New life for old structures

The collapse of the Palau Bridge in 1996 received considerable attention at the time, but there has been very little reported in the literature about the investigation of the collapse mechanism, partly because of a legal agreement between the parties involved. This paper has been prepared from publicly available sources to ensure that the wider structural engineering community learns something from the failure. Since the collapse occurred soon after a repair to the bridge, it has been widely assumed that the repair was the cause of the failure, but it is shown that this is very unlikely. Instead it is concluded that lack of robustness in the original design meant that the structure had always been vulnerable to accidental damage, which eventually occurred as part of the resurfacing works. Chris Burgoyne, MA, MSc, PhD, CEng, FIStructE, MICE University of Cambridge Richard Scantlebury, BA, MEng Benaim (UK) Ltd

This paper starts by reporting on three different types of structural failure observed in various structures during the tsunami of December 2004, namely sliding, overturning and undermining through scouring. It then describes some guidelines that have been drawn up for low cost single storey buildings at risk from the natural disasters of coastal flooding, cyclones and earthquakes, covering zoning and siting issues in addition to building planning and structural recommendations. Finally, the paper presents engineering calculations for three case studies, namely a school building that has lost a corner column due to undermining, the same school building subjected to tsunami loading and a boundary wall experiencing a lateral water load. These calculations help to identify strategies for designing efficiently against the very large effects of tsunamis. Professor W .P. S. Dias, PhD, DIC, MIStructE H. M. Y. C. Mallikarachchi, BSc (Eng) Department of Civil Engineering, University of Moratuwa, Moratuwa, Sri Lanka