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Following on from my last blog where I considered earthquakes as the real weapons of mass destruction in the developing world, I wanted to offer some real world thoughts to design and architecture professionals about how we can go about ensuring seismic mitigation. After all, as I mentioned in an earlier blog, seismic mitigation is provenly effective. What’s more, it doesn’t have to be cost prohibitive.
Seismic mitigation for buildings is an arcane subject. It has evolved from a highly specialized field of structural engineering focused entirely on earthquake engineering. Which can mean that comprehending seismic design intent can be difficult to grasp for design professionals without this particular esoteric expertise. The resultant knowledge gap can at best hinder efficient implementation of code compliant mitigation, and at worst cause complete noncompliance.
At the apex of the implementation task is the architect. The task of mitigation is associated with each and every nonstructural item attached to the load bearing building structural system. In 1996, when I was first tasked with bringing together the guidance on offer to design professionals, it seemed to me that much of it had more in common with Greek mythology than academic thought. Today, I’d offer the following five pieces of advice:
1. The main thing is keeping the main thing the main thing – Seismic Demand
One of the most important concepts we learned early on for equipment code compliance was to stay centered on the simple concept of determining the “seismic demand” for the location specific site under evaluation and then compare that to the “tested or qualified seismic capacity” of the equipment. If the capacity exceeds the demand then the equipment is code compliant, it’s really that simple.
2. Good design must be followed by accurate installation – the devil is in the detail
Findings from numerous post-earthquake surveys consistently conclude that it is rare for shake table qualified equipment to fail. When failure is observed, the single largest contributing factor is the equipment anchorage, or seismic restraints which were proved inadequate, improper or poorly installed.
For qualification to be valid, essential building equipment and its distributed systems must be attached to the building structural system in accordance with the manufacturers’ instructions and the responsible registered design professional’s seismic restraint detailing. The devil is in the detail – the “seismic load path” that transfers the earthquake induced demands into the equipment must be transferred to the building structural system. Pay special attention to the hidden killer of many critical systems – architectural flourishes (cladding, parapets etc.) that may detach and fall onto essential equipment.
3. Remember the three B’s: Build Back Better!
In my third blog I wrote about the remarkable work of documenting and utilizing workable earthquake-resistant construction techniques localized for the realities of each seismically active region. The underlying concept is to improve the connections between key building structural elements (wall to floor etc.), so that the building load-bearing structural components stay connected during an earthquake to greatly improve life safety performance.
These methods have already been deployed in a “build back better” strategy in a number of hard hit locations and will make a significant difference when the next event occurs. However, for seismically active areas in the developing world it will take a meaningful enforcement of modern building codes and modification of owner expectations to move the mitigation needle in the improved performance direction and provide a steady foundation for smart cities.
4. Get the word out; Seismic Mitigation works!
In my second blog I detailed examples of mitigation strategies so robust that post-event research revealed insignificant levels of damage even in the face of strong levels of ground shaking. However, communicating the effectiveness of mitigation has been a historic challenge due to a lack of witnesses and the propensity of media to focus exclusively on death and destruction.
Since such stories mostly emanate where no mitigation exists and in the absence of informed examination, conventional wisdom has it that better codes don’t work and are also killers for development. Happily, such conventional wisdom is quickly shattered when the evidence of effective mitigation is examined. As a result, the governments that have to pick up the tab for disaster recovery and the risk sensitive reinsurance industry are influencing the development and enforcement of better codes with focus on a build back better and smarter mandate to make future recovery far less costly through more resilient, safe-built infrastructure.
Figure 4: Modern building codes are in improving earthquake performance. This image from the 2010 M 7.0 Haiti earthquake shows two reinforced concrete buildings: The remains of a collapsed hospital in the foreground of non-ductile concrete contrasted with a recently completed multi-story office block in the background with a modern ductile concrete structural system. (Photo: Philip Caldwell)5. The only things we need to keep breaking are professional silos!
Due to the diverse range of specialties involved in the commercial building industry, it has been an enduring challenge to communicate the technical details of mitigation requirements across many specialized professional silos. However, today thanks to the role governments have played to build collaboration between private practice, academia and industry, research gaps are being closed and essential tools developed to simplify the task of integrating code compliant seismic mitigation into commercial building designs. We need to ensure that we continue to not respect artificial boundaries as they are harmful to property and people!
In my next blog I’m going to round out this series with a list of what I consider to be the essential publications to grace any design professional’s bookshelves. In the meantime, “Earthquake Protection of Building Equipment and Systems, Bridging the Implementation Gap” can be ordered from the ASCE website or book sellers globally and you can register for our dedicated Consulting Engineer portal site to access additional tools, resources and product information.
