The Darwin Cyclone — Valuable Lesson in Structural Design

by George R. Walker, Sr. Lect. in Engrg.; James Cook University of North Queensland, Townsville, Australia,
Richard D. Marshall, Struct. Research Engr.; National Bureau of Standards, Washington, D.C.,
Joseph E. Minor, (M.ASCE), Director; Institute for Disaster Research, Texas Tech Univ., Lubbock, Texas,

Serial Information: Civil Engineering—ASCE, 1975, Vol. 45, Issue 12, Pg. 82-86

Document Type: Feature article


Eighty percent of Darwin, Australia's residential buildings were severly damaged in the wake of cyclone Tracy in the early hours of December 25, 1974. Overall damage was caused by roof failure and inadequate bracing. Residential building codes are based on tradition, intuition, and little engineering input. Roof cladding is made of galvanized, corrugated iron, in some cases with combinations of asbestos sheeting. It was found that low-cycle fatigue adjacent to the screw fastenings resulted in inadequate bracing and left the walls unsupported and prone to being blown out. The results in public service buildings was similar. Pan-type steel roofed buildings, supported by open web steel joists; steel clad, steel framed buildings with diagonal wind bracing; and prefabricated buildings utilizing light gauge cold-formed channel sections for the main room members all failed, either by buckling of the lower chords under uplift loads, which resulted in deflection of joists; loss of cladding, particularly in gabled roofs; and/or the instability of cold-formed members in bending under wind loads.

Subject Headings: Steel frames | Roofs | Cold-formed steel | Bracing | Wind loads | Structural design | Residential buildings | Damage (structural)

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