“Developing nations need to plan how they will recover from large natural disasters and consider how to make their economies more resilient,” comments Sean Gledhill, Aurecon Building Structures Service Leader, and multiple award winner for low damage seismic solutions.
Internationally, structural codes of practice for a normal building nominate a ‘design level’ for earthquakes that requires collapse prevention, but allows seismic damage to help dissipate energy, should bigger earthquakes occur.
To reduce vulnerability in developing nations, governments and local authorities firstly need to adopt strict earthquake zoning rules. These rules should identify and limit development on:
To reduce vulnerability to damage, developing nations need to adopt internationally accepted codes of practice which are harmonised to best suit locally available materials and building practices. Many developing nations have either undertaken the steps or are conducting research into affordable local solutions.
Low damage technologies suitable for developing countries need to be simple, affordable and reliable. The simplest way of improving new commercial building response is to:
For new residential housing this may involve reduction in the use of unreinforced concrete, masonry or stone and increases in the use of processed materials such as treated timber and lightweight metal roofs. Ensuring walls and foundations are well connected, will significantly reduce collapses due to instability.
For new bridges, rail, roads and in-ground infrastructure, increasing designer and constructor awareness should allow for flexibility and ground displacement but ensure key items are robust and remain connected after the earthquake, at least making it easier to repair. A simple way to reduce the vulnerability of core public assets is duplication of key assets and careful geographical zoning.
Affordable isolation building system
New buildings, where budgets allow, should be developed to reduce shaking related damage. The simplest way of achieving this is with the concept of base isolation. This works best on relatively stiff, heavy and low rise structures, where simple steel plate sliders, or lead rubber bearings are introduced.
Base isolation ‘isolates’ the building from the ground during shaking, to alter the foundation connection and hence the response the building feels. Importantly, these need ‘rattle space’ – adequate movement space between adjoining structures.
Aurecon has delivered relatively cost neutral award winning isolation systems, constructed from slides with curved steel plates or simple rocking systems.
All these provide buildings with greater degrees of resilience by ensuring any seismic energy is concentrated in very ductile replaceable parts, or by providing mechanisms of dissipating energy such as rocking structures.
Other more modern systems include rocking steel frames, special friction joints and PRESS systems.