George Walker

Earthquake Insurance: An Australian Perspective

Abstract This paper explains why Australian insurance companies are among the world’s largest purchasers of earthquake reinsurance, notwithstanding Australia being regarded as a region of relatively low seismicity. The basic principles of earthquake insurance and the manner in which it is priced are described, followed by their application in Australia. It is concluded that insurance of Australian property against losses from earthquake damage costs Australians about

OBSERVED EFFECTS OF TOPOGRAPHY ON THE WIND FIELD OF CYCLONE WINIFRED

450 million per year, most of which goes to off-shore reinsurance companies.

Comparison of the Impacts of Cyclone Tracy and the Newcastle Earthquake on the Australian Building and Insurance Industries

This paper describes some of the evidence of marked topographic effects associated with a moderately severe tropical cyclone which crossed the North Queensland Coast in February 1986. These effects include funnelling, increased turbulence, anomalous wind records and increased wind speeds over hills.

Cyclone Tracy and the road to improving wind-resistant design

Abstract Cyclone Tracy and the Newcastle earthquake were two of the largest natural disasters to impact Australia during the past 40 years. Each was an unexpected event, they resulted in similar overall damage costs, and they both had significant impacts on the building and insurance industries. However, although extensive recommendations for changes in building practice were made in the reports on both events, Cyclone Tracy caused far greater changes in building practice than did the Newcastle earthquake. Cyclone Tracy also had a much bigger impact on the insurance industry. Another significant difference was that building costs almost doubled in Darwin following Cyclone Tracy, but hardly changed in Newcastle following the Newcastle earthquake. In respect of building practice it is suggested that the greater influence of the Commonwealth Government in Darwin at the time of Tracy was a major factor in driving the resulting Australia wide changes in building practice. In respect of the insurance industry the lessons learned from Cyclone Tracy lessened the impact of the Newcastle earthquake, although the latter was the catalyst for a major change in the way catastrophe insurance risk is assessed in Australia. The differences in post-event building costs are attributed to differences in the supply and demand for building services following the events. The analysis of comparative costs also revealed major anomalies in the current published data on the costs of both events and revised estimates of these are presented.

Application of wind engineering to low rise housing

Early on Christmas morning 1974, tropical cyclone Tracy devastated the city of Darwin leaving only 6 per cent of the citys housing habitable and instigating the evacuation of 75 per cent of its population. The systematic failure of so much of Darwins building stock led to a humanitarian disaster that proved the impetus for an upheaval of building regulatory and construction practices throughout Australia. Indeed, some of the most enduring legacies of Tracy have been the engineering and regulatory steps taken to ensure the extent of damage would not be repeated. This chapter explores these steps and highlights lessons that have led to a national building framework and practice at the fore of wind-resistant design internationally. Tropical cyclone Tracy was a small but intense cyclone, with a landfall radius to maximum winds of 7 km, a forward speed of 7 km/h and central pressure of 950 hPa (Bureau of Meteorology, 1977) (Figure 9.1). Tracy was an Australian Category 4 cyclone with estimated maximum-gust wind speeds on the order of 250 km/h (70 m/s) (Walker, 1975). The recorded gust of 217 km/h (60 m/s) at Darwin Airport before the anemometer failed was, to that time, the highest wind speed measured anywhere on mainland Australia. Tracys small size minimised the spatial extent of damage, but its slow translational speed meant areas impacted suffered more damage than might otherwise have been the case. Of cyclones that form in Australian waters, one passes within 200 km of Darwin every one to two years. The expected recurrence interval of an event similar to or stronger than Tracy impacting Darwin is greater than 100 years based on historical records.

A simplified wind loading code for small buildings in tropical cyclone prone areas

Abstract Despite considerable knowledge about wind loads on houses, until recently very little of this knowledge has been reflected in housing design, with the result that damage to housing continues to dominate wind damage losses world wide. Reasons for this are discussed and a methodology outlined, based on recent Australian experience, for overcoming this major gap in the application of wind engineering knowledge. Some of the key factors identified are standardisation of loads, test methods and construction details, together with widely based building industry involvement and public education.

Distribution of Wind Loads in Metal-Clad Roofing Structures

Abstract A case for the development of a simplified wind loading code for use in regions prone to tropical cyclones is presented together with a proposal that could form the basis for such a code. The proposal is based on a simplified wind loading code being developed in Australia.

Structural engineering and resilience

The roof is the part that experiences the largest wind load and is usually the most vulnerable part of a house. However, data on how the wind loads are transferred through the roof structure are scarce. The fluctuating nature and variable spatial distribution of wind loads combined with the structural response can cause significant challenges for assessing the distribution or sharing of loads in a roof. Such studies are required to obtain more reliable estimates on vulnerability assessment to windstorms. This paper describes the transmission of wind loads from the pressure on the cladding through the cladding-to-batten connections to the batten-to-truss connections on a roofing system typical of that in many contemporary houses constructed in cyclonic regions of Australia. The study found that the use of normal design practices can significantly underestimate connection loads when highly correlated large-scale wind pressures act on these roof systems.

Disaster Risk Reduction and the Earthquake Code - A Disconnect

Over three and half thousand years ago, King Hammurabi of Babylonia decreed that if a builder built a house which fell down due to faulty construction and killed the owner then he would be put to death, and if it didn’t kill anyone then he must rebuild the house at his own expense and compensate the owner for damaged contents. Since then the design and construction of houses and other buildings has improved very significantly. This was due initially to improvements in understanding the mechanics of the structural behaviour of building elements, then improvements in understanding the structural behaviour of building materials, and finally during a period beginning when I was undertaking my PhD in the early 1960s the use of computers which has enabled our continually improving knowledge of structural mechanics and material behaviour to be integrated to describe the behaviour of not just the elements of buildings but of whole complex building systems. Nevertheless, with some modifications, the principle embodied in the Code of Hammurabi of focusing on life safety and financial responsibility for losses associated with failure due to negligence in design and construction still underpin structural design philosophy. The most significant modification in Australian society at least is that the penalty for failure of buildings resulting in fatalities is no longer a capital offence. But equally important from the point of view of structural design philosophy is that limits have been placed on the responsibility of structural engineers which if exceeded relieve the designer of this responsibility if failure occurs, providing the design satisfies these limits. We call these limits the Limit States. The Ultimate Strength Limit State satisfies the requirement for life safety and is rigorously enforced. The Serviceability Limit State, which defines requirements for acceptable lifetime structural performance of buildings under expected loadings, is only enforced if it is associated with a risk to health or amenity. A consequence of this approach is that design is focused on individual building behaviour only, the socio-economic consequences of structural failure for the community in which the building is located is generally not considered, and efficient structural design is generally considered a desirable objective which is being achieved by the sophisticated computer-based analysis increasingly being made available to designers. In a world focused on economic efficiency this is considered a good thing. However, it is a world in which sustainability is also an increasing community focus, in response to which in Australia sustainability has been added to safety, health and amenity as one of the primary factors listed in the National Construction Code to be addressed in the design and construction of buildings. Judging by the presentations at the recent Australasian Structural Engineering Conference, the implications for structural design philosophy of this inclusion of sustainability in design requirements have not been widely recognised by the structural engineering profession. It was an excellent conference in many regards with its focus on the changing roles of structural engineers both in respect of the continuing advances in computing technology and the importance of considering sustainability. However, sustainability seemed to be largely understood only in terms of utilisation of the earth’s resources and greenhouse emissions, and improving the efficiency of structural design of standalone structures still seemed to be a driving force of much of the research and improvements in design procedures described. What did not appear to be generally recognised is that a major component of sustainability, and one being increasingly reflected at national and international level, is community resilience to disasters. In respect of earthquakes and tropical cyclones in particular, this is largely the result of the increasing magnitude of the economic and social disruption arising from damage to the built environment in disasters, even in developed countries where loss of life from such events has shown dramatic reductions due to improved building codes. Modern building codes are clearly not as effective in reducing this aspect of disaster risk as they are in reducing life safety – primarily because they do not address community resilience. Many structural engineers equate incorporating robustness with resilience. It is a misconception. Robustness is about improving life safety in the event of structural failure, not improving the recovery of functionality of the community as quickly as possible, which is what resilience is about. It is a different Limit State. In Christchurch, all but one of the modern buildings in the CBD displayed excellent robustness by not collapsing even though damaged to the extent they need to be demolished and replaced. But the time taken to demolish and reconstruct these buildings has had a negative impact on the resilience of the Christchurch CBD – i.e. on the recovery of its functionality. If efficient design means individual structures designed to just meet the current minimum structural requirements, then efficient design is likely to result in lowering community resilience, particularly in respect of communities with large concentrations of wealth and people. Structural redundancy may be the enemy of efficient design of a standalone building but it is the friend of community resilience if the building is part of a large community. Consequently, designing the built environment to improve resilience requires a major change of the structural design philosophy which has underpinned design since its

Distribution of Wind Loads in a House Roof System and Application to Fragility Analysis

Abstract The application of current earthquake engineering knowledge through structural design codes has greatly reduced the loss of life from earthquakes in countries where the use of such codes has been normal practice for several decades. However it has not had a commensurate effect on disaster risk reduction as was clearly demonstrated in Christchurch by the Canterbury earthquakes. Although the great majority of lives which were lost were the result of the failure of just one modern building - which evidence suggests was from poor design and not a code problem - many modern buildings, while performing well in terms of life safety, were nevertheless damaged beyond repair imposing major economic and social costs on the citizens of Christchurch in particular and, through greatly increased insurance premiums, New Zealand generally. This paper describes the disconnect between the nature of disaster risk reduction and current structural earthquake engineering design philosophy which arises because disasters are a function of community size as well as building vulnerability, whereas current design philosophy is focused entirely on the safety of individual buildings. It draws on ideas jointly developed with the late Paul Grundy and is presented as a tribute to his major contribution to this field.