By Matt Barnard
Somewhere, the earth is shaking. Earthquakes happen frequently throughout the world but often go unnoticed or are of little concern. Occasionally, earthquakes are much larger with shaking that impacts people and the built environment and cause tremendous loss of life, as we saw last year with the disaster in Turkey. In a world that seems to be more connected than ever, whether through our instantaneous sharing of everything to our global economies and supply chains, we now almost immediately see and then are impacted by these large earthquakes whether we have personally felt the shaking or not.
As structural engineers, we are uniquely able to help our communities mitigate the impacts of these earthquakes. With the continued advancements in the science and understanding of plate tectonics, we better understand the breadth of the seismic hazard facing communities, including those places in where, in decades past, designing for earthquakes was not common. The science and understanding of structures subjected to significant ground shaking also continue to grow. The analytical resources available to engineers continue to improve and allow quicker and more accurate modeling of structures. We continue to bring improvements in detailing and the construction of parts and portions of the structure into our building codes and our typical practices.
While significant resources are available for engineers to learn the latest about engineering structures for seismic hazards, there is less information available about how to go beyond engineering and have a business that is prepared for the impacts of an earthquake. CASE has published CASE Guideline 962-J, “Business Practice Guidelines of Seismic Design for the Structural Engineer,” to introduce readers to seismic and structural engineering and to provide business practices insights. The Guideline outlines some of the basic engineering considerations that will prove useful for those new to considering seismic hazards. There are summaries of the basic theory, key concepts, and differences between new and existing structures. The Guideline also touches on trends in seismic and structural engineering and provides some recommendations on business practice considerations.
The Guideline also highlights common myths associated with buildings and earthquakes. Be aware of these myths if you are going to start practicing where there is an earthquake hazard. Common myths include:
• “My building did fine in the last earthquake, so there is nothing wrong with it.” People wrongly assume that all buildings in a geographic area that survived an earthquake were subjected to the same ground motion. Since every earthquake is different, so are the effects on a given building, even similar buildings near each other. View an earthquake as the equivalent of playing roulette; if your number does not come up this time, it might next time. While a poorly designed structure may survive a given earthquake, that does not mean that the structure will perform during a future earthquake.
• “My building is built to current code, so it is earthquake-proof.” There is no such thing as an earthquake-proof building. A structure designed according to the current code is expected to protect life safety for the code-defined earthquake hazard, but that does not mean that the structure is going to be free of damage or even repairable. This is often not understood by the public and sometimes not by engineers either.
• “Isn’t code minimum good enough?” Many buildings wrongly assume that code minimum will result in “satisfactory” performance. However, that is defined. The owner will benefit from a candid conversation about what the real expected performance of their building is likely to be. It is also an important way to protect yourself from a disgruntled owner after a major earthquake.
• “The City approved it, so everything with my building is fine.” Just because something was approved does not mean it is compliant with the code or even the right design approach. A rigorous plan check or peer review can be an invaluable service provided to a building owner.
• “The computer model shows that it is okay.” The quality of output from a computer model depends on the quality of input, how the model was built, and the software used. It is important to view the results of any analysis with a critical eye and ask yourself whether the behavior predicted by the model is consistent with what you expected. However, just because a computer model says something is okay does not mean that the result is correct.
• “There has never been an earthquake here, so we are fine.” We all are guilty of trying to predict the future based on our past experiences. But human lives are short compared to geologic time associated with major earthquakes. It should come as no surprise that many owners are surprised that they must consider earthquake hazards when they have never experienced one themselves. However, we need to be patient and educate owners and the public about the hazard and why we are now designing for seismic hazards in areas that traditionally have not done so.
• “My building has been retrofitted, so we are as good as new.” This is one of the most dangerous myths. Often, retrofits only address a specific deficiency that requires immediate action or are targeted at a specific level of improvement. While retrofits are critical to improving the safety of the built environment, these retrofits might not address every problem in a building; they might have only addressed the most pressing ones.
• “That building over there is not my problem; that’s my neighbor’s problem.” When your neighbor’s building falls on yours, it becomes very much your problem. When your neighbor’s building is abandoned because of damage, it negatively impacts you and the entire community.
Have you come across these common myths in your practice? Are there other myths that we should include on this list? Please share them with us. We will gladly continue to update this list so others can avoid the associated pitfalls. ■
Matt Barnard is a Senior Principal with Degenkolb Engineers and is based in Orange County, California. He is a past President of the Structural Engineers Association of Southern California and serves on the Council of American Structural Engineers Guidelines Committee.