Building damage in Rabaul, Papua New Guinea, 1994

Abstract.

Damage information on 173 buildings was collected in the immediate aftermath of the September 1994 eruption which destroyed large sections of Rabaul town, Papua New Guinea. The extent of damage is presented on a five-point scale and related to construction characteristics and tephra load. Total roof loads in Rabaul town ranged from 2 to 16 kN m^–2 (about 100- to 950-mm tephra thickness). Most buildings which collapsed completely experienced loads >7.5 kN m^–2, but many buildings sustained half this load with little more than cosmetic damage. Timber-framed buildings suffered more than buildings with at least some concrete block walls. However, some old, steel-framed buildings experienced severe damage with tephra loads as low as 2 kN m^–2. Comparisons with tephra loads and building damage elsewhere are limited but suggest that Rabaul buildings experiencing roof loads of 2–5 kN m^–2 generally survived reasonably well. However, the comparisons are unsatisfactory because of inadequate data on tephra unit weights, roof design, building ages, the quality of workmanship, and the natural variability of construction materials, particularly timber. The Rabaul data suggest that concrete block walls increase building resistance to tephra loads but it is doubtful that conventional residential buildings can be designed to sustain tephra loads exceeding 7 kN m^–2. The Rabaul experience also indicates that building codes for volcanic areas need to consider mudfills and post-eruption corrosion of sheet metal roofs and wall cladding. Most importantly, had the majority of buildings in Rabaul survived the September 1994 tephra falls, wet season mudflows a few months later would still have made most of the town unsafe and uninhabitable.