The rocking steel shear wall utilising energy dissipation devices

Abstract

Current earthquake building design philosophy is to prevent collapses of buildings in severe earthquakes and to allow tenants to escape out of the buildings safely even when the building is damaged. In the severe 2010/2011 Canterbury Earthquake series, steel buildings withstood severe earthquakes with some damage, as intended in the current earthquake building design. However, the damaged steel buildings required structural repairs causing business disruption in that city. Hence, a low damage design is introduced to withstand severe earthquakes without structural repairs using isolating systems or sacrificial systems that either do not need repair or are readily replaceable.

An innovative Centralised Rocking Concentrically Braced Frame[1] (CRCBF) system has been developed to allow a building to rock back and forth under severe earthquakes and return to original position after an earthquake. This system uses friction ring springs to dissipate earthquake energy and provide a return force to make the building back to the original position without any significant damage. Then, tenants are able to occupy their buildings immediately.

A design concept and procedure have been developed and a series of experimental testing have been conducted. In the experimental testing, the CRCBF, which is represented as single rocking frame, performed well with a uniform, stable, and repetitive behaviour under severe earthquakes. Therefore, the CRCBF system is a practical solution for a low damage design in steel buildings.

 

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Technical Abstract

In the severe 2010/2011 Canterbury Earthquake series, ductile steel structures were subjected to inelastic demand which required structural repairs. Steel structures designed for low ductility had minor damage and re-centred effectively. However, as the probability of severe earthquakes is infrequent, it would be uneconomical in terms of costs and member sizes to design a structure to be very stiff and remain elastic in a severe earthquake. Therefore, in order to keep a structure undamaged in a severe earthquake and yet be cost-effective, the concept of a low damage design is introduced. Seismic resisting systems using this concept are expected to withstand severe earthquakes without major post-earthquake repairs using isolating mechanisms or sacrificial systems that either do not need repair or are readily replaceable.

A Centralised Rocking Concentrically Braced Frame (CRCBF)[1] has been developed utilising a central rocking mechanism and energy dissipation devices at the bottom of CRCBF columns. This system is designed and detailed to be stiff under gravity loading and minor earthquakes, remain essentially elastic under major earthquakes by undergoing controlled rocking, and actively self-centre following earthquakes. As the rocking happens at the centre of the system, the energy dissipation devices, Ringfeder®, are arranged to work as a double acting spring to dissipate earthquake energy and provide restoring forces to make a structure back to the original position.

A series of experimental testing have been conducted, showing the hysteresis curves of the CRCBF system are flag-shaped, stable, and repeatable at any loading rates and the system dependably returns to its original position after unloading. The system has also been verified in SAP2000 where the SAP2000 analysis results correspond to the experimental testing results. In addition, a design procedure has been developed as the final part of this research to make the CRCBF system as a practical solution for a low damage design in steel structures.

 
[1] Steel Shear Walls (SSWs) are replaced by Concentrically Braced Frames (CBFs) as through research, CBFs are stiffer and more suitable than SSWs for this rocking system.