Effect of Variability in Damping Ratios on the Seismic Risk of Steel Moment-Frame Buildings

Abstract

This paper evaluates the sensitivity of seismic risk to variations in damping ratio in four steel moment-frame buildings of 4, 9, 20, and 50 stories. Seismic risk is quantified through the expected annual loss (EAL) due to earthquake ground motions. Nonlinear models of the buildings are developed using OpenSees, where damping ratios are systematically altered within defined ranges. The influence of damping ratio on collapse fragility and EAL deaggregation is assessed using PEER's framework for performance-based earthquake engineering, considering the contribution from structural and nonstructural elements, as well as contents. Results show that when the damping ratio is varied within two standard deviations from its median value based on height, the probability of collapse of the buildings when subjected to the maximum considered earthquake varies between −60% and +35%. This same range of damping ratio generates a variation of up to approximately ±35% in the EAL of the buildings. It is found that EAL deaggregation is highly sensitive to the damping ratio at low intensities, where nonstructural components dominate economic losses. The study establishes a moderate effect on deaggregation at intensities where demolition costs contribute significantly to EAL. Conversely, at large intensities, where collapse governs the EAL, deaggregation becomes insensitive to changes in the damping ratio. Finally, the impact of damping models on EAL is explored, demonstrating differences of up to 10% when employing modal damping versus various variations of Rayleigh damping in the 50-story building.