Civil Engineering Reference
In-Depth Information
nonlinear material properties of concrete in this topic is based on specified
properties provided in current codes of practice. This is attributed to that
experimental and numerical investigations reported in the literature on non-
linear material properties are unlimited and differ from a country to another.
Since the main objective of this topic is to provide a consistent and robust
nonlinear approach for designing and finite element modeling of steel-
concrete composite bridges, only specified values in current codes of practice
are highlighted in this topic.
2.3.2 Concrete Stresses
that the compressive strength of concrete is denoted by concrete strength
classes, which are based on the characteristic cylinder strength
f
ck
determined
at 28 days with a recommended maximum value
C
max
(
f
ck
/
f
ck,cube
) of C90/
105. The characteristic strengths for
f
ck
and the corresponding mechanical
In certain situations (e.g., prestressing), it may be appropriate to assess the
compressive strength of concrete before or after 28 days with reference to
test specimens stored under other conditions rather than those prescribed
t>
28 days, the values
a
cc
and
a
ct
, which are coefficients taking account
of long-term effects on the compressive and tensile strengths, respectively,
should be reduced by a factor
k
t
. EC2 recommends the value of
k
t
as 0.85.
According to EC2, when it is required to specify the concrete compressive
strength,
f
ck
(
t
), at time
t
for a number of stages (e.g., transfer of prestress), the
following relationships can be used:
f
ck
ðÞ¼f
cm
ðÞ
8 MPa
ð
Þ
for 3
<
t
<
28 days
:
ð
2
:
5
Þ
6
Þ
The compressive strength of concrete at an age
t
depends on the type of
cement, temperature, and curing conditions. For a mean temperature of
strength of concrete at various ages
f
cm
(t) may be estimated as follows:
f
ck
ðÞ¼f
ck
for
t
28 days
:
ð
2
:
f
cm
ðÞ¼b
cc
ðÞf
cm
ð
2
:
7
Þ
with
t
1
=
2
28
b
cc
ðÞ¼
exp
s
1
ð
2
:
8
Þ
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