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Monday, 5 September 2011

Anti-Seismic Master Plan

Selim Bayer


Earthquakes continue to be the most damaging of all natural disasters. Each year seventy to seventy-five earthquakes occur around the world that are strong enough to cause damage to structures and claim lives; many others occur that go unnoticed or are only locally felt by very few. As populations of cities are rapidly growing, seismic design continues to be a vital topic. Recent scientific research proposes that with the use of concentric circular cloaks, it is possible to render objects invisible to surface waves propagating in isotropic heterogeneous plates by bending them around the isolated area . Also, the range of frequencies, and thus wavelengths, at which this is possible, is scalable. This research proposal makes the cloaking method relevant in the realm of seismic design, as buildings, urban blocks, or even cities could be cloaked. It is important to recognize that the cloaking method is only effective in bending surface waves; thus body waves are not an element of this discussion. It is however, also important to note that surface waves cause most significant damages to structures during an earthquake.
Although the science and technology of seismic design continues to progress, structures are still being individually protected against seismic waves. The 1995 Kobe event was a reminder that regardless of how well a city may be prepared against a major earthquake, damage is inevitable; maintaining a functioning city network becomes as important as a single building surviving the event. With the cloaking method, a new opportunity for seismic design emerges, where not only singular structures, but clusters of structures can be simultaneously protected against seismic waves. This research investigates the consequences of this new approach to seismic design on architecture and urban planning through an ‘anti-seismic urban masterplan’ proposal in a 1.7 kilometre squared area on the highly seismic coast of the Silivri district of Istanbul province.
Digitally modelled cloaks and plates (ground) are assigned relevant material properties (concrete properties for the cloaks; various soil properties for the plates) and tested for performance under simulated environmental parameters (variations of frequency, velocity and acceleration corresponding to earthquake properties) within Finite Element Analysis software. Outputs of the experiments provide the basis of a string of parameters for the dimensions and proximity of cloaks to be used in the development of the ‘anti-seismic urban masterplan’.
Three main types of urban zones emerge out of the cloaking method: isolated zones, non-isolated zones and buffer zones. Using the term ‘protected zone’ is deliberately avoided as protection strategies for all types of zones are developed. Conventional earthquake engineering methods will continue to be applied to all structures. In the isolated zones, which are the areas within the cloaked regions, high-density developments with height restrictions of up to eight-storey construction are permitted. For efficient use of the isolated zones, a minimum restriction of four-storey construction is implemented. In the non-isolated zones, which are the interstitial areas between multiple cloaks, height restrictions of only one-storey construction are permitted, in order to reduce the risk of buildings collapsing. There is no building construction permitted in the buffer zones, which are the areas directly above the rings of the cloaks that fall between the isolated zones and the non-isolated zones. Should any building collapse in one of the two zones, the buffer zones ensure an alternative clear network for transport during the post-disaster scenario.

Masterplan Proposal

The ‘anti-seismic urban masterplan’ proposal is a superimposition of five competing networks of different speeds and scales: the high-speed network, the medium-speed network, the isolated low-speed network, the non-isolated low-speed network and the pedestrian-only network. Each of these networks have assigned functions at all times as the masterplan is designed to be responsive to normal times as well as to the post-disaster scenario. As the networks progress from the global urban scale of the city to the local neighbourhood scale of the isolated-zones, the speed of travel is reduced as are the travel distances.
The proposed masterplan contains hospitals, emergency clinics, police stations, fire stations and other key institutions to the post-disaster scenario. Developing a network of strategically located masterplans that connect to one another in and around Istanbul, developed with similar methods to the one proposed, will mitigate damage to structures and most importantly will ensure a functioning city scale network after the unavoidable damaging earthquake event.

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