14 July 2005

We’ve seen the headlines before. We have sat in workshops and proposed ways to address the problems. The risks will not go away any time soon. Given the chance to do something and the committed leadership, we can improve our buildings’ performance and sustainability to reduce the hurricane-related losses to society. It is shame that given the knowledge we have accumulated over the past 40 years of wind engineering research about the structure of the wind and its interaction with buildings, that once again in 2005 the roofs of hospitals and police stations in Carriacou and Grenada are lost due to the impact of small to moderate wind events.

Perhaps we should step back from the immediacy of the disaster that is the landfall of Hurricane Emily, and ask the question, what is an acceptable loss to society? How much damage should occur and at what wind level for the damage to be “tolerable”? This is an intriguing question for which I would expect different answers depending on whom one asks. To the insurance company executive, the loss of the roof of a hospital is probably not a significant event as the premiums would easily cover the cost of replacement. To the government which owns such a facility, the only facility serving the medical needs of its people in the immediate post-storm period, the loss of a hospital’s roof may be seen as catastrophic. Similarly, the loss of power to the average homeowner is a much less significant event as the loss of power to a communication tower that prevents the protective services and fire stations from speaking to each other. Depending on how we choose to define damage that hurricanes cause, and who is affected will determine what we do to prevent it. It is up to the society to decide when enough is enough.

We continually see pictures of building that have their building envelope components (roofing materials, wall cladding and window systems) ripped off and allowing enough rainfall and wind to enter a building to render the facility inoperable. We see fewer buildings that collapse due to wind loads threatening life safety of its occupants. Yet most of our design efforts as structural engineers are focused on the retrofitting the structural systems. The problem is not the main structural system being overloaded by wind forces, it is the large roof eaves that trap the high wind pressures,it is the poor selection of cladding materials that have not been tested for wind loads, it is inadequate connections, it is the inattention to designing a structure to exclude water penetration. The list goes on. This problem in fact results from our ignoring the serviceability limit states of design, not through malice but because our current building codes do not explicitly provide guidelines for systematically addressing these issues. The difficulty the codes face is that the level of acceptable damage changes depending on whom you ask. The problem is made worse because in traditional construction practice responsibilities for the design of critical building envelope components are split among structural engineers, architects and sometimes the technician installing a window with little direction in the field. This approach is ripe for errors and omissions that while small in themselves can lead to significant economic losses, disruptions in service and hardship to a community at large.

It is time for us to rethink the design process for structures, in particular the design of our critical facilities that are subjected to wind loads. We should understand there are many performance objectives that need to be met for a functional building and the acceptability of looses from a society should be used to determine how much effort we spend on making sure that those performance objectives are met. The earthquake engineering community did this in 1995 with the Vision 2000 document. It is time that wind engineers do the same.

We who live in hurricane -prone regions have the means to do this now. It will not take us to re-invent a better mousetrap or develop some new theory. What we need to do is to develop and understand what are the performance objectives that we want to be met and to know how the building envelope components actually behave. Through traditional tools of full-scale testing, and proper engineering (field surveys, and design and system selection) we can minimize the chance that the operating room in a new hospital in Grenada will again lose its roof in next year’s hurricane season.

The time when many years pass with little or no hurricane activity in the Atlantic Hurricane Basin appears to be behind us as the four hurricanes in Florida, and the effects of Hurricane Ivan and Jeanne in the Caribbean have shown. We should decide how many more preventable disasters are necessary before we as a societies decide we wish to do something about the current situation and what we will do to reduce the losses to levels that society’s can tolerate and recover from? When society has had its fill of the damage and suffering caused by hurricanes and are willing to do something about it, call me and researchers working together at Clemson, and other institutions through the south-east and we stand ready to assist and contribute to the solution of building structures with more predictable behavior when exposed to wind and rainfall from extreme wind events.