Although Katrina was a major hurricane, her maxi- mum wind speeds do not appear to have exceeded those used for structural design guidelines in the region. The storm surge was estimated to be as high as 30 ft, with probabilities of occurrence greater than once in 500 years in many areas along the coast. The surge and high winds dev- astated the coastal cities of Biloxi and Gulfport, Mississippi. There was also extensive wind damage in New Orleans, most notably the loss of office tower and hotel windows, as well as the roof panels on the Superdome, where thousands of people were taking refuge from the storm. Worst of all, the storm surge also caused the levees surrounding the city to burst, lead- ing to massive flooding. Tens of thousands of homes were destroyed in New Orleans and along the Mississippi coast.
All levels of government were slow to respond to the crisis and have since been widely criticized. This was truly both a natural disaster, due to the hurricane itself, and a management disaster, due to the slow response of those responsible for emergency preparedness.
It is enlightening to compare what happened during Katrina with a more positive example: the 1997 Red River flood in Manitoba. Following the 1950 flood, which destroyed over 10,500 homes in Winnipeg, a 47-km floodway to bypass the city was built for $63 million. ”œDuff’s Ditch,” named for Manitoba premier Duff Roblin, who was its leading propo- nent, was mocked at the time, but it protected Winnipeg four decades later when similar flood levels occurred.
Other factors prevented disaster in 1997 as well. Accurate forecasting predicted the actual flood levels. In particular, after the flooding of Grand Forks, North Dakota, proved the forecasters correct, the residents of Manitoba worked together with military personnel to raise the dykes south of Winnipeg so that the river could not do an ”œend run” around the floodway. The capacity of the Winnipeg floodway is currently being expanded.
Natural disasters are the interaction of naturally occur- ring hazards with human populations. We can do nothing about the actual natural hazards, so to minimize their risks and consequences, we must manage the other half of the equation " the human population and infrastructure. Wind, snow and rain hazards are different than floods. Flood damage is controlled by limiting development in high-risk areas or providing large-scale diversion infrastruc- ture like floodways (an effective strategy for Winnipeg) or levees (an ineffective strategy for New Orleans).
Wind, snow or rain damage is con- trolled through design, construction and maintenance of each individual structure by builders and individual homeowners. Houses and other light-frame structures, in spite of their widespread use and apparent simplicity, are among the most complex structural assemblies used by Canadians. The complexity comes from the highly redundant yet vaguely defined system of structural elements that are not truly ”œengineered” based on scientific principles, but rather ”œpropor- tioned” using prescriptive rules derived from traditional practices that specify, for example, the maximum spacing of 2-by- 4 studs in a wall or the minimum num- ber of nails in a connection. Prescriptive rules ensure that house collapses are infrequent while keeping construction affordable. This does not necessarily ensure that they are optimal in an engi- neering sense.
The environmental protection sys- tems in houses are also complex. Insulation keeps the heat in, but may alter the moisture movement necessary to keep interior walls dry. Moisture arises within a house because of human activi- ty, rain and humidity. Rain is a particular problem because the pressure gradients that generate significant forces on the structure also propel rain through cladding materials, such as brick or sid- ing. Trapped water can allow mould to grow, leading to a health hazard that is also an eyesore. Thus, there need to be built-in mechanisms to allow the walls to dry out, a particular challenge in Canada since they may conflict with our need to retain heat. Because houses are not engi- neered, but designed and built largely based on experience through prescriptive rules, damage surveys following signifi- cant environmental (e.g., wind, snow, rain, hail) events and laboratory testing under realistic yet extreme conditions are critical. Post-disaster investigations of damage to housing due to extreme winds and rain do not always uncover the caus- es of a progressive structural failure or water entry, so laboratory-based experi- ments are also necessary.
Figure 1 shows a relatively new house with significant structural damage sustained from Katrina. At first glance, these may not be surprising images. What actually makes the image surpris- ingiswhatisnotshown"the100orso other houses in the neighbourhood, of the same age and style, without any sig- nificant structural damage. This was the only house in this neighbourhood that sustained major structural damage. Many houses had shingle and/or siding loss (like those in the background of the photograph). Many more had no visible damage. Clearly, most the roof shown in figure 1 has been torn off by wind uplift loads, with the left end probably secured by the chimney. Did the missing roof go as a single unit, or was it torn away in pieces? Was the failure due to internal pressurization caused by the breakage of the second floor window (shown circled in the figure)? Was some element or con- nector improperly installed? What components or connections actually need to be strengthened to prevent this type of failure from occurring in the next wind- storm? Efforts to rescue anyone buried in the collapsed structure and to return the structure to some degree of functionality can hamper forensic investigations, as can the clean-up by the homeowner (notice the clean lawns around the hous- es at the time of the photograph, three weeks after the storm).
While Canada does not have the same hurricane risk as coastal Florida and the Gulf states, we do occa- sionally experience them, as Hurricanes Hazel in 1954 and Juan in 2003 illustrate. We also have significant wind events associated with tornadoes and other thunderstorm winds that can be accom- panied by large amounts of rainfall. Building codes play a crucial role in the safety of our homes. Timothy Reinhold, vice-president of research for the Institute for Business and Home Safety in Tampa, observed after the 2004 Florida hurricane season that ”œbuilding codes make a huge difference. If we can get better codes in place, then we can reduce the amount of post-disaster assistance that the govern- ment is going to have to provide.” Reports from the United States Federal Emergency Management Agency (FEMA), based on observations from the 2004 hur- ricanes, indicated that the performance of housing was dependent on which code it was built to. Newer homes built to the newer Florida codes performed well, with only a few failures due to errors in con- struction or the incorrect installation of structural features and materials. Improved codes also have the potential to reduce insurance claims and the resulting rates homeowners must pay. Risk opti- mization is possible: stronger structures have higher first costs but require fewer repairs after extreme events.
The question of ”œhow safe is safe enough” is not one that interests the average homebuyer, so at least minimum safety levels must be assured by govern- ments through building codes. Sufficient resources are necessary for education and enforcement to ensure that code provi- sions are successfully implemented. Professor Paul Gauvreau of the University of Toronto observes that ”œbuilding codes freeze technology and innovation” by at best providing prescriptive rules for exist- ing or recently discovered solutions. New editions are published at five- or 10-year intervals. Code development has an inherent inertia as changes must be learned by the design profession and the various stakeholders in the construction industry. For example, a recent study by the American Concrete Institute identi- fied a ten-year interval between the pub- lication of new information in scientific journals and the adoption of the infor- mation in the Institute’s Building Code Requirements for Structural Concrete. Recognizing this, the 2005 edition of the National Building Code of Canada will initiate the replacement of prescriptive design criteria with objective-based design requirements. The Canadian Commission on Building and Fire Codes identified several general objectives that the code is intended to achieve, includ- ing safety, health, accessibility, and fire and structural protection.
In the long term, the movement towards objective-based design codes is likely to impact the structural engineer- ing design profession and construction industry as significantly as the Charter of Rights and Freedoms has impacted the legal profession. The transition is likely to be challenging, as designers struggle to define problems using broad objectives in place of familiar technical criteria. A large part of the challenge is that many of our current technologies are not ade- quately benchmarked, for example, 2-by- 4 studs on 16-inch centres may be a widely used form of construction, but what specific features make it attractive? Quantification of the performance of tra- ditional forms of construction is essential to measure the adequacy of new forms of construction through the development of new testing standards and protocols.
The University of Western Ontario’s ”œThree Little Pigs” research facility is a full-scale testing facility to study struc- tural, building envelope and moisture- related issues in houses. It will permit, for the first time anywhere, the application of realistically simulated time and spatially varying wind loads to full-scale houses in a controlled manner up to fail- ure. It is this aspect of the project that led to naming of the facility after the famous children’s story. Construction is now under way at a site at London International Airport: the first house ”œspecimen” will be completed in spring 2006 and the facility will become fully operational by the end of 2006. A novel loading system (the ”œBig, Bad Wolf” in the story), is under development. Different building materials can be tested within the structural system (i.e., on the house) and separately under more standard testing condi- tions. Water will be intro- duced to see how it moves through the building envelope. Novel, real-time mould growth sensors are being developed to determine drying rates necessary to mitigate its formation and growth. In other words, all aspects of Canadian housing will be studied.
The resilience of houses to wind, snow or rain damage is controlled through the design, construction and maintenance of each individual struc- ture, by builders and individual home- owners. The success of this strategy requires building codes that provide adequate levels of reliability without unduly inhibiting the implementation of new technologies. Moreover, builders and homeowners have to be educated about the importance of get- ting it right. Damage surveys after major failure events and full-scale test- ing, like the testing conducted at the Three Little Pigs facility, provide valu- able scientific data that is necessary to improve our building codes and edu- cate our construction industry.