Seismic risk models for aging and deteriorating buildings and civil infrastructure - Seismic Risk Analysis and Management of Civil Infrastructure Systems - page 381

mechanisms and the associated uncertainties, which are essential for effec-
tive decision making.
Structural deterioration is a combination of both progressive (e.g., cor-
rosion, fatigue) and sudden (e.g., earthquakes) damaging events (Fig. 15.1).
Progressive deterioration results from adverse environmental conditions
such as high temperature, humidity and carbonation, chloride ingress, bio-
deterioration, etc. The main effect of the surrounding environment on rein-
forced concrete (RC) structures, in particular, is the loss of effective
cross-section of steel reinforcement due to corrosion, concrete cracking, loss
of bond and spalling. Among all these phenomena, corrosion is probably
the problem that has attracted most attention. According to Bhide (1999),
about 173 000 bridges on the interstate system of the United States are
structurally defi cient or functionally obsolete due in part to corrosion. RC
structures are susceptible to corrosion when they are placed in environ-
ments with high concentrations of chloride ions or carbon dioxide. Chloride
ingress into a concrete matrix is dominated by a complex interaction
between physical and chemical processes and although the details of these
deterioration mechanisms are beyond the scope of the chapter, they are
well described by, for instance, Vu and Stewart (2000), Duracrete (2000) and
Bastidas et al. (2009).
On the other hand, deterioration caused by successive extreme events is
mainly associated with the occurrence of earthquakes, hurricanes or blasts

Progressive
deterioration

v 0

Y 1

Shocks

Y 2

Serviceability limit

k*

Y i

Ultimate limit state

s*

Failure

t f

Time

X 1 X 2 X 3 X 4

Time between shocks

15.1 Description of deterioration mechanisms.