multiPlas - Dynardo GmbH

-σm
a) b)
Fig. 3-10 Singular Drucker-Prager flow condition:
a) yield surface in the main stress domain; b) Illustration in the σx-σy-τxy-space
3.3.6.1 Nonlinear deformation behaviour in case of pressure load
In general the uniaxial stress-strain relationship of concrete is characterized by three domains:
A linear elastic domain which generally reaches up to about a third of the compressive strength.
This is followed by an increasingly bent run until the compressive strength is reached. The
nonlinear relation between stress and strain is caused by an initially small number of micro-cracks
which merge with higher stress levels.
The achievement of the compressive strength is associated with the forming of fracture surfaces
and cracks which are aligned parallel to the largest main stress.
The softening area is characterized by a decreasing strength. Finally, it leads to a low residual
strain level. The slope of the decreasing branch is a measure for the brittleness of the material.
Fig. 3-11 shows the typical nonlinear stress-strain relation of normal concrete in uniaxial compressive
tests [6-9].
Fig. 3-11 Nonlinear stress-strain relation (uniaxial compression test) of normal concrete used in
codes (DIN 1045-1 [6-9] and EC2 [6-10)
In Fig. 3-12 the stress-strain relation which is available in multiPlas is shown. Thereby linear softening
(mlaw = 0, 2) or parabolic-exponential softening (mlaw = 1) can be chosen. Up to reaching the strain εu
the parabola equation (as seen in Fig. 3-11) is used.
σx
F2
F1
σy
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USER’S MANUAL, January, 2013