Civil Engineering Reference
In-Depth Information
t
insp
. In this formulation,
t
eq,
k
provides a shift along the time
axis of
Ĝ
F
,
k
to adjust the initiation of the deterioration process; however, no
correction is made to the deterioration rate. Alternatively, in case both the
initiation time and the rate of the deterioration process need to be adjusted,
then the fragility at time
t
after the inspection can be estimated as
where
Δ
t
=
t
−
⎡
⎢
⎛
⎜
t
t
⎞
⎟
⎤
⎥
×
ˆ
ˆ
eq
insp
Δ
,
k
(
)
=
(
)
FtS
,
G
x
,
t
+
tS
,
F
x
t
insp
>
[19.11]
k
a
F k
,
0
eq
,
k
a
k
0
In this case
t
eq,
k
is used to shift
Ĝ
F
,
k
along the time axis and to contract or
dilate the time axis to account for a difference in the deterioration rate.
19.4 Conclusions
Although little information is available on deterioration rates of structures
exhibiting ASR and other mechanisms of deterioration, models are avail-
able for corrosion-induced deterioration. Preventive measures must con-
sider the environment in which the structure is to be constructed and the
materials used to construct the structure. In an environment that contains
aggressive conditions, such as chlorides, sulfates, freeze-thaw cycles, carbon-
ation, or other harmful conditions, their impact on deterioration must be
considered during the design phase, and strategies to mitigate damage must
be implemented. Concrete is a good material for civil engineering struc-
tures, enabling society to place structures in environments that were con-
sidered to be too harsh years ago. Using marginal materials and placing
concrete in aggressive environments present challenges, especially if proper
materials, design, and construction practices are not used, resulting in pre-
mature deterioration.
A deteriorating structure that continues to provide safe functionality still
has value. In fact, mitigating the deterioration can add further value. This
chapter provided a brief overview of typical deterioration mechanisms and
developed a general damage model that is useful for assessing the reliability
of bridges experiencing deterioration due to corrosion. This information
can provide engineers and decision makers with quantitative information
on the safety of the structure such that decisions can be made regarding
repair, rehabilitation, or if demolition needs to occur. The limits for making
these decisions are based on many factors (degree of damage, structure
importance, use, etc.) and decision makers will have to identify which factors
are more important in making an optimal decision. Although the procedure
provided here focused on corroding bridges, the general procedure can be
applied to a wide range of structure types and deterioration mechanisms.
The literature on modeling the time-variant performance of RC structures
is limited and signifi cant research is needed to better understand the effects
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