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In order to ensure the entire social safety against seismic hazard the sufficient seismic performance has
to be secured for the existing structures as well as new ones. In Korea many multi-span continuous
bridges had been constructed in which earthquake load was not considered adequately. They can be
very vulnerable to the earthquake ground motion especially in longitudinal direction. Hence many
alternative retrofit methods are considered and/or implemented such as isolation bearings and shock
transmission units. The project to develop the seismic performance assessment method has been
initiated by the Ministry of Construction and Transportation of Korea (KMOCT). In this year the
manual for seismic assessment of bridges was drafted and approved. It will be distributed soon. In this
manual a new philosophy is introduced in the determination of design earthquake for the retrofit of
bridges. In this paper, this new concept is introduced briefly. And several retrofit examples are
reported.
SEISMIC DESIGN OF BRIDGES IN KOREA
Seismic Design Code of Bridges
The history of seismic design in Korea is not as long as that of countries in high seismicity region. It
has been introduced to Korea since 1986 for high-rise buildings, since 1992 for highway bridges and
even earlier than that for nuclear power plants. The basic idea in these codes has been borrowed
heavily from those developed for the high seismicity region. However the public did not aware the
necessity of seismic design in general until Kobe earthquake yielding severe damage and huge
casualties in 1995. Taking opportunity of this earthquake KMOCT decided to develop new
performance based seismic design code system that can be commonly applicable to most types of
facilities. As the first step, the high-level criteria of performance-based seismic design had been
completed to regulate seismic design loads and seismic performance level of structures. Based on this,
the low-level criteria and technical standards specific to each own type of facility have been under
development. The 2002 edition of Korea Highway Bridge Standard (KHBDS) adopted this design
concept.
In Korea, the seismic design has been carried out in two ways. The one is relying on the ductility of
column bents, and the other is adoption of various types of earthquake protection systems such as
isolation systems. For the former, the identical reinforcement details to those in zone II of AASHTO
code have been adopted as shown in TABLE 1. It is remarkable that the lap splice of longitudinal bars
in the plastic hinge zone is implicitly allowed. Due to this lap splice detail same amount of transverse
reinforcement as specified in high seismicity zone is required to attain satisfactory ductility. Unlike
high seismicity zone, the limited ductile behavior is expected in the moderate seismicity regions. In
Korea the sectional dimension of piers designed conventionally is as large as 3.5m diameters.
Therefore they can have considerable amount of inherent lateral load resistant capacity. However the
current codes requires relatively larger amount of transverse rebar than necessary. Therefore, it is
necessary to develop limited ductility design that is appropriate to the seismicity of Korea and the
characteristics of columns. This design approach should take advantage of the inherent seismic
capacity of conventional designed piers.