Civil Engineering Reference
In-Depth Information
Figure 2.3
Conditions of equilibrium.
You will study conditions for equilibrium of forces in other courses on mechanics or
strength of materials and this is just the same.
Compatibility of displacement is examined most conveniently by construction of a
displacement diagram. Figure 2.4(a) illustrates two triangular blocks moving as illus-
trated by the arrows; we will see later that this could represent the displacement of soil
below a foundation at the point of failure. Each block is given an identifying letter and
O represents stationary material. In Fig. 2.4(b) each arrow represents the direction
and magnitude of the displacement of one of the rigid blocks and the displacement
diagram closes. The letters on the arrows represent the relative displacements, thus
oa is the displacement of A with respect to O and ab is the displacement of B with
respect to A.
The relative movements of rigid bodies in mechanisms like that shown in Fig. 2.4
can be examined by making simple models from stiff card. (From a flat sheet of card
cut a triangular recess, cut two triangular shapes like A and B and demonstrate that
you have a compatible mechanism. To get them to move it is necessary to drill small
holes at the corners.)
Figure 2.4
Conditions of compatibility.
