Civil Engineering Reference
In-Depth Information
Graphical interpretation of the Föppl-Papkovich formulae is to be seen in Fig. 3.8. The
diagrams clearly show that the interaction always reduces the value of the critical load.
The maximum reduction is 50%; it occurs when the two part critical loads are of the
same value (Fig. 3.8/a). When one of the part critical loads is much smaller than the
other one, the value of the critical load is controlled by the smaller value (Fig. 3.8/b/c).
The situation with torsion is somewhat different. The nature of the interaction
between soil and structure is much more complicated and it would depend on
several factors, e.g. the structure and geometry of the foundation (separate
footings, flat-slab foundation, rigid-box foundation, raft foundation, piled
foundation). Each type should be handled individually. The treatment of torsional
interaction is outside the scope of this topic; it is only mentioned here that
equivalent spring constants for horizontal and torsional deformations are given
by Key [1988] for circular and rectangular bases. Wolf's [1985] monograph offers
a detailed analysis of soil-structure interaction.
