Retrofit of Ductile Moment Frames Using Fluid Viscous Dampers

In 2010–2011, a series of devastating earthquakes occurred in Christchurch (New Zealand) damaged many buildings and killed people. The Earthquake Commission’s (EQC) research for New Zealand showed that such disasters could recur in Christchurch over time, and now the seismic safety of the new buildings has become the city’s authorities great concern.

The seismic strengthening of the former Commerce Building at the University of Canterbury using fluid viscous dampers provides a case-study for using velocity dependent supplemental damping to improve the seismic performance of ductile reinforced concrete moment frames. While the building was designed and detailed to essentially current standards, it was very flexible and, utilized a precast hollowcore floor system with thin topping slab that is vulnerable to large drifts associated with moment-frames. This paper highlights a simple displacement-based approach to setting retrofit design targets, and the considerations to demonstrating code compliance.

The retrofit using viscous dampers manufactured and tested in New Zealand provided an efficient means to reducing ground-motion induced deformations and accelerations. The structural benefits to the rest of the project included no foundation strengthening and floor diaphragm strengthening being limited to only the perimeter hollowcore units. Development of the final design and viscous damper specification involved close coordination with the manufacturer in the optimisation of the design, fabrication tolerances and site installation methods.

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Translation of an article represented at the 2017 NZSEE (The New Zealand Society for Earthquake Engineering) Conference
Authors: Didier Pettinga and Andrew Brown, Holmes Consulting, Christchurch, New Zealand