibility. To do this, they drill a well down to a depth of two meters in order to determine the earth’s composition and the groundwater line.
The following table illustrates how soil type affects the resistance of different soil masses:
| Priming | Characteristic | Resistance R, kg/cm2 | ||
| Gravel | Object plate | 4.0 | ||
| Sand aggregate | 5.0 | |||
| Crushed stone, pebbles | Object plate | 4.5 | ||
| Sand aggregate | 6.0 | |||
| Sands | dense | average density | ||
| Large | 4.5 | 3.5 | ||
| average density | 3.5 | 2.5 | ||
| Small | Little moisturized | 3.0 | 2.0 | |
| wet | 2.5 | 1.5 | ||
| dusty | little hydrated | 2.5 | 2.0 | |
| wet | 2.0 | 1.5 | ||
The following steps comprise the applied calculation of a site’s bearing capacity:
- The mass of the structure is found by multiplying the structural elements by the specific gravity of the building material.
- The snow load is determined by multiplying the roof area by the standard weight (m2) of the snow cover.
- Find operational loads at the rate of 100 kg per square meter of each floor.
- Calculate the weight of the base by multiplying the volume of the tape by the specific gravity of 1 m3 of reinforced concrete.
- Sum up the results obtained and multiply by a reliability coefficient equal to 1.2.
- Calculate the supporting area of the base by multiplying the width by the length.
- Determine the total pressure of the structure per unit area of soil by dividing the total value from point (5) by the supporting area (6).
The basic process of design analysis involves comparing the standard soil resistance to the design load of the structure that is being built, accounting for the foundation. Increase the support area and do the calculation again if the actual load is greater than the allowable limit.
Basic information about shallow LFs
At a height of 0.7 meters above the ground, shallow tapes are placed above the frost line. When building on soil that is prone to heaving at low ambient temperatures, the structural solution is appropriate.
Even with the foundation’s strength and resilience to the weight of the building, the entire structure cannot move uniformly with the soil masses unless it is deeply buried. The possibility of destruction from vibrations is removed with accurate foundation calculation.
The type of foundation that is being presented is appropriate for low-rise building construction, such as residential buildings, foam concrete, lightweight brickwork, and frame-panel buildings. At the same time, you can construct heavier houses with an attic by widening the tape.
The table below provides recommendations for selecting the foundation’s width based on soil type for different types of structures:
| Soil type | Shallow belt width, m | ||
| structures of II and III levels of responsibility, load up to 20 kN/m2 | multi-storey cottages, load 50 kN/m2 | multi-storey buildings, load 70 kN/m2 | |
| Rocky | 0.25 | 0.30 | 0.50 |
| Loam | 0.32 | 0.35 | 0.60 |
| Sandy loam, dense clay | 0.40 | 0.65 | a different type of foundation is required |
| Soft sand, silty soil | 0.65 | 0.85 | |
It is essential to comprehend strip foundations in the field of construction. Stability and durability are ensured by these foundational structures, which distribute the weight of buildings evenly across the ground. They are constructed by digging a trench, adding concrete to it, and then fortifying it with steel bars. This procedure is essential for properly distributing loads and supporting walls, which guarantees that buildings will last for many years. This article delves into the fundamentals of designing and implementing strip foundations, providing a clear manual for anyone interested in learning about the foundation of robust construction projects.
Sequence of design work
The design of a strip foundation ultimately involves resolving several issues:
- Geological analysis of the site to determine the type of soil, frost line, groundwater level.
- Determination of soil resistance.
- Calculation of technological dimensions of the base.
- Finding the total loads of the structure being built.
- Comparison of standard soil resistance with the load of the structure, including the foundation.
- Selection of an economically feasible engineering solution for construction.
- Definition of reinforcement.
- Drainage system design.
After determining the reinforced concrete base’s measurements, they meticulously sketch out all of its important parts and architectural details. We are able to create an installation flow chart and accurately determine the quantity of building material needed thanks to the information gathered.
Building construction requires the use of strip foundations, which provide load-bearing walls a stable base. This kind of foundation ensures longevity and safety by distributing the structure’s weight uniformly throughout the soil below.
The load-bearing walls will be positioned along the building’s perimeter, which will be excavated during the construction process. The concrete that will be poured into the trench is then strengthened by the placement of reinforcement bars, or rebar. This reinforcement improves the foundation’s resistance to both vertical and horizontal forces and helps to prevent cracking.
To create a solid base, concrete is poured into the trench after the rebar is in place. The size, weight, and properties of the building, in addition to the properties of the soil, all influence the strip foundation’s depth and width. Compaction of the soil around and beneath the foundation in a proper manner guarantees its stability over time.
A well-built strip foundation aids in preventing settlement and movement by bearing the weight of the building’s walls, preserving the structural integrity of the entire structure. To find problems early and maintain the building’s stability and safety, regular foundation inspection and maintenance are crucial.
