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• EDC III – dynamic analysis: This is the most sophisticated check and
is used only rarely. It is reserved for the tallest buildings, for buildings
of intermediate height on softer soils, and for the most important
buildings that are taller than 12m. The analysis is dynamic in the
sense that it examines the forces created as the building oscillates
during an earthquake event;
• EDC II – equivalent static analysis: This method assumes the
application of a constant static force to the building and is
computationally less demanding than EDC III. Equivalence is
maintained by magnifying the static force in a manner calculated to
mimic the dynamic stresses; and
• EDC I – minimum static check: This is a minimum check to confirm
that the structure can resist a horizontal force that relates to the
‘seismic weight’ of the structure, which is a function of its mass and
stiffness. It is not an acceptable method for any structure that is taller
than 12 m.
Given this account of how BCA2008 will engage AS1170.4-2007, it remains to
describe the Standard’s content. Putting aside the definitional material in
section 1 of AS1170.4-2007, the remaining 7 sections and appendix can be
grouped as follows:
• Sections 2, 3 and 4: These sections show the structural engineer how
to determine which design procedure is required, if any. This includes
for example, maps showing the variation in earthquake hazards across
Australia, methods for determining the class of sub-soil, and the rules
for combining this environmental information with building factors
(height and importance) to determine the design procedure;
• Sections 5, 6 and 7, plus Appendix A: These contain detailed
instructions for each of the design procedures, focusing on the
performance of the ‘seismic-force-resisting-system’ within the structure
of the building. With the exception of the general principles and static
tests, this material tends to be highly technical; and
• Section 8: This section deals with non-structural elements such as the
architectural, mechanical and electrical components of a building. It
provides for both simple and more complex methods of analysis.
3.2 How BCA2008 would differ from BCA2007
The proposed and existing arrangements allocate tasks to the BCA and the
Standard in the same manner. The BCA says what is required: for example,
whether the building should be built to resist an earthquake that is exceeded
once in 500 years, or an earthquake that is exceeded once in 1,000 years.
The Standard says how compliance with any such requirement can be
demonstrated. Within that framework, there are differences in both
requirements (in the BCA) and the process for demonstrating compliance (in
the Standard).
ABCB Regulation Impact Statement (RIS 2007-03)
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