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maintain economy of design but may need to be prohibited for frames designed to resist seismic loads.
Ductility of heavily reinforced sections
It is not unusual in Hong Kong for columns to have nearly 6% reinforcement and even to use staggered
laps and couplers to comply with the maximum 10 % allowable by BS 8110. If plastic hinges are not
expected it may be possible to continue to allow heavily reinforced concrete members.
Avoidance of shear failure of vertical members
The capacity design requirement to provide sufficient shear reinforcement at ends of beams to ensure
that the longitudinal reinforcement yields before shear failure occurs is a straightforward concept for
beams. It is not as straightforward for compression members or where the gravity loads determine the
design of the beams. Recent experience from the 1999 Athens earthquake indicates that even
seismically designed columns failed, in shear, at mid height rather than at the top or bottom of the
column. This will need further consideration when defining the nominal detailing rules especially since
in HK column cross sections frequently are large compared to their length..
Development of HK Seismic Code
The New Zealand (NZ) and Australian concrete codes closely follow the US code that uses strength
reduction factors to reduce the ultimate design capacity, rather than material factors which are used in
the Chinese, British and European standards. Since the US and NZ codes have been developed mainly
for regions of high seismicity they may not be the most suited for development of a HK seismic code.
One of the main difficulties in Hong Kong will be to extend the material design codes currently used,
to allow seismic detailing. Neither the concrete code - BS 8110, nor the steel code - BS5950 has any
guidance in this regard. Most countries separate the material design codes from the loading code. It
will therefore, be a major decision as to what to do in Hong Kong where the material design codes
have been adapted from British versions a number of years after their introduction in Britain. Even
today HK uses the 1985 Version of the concrete design code even though the latest British version is
1997. The British codes never had seismic design and in any case are being superseded by the Eurocodes
so Hong Kong could follow the European seismic design code. However the Eurocode has
tended to follow the rather complicated, yet pioneering seismic design codes developed in NZ,
It is thus probable that using the Euro-code as a model to particularise for HK conditions will be the
quickest way to produce a Hong Kong seismic code, however serious consideration should be given to
adopting the Chinese code approach to seismic design. After all, HK is part of China and so it would
be shortsighted to adopt a different system when first introducing a seismic code in HK. Whatever
method is used, the main aim of the Hong Kong Seismic Code should be to keep it simple and make it
easy to understand and use.
CONCLUSION
Before introducing a seismic code in HK, one of the challenges for educators will be to ensure that
designers are confident in the determination of base shear and are familiar with the highly variable
values derived. The key seismic code requirements for Hong Kong will be to provide clear guidance
on the ductility factors and analysis methods to be adopted and that nominal detailing rules do not
require high percentages of ductility reinforcement at all column beam joints.