Both entire buildings, as well as its individual elements, they usually experience horizontal and vertical displacements. These displacements can cause changes to the original dimensions (length, width) or changes in the geometric shape. Horizontal and vertical displacements can induce: wind, temperature, shortening or lengthening of elements, settlement of the building and shrinkage of concrete.
Displacements that change the geometrical shape of plates and walls are the cause of their damage, visible in the form of scratches and cracks.
Scratching the wall due to column subsidence: a) view, b) frame-wall scheme;
The figure shows the scratching of the filling wall, caused by an unequal displacement of the frame rafter caused by subsidence of the spread footing under the column. Uneven settlement of the building causes scratching of the wall. The arrangement of cracks in the wall caused by the elongation of the roof under the influence of temperature (heating up) shown in the figure.
Larger ceiling and floor slabs are scratched due to concrete shrinkage.
In order to avoid the formation of scratches or to limit displacement, special gaps are made - expansion joints, dividing walls and ceilings (plates) into smaller sections. These gaps allow structures and components to move without damaging consequences.
Division of the building due to uneven settlement; 1 - a break along the entire height, 2 - foundation.
In case of; when uneven settlement of the building may occur due to the different bearing capacity of the soil under the foundation, or uneven load resulting from e.g.. from buildings of different heights, expansion joints should be used that cut across the building along its entire height, including the foundation. Due to thermal influences, the building is usually divided by expansion joints at its height above the foundation.
Antispasmodic expansion joints of floor and roof slabs divide the fields into smaller areas.
The distances between expansion joints should be determined on the basis of an analysis of the work of the structure subjected to concrete contraction and the temperature difference. If we do not carry out such an analysis of the work of the structure, then the distances between expansion joints given in the standards should be used.
The table above shows the maximum distances between expansion joints in masonry structures, and in the table in concrete structures. Expansion gaps should not be less than 20 mm and be filled with permanently plastic putty.
Antispasmodic expansion joints of floor and roof slabs divide the fields into smaller areas. Expansion joints in floors are made in “spacing no more than 6 m, additionally dividing into smaller fields (every ok. 3,0 m) by cutting with a diamond disc to 1/3 floor thickness.