Continuous footings, part 3

The benches still under the rows of columns are most often used then, when the distance between the feet of individual poles is too small, or when independent foundation of the columns could lead to significant differences in settlement, e.g.. with large differences in force in poles or large differences in the compressibility of the subsoil. The most common shapes of continuous footings under a row of columns are shown in the figure.

tmp2d9-1tmp7dd3-1Types of row benches: a) lava with rectangular cross-section, b) a bench with a T-section, c) variable width bench, d) detail of the T-bar reinforcement, e) a bench with a trapezoidal cross-section.

Fixed height benches (Lynx. a, c) used for smaller column spacing. For larger spacing of columns and in order to increase the footing stiffness, fixed or variable height T-sections are used, shown in fig. b, d. The calculation and dimensioning of the footings with the rib protruding at the top is performed in the transverse and longitudinal directions.

tmp7dd3-2Reinforcement of the benches: a) at the door opening, b) in the place of disturbed or removed soil.

Figure a shows the lava reinforcement under a continuous wall in the basement, in which is the door opening, and to the line. b bench, under which the breach or removal of the land took place. In both cases, additional reinforcement bars were used in this zone, where there are tensile stresses in the concrete.

If the ground under the bench or the foot is mistakenly chosen too deep, these depressions should not be covered with soil from the excavation, as such substrates settle and therefore the bench and the wall may break. The depressions in the bottom of the trench should only be leveled with concrete.

Reinforced concrete footings are usually made on a concrete layer with a thickness 5-10 cm of lower grades. Covering the reinforcement with concrete should not be less than 5 cm. In the longitudinal direction, reinforcement is assumed in concrete and reinforced concrete footings 4 Phi 10 or 4 Phi 12, connected with stirrups φ 6 co 30-50 cm, preventing the bench from cracking during uneven subsidence.

tmp37a6-1Prefabricated benches: a) top view and section of lava and wall, b), c) reinforced concrete elements.

Due to the simplification of execution on the construction site, prefabricated concrete benches are used, mainly there, where and other structural elements of the building - walls, ceilings - are also assembled from prefabricated elements.

The most commonly used types of precast concrete elements are shown in the figure. The prefabricated elements are placed on a layer of lean concrete, which is the leveling of the trench bottom.