DESIGN APPROACH FOR FRICTION SPRING DAMPERS IN STEEL FRAMED BUILDINGS. EXPERIENCES FROM CHRISTCHURCH / NZ.

The 2010/2011 Christchurch earthquake series comprised 6 strong earthquakes that severely damaged New Zealand's second-largest city. One of these, in February 2011, delivered the highest peak ground accelerations recorded to date worldwide. This event caused damage to all multi-storey buildings in the city and rendered most of them unrepairable. It therefore highlighted the advantage of design for low damage in a major event, so that the building remains functional. Friction springs are key components in many low damage solutions. Friction springs can be used by themselves as base isolation or together with other low damage systems such as sliding hinge joints (SHJ) or lead rubber bearings (LRB). The friction spring damper is integrated in the SAP2000 software for the structural analysis and design of buildings. There already are buildings in New Zealand which are equipped with friction springs as part of a low damage design solution, for example Te Puni Village Student Accommodation, One Market Lane (all in Wellington) and Tait Communication Campus (Christchurch). The Te Puni Village was completed in 2008 and on July 21st 2013 was struck by an earthquake measuring 6.5 on the Richter Moment Magnitude Scale (MMS) and the following aftershock measuring 5.8 on the MMS. The main earthquake exceeded the elastic threshold of the building, activating the low damage features which then returned the building to its original position with no structural damage and full functionality.