17 2 STRESS FIELDS FOR SIMPLE STRUCTURES 2. 1 INTRODUCTION In this
chapter the behavior and strength of simple structures made of rein-
forced or prestressed concrete is investigated with the aid of stress
fields. In particular, the webs and flanges of beams, simple walls,
brackets, bracing beams and joints of frames are investigated. By this
means, the majority of design cases are already covered. In reality, all
structural components are three-dimensional. Here, however, components
are considered either directly as two-dimensional plate elements (i. e.
the plane stress condition with no variation of stress over the
thickness of the element) or they are subdivided into several plates.
Since two-dimensional structural elements are statically redundant, it
is pOSSible for a particular loading to be in equilibrium with many
(theoretically an infinite number of) stress states. If the lower bound
method of the theory of plasticity is employed, then an admissible
stress field or any combination of such stress fields may be selected.
In chapter 4 it is shown that this method is suitable for the design of
reinforced concrete structures, and the consequence of the choice of the
final structural system on the structural behavior is dealt with in
detail. The first cases of the use of this method date back to Ritter
[6] and Morsch [4], who already at the beginning of the century
investigated the resultants of the internal stresses by means of truss
models.
