A model for time varying wind loads on a low-rise structure
Fagan, Rebecca Bimmerman
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Overall loads acting on a full scale building in the natural vdnd environment are characterized in this work. The first objective of this research is to directly measure the overall wind loads on the test building at the Wind Engineering Research Field Laboratory (WERFL) in the natural wind environment. The measurements are accomplished using four load cells, with one load cell placed at each comer of the building. These four load cells support the entire weight of the building, and each cell measures two shear forces and one vertical force acting at its comer of the building. These twelve forces were combined to measure total uplift, total horizontal shear, along, and across wind response. Mean drag coefficients are calculated from these measurements in the natural wind environment and are compared to wind tunnel. Uncertainty in the measurements was expected, as several aspects of full-scale testing are difficult to control. Thermal reactions of the WERFL undercarriage were time varying and the variable weight distribution occurred upon lowering the undercarriage onto four point supports. The second objective of this research is to develop a mathematical model using system identification to relate the three orthogonal fluctuating components of wind induced forces to the along, cross and vertical components of wind speed. An ARX (5,5) was found to be appropriate to capture the relationship between the free-stream wind turbulence and the turbulent wake characteristics. This model may then be used to generate modeled data or describe spectral relationships. Investigation in the frequency domain indicates that the building acts as a low-pass filter with the half-power frequency of 0.08 Hz.