Portland is retrofitting fire stations and bridges to meet seismic code. While this might sound comforting, not all seismic standards are created equally. Portland’s “zone 3” seismic code standards are weaker than California’s “zone 4” standards, and even “zone 4” standards are not intended to withstand a sustained M9+ event, which we now know to expect from our Cascadia subduction zone.
It is also important to understand that seismic standards are intended only to protect lives by preventing total structural collapse; the building may not be safe or usable afterward. For earthquakes larger or longer than the seismic code zone anticipates, total collapse may occur. So a school or fire station built to meet Portland’s seismic code has no assurances it will remain standing nor protect life, much less remain functional and safe, after a Cascadia subduction zone megathrust earthquake.
But there is an economical way to construct buildings which can be expected to survive such tremendous forces. Conventional buildings contain many joints between walls, roof & foundation. During an earthquake these joints – called “moment connections” – are subjected to enormous stresses. If the stress is great enough or prolonged enough, the joint fails and the building collapses. Creating stronger joints can rapidly escalate construction costs, yet failure of the joint is still possible. A better and more economical approach is to reduce the number of moment connections in a building. A building without any would distribute seismic loads evenly across the entire structure. A thin-shelled one-piece (i.e. monolithic) dome made of steel- & fiber-reinforced concrete would have few, if any, consequential moment connections an earthquake could damage. This type of building has by far the best chance of surviving Portland’s greatest seismic threat. Amazingly, a large monolithic dome structure is less costly to build, heat or maintain than similar sized conventional structures.