Kurtis R. Gurley

Damping in structures: its evaluation and treatment of uncertainty

Abstract This paper concerns the damping in structures with emphasis on treatment of inherent uncertainty in its prediction and estimation. Material or structural damping is addressed as well as damping due to the aerodynamic and hydrodynamic forces of the fluid surrounding the structure. The reported data base on damping information is examined in light of wind sensitive structures that rely heavily on damping for their performance under winds. The basic techniques for estimation of damping from response time histories are reviewed, and the random decrement technique is considered in some detail. The implications of the uncertainty of damping on system response are analyzed in terms of a perturbtion technique, second-moment analysis and Monte Carlo simulation. Several simple illustrative examples are provided throughout the text.

Analysis and simulation tools for wind engineering

This paper examines state-of-the-art analysis and simulation tools for applications to wind engineering, introduces improvements recently developed by the authors, and directions for future work. While the scope of application extends to a variety of environmental loads (e.g. ocean waves and earthquake motions), particular reference is made to the analysis and simulation of non-Gaussian features as they appear in wind pressure fluctuations under separated flow regions and non-stationary characteristics of wind velocity fluctuations during a gust front, a thunderstorm or a hurricane. A particular measured non-Gaussian pressure trace is used as a focal point to connect the various related topics herein. Various methods of non-linear system modeling are first considered. Techniques are then presented for modeling the probability density function of non-Gaussian processes. These include maximizing the entropy functional subject to constraints derived from moment information, Hermite transformation models, and the use of the Kac-Siegert approach based on Volterra kernels. The implications of non-Gaussian local wind loads on the prediction of fatigue damage are examined, as well as new developments concerning gust factor representation of non-Gaussian wind loads. The simulation of non-Gaussian processes is addressed in terms of correlation-distortion methods and application of higher-order spectral analysis. Also included is a discussion of preferred phasing, and concepts for conditional simulation in a non-Gaussian context. The wavelet transform is used to decompose random processes into localized orthogonal basis functions, providing a convenient format for the modeling, analysis, and simulation of non-stationary processes. The work in these areas continues to improve our understanding and modeling of complex phenomena in wind related problems. The presentation here is for introductory purposes and many topics require additional research. It is hoped that introduction of these powerful tools will aid in improving the general understanding of wind effects on structures and will lead to subsequent application in design practice.

SIMULATION OF A CLASS OF NON-NORMAL RANDOM PROCESSES

Abstract This study addresses the simulation of a class of non-normal processes based on measured samples and sample characteristics of the system input and output. The class of non-normal processes considered here concerns environmental loads, such as wind and wave loads, and associated structural responses. First, static transformation techniques are used to perform simulations of the underlying Gaussian time or autocorrelation sample. An optimization procedure is employed to overcome errors associated with a truncated Hermite polynomial transformation. This method is able to produce simulations which closely match the sample process histogram, power spectral density, and central moments through fourth order. However, it does not retain the specific structure of the phase relationship between frequency components, demonstrated by the inability to match higher order spectra. A Volterra series up to second order with analytical kernels is employed to demonstrate the bispectral matching made possible with memory models. A neural network system identification model is employed for simulation of output when measured system input is available, and also demonstrates the ability to match higher order spectral characteristics.

Post-2004 Hurricane Field Survey of Residential Building Performance

This paper presents the methodology and results of a study of the performance of site-built single-family structures in Florida constructed after Andrew-related changes to the Standard Building Code. A detailed investigation of wind damage as a result of the 2004 hurricane season was conducted. The study provides a quantitative comparison of the relative performance of homes built between 1994 and 2001 with those built after the 2001 Florida Building Code replaced the Standard Building Code.

Analysis interpretation modeling and simulation of unsteady wind and pressure data

Abstract This paper addresses the analysis, modeling and simulation of measured full-scale wind pressure and velocity data. The records exhibit both non-Gaussian and non-stationary features, and are ideal for the application of a number of contemporary methods for handling the types of problems associated with these characteristics. Modeling the probability density function (pdf) of non-Gaussian pressure is first addressed, followed by the simulation of pressure data through new static transformation techniques. The non-stationary portion of the pressure data is isolated and decomposed into a set of localized basis functions using wavelet transform techniques. Wavelet analysis is used for the identification of energy flux in time and for simulation of the non-stationary wind velocity records.

A conditional simulation of non-normal velocity/pressure fields

The simulation of random velocity and pressure signals at un-instrumented locations of a structure conditioned on measured records is often needed in wind engineering. Malfunctioning equipment may leave a hole in a wind data set or information may be lacking due to a limited number of instruments or diƒculty in monitoring at certain locations. This paper presents a non-Gaussian conditional simulation technique in the context of non-Gaussian pressure fluctuations in separated flow regions, or velocity fluctuations in atmospheric flows. First, a uni-variate non-Gaussian simulation technique is developed. This is extended to multi-variate, and subsequently utilized as a mapping technique in a conditional simulation algorithm. This technique is applied to both the extension of existing records beyond recorded lengths, and the simulation of missing or damaged records based on measured data at other locations. ( 1998 Published by Elsevier Science Ltd. All rights reserved.

Validation of a probabilistic model for hurricane insurance loss projections in Florida

The Florida Public Hurricane Loss Model is one of the first public models accessible for scrutiny to the scientific community, incorporating state of the art techniques in hurricane and vulnerability modeling. The model was developed for Florida, and is applicable to other hurricane-prone regions where construction practice is similar. The 2004 hurricane season produced substantial losses in Florida, and provided the means to validate and calibrate this model against actual claim data. This paper presents the predicted losses for several insurance portfolios corresponding to hurricanes Andrew, Charley, and Frances. The predictions are validated against the actual claim data. Physical damage predictions for external building components are also compared to observed damage. The analyses show that the predictive capabilities of the model were substantially improved after the calibration against the 2004 data. The methodology also shows that the predictive capabilities of the model could be enhanced if insurance companies report more detailed information about the structures they insure and the types of damage they suffer. This model can be a powerful tool for the study of risk reduction strategies.

Post 2004 Hurricane Field Survey -- An Evaluation of the Relative Performance of the Standard Building Code and the Florida Building Code

This paper presents the methodology and results of an ongoing study of the performance of residential structures in the State of Florida. Site built single family homes constructed after Andrew-related changes to the standard building code were in effect were targeted for a detailed investigation of wind damage as a result of the 2004 hurricane season. The purpose of this study is to provide a quantitative statistical comparison of the relative performance of homes built between 1994 and 2001 with those built after the 2001 Florida Building Code replaced the Standard Building Code.

Impact simulation and full scale crash testing of a low profile concrete work zone barrier

The development of a new low profile portable concrete barrier system for use in roadside work zone environments is presented. By making extensive use of non-linear dynamic finite element impact simulation, several cycles of concept refinement were carried out using simulation rather than expensive full scale crash testing. Issues such as ensuring stable vehicle redirection during impact, properly accounting for frictional effects (and associated energy dissipation), and monitoring system energy parameters are discussed together with corresponding example simulations. Results obtained from full scale crash testing of the barrier validate the simulation methodology and demonstrate successful barrier performance.

Modeling and analysis of quadratic term in the wind effects on structures

Abstract Historically, the quadratic drag term containing the square of the fluctuating velocity component has been often ignored in analyses of wind-excited structures. This paper addresses a technique to model the contribution of this term to the system response extremes. Among the topics covered are the development of a non-Gaussian gust loading factor via moment-based Hermite transformation. A frequency domain analysis approach involving Volterra theory and higher-order response cumulant calculations from direct integrations or Kac-Siegert technique is employed to obtain information needed for this transformation.