{'fraction_non_alphanumeric': 0.010608695652173913, 'fraction_numerical': 0.0006956521739130435, 'mean_word_length': 5.375831485587583, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Structural engineering and resilience

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