Design of masonry structures for Earthquakes from Electronic Blueprint
Electronic Blueprint and ENVIROSPEC provide building specifications
and training, on safe and sustainable buildings, for architects, engineers and builders.
Until the 1970's, there was no comprehensive design standard controlling the design of
masonry buildings in Australia. These were designed by a combination of engineering
judgement, rule of thumb and experience. Over the last thirty years, piecemeal introduction
of loading rules and capacity rules has led to a situation where, using AS 3700-2001
Masonry structures with AS 1170.4-1993 Earthquake loads, traditional construction can
no longer be justified in many cases. The simultaneous publication of AS 1170.4-2007
and AS 3700 Amendment 3 seeks to redress these anomalies. The following paper covers:
- Probability of exceedance of load and probability of failure.
- Design of masonry at base of the building for in-plane base shear.
- Design masonry walls for out-of-plane face load.
- Geometric limitations on masonry building height.
Johnston, R.K, "Design of Masonry Structures for Earthquake in Australia," 14th
International Brick & Block Masonry Conference, Sydney, Australia, 2008.
Recommendations include:
- The BCA (Building Code of Australia) does not overtly regulate the probability of
building failure, only the exceedance of loads. There are inconsistencies in the
probabilities of exceedance of various loads (e.g. wind and earthquake load) in the BCA.
- It is suggested that designers consider detailing housing to resist racking forces
due to moderate earthquake, even though AS 1170.4-2007 exempts most houses.
- Horizontal loads assumed using EDC I to be equal to 10% of seismic weight are often
less than the corresponding values calculated using EDC II.
- When considering the use of loadbearing unreinforced masonry, adhere to the height
limits of AS 3700 Appendix AA.
- For minor masonry structures and mezzanine floors supported by loadbearing unreinforced
masonry within larger buildings, adhere to the restrictions in AS 3700 Appendix AA.
- AS 3700 Appendix AA includes typical details for the incorporation of masonry into
building subject to earthquake loads. It is suggested that reinforced masonry or
reinforced concrete shear cores be incorporated into buildings supported by unreinforced
loadbearing masonry.
- The design process should include a check of vertical load capacity of all loadbearing
unreinforced masonry elements (including piers), when subjected to the expected inter-storey
drift.
For further information, please contact the publishers, University of Newcastle, Callaghan,
NSW, 2308, Australia or Electronic Blueprint www.electronicblueprint.com.au.
For further information contact:
Electronic Blueprint
phone: +61 2 4360 2255
fax: +61 2 4360 2256
web: www.electronicblueprint.com.au
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