Methods and features of calculating strip foundations

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Knowing the basics of foundation design is essential before starting any kind of construction project. Of all the foundation types, strip foundations are essential for uniformly distributing building loads to the underlying soil. Their computation entails evaluating a number of crucial elements to guarantee structural longevity and stability.

When soil conditions allow for a wider distribution of building loads, strip foundations are frequently utilized. In order to calculate these foundations, the total load from the structure must be assessed, the soil’s bearing capacity must be taken into account, and the dimensions required to avoid settlement or structural failure must be determined.

The kind of soil that is present is a crucial factor in strip foundation calculations because different soils can support different loads in different ways. Soils are usually categorized by engineers according to their strength and compressibility, which have an immediate impact on the foundation’s dimensions and reinforcing needs.

Furthermore, in order to avoid frost heave or water-induced damage, environmental factors like groundwater levels and frost depth must be taken into account during the design process. These factors guarantee that the foundation will continue to be sturdy and resistant to environmental stresses and seasonal variations.

We explore the procedures and finer points of strip foundation calculation in this piece, providing builders, engineers, and architects with knowledge that is critical to guaranteeing the long-term stability and durability of any building project.

Methods

There are several techniques for doing calculations. Calculating strength and stability is one of them. It is predicated on the foundation’s bearing capacity calculation.

This method is applied in specific circumstances, such as when building construction will be completed by:

• on the slope,
• on rocky ground,
• in areas with strong seismic influence.

A series of intricate formulas are used in the calculations, which are completed by skilled professionals.

Based on the soil’s bearing capacity, a strip foundation can be calculated in a certain way. It is a computation of the tape’s minimum base area, at which the structure and base together won’t press down on the earth and cause it to sag.

We’ll go into more detail below on how to calculate the width of the foundation base and the width of the tape. A soil bearing capacity table is used for these types of evictions.

You can use calculations based on the soil deformation modulus in place of the more popular and straightforward bearing capacity of soils calculations. This is a more intricate engineering procedure that makes use of intricate formulas.

Limit state groups

Limit states of foundations are conditions where the building structure can no longer meet the necessary requirements (damage occurs, displacements are unacceptable, and resistance to loads decreases).

Generally speaking, two categories of limit states are used to compute all load-bearing foundations. The base is determined for strength and stability in accordance with the first group, and for deflections, deformations, and the size of crack opening in accordance with the second group:

1. First group (loss of bearing capacity) – main, t.To. if the design does not pass the calculations for it, it will pose a threat to life.
2. Second group associated with the unsuitability of structures for normal operation.

It is essential to comprehend the procedures and factors that go into calculating strip foundations. These foundations are necessary for dispersing building loads to the earth, thus it’s important to carefully evaluate the properties of the soil, the weight of the building, and the structural dimensions. By exploring these variables, this article seeks to provide practical insights into how engineers determine dimensions and reinforcement requirements, demystifying the process of calculating strip foundations. Important factors like soil bearing capacity, depth requirements, and the impact of nearby structures will be highlighted with concise explanations. In the end, this investigation will provide readers with the understanding required to efficiently plan and implement strip foundations in building and remodeling projects.

What you need to know?

To compute a strip foundation, one must ascertain the soil’s bearing capacity beneath the base. 50 cm below the base of the future foundation, examine the soil layer.

Every kind of soil has a different carrying capacity. The table illustrates this:

Types	dense	medium density
Coarse gravelly sand	6 kg/cm²	5 kg/cm²
Medium dispersion sand	5 kg/cm²	4 kg/cm²
Fine low-moisture sand	4 kg/cm²	3 kg/cm²
Fine wet sand	3 kg/cm²	2 kg/cm²
Dry sandy loam	3 kg/cm²	2.5 kg/cm²
Plastic wet sandy loam	2.5 kg/cm²	2 kg/cm²
Dry loams	3 kg/cm²	2 kg/cm²
Plastic wet loams	3 kg/cm²	1.5 kg/cm²
Dry clays	6 kg/cm²	2.5 kg/cm²
Plastic wet clays	4 kg/cm²	1 kg/cm²

Additionally, in order to identify the tape penetration point, you must know the depth at which soil freezes in a specific location.

• parameters of permissible soil deformation,
• tape length (depending on the architectural solution),
• total building weight,
• temporary load on it in different seasons.

It is necessary to gather all of the aforementioned data before beginning the computations. The necessary information is used to create a foundation project.

It provides information about the tape’s specifications as well as the supplies that construction workers will need. The reinforcement that will be used to reinforce the tape and the grade of concrete that should be poured into it are decided by the designer.

Special programs

You can use specific construction formulas to calculate the foundation during the design process. However, using apps or calculators available online makes this process simpler.

Certain calculation techniques are already included in them; the user just needs to input his data:

• tape length,
• building weight,
• soil type, etc. d.

Calculators are more convenient for one-time calculations; professional designers use applications that are more dependable, have a history of calculations saved, and can be configured more accurately.

Professional builders and private developers have reviewed this link as having the most user-friendly and informative calculator for calculating strip foundations.

It makes it simple to calculate:

1. Tape size.
2. Formwork parameters.
3. Diameter and quantity of reinforcement.
4. Volume of concrete to pour.

This service is advised for material calculations that account for their cost. In this instance, the form contains information that can be gleaned from the architect’s explanatory notes, such as concrete proportions, the kind of reinforcement, formwork board sizes, and other details.

There aren’t any trustworthy services that let you quickly determine the tape’s specifications and price. Prior to calculating the estimate, you need to compute and consider the foundation design.

How to calculate it yourself?

Experts should perform foundation calculations for large cottages. For a modest country home or outbuilding, you can compute the tape on your own. Furthermore, great caution must be used, adhering to building codes and regulations.

It’s crucial to keep in mind that while the tape’s width is calculated, the building’s architecture, the qualities of the soil, and the local climate all affect the other parameters.

Load collection

The process of determining the building’s total weight that will support the foundation while it is in use is known as load collection. At this point, the building’s total structural element weight is determined first:

• floors,
• walls,
• partitions,
• roofing pie,
• Communication systems,
• interior and exterior decoration.

The design and architectural tables can be used to calculate the mass of the primary architectural structures:

The reliability coefficient must be considered when computing, per the standards and codes of construction rules (SP). In other words, every value extracted from the table needs to be multiplied by the matching coefficient.

Loads	Reliability factor by load, γf
Permanent
Self-weight of structures	1.1 (0.9)
Weight of stationary equipment	1.05
Thermal insulation and sound insulation products	1.2 (0.9)
Strengthening prestress in a structure	1.1 (0.9)
Temporary
Loads from the weight of people, parts, repair materials, specified by the technological task, with:
q< 300 kgf/m3	1.4
300< q< 500 kgf/m3	1.3
q ≥ 500 kgf/m3	1.2
Own weight of the equipment	1.2
Liquid weight	1.1
Weight of bulk materials filling containers	1.2
Loads from cranes, with a carrying capacity of up to 5 tons	1.3
Loads from forklifts and trucks	1.2
Snow load	1.4
Wind load:
for industrial buildings and structures	1.2
for structures in which the wind load is of decisive importance in the calculations	1.3

Useful

The primary load is increased by the payload. It takes into account the weight of everything positioned inside the house while it is in use. This covers the residents’ personal belongings as well as their furniture, equipment, and appliances.

Snow

Snow load is a transient phenomenon that needs to be considered. This should be increased by the weight of heavy rains and winds.

Snow load is controlled by SNIP 2.01.07-85, which is derived from a publicly accessible table and depends on the region.

Dimensions

The dimensions of the tape are ascertained at the following step:

Soles

The computation is performed based on the second set of limit states. The tape is placed evenly throughout the height and rests on a cushion of crushed stone that has been scoured with sand when building homes made of lightweight materials or in locations with high-quality, dense soil.

The tape should be supported on an expanded reinforced concrete base if the house is too large or heavy due to the wall materials, or if construction is planned on a site with poor soil.

The bearing capacity or degree of shrinkage of the soil determines the sole’s dimensions. The most popular approach is the second one. It is required to compare the site’s soil resistance indicator with the building’s total load, expressed in kilograms per square meter.

You can construct a house without a sole if the first number is less than the second because it will stand without causing the soil beneath the base to shift. A sole is required if the specific gravity is greater than the soil resistance.

Resistance of soil:

1. Coarse sand – 60-50 t/m².
2. Medium-grained sand – 50-40 t/m².
3. Sandy loam – 30-20 t/m².
4. Loams – 30-10 t/m².
5. Clay – 60-10 t/m².
6. Crushed stone – 60-40 t/m².
7. Gravel – 50-35 t/m².

The sole gives the foundation rigidity, guarantees even weight distribution from the building to the ground, and guards against uneven subsidence. It must be at least twice as wide as the tape.

The formula B = 1.3×P/(L×Rо) is used to determine the minimum value of the sole width, where:

• Rо is the resistance of the bearing soil;
• L is the length of the tape in centimeters;
• P is the total weight of the building;
• 1.3 – safety factor.

Depth and height

You can have a deep or shallow strip foundation. Shallow options are used for small buildings on rocky or dense soil. Here, the strip is excavated to a depth that is 20–25% below the freezing point of the soil. For instance, a support 75 cm deep is made at a freezing depth of 1 meter.

If the soil has weak heaving, a conventional deep foundation is drilled 30 to 50 cm deeper than the level of soil freezing.

By using the relevant online resources or by examining the tables of indicators by region, you can determine the freezing depth.

The base, or the portion of the foundation that rises above the soil’s surface, is represented by the height of the tape. There must be a minimum of 30 cm between them. However, homes with high plinths—up to one meter—are constructed in areas with high rainfall. In the event that the home has a basement, the base height must be at least 40 cm in order to allow for ventilation windows.

Thickness

The formula B = P/L*R can be used to determine the tape’s thickness, where:

• P – mass of the house;
• L – tape length;
• R – soil bearing capacity.

The foundation needs to be at least 30 centimeters thick. It is preferable to make it somewhat wider than the house’s above-ground walls. The more accurate the geometry of the building elements should be, the smaller the difference between the width of the tape and the wall resting on it.

If the width is less than 30 cm after applying the formula to the calculations, adjust it to match the wall’s measurements. If the foundation’s width calculation yields a result that is marginally wider than the walls’ width, it can be made wider to reach the required value.

However, if it turns out that the house needs to rest on a broad base and creating a strip that wide is not feasible, it is constructed to be between 30 and 60 centimeters wide and has an enlarged base in the shape of a sole.

By strength

The process of determining the strength of strip foundations involves determining whether the height of the sand cushion is adequate to withstand lateral force and allocating reinforcement within the sand cushion. Based on the first set of limit states for design loads, the foundation strength is calculated.

Rigid bending tapes

Concrete is a reasonably robust material that has a high compressive strength. However, it has poor tolerance to bending loads.

Pouring reinforces it to give it the right characteristics. SNIP controls the selection of reinforcement for longitudinal frame elements. At least 0.01% of the tape’s cross-section must make up the total cross-section of the main reinforcement.

Adjusting parameters

Sometimes the calculations indicate that the foundation strip will be too wide if the initial construction plans call for heavy materials and the soil has low resistance.

Any strip foundation wider than sixty centimeters is excessively pricey. In these situations, the project designer must recalculate using different building materials as a starting point.

For instance, building a frame or foam concrete home might be more practical than building a brick one. Making the foundation itself a different structure, such as a pile or columnar structure, makes more sense sometimes.

How to calculate cubic capacity?

For accurate calculations of concrete consumption, the cubic capacity is required. You must multiply the tape’s length, width, and height in order to determine it.

We count all materials

You are able to compute the materials on your own. Every material is taken into account independently. Sand and crushed stone should be used first, with consideration for the pillow’s length, width, and height. Next, wood and boards for the formwork.

The primary reinforcement, the thin reinforcement, and the reinforcement wire come next. The consumption of concrete is then computed.

All of this can be computed by entering the following into an online calculator:

• form,
• size,
• depth,
• width of the future foundation.

Example for a frame house

Because frame houses are light in weight, they are built on lightweight foundations. For instance, you have to construct a six-by-nine-inch house on stable ground with a freezing depth of seventy-five centimeters and walls that are thirty centimeters wide.

In addition to the allowed minimum width, we can use a shallow foundation (50 cm) and allow for error tolerances of 30 to 40 cm when building walls.

Upon verifying these numbers with a calculator or formula, it becomes evident that a foundation of this kind will provide a substantial safety margin for a frame house.

For any building to be stable and long-lasting, it is essential to know how to calculate strip foundations. Engineers can precisely design strip foundations that evenly distribute weight by determining the soil’s load-bearing capacity and the building’s structural requirements.

Analyzing the soil conditions is one of the most important steps in strip foundation calculations. This entails evaluating elements that directly affect the amount of weight the soil can support without experiencing undue settlement, such as soil type, density, and moisture content. To precisely determine these parameters, engineers use a variety of tests and data.

Strip foundations are designed with consideration for the structural loads that are imposed by the building above. This covers both horizontal loads like wind and seismic forces as well as vertical loads from the weight of the structure itself. In order to guarantee that the foundation can securely support the entire structure, these loads are computed using engineering standards and architectural plans.

Furthermore, it is imperative that safety factors be included in the computation procedure. Safety margins are used by engineers to take into consideration variations in construction, unpredictability in soil conditions, and possible future changes in building use. This guarantees that the strip foundation will continue to be robust for the duration of its intended use in addition to meeting current requirements.

Video on the topic

Calculation of strip foundation formwork

Collection of foundation loads online | Correct calculation of the foundation based on bearing capacity