GGU-FOOTING: Settlement analysis
- Katrin Krause
Settlement analyses are carried out according to DIN 4019. Once the program has determined the characteristic or allowable footing pressure for the proposed footing, the settlements are determined using these characteristic or allowable values. DIN 4019 Table 1 allows correction coefficients kappa to be taken into consideration for modelling settlements (see menu item "File/New").
The program calculates stresses and deformations according to the theory of elastic-isotropic half-space. Very comprehensive diagrams and tables were developed, particularly in the time before pocket calculators and personal computers were available. A bibliography of tables can be taken from DIN 4019. Please also see the article "Spannungsberechnung" ("Stress analysis") in the Geotechnical Engineering Handbook (1990; Fourth edition). This also contains complete relationships for deformations and stresses below a rectangle in elastic-isotropic half-space (equations 8 to 10 and equations 14 and 15). The program is based on these relationships.
The stress relationships are only utilised for limiting depth calculations and for representation of stress distributions. The deformations are calculated directly from the relationships given in the Geotechnical Engineering Handbook. Numerical integration with associated loss of precision id therefore not necessary. If a base tilt results when analysing a pad footing these relationships can no longer be used because the pressure zone is no longer rectangular. In this case, an analytical-numerical settlement analysis is required.
The limiting depth can be defined in three different ways:
with a fixed, user-defined value
as a multiple of the footing width
as the depth at which the total vertical stress exceeds the overburden stress by x% (as a rule 20%).
The settlement curves in the footing analysis diagram are attained from the footing pressure by linear interpolation. Thus, analysis using the x%-criteria only takes place for the maximum footing pressure of each footing width. However, if you open "Edit/Analysis options" menu item and activate the "Stress variable" check box, the limiting depth is calculated for a number of stresses (here for 25 stresses).
