Shake table test a structure retrofitted using a 2-4 Direction and Displacement Dependent (D3) viscous damper
Seismic codes are continuously modified to incorporate the latest knowledge in structural behaviour and increased hazard or performance expectations of newly designed structures. On the other hand, many existing structures, designed to older design provisions and requirements, do not offer the same level of seismic performance as newly designed structures and it is desirable to improve these in-place. Fluid viscous dampers can add energy dissipation without requiring major structural modification. However, their addition can lead to increases in the maximum base shear and column axial forces in non-linear structures. These increases in demand would likely require strengthening of the columns and the foundations, thus increasing cost and reducing the ease and the benefits of this approach. The 2-4configuration of a passive Direction and Displacement Dependent (D3) damper provides damping in only quadrants 2 and 4 of the force-displacement response plot, thus substantially reducing the peak base shear loads compared to a conventional viscous damper. The paper studies the seismic performance of a 1/2 scale, two storey steel frame building retrofitted with passive 2-4 D3 dampers and subjected to uni-directional shake table testing. Performance in mitigating structural response and foundation demand are assessed by evaluating base shear, maximum drift and acceleration. The overall results show that simultaneous reductions in displacement, base-shear and acceleration demand are only available with the 2–4 D3 viscous device. This device is entirely passive and provides a unique retrofit option that would not require columns and the foundations to be strengthening.