Improvements in the direct displacement-based design procedure for mid-rise steel MRFs equipped with viscous dampers

Abstract

This paper aims to propose straightforward modifications in the direct displacement-based design (DDBD) procedure to reach an optimal design for mid-rise steel moment-resisting frames (MRFs) equipped with linear fluid viscous dampers (FVDs). The modifications include using an alternative equivalent damping as well as applying the ratio of pseudo-spectral velocity to spectral velocity. To compare the proposed method with respect to the conventional DDBD procedure, the seismic performance of a set of low to mid-rise structures consisting of 3-, 6-, 9- and 12-story steel MRFs is investigated. This is carried out via nonlinear time-history analyses by using a set of design spectrum compatible ground motion records at two seismic hazard levels, i.e., the design earthquake (DE) and maximum considered earthquake (MCE). Furthermore, two different patterns, i.e., uniform and non-uniform, for distribution of damping coefficients at the height of the structures are used. Results show that the proposed method can meet the performance targets defined at the DE and MCE hazard levels. Moreover, the peak roof displacement of the structures that is estimated by the proposed method is acceptably the same as captured via the nonlinear analyses. Finally, implementing the proposed method leads to a reduction in the weight of the steel used in the MRFs in comparison with the structures designed by the conventional DDBD procedure and smaller damper forces, i.e., lighter damper constants, can also be achieved.