Strip foundation reinforcement schemes
Reinforcement is a steel rod of a smooth or ribbed profile. The most commonly used diameters are from 6 to 32 mm.
During operation, the foundation is constantly subjected to various loads, for example, from the weight of the house itself or various ground movements, including due to the forces of frost heaving. In a simplified way, the lower part of the foundation tape experiences predominantly a tensile load, and the upper part a compressive load.
Since the resistance of concrete to compression is 50 times higher than to tension, and
steel reinforcement, on the contrary, is capable of absorbing large tensile loads, it can be concluded that reinforcement of the lower part of the strip foundation is necessary. At the same time, one must be aware of the forces of frost heaving, the lifting force of which can exceed the weight of the house and cause tension in the upper part of the strip foundation.
Therefore, it is necessary to reinforce the lower and upper parts of the strip foundation. In fact, concrete with the help of reinforcement is turned into a new material - reinforced concrete, which is able to withstand tensile and compressive loads. It makes no sense to reinforce the middle part of the strip foundation, since it practically does not experience loads.
The figure shows an approximate scheme for reinforcing a strip foundation.
Longitudinal tiers of reinforcement are located in the upper and lower parts of the foundation, since together with concrete they perceive the main compressive and tensile loads acting along the longitudinal axis of the foundation. If necessary, if required during the calculation, you can install additional tiers. Class AIII reinforcement is used as a longitudinal one, which is a round profile, usually from 10 to 16 mm in diameter, with two longitudinal ribs and transverse protrusions running along a three-start helix.
If the height of the foundation is more than 15 cm, it is necessary to install vertical transverse reinforcement, which is mainly used as smooth rods of class AI with a diameter of 6–8 mm.
When reinforcing a strip foundation, transverse reinforcement is installed based on the calculation of loads acting along the transverse axis of the foundation. The installation of transverse reinforcement limits the development of cracks in concrete and fixes the working longitudinal rods in the design position. It is better to bend transverse reinforcement into frames and install longitudinal reinforcement inside these frames.
The distance between the bars of longitudinal reinforcement and the pitch of the transverse reinforcement of the strip foundation is determined by SNiP 52-01-2003:
7.3.4 The minimum distance between the reinforcement bars in the clear should be taken depending on the diameter of the reinforcement, the size of the large concrete aggregate, the location of the reinforcement in the element in relation to the direction of concreting, the method of laying and compacting the concrete.
The distance between the reinforcement bars should be taken not less than the diameter of the reinforcement and not less than 25 mm.
Longitudinal reinforcement
7.3.6 The distance between the rods of longitudinal working reinforcement should be taken taking into account the type of reinforced concrete element (columns, beams, slabs, walls), the width and height of the section of the element and not more than a value that ensures effective involvement of concrete in the work, uniform distribution of stresses and deformations across the width section of the element, as well as limiting the width of the crack opening between the reinforcement bars. In this case, the distance between the rods of the longitudinal working reinforcement should be taken no more than twice the height of the section of the element and no more than 400 mm, and in linear eccentrically compressed elements in the direction of the bending plane - no more than 500 mm.
Transverse reinforcement
7.3.7 In reinforced concrete elements, in which the transverse force cannot be absorbed only by concrete, according to the calculation, transverse reinforcement should be installed with a step of no more than a value that ensures the inclusion of transverse reinforcement in the formation and development of inclined cracks. In this case, the step of transverse reinforcement should be taken no more than half of the working height of the section of the element and no more than 300 mm.
Also, when reinforcing the strip foundation, it should be remembered that the reinforcement should be 5-8 cm from the edges of the formwork and the upper level of pouring concrete.
The connection of individual reinforcement rods is carried out using a knitting wire and a special knitting hook. It is allowed to weld only fittings that have the letter “C” in their marking, for example, A500C.
Reinforcement schemes for corners and junctions of a strip foundation
For reinforcing corners and junctions, class AIII reinforcement is required to be bent. Reinforcement of corners with a simple crosshair of reinforcement is not allowed if reinforcement of corners of the foundation is carried out with separate rods of longitudinal reinforcement.
A monolithic foundation should be a single rigid spatial frame, and this is possible only with proper reinforcement of the corners and junctions of the foundation.
1 - horizontal reinforcement; 2 - overlap; 3 - foot; 4 - vertical reinforcement; 5 - transverse reinforcement; 6 - additional transverse reinforcement; d is the diameter of the reinforcement bar; 50 cm Corner reinforcement scheme with overlap and foot 1 - horizontal reinforcement; 2 - overlap; 3 - vertical reinforcement; 4 - transverse reinforcement; 5 - additional transverse reinforcement; 6 - L-shaped clamp; d - reinforcement diameter; 50 cm Scheme of reinforcing the corners of a strip foundation using an L-shaped clamp 1 - horizontal reinforcement; 2 - overlap; 3 - vertical reinforcement; 4 - transverse reinforcement; 5 - additional transverse reinforcement; d is the diameter of the reinforcement bar; 50cm= Scheme of reinforcement of the strip foundation at the junctions
