Impact statistics of Tracy and an opportunity missed

Abstract

When cyclone Tracy struck Darwin in 1974 it caused extensive damage to housing. A survey conducted by the authors included measurement of a damage index for about 1500 timber framed elevated houses of similar size and construction. This large sample provided a unique opportunity for quantifying the spatial variation of the wind-field impact of a typical tropical cyclone. In addition it was observed that unacceptable levels of damage occurred to all types of housing. An examination of this damage gave rise to the suspicion that the concept of using conventional structural engineering principles to develop ‘engineered cottage construction’ would not lead to an acceptable level of risk in the event of the occurrence of rare structural hazards. Subsequent data obtained from field studies and laboratory tests have served to reinforce this observation. As a result, it is proposed that the design of houses to resist rare structural loads should include the use of a reliable ‘anchor structure’. The destruction by Tracy was so extensive, that it could have been used at that time as a trigger to introduce the radical concept of an anchor structure into building regulations. This was not done, and it was a unique opportunity missed.