This paper evaluates the seismic resistance of steel moment resisting frames (MRFs) with supplemental fluid viscous dampers against collapse. A simplified design procedure is used to design four different steel MRFs with fluid viscous dampers where the strength of the steel MRF and supplemental damping are varied. The combined systems are designed to achieve performance that is similar to or higher than that of conventional steel MRFs designed according to current seismic design codes. Based on the results of nonlinear time history analyses and incremental dynamic analyses, statistics of structural and non-structural response as well as probabilities of collapse of the steel MRFs with dampers are determined and compared with those of conventional steel MRFs. The analytical frame models used in this study are reliably capable to simulate global frame collapse by considering full geometric nonlinearities as well as the cyclic strength and stiffness deterioration in the plastic hinge regions of structural steel members. The results show that, with the aid of supplemental damping, the performance of a steel MRF with reduced design base shear can be improved and become similar to that of a conventional steel MRF with full design base shear. Incremental dynamic analyses show that supplemental damping reduces the probability of collapse of a steel MRF with a given strength. However, the paper highlights that a design base shear equal to 75% of the minimum design base shear along with supplemental damping to control story drift at 2% (i.e., design drift of a conventional steel MRF) would not guarantee a higher collapse resistance than that of a conventional MRF. At 75% design base shear, a tighter design drift (e.g., 1.5% as shown in this study) is needed to guarantee a higher collapse resistance than that of a conventional MRF.The 2010 ASCE/SEI-7 provision [5] specifies that the design base shear force for the primary lateral force-resisting system of a building with supplemental dampers can be reduced to 75% of the design 2136 C.-Y. SEO ET AL.

This paper evaluates the seismic structural and non-structural performance of selfcentering and conventional structural systems combined with supplemental viscous dampers. For this purpose, a parametric study on the seismic response of highly damped single-degree-of-freedom systems with self-centering flag-shaped or bilinear elastoplastic hysteresis is conducted. Statistical response results are used to evaluate and quantify the effects of supplemental viscous damping, strength ratio and period of vibration on seismic peak displacements, residual displacements and peak total accelerations. Among other findings, it is shown that decreasing the strength of nonlinear systems effectively decreases total accelerations, while added damping increases total accelerations and generally decreases residual displacements. Interestingly, this work shows that in some instances added damping may result in increased residual displacements of bilinear elastoplastic systems. Simple design cases demonstrate how these findings can be considered when designing highly damped structures to reduce structural and nonstructural damage.

The maximum inelastic response of bilinear single-degree-of-freedom systems when subjected to ground motions without distinguishable pulses is revisited with dimensional analysis by identifying time scales and length scales in the time histories of recorded ground motions. The characteristic length scale is used to normalize the peak inelastic displacement of the bilinear system. The paper adopts the mean period of the Fourier transform of the ground motion as an appropriate time scale and examines two different length scales which result from the peak ground acceleration and the peak ground velocity. When the normalized peak inelastic displacement is presented as a function of the normalized strength and normalized yield displacement, the response becomes self similar and a clear pattern emerges. Accordingly, the paper proposes two alternative predictive master curves for the response which involve solely the strength and yield displacement of the bilinear SDOF system in association with either the peak ground acceleration or the peak ground velocity, together with the mean period of the Fourier transform of the ground motion. The regression coefficients that control the shape of the predictive master curves are based on 484 ground motions recorded at rock and stiff soil sites and are applicable to bilinear SDOF systems with post-yield stiffness ratio equal to 2% and inherent viscous damping ratio equal to 5%.

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