Comparison of optimal versus a convenient distribution method of viscous damper design

Abstract

A simple and convenient method often adopted by practicing engineers designing supplemental viscous dampers to a building is to calculate damping coefficients of viscous dampers corresponding to a desired added damping ratio. Various methods for distributing damping coefficients along the height of the building are proposed such as direct displacement-based design (DDBD) methodology or shear strain energy (SSE) method.

In the article, mathematically optimization algorithm (MOA) method is proposed and compared with some often-adopted methods. Nonlinear time history analysis of two 10-storey structures with steel moment frame and K-brace lateral systems with viscous dampers under number of ground motions have been carried out. The objective of optimization is to obtain the target inter-story drifts and floor absolute accelerations by determining the optimal damper placement and damper coefficient distribution up the building height.

Result of analysis have indicated that all distribution methods may result in similar seismic responses if added damping ratio are the same. If the viscous dampers are selected to have the same damping coefficient, the MOA will require the least number of dampers but with the largest damper force capacity. Alternately, using DDBD/SSE methods, if more dampers with smaller force capacity are adopted, the dampers may have to be installed to number of parallel frames, the architectural concern of space arrangement may make this option infeasible. From the above comparison, it is realized that the total number of dampers and the maximum force capacity of each damper should be compromised when justifying the design for supplemental viscous dampers.