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Stability and response of suspension bridges under turbulent wind excitation
 Date Issued:
 1988
 Summary:
 This research addresses the linear flutter theory for bridges. A new model for the selfexcited loads is proposed in which oscillatory variation in the loads due to motioninduced vortex activity in the wake, is accounted for. The addition of complex exponential terms generalizes the traditional Prony series representation of the indicial function for the selfexcited loads. Turbulence in the flow direction is included in the selfexcited loads. Hence the system is parametrically excited and its governing equations have randomly varying coefficients. The state vector of the response is approximated by a Markov vector process. Stochastic averaging is utilized to convert the physical equations into Ito's stochastic differential equations which govern the Markov vector process. Ito's differential rule is then used to construct the equations for the second statistical moments. Motion stability of the system is interpreted as stability of the first and second statistical moments. The computed stability boundaries for the first and second moments are shown to be crucially dependent upon the coupled loads. Unfortunately, parameters for the indicial functions calculated indirectly from the frequencydomain flutter derivatives, are nonunique. Nevertheless, it can be concluded that a bridge deck that exhibits oscillatory selfexcited load behavior is generally less stable (in the mean square) than one with nonoscillatory behavior. The new model that captures the oscillatory behavior concisely, reduces the critical wind speed by more than 10%. Buffeting loads result essentially from the vertical turbulence component. In the present thesis the buffeting loads are expressed as convolution integrals, that account for past history of the fluid flow. Thus the buffeting model considered is based on unsteady aerodynamics rather than the quasisteady model that has been traditionally used in many previous analyses. The time domain unsteady buffeting response analysis, that also incorporates the randomly varying parameters of the selfexcited loads, is the first of its kind. In the illustrative examples, the unsteady buffeting effect is shown to be significant on a singledegreeoffreedom system, whereas it is comparatively less significant with a coupled twodegreeoffreedom system.
Title:  Stability and response of suspension bridges under turbulent wind excitation. 
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Name(s): 
Sternberg, Alex. Florida Atlantic University, Degree grantor Lin, Y. K., Thesis advisor College of Engineering and Computer Science Department of Ocean and Mechanical Engineering 

Type of Resource:  text  
Genre:  Electronic Thesis Or Dissertation  
Issuance:  monographic  
Date Issued:  1988  
Publisher:  Florida Atlantic University  
Place of Publication:  Boca Raton, Fla.  
Physical Form:  application/pdf  
Extent:  179 p.  
Language(s):  English  
Summary:  This research addresses the linear flutter theory for bridges. A new model for the selfexcited loads is proposed in which oscillatory variation in the loads due to motioninduced vortex activity in the wake, is accounted for. The addition of complex exponential terms generalizes the traditional Prony series representation of the indicial function for the selfexcited loads. Turbulence in the flow direction is included in the selfexcited loads. Hence the system is parametrically excited and its governing equations have randomly varying coefficients. The state vector of the response is approximated by a Markov vector process. Stochastic averaging is utilized to convert the physical equations into Ito's stochastic differential equations which govern the Markov vector process. Ito's differential rule is then used to construct the equations for the second statistical moments. Motion stability of the system is interpreted as stability of the first and second statistical moments. The computed stability boundaries for the first and second moments are shown to be crucially dependent upon the coupled loads. Unfortunately, parameters for the indicial functions calculated indirectly from the frequencydomain flutter derivatives, are nonunique. Nevertheless, it can be concluded that a bridge deck that exhibits oscillatory selfexcited load behavior is generally less stable (in the mean square) than one with nonoscillatory behavior. The new model that captures the oscillatory behavior concisely, reduces the critical wind speed by more than 10%. Buffeting loads result essentially from the vertical turbulence component. In the present thesis the buffeting loads are expressed as convolution integrals, that account for past history of the fluid flow. Thus the buffeting model considered is based on unsteady aerodynamics rather than the quasisteady model that has been traditionally used in many previous analyses. The time domain unsteady buffeting response analysis, that also incorporates the randomly varying parameters of the selfexcited loads, is the first of its kind. In the illustrative examples, the unsteady buffeting effect is shown to be significant on a singledegreeoffreedom system, whereas it is comparatively less significant with a coupled twodegreeoffreedom system.  
Identifier:  11921 (digitool), FADT11921 (IID), fau:8841 (fedora)  
Collection:  FAU Electronic Theses and Dissertations Collection  
Note(s): 
College of Engineering and Computer Science Thesis (Ph.D.)Florida Atlantic University, 1988. 

Subject(s): 
Suspension bridgesStability Winds 

Held by:  Florida Atlantic University Libraries  
Persistent Link to This Record:  http://purl.flvc.org/fcla/dt/11921  
Sublocation:  Digital Library  
Use and Reproduction:  Copyright © is held by the author, with permission granted to Florida Atlantic University to digitize, archive and distribute this item for nonprofit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.  
Use and Reproduction:  http://rightsstatements.org/vocab/InC/1.0/  
Host Institution:  FAU  
Is Part of Series:  Florida Atlantic University Digital Library Collections. 