Earthquake Engineering Research - HKU Libraries - The University ...

greatly from those regions of the world with low to moderate seismicity, usable ground motion
records are scarce, thus recordings are often borrowed from high seismic regions.
PBD FOR SEISMIC RETROFIT
The implicit inclusion of performance limit states is advantageous to designers trying to evaluate
the benefits of retrofitting a structure. Furthermore, it assists in providing a reasonable
perspective to tangible outcomes for owners. However, costs to owners will need to be evaluated
in terms of the remaining life of the structure. The result is that the need to plan and conduct a
seismic retrofit program in low to moderate seismic regions becomes a trade-off between the
structures remaining design life and the anticipated return period of a strong enough earthquake
(which is generally much longer). Communication to the general public becomes even more
important in such a case where the lesser occurrence of earthquakes reduces public awareness.
To convince the public, engineers must benchmark against other kinds of risk, for example,
earthquake risk compared with risks due to typhoons in Hong Kong.
In many regions (such as Hong Kong), seismic design procedures do not exist, thus adoption of
seismic performance-based approaches and evaluation of retrofit plans must be exceedingly
simple as well as justified in light of other natural hazards (e.g. typhoons). Hong Kong, for
example, has adopted the approach of first developing a holistic study encompassing all risks to
structures to evaluate the need for seismic retrofit. In order to convince legislators of this need, a
quantitative risk assessment is pursued, whereby earthquake risk is placed in the context of other
risks to structures. In Korea, for example, convincing building owners to retrofit for seismic
loads has been more challenging, while retrofit programs for bridge structures are more readily
accepted since bridge structures are controlled by the government and life expectancy is more
carefully scrutinized. Incremental seismic retrofit programs, which have been adopted in the
United States, may alleviate large sudden financial burdens. If these programs are put in the
context of multi-hazard mitigation, this too may be successful in convincing the public. It should
be emphasized to the stakeholder that conducting a thorough performance-based seismic design
for a new building requires minimal costs, when compared with the potential costs associated
with post-construction seismic retrofit.
PERFORMANCE-BASED DESIGN VERSUS PERFORMANCE-BASED PROVISIONS
Performance-based design is really nothing new and to many extents has been codified, although
transparent to designers, for many years. New aspects of PBD include the details and levels of
performance and the understanding of the implications of such performance. The most important
outcome of PBD is the development of performance-based provisions to effectively
communicate these outcomes. Performance-based provisions must carefully be balanced with
minimal complexity. Transparent physical concepts must be provided that do not make the
process overly complex. This is particularly important in low to moderate seismic zones where
earthquake design provisions struggle for adoption. Provisions that are too cumbersome will
receive little embrace by the community and not be adopted. The recent Japanese
implementation of performance-based provisions is highlighted as an example of successful
integration with practice.
Following the 1995 Kobe earthquake in Japan, a revised building standard was implemented
(Building Standard Law, 1998). Revisions incorporated performance-based provisions with the