Degree Type

Thesis

Date of Award

2020

Degree Name

Doctor of Philosophy

Department

Aerospace Engineering

Major

Engineering Mechanics

First Advisor

Partha P. Sarkar

Abstract

Wind-induced vibration is a major concern for tall buildings. Failure to limit the vibration of tall buildings subject to moderate to extreme wind loads could lead to structural damage, occupant discomfort or even catastrophic failure. As average height of tall buildings is observed to increase in the past two decades, it will be increasingly expensive and more challenging to perform physical tests in wind tunnels which is the primary mode for testing their design performance in the wind. A novel method is therefore proposed to predict the wind-induced buffeting response of tall and slender structures in time domain, including tall buildings of any height and shape, subject to a known wind field – synoptic (straight-line) or non-synoptic (e.g. tornado). This method uses the cross-sectional-aerodynamic properties and structural dynamic properties of the tall structure. It is demonstrated by an example building, CAARC standard tall building, with a rectangular cross section (B/D=1.5), used in past benchmark studies. Aerodynamic properties, e.g. load coefficients, flutter derivatives, buffeting derivative indicial functions, for this building were identified using section model tests in a wind tunnel. The identified properties were then used to numerically calculate the across-wind buffeting response of the example building at wind tunnel model scale by employing a buffeting load model in a simulated boundary-layer wind condition. Several parameters that could affect the building’s buffeting response, such as building’s height and mode of vibration, and wind load correlation along its height, were considered and their effects on the response were studied. Good agreement was observed between the simulated results and those from the CAARC building benchmark model study in wind tunnels, which indicates the potential of the proposed method to predict buffeting response of a tall structure in real time. To further study the characteristics of vibration of tall buildings and distinguish their differences in straight-line wind and tornado wind and to investigate the ability of the proposed method to simultaneously predict the building response along all three degrees of freedom (along-wind, across-wind and torsional) and to provide more experimental data for validation of the proposed method, a three-degree-of-freedom aeroelastic model of the CAARC building was built and tested in both boundary-layer wind tunnel and a tornado simulator. Time histories of acceleration at roof-height and mid-height of the building model were measured at different wind speeds. The normalized acceleration response of the building model was obtained with respect to reduced velocities at critical angles of attack for the boundary-layer wind and at critical locations and orientations with respect to the tornado’s path. The aerodynamic damping of the tall building was identified using the identified flutter derivatives from the measurements and validated with other standardized tests of rectangular sections of similar aspect ratios. The numerically simulated responses were validated with the help of the aeroelastic model test results. Moreover, the response of a tall building with two other cross-sectional shapes, circular and elliptical, was calculated and compared amongst the three cross-sectional shapes to study the effect of cross sections on wind-induced response. In the second part of this study, a mechanism to control the tall-building vibration, a novel smart morphing façade (SMF) system that uses the concept of an aerodynamically modified building façade, was proposed and tested. Compared to a fixed façade system, the SMF can be dynamically modified in real time based on rapidly changing wind speed and wind direction in a windstorm. Therefore, such system can be further developed into an active control system. The SMF consists of a set of circular ducts embedded in a flat plate and arranged in a matrix formation that is fixed on the original façade with a gap between the two facades. Each circular-shaped duct comprises of two parts, a fixed base with alternate open and closed surfaces that are shaped like a fan-blade and a rotating part placed inside the fixed one that is similar in shape like the fixed one and can be rotated by a protruding fin. By rotating the fin, the porosity of the duct as well as the fin inclination angle can be changed simultaneously enabling the control of flow through the duct. The performance of the SMF system with different configurations was studied using the CAARC building model under atmospheric boundary layer wind and its effectiveness in reducing the building response was examined by comparing the results from the building with a SMF system and the one without it. It was found that the effectiveness of the SMF system is dependent on many factors, such as configuration, wind speed, angle of attack and direction of vibration.

DOI

https://doi.org/10.31274/etd-20210114-62

Copyright Owner

Fangwei Hou

Language

en

File Format

application/pdf

File Size

203 pages

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