Introduction - Unified Theory of Concrete Structures - page 3

Figure 1.1 A typical frametype reinforced concrete structure

with the low ceiling, serves as offices. The roof beams of the office are supported by spandrel
beams which, in turn, are supported by corbels on the left and columns on the right.
The structure in Figure 1.1 is subjected to all four types of basic actions - bending M , axial
load N , shear V and torsion T . The columns are subjected to bending and axial load, while the
beams are under bending and shear. The spandrel beam carries torsional moment in addition
to bending moment and shear force. Torsion frequently occurs in edge beams where the loads
are transferred to the beams from one side only. The magnitudes of these four actions are
obtained by performing a frame analysis under specified loads. The analysis can be based on
either the linear or the nonlinear material laws, and the cross-sections can either be uncracked
or cracked. In this way, the four M , N , V and T diagrams are obtained for the whole structure.
This process is known as 'structural analysis'.
Table 1.1 illustrates a four-step general scheme in the structural engineering of a reinforced
concrete structure. The process of structural analysis is the first step as indicated in row 1
of the table. While this topic will not cover structural analysis in details, information on this
topics can be found in many standard textbooks on this subject.

1.2.2 Main Regions vs Local Regions
The second step in the structural engineering of a reinforced concrete structure is to recognize
the two types of regions in the structure, namely, the 'main regions' and the 'local regions'. The
local regions are indicated by the shaded areas in Figure 1.1. They include the ends of a column
or a beam, the connections between a beam and a column, the corbels, the region adjacent to a
concentrated load, etc. The large unshaded areas, which include the primary portions of each
member away from the local regions are called the main regions.