Probabilistic analysis of load effects on tall buildings under stationary and nonstationary extreme winds



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Modern tall buildings tend to be more flexible and lightly damped due to the use of high-strength and light-weight materials. More reliable and economic design of tall buildings against strong winds needs a better understanding of wind-structure interaction and advanced tools for quantifying the wind load effects on these wind-sensitive structures. The objective of this dissertation research is to improve the understanding and quantification of probabilistic load effects of tall buildings under stationary and nonstationary strong winds. A comprehensive analysis of wind load effects and modeling of equivalent static wind loadings of tall buildings are conducted based on pressure measurements under stationary boundary layer winds. The variations of the gust response factors and higher mode contributions for various building responses are studied. A comparison of building response with that based on wind loads specified in ASCE 7-05 is made. Based on the detailed dynamic wind load, the mode shape correction factors used in the high frequency force balance technique are revisited to examine the efficacy of empirical formulas adopted in current practice.

Nonstationary extreme winds such as thunderstorm downbursts are responsible for many damages of structures. Their time-frequency characteristics can be described by evolutionary power spectra density (EPSD) functions. This research presents a wavelets-based approach for estimating EPSD functions of vector-valued evolutionary nonstationary processes. The proposed approach is then used to characterize full-scale nonstationary downburst wind data. Based on the estimated EPSDs, multiple samples of nonstationary downburst wind fluctuations are simulated. The resulting alongwind tall building responses are analyzed in the time domain. The influence of transient wind load on various building responses including time-varying mean, root-mean-square value and peak factor is studied.

A comprehensive study concerning the peak factors of wind-excited responses including alongwind, acrosswind tall building responses and vortex-induced vibration considering the influence of bandwidth parameter is conducted. The advanced upcrossing theory with consideration of bandwidth parameter of response process can better predict the peak factor of wind-induced response of very lightly damped tall buildings. A framework for estimating the extreme value of combined acceleration of three-dimensional tall buildings, featured by non-Gaussian characteristics, is also presented. A comprehensive parameter study is conducted to identify the controlling parameters for estimating the extreme value. The accuracy of the current empirical combination approach for combining uncorrelated alongwind and acrosswind accelerations is evaluated. This research proposes an improved formula for estimating the extreme value of combined acceleration contributed from correlated alongwind, acrosswind and torsional responses.

In reliability-consistent performance-based structural design, it is essential to estimate the extreme wind loads or load effects on structures for given mean return intervals. This research presents an advanced framework for estimating probabilistic wind load effects of rigid and flexible structures considering randomness of mean wind speed and wind load coefficient. This framework can be used for any type of extreme distribution of wind speed, wind load coefficient, and wind effect. A comprehensive study is conducted to investigate the influence of randomness of mean wind speed and wind load coefficient on the estimation of wind load effects for given mean return intervals.



Porbablistic analysis, Wind, Wind load effect