Date of Award

2016

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Cheng, Shaohong

Second Advisor

Ghrib, Faouzi

Keywords

cable-stayed bridge, cable vibration, cross-tie, damper, damping, vibration control

Rights

CC BY-NC-ND 4.0

Abstract

Stay cables on cable-stayed bridges are vulnerable to dynamic excitations due to their long flexible feature and low intrinsic damping. Connecting a vulnerable cable with the neighbouring ones through cross-ties to form a cable network is one of the commonly used field solutions. The current dissertation is dedicated to explore the in-plane dynamic behaviour of the conventional (cross-tie only) and hybrid (combined use of cross-ties and external dampers) cable networks used for controlling undesirable bridge stay cable vibrations. Their performances are evaluated based on the system in-plane stiffness, damping and the severity of local mode formation. A number of analytical models have been developed to analyze the in-plane modal response of conventional cable networks by gradually extending the model of a basic undamped two-cable network with a rigid cross-tie to include the cross-tie stiffness, the damping property of main cables and cross-tie, and more number of main cables and cross-tie lines into the formulation. A damping transfer phenomenon between cable network elements having different damping properties was observed. Two criteria, the degree of mode localization (DML) coefficient and the local mode cluster (LMC), were proposed to quantify the severity of local mode formation. Based on the proposed analytical models, key system parameters which dictate the dynamic behaviour of conventional cable networks were identified. A parametric study was conducted to explore their respective role in influencing the in-plane stiffness, the damping ratio and the local mode formation of cable networks. Analytical models of two-cable hybrid networks with different configurations have been developed to assess the system in-plane modal behaviour. A concept of “isoquant curve” was proposed to optimize the performance of a selected hybrid system mode. A state-of-the-art generalized approach was developed to derive analytical models of a more complex conventional or hybrid cable network from a relatively simple parent system. Results indicated that the existing universal damping estimation curve for a single isolated damped cable was no longer applicable once the cable became part of a hybrid system. Thus, approximate relation equations were developed to predict the optimum damper size and the maximum attainable fundamental modal damping ratio of a basic two-cable hybrid system. All the proposed analytical models were validated through independent numerical simulations using the commercial finite element software Abaqus 6.10. Besides, an experimental study was conducted for two-cable conventional and hybrid networks to not only verify the validity of the corresponding analytical and numerical models, but also evaluate the impact of different assumptions made in the formulation of these models on the system modal response. The outcomes yielded from this study are expected to add valuable knowledge to comprehend the current understanding of the mechanics associated with the conventional and hybrid cable networks. The developed tools will greatly contribute to the bridge industry by assisting optimum design of conventional and hybrid cable networks, especially in the preliminary design stage. Besides, it is worthy pointing out that the current findings will also contribute to the knowledge of structural health monitoring, assessment and management of bridges, and the development of more sustainable civil infrastructures.

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