A displacement-based seismic design method for building structures with nonlinear viscoelastic dampers

This paper presents a displacement-based seismic design method for building structures equipped with viscoelastic dampers (VEDs) featuring strong nonlinear characteristics. First, major insights from recent analytical and experimental research on this type of VEDs, including their behavior and sources of nonlinearity, are briefly introduced. Then, a simplified response spectra-based method for estimation of the peak seismic response of the structure without and with VEDs is proposed. Here, the undamped and damped structures are reduced to equivalent single-degree-of-freedom (SDOF) systems through linearization procedures. The simplified analysis method allows for the assessment of the effects of VEDs on the structural response through a set of analytical expressions formulated in terms of two parameters controlling the design of the dampers: (1) the VED design strain; and (2) the stiffness ratio of the dampers to the main structure. In the displacement-based design procedure proposed here, the VED design strain is obtained from response history analyses of the base frame, whereas the stiffness ratio is determined through iterative calculations based on the simplified analysis method. Then, the design parameters are extended to the multi-degree-of-freedom (MDOF) system of the actual structure and VEDs are sized at each story. Finally, verification of the design layout is done through nonlinear time-history analysis. The use of time domain analysis procedures and simplified analysis tools to find the design parameters of the dampers provide the proposed methodology with a balance between accuracy and effectiveness. To illustrate the design process, the paper concludes with a design example of supplemental VEDs for the seismic retrofit of a 7-story reinforced concrete frame building.