Abstract Rectangular prisms with different depth‐to‐width ratios (B/D) were placed in flow fields with various turbulence intensities (T.I.) and length scales to study the unsteady structures of separated shear layers. Velocity profiles, turbulence intensity profiles, velocity gradient profiles, and wake spectra of the prisms were measured. When B/D=0.4 to 1.0, differences between the acceleration and deceleration phases of these profiles were prominent, indicating strong vorticities especially when B/D=0.6. These differences, also supported by the spectra peaks, became less obvious when B/D=2.0 and 3.0. The approaching field T.I. had a larger effect than the length scale. Higher T.I. led to increased intensity, flow mixing, and thickness of the boundary layer, but weaker wake vorticity.
Multiple tuned mass dampers are proposed to suppress the vertical and torsional buffeting and to increase the aerodynamic stability of long-span bridges. Each damper has vertical and torsional frequencies, which are tuned to the corresponding frequencies of the structural modes to suppress the resonant effects. These proposed dampers maintain the advantage of traditional multiple mass dampers, but have the added capability of simultaneously controlling vertical and torsional buffeting responses. The aerodynamic coupling is incorporated into the formulations, allowing this model to effectively increase the critical speed of a bridge for either single-degree-of-freedom flutter or coupled flutter. The reduction of dynamic response and the increase of the critical speed through the attachment of the proposed dampers to the bridge are also discussed. Through a parametric analysis, the characteristics of the multiple tuned mass dampers are studied and the design parameters - including mass, damping, frequency bandwidth, and total number of dampers - are proposed. The results indicate that the proposed dampers effectively suppress the vertical and the torsional buffeting and increase the structural stability. Moreover, these tuned mass dampers, designed within the recommended parameters, are not only more effective but also more robust than a single TMD against wind-induced vibration.
Abstract In order to gain further understanding of aerodynamic forces and their effects on groups of high‐rise buildings, this study used wind‐tunnel experiments. Two square prisms were arranged both in tandem and side‐by‐side arrangement with different spacings in between. Similar experiments were carried out to study the interactions of aerodynamics between the two prisms when both were stationary, when only one prism oscillated, and finally, when both prisms oscillated. The results showed that the aerodynamic responses were either enhanced or suppressed by the spacing ratios, the oscillating frequencies, and the mutual influences of the two square prisms in various arrangements. The aerodynamics also changed due to the occurrences of different flow patterns, such as channel flow, deflected flow, pulsating flow, and so on. Obviously, the aerodynamics of the flow patterns of the two square prisms in tandem and side‐by‐side arrangements proved to be more complex than those of a single square prism.
This article presents the development of a wind tunnel aero-data based wind resistant design procedure for tall buildings. The objective is to provide more accurate design wind loads than the current wind code is capable of. The major works involve conducting large amount of wind tunnel experiments of rectangular tall buildings and formulating calculation models for alongwind, acrosswind and torsional design wind loads. The main challenge of the work is to be able to provide enough incentives to justify the extra effort needed from engineers. On the other hand, the tradeoff between wind load accuracy and calculation complexity needs to be carefully considered. Therefore, the development of artificial neuron networks and easy-to-use computer programs to facilitate the engineering application of the methodology were performed.
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