Improving seismic performance

Add stiffness or damping?

  • Trevor E. Kelly Holmes Consulting Group, Auckland, New Zealand


Structural engineers typically improve the seismic performance of deficient structures by adding strengthening elements to the structural system, which also add stiffness to the structure. However, as performance based design becomes more common practice, the focus is on the total performance of not only the structural system but the building components and contents. A stiffer and stronger building will generally be subjected to lower drifts but higher floor accelerations than a weaker and/or more flexible building. Reduced drift related damage may be accompanied by increased damage to components and contents which are sensitive to accelerations.

This paper examines two common forms of hardware used to strengthen existing buildings, buckling restrained braces (BRB) and viscous damping devices (VDD). Both types of device augment the existing structural system, rather than replace it. A series of nonlinear analyses is used to quantify the performance of two prototype frame buildings strengthened with each type of device. It is shown that equivalent structural performance, in terms of overall deformations, can be achieved with both types of device, and generally for lower cost by BRBs if only moderate levels of drift reduction are required. However, when the total building performance is examined the VDDs provide additional benefits in the form of reduced floor accelerations. The benefits of this may be
sufficient to warrant the higher cost solution.


ASCE, American Society of Civil Engineers, (2000). “Prestandard and Commentary for the Seismic Rehabilitation of Buildings”, prepared for the SAC Joint Venture. Federal Emergency Management Agency FEMA-356, Washington, D.C.

Kelly, T.E. (2001). In-Structure Damping and Energy Dissipation Design Guidelines, Holmes Consulting Group, Revision 0, July. Available on

Mondkar, D.P. & Powell, G.H. (1979). “ANSR II Analysis of Non-linear Structural Response User's Manual”. Earthquake Engrg. Research Center EERC 79/17, University of California, Berkeley, July.

Standards New Zealand (2005). Structural Design Actions, AS/NZS 1170 Parts 0, 1, 2, 3 & 5. Standards New Zealand.

How to Cite
Kelly, T. E. (2008). Improving seismic performance. Bulletin of the New Zealand Society for Earthquake Engineering, 41(1), 24-30.