Protecting old buildings from earthquakes
It’s not earthquakes that kill people, buildings do. And architects are now designing buildings that are extremely earthquake resistant. The Fukushima nuclear plants, after all, withstood the 2011 Tohoku earthquake in Japan just fine, it was the ensuing tsunami that caused the problems. But constructing new buildings is only part of the solution: we also need to protect existing buildings, including those that are of historical value. Luckily there is a way to do this, as Adam Murphy has been hearing from the University of Brighton's Pierfrancesco Cacciola…
Adam - An earthquake can level a city so a lot of effort is put into trying to protect buildings. There's plenty of options that can be done to new buildings - you can put in large weights which shake in such a way that it damps down the buildings own shaking, or the whole structure can be reinforced. But what about buildings that are already there that can't be retrofitted? Maybe there isn't enough money or it's old enough to make that tricky. You don't want to be drilling into the pyramids after all. Well, Pierfrancesco Cacciola from the University of Brighton has a potential solution - the vibrating barrier or VIBA
Pierfrancesco - The vibrating barrier is essentially a big box in the soil with a mass that is able to oscillate inside the box. The device is designed to protect nearby structures without touching them. So practically you need to see this device as something completely detached from a structure but next to it, and because of this oscillation of the mass it’s able to absorb the energy from an earthquake, and to reduce therefore the action of the ground motion underneath the structure and reduce the vibration of the structure that you want to protect.
Adam - It is potentially quite a simple solution to a very difficult problem, but how does it work?
Pierfrancesco - It has been proved a very long time ago now that when an earthquake arrives a building reacts in a different way if it is on it's own or built next to another one, because practically the buildings hold each other to the soil. And this phenomenon is called 'the structure-soil-structure' interaction. A structure that is built next to another structure will have its dynamic response altered, and altered means either larger or smaller. There is a dummy structure, designed in such a way, the structure that you want to be protected will have a reduced vibration, a reduced dynamic response. You want to create a weak link in a chain if you want, so to create an element that is able to vibrate more, and will be, if you want, weaker, will absorb more energy and because this energy is absorbed there it will be a reduced from the energy underneath the structure that you want to protect.
Adam - So you can think of it as a big, heavy cube, say, that can shake, maybe it's on springs or it can oscillate in some way. And it's connected to the structure you want to protect. When the earthquake's waves come rolling in this cube shakes, and it absorbs all the shaking, all the energy that would have gone to destroying the building, keeping your buildings standing and safe. Now the cube does need to be very heavy, about 50% of the mass of what you want to protect, but you could use a lot of smaller ones. And Pierfrancesco has been working on getting the mass required down to something really feasible. So given that the vibrating barrier has been in the works for a while now, and these things do take time to develop, that's understandable, what state is it currently in?
Pierfrancesco - So we are working on two other projects. One is a project about the protection of the cultural heritage in Egypt. And we have, as a case study, the Zoser pyramid, one of the most ancient pyramids in Egypt in Sakara, and the Citadel of Saladin in Cairo. We are working at the moment on the seismic protection to the vibrating barrier of the Zoser pyramid. Our preliminary results are quite promising. And another project that is a PhD scholarship on the seismic protection of historical buildings with the vibrating barrier - in this advisory group there are colleagues from the ministry of the cultural heritage in Greece. And another case study is the seismic protection of the Messina Cathedral in Sicily. The Messina Cathedral has the bell tower that is the largest astronomical bell tower in the world. So we started to protect this bell tower that has been already damaged by an earthquake in 1908.
Adam - And Pierfrancesco is quietly confident about the future of the vibrating barrier.
Pierfrancesco - I believe that this technology might provide a different angle to protect existing buildings from our earthquakes. Honestly, I do believe that when the first vibrating barrier will be built, quite few more will follow.