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Browsing by Author "Bienkiewicz, Bogusz, advisor"

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    Analysis of multi-channel wind loading using proper orthogonal decomposition
    (Colorado State University. Libraries, 2014) Adhikari, Rajendra, author; Bienkiewicz, Bogusz, advisor; Chen, Suren, committee member; Sakurai, Hiroshi, committee member
    Wind tunnel testing utilizing multi-channel pressure measurement system leads to large volume of the acquired wind pressure data. In the presented research, use of Proper Orthogonal Decomposition (POD), to analyze such data, is described. Wind pressure time series acquired for a generic low-rise building were used in the analysis. First, the pressure covariance matrices were calculated. They were subsequently used to determine the pressure eigenvalues and the eigenfunctions. These quantities were next employed to calculate the POD principal coordinates. Finally, the eigenvectors and the principal coordinates were used to reconstruct the pressure time series. This analysis was carried out for pressures exerted on the whole building and on its distinct surfaces - side walls and roof. The convergence of the pressure time series reconstruction was inspected. The mean, standard deviation and the peak values of the reconstructed pressure were evaluated. The effects of wind direction on the original and reconstructed pressures were investigated. The POD modal contributions and the convergence of the pressure reconstruction were quantified. Overall, the obtained results were found to be consistent with findings of related POD studies reported by other researchers. High spatial and temporal resolutions of the wind loading data used in the present research made possible refined quantification of the effects of the studied parameters.
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    Application of model reduction tools in analysis of wind-induced pressures on low-rise buildings
    (Colorado State University. Libraries, 2012) Wu, Chieh-hsun, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Sakurai, Hiroshi, committee member
    Recent advances in laboratory and field measurement techniques and numerical simulations of wind-induced loading on buildings and structures made possible generation of large data sets, suitable for database-assisted wind-resistant design. In parallel, data reduction tools have been developed to aid storage, management and accessibility issues associated with large datasets/databases. In the presented research, application of such tools in analysis of stationary and non-stationary wind-induced pressures on a generic low-rise building is discussed. Both stationary and non-stationary cases are addressed. In stationary analyses, Proper Orthogonal Decomposition (POD) and Method of Snapshot (SPOD) were used to identify the most energetic spatio-temporal structures of the pressures. Linear Stochastic Estimation (LSE) and Gappy POD (GPOD) were employed to generate the pressures at specified target locations via extrapolation of the pressures provided at chosen reference locations. Optimized reference positions were determined using algorithm-based and empirical approaches. In non-stationary analyses, Wavelet De-noising and Two-Stage-Moving-Averaging were applied to decompose the non-stationary pressure into time-varying mean, standard deviation and normalized fluctuation. The techniques developed for stationary pressures were adapted for non-stationary cases. In analysis of the stationary data, the extrapolation techniques (GPOD and LSE) were found to reduce the data more efficiently than the modal reduction tools (POD and SPOD). In pressure extrapolation, LSE provided more accurate pressure predictions than GPOD. A hybrid approach combining the use of GPOD, with algorithm-based reference positions selection, and LSE extrapolation enabled the most efficient capturing of the primary and secondary spatio-temporal features of the pressure. This technique is recommended for analyses focused on development of reduced models of wind pressures induced on low-rise buildings. In the non-stationary investigations, the hybrid GPOD-LSE technique, developed in analysis of the stationary pressures and modified for the non-stationary cases, led to accurate pressure predictions and model reductions. This methodology appears to be a suitable tool for similar analyses of non-stationary wind-induced pressures on low-rise buildings. Follow-up investigations of stationary and non-stationary cases are recommended to assess potential for further optimization of the developed techniques and their application in analyses of wind-induced loading on other buildings and structures.
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    Application of symbolic computing in analysis of modal properties of structurally coupled twin tall buildings
    (Colorado State University. Libraries, 2011) Richards, Eric Lee, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Shuler, Scott, committee member
    This thesis develops non-dimensionalized symbolic expressions for the normalized natural frequencies of two identical tall buildings structurally connected by a skybridge. Symbolic expressions for the modal shapes are also developed to express the coupled movements of the two buildings. The mass and stiffness of the two tall buildings are generalized and reduced to the skybridge level, and the equations of motion are evaluated with Maple 13 math and engineering software. A parametric study of the effects of coupling stiffness on the modal properties is carried out using formulas resulting from symbolic computing. The obtained symbolic expressions are compared with the results of numerical analysis performed using Risa-3D structural engineering analysis software. Findings of this thesis show a good agreement between the symbolic expressions and Risa-3D results. The developed symbolic equations are proposed as a tool for use in the preliminary analysis of tall buildings connected by a skybridge.
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    Structural coupling and wind-induced response of twin tall buildings with a skybridge
    (Colorado State University. Libraries, 2008) Lim, Juntack, author; Bienkiewicz, Bogusz, advisor
    Twin tall buildings with a connecting skybridge involve two types of coupling: the structural coupling, developed by a skybridge and synchronizing the motions of vibration of the two building and the aerodynamic coupling resulting from high cross-correlations of the components of wind loading. The physical understanding of these couplings and their impacts on the wind-induced response of the buildings are not fully understood, when using a high-frequency force balance (HFFB) approach tailored for single tall buildings. Detailed laboratory mapping of the aerodynamic loading and coupling requires specialized experimental techniques. Predictions of the response of the structurally coupled buildings, due to correlated wind loading, involve utilization of advanced dynamic analysis. This dissertation addresses the issues associated with correlated wind loading and structurally coupled response of twin buildings with a skybridge. Wind tunnel testing to acquire the correlated wind loading on twin buildings is described. The effects of the relative positions of the buildings on the loading correlations and coherences are discussed. These results are next used as an input to an analytical model developed to calculate the building wind-induced response. The building system, including the structural coupling, is represented by a six-degree-of-freedom model lumped at the skybridge level. In free vibration, the natural frequencies and modal shapes are obtained for various levels of the relative stiffness of the (inter-building) beam representing the skybridge. The model is subsequently used to investigate the effects of aerodynamic and structural couplings on the roof top accelerations of the buildings. Spectral integration and white-noise approximation approaches are employed in calculations of the building responses. The presented results show significant effects of both the aerodynamic and structural couplings. Simplified empirical relations for application in preliminary design of structurally connected tall buildings are proposed. Recommendations for follow-up studies of coupled wind-induced response of tall twin buildings are discussed.
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    Wind tunnel modeling and analysis of wind effects on low-rise buildings
    (Colorado State University. Libraries, 2011) Endo, Munehito, author; Bienkiewicz, Bogusz, advisor; Criswell, Marvin E., committee member; Neff, David E., committee member; Young, Peter, committee member
    Wind tunnel modeling is a robust technique which allows determination of wind effects on buildings and other structures. Due to complexity of flows and induced wind loads, other techniques can not be reliably used in practical analyses of such effects. Information deduced from wind tunnel testing has been successfully employed in development of design guidelines and in direct applications in wind-resistant design of variety of structures, including low-rise buildings. Although wind tunnel modeling of wind loading has been generally accepted as a viable tool, over the years a number of questions regarding accuracy and limitations of this technique have been raised. Some of the questions related to modeling of wind loading on low-rise buildings were addressed in the research described in this dissertation. Investigation of reported discrepancies in the laboratory-field and inter-laboratory comparisons was one of main focuses of this study. To identify the origins of the discrepancies, careful studies of reported wind tunnel set-ups, modeling of field/target approach wind conditions, measurement techniques and quality of obtained data and data analyses were carried out. Series of experiments were performed in boundary-layer wind tunnels at the Wind Engineering and Fluids Laboratory, at Colorado State University, to aid these analyses. It was found that precise matching of characteristics of approach field wind and flows modeled in wind tunnels was essential to ensure compatibility of the simulated building wind loads. The issue of the accuracy of predictions of the extreme wind-induced loading based on the results of wind tunnel modeling was addressed. In this investigation, the peak wind-induced pressures on low-rise buildings were analyzed using two advanced techniques: the extreme value distribution theory (GEV) and the peak-over-threshold approach. The extreme roof suction pressures predicted from these two approaches were compared with field observations. The degree of convergence of the EVD fits was discussed for Type I and Type III EVDs. The advanced experimental tool, electronically-scanned 1024-channel pressure measurement system, was developed and employed in wind tunnel modeling of wind loads on low-rise building. The wind-induced pressures were simultaneously acquired at 990 locations uniformly distributed over the surfaces of a model of a generic low-rise building. The Proper Orthogonal Decomposition (POD) analysis was performed to capture the spatio-temporal characteristics of the acquired pressure field. It was found from POD analysis that the pressure data sets can be substantially reduced, while preserving the main spatio-temporal features of the building wind loading.