Civil Engineering Reference
In-Depth Information
curves providing a full description of the behaviour of such specimens are given
in
Figure 2.1
which indicates that a characteristic feature of the curves is that
they comprise an ascending and a gradually descending branch. (It will be seen
later, however, that perhaps the most significant feature of concrete behaviour is
the abrupt increase of the rate of lateral expansion that the specimen undergoes
when the load exceeds a level close to, but not beyond, the peak level. This level
is the minimum volume level that marks the beginning of a dramatic volume
dilation which follows the continuous reduction of the volume of the specimen
that occurs to this load level. The variation of the volume of the specimen under
increasing uniaxial compressive stress is also shown in Figure 2.1). Although the
curves shown in Figure 2.1 describe the deformational response of concrete in
both the direction of loading and at right angles with this direction, it is only the
former which is considered essential by the plane sections theory for the
description of the longitudinal stress distribution within the compressive zone of
the beam cross-section.
The axial stress-axial strain and the axial stress-lateral strain curves of
Figure 2.1 may be combined to form the axial strain-lateral strain curve shown
in Figure 2.2. The curve of Figure 2.2 also comprises two portions, which
correspond respectively to the ascending and descending branches of the
stress-strain curves of Figure 2.1. The transition between these portions
corresponds to the portions of the stress-strain curves between the minimum
volume and peak stress levels. If uniaxial stress-strain data do indeed describe
the deformational behaviour of the compressive zone of the beam, an axial
strain-lateral strain relationship (such as that shown in Figure 2.2) should
provide a realistic description of the deformational behaviour of an element of
concrete in this zone throughout the loading history of the beam.
Figure 2.2
Typical axial strain-lateral strain curve constructed from the stress-strain curves in
Figure 2.1 (branches a and b correspond to ascending and descending branches, respectively).
