Period and damping selection for the design and analysis of building structures

Fundamental period and damping ratio are two of the most important parameters involved in dynamic analyses of buildings. These parameters are usually assigned constant values typically through the use of simplified models or by using engineering judgment. The variability associated with these values is frequently ignored. Measurements of these parameters in the completed structure may or may not match those assumed at the design stage and the effects and implications of such differences are usually not fully explored or understood.; To develop models that reliably estimate the values of period and damping expected in actual structures, a comprehensive database of full-scale measurements was compiled and rigorously analyzed. An analysis of variance (ANOVA) identifies the number of stories for the period data and the number of stories and level of vibration for the damping data as key factors that potentially affect each parameter. Estimation models are developed for different combinations of factors and model performance, which is measured through the standard error, is observed to improve with additional factors. Models are greatly simplified through constrained variations in model coefficients and are considered to appreciably improve the state-of-the-art in period and damping estimation.; The large quantity of data allows for a proper and careful analysis of the variability in each estimation model. Model variability is quantified through two functions: a scalar value that represents the variability among measurements made on the same building and in the same lateral direction, and a function that represents the variability observed from building to building. A rigorous form representing the model variability is provided along with a much simpler form developed for possible inclusion into standards.; The effect of parameter variability on seismic response estimates was investigated. A proposed, performance-driven design procedure identifies period and damping values that achieve a specified level of performance. For a general seismic design spectrum, the engineer can apply a level of conservatism to the performance level or to period and damping selection from regions of practical values, which are defined through the parameter distributions. The effects of variability reduction are observed and possible direction for future development is discussed.