Limits for the interstorey drift sensitivity coefficient θ of steel MRFs with viscous dampers designed according to Eurocode 8

In this paper, steel moment-resisting frames (MRFs) of five, 10, and 20 stories with or without viscous dampers are designed according to Eurocode 8 (EC8). The MRFs have different mechanical properties (i.e. period of vibration, base shear strength, and total viscous damping ratio), yet all of them satisfy the minimum strength and peak interstorey drift requirements of EC8. First, flexible steel MRFs with viscous dampers are designed for peak interstorey drifts similar to those of MRFs without dampers. Due to supplemental viscous damping, these designs are substantially more flexible and have higher values of the coefficient θ of EC8 in comparison to MRFs without dampers, where θ quantifies P-Δ effects and ensures stability under earthquake loading. Then, more conservative designs of steel MRFs with viscous dampers are obtained by imposing limits on θ. This process has resulted in a family of 23 frames. Incremental dynamic analyses for 44 ground motions are conducted for all the frames and their collapse fragility curves are constructed. The latter allows to identify limits for θ that ensure that flexible, lighter in steel weight, steel MRFs with viscous damper that satisfy the design criteria of EC8, have collapse resistance similar to that of MRFs without dampers. More work is though needed to expand the applicability of these limits to steel MRFs with different geometry and a broader range of mechanical properties of the in-series brace-damper assembly.