A comparative and parametric study of experimentally obtained flutter derivatives of four bridge decks - streamlined and bluff shapes

Predicting instability for flexible structures has always been a crucial activity in the science of aeroelasticity. Instability for actual structures, such as bridge decks, can be predicted by extracting flutter derivatives from a wind tunnel section model study. A variety of methods have been employed to extract flutter derivatives including free-vibration, forced-oscillation, and computational fluid dynamics. A recent technique developed in the Iowa State University Wind Simulation and Testing Laboratory (ISU WiST Lab) utilizes a three degree-of-freedom (DOF) free-vibration suspension system for data acquisition and the Iterative Least Squares method incorporated with System Identification (ILS System ID) software for data analysis. Validation of this technique was critical for establishing confidence in the obtained flutter derivatives. Another important aspect of wind tunnel testing is the ability to develop realistic models capable of providing means to obtain reliable pressure and/or force data while maintaining rigidity and minimal weight. The purpose of this research was to scrutinize the free-vibration technique used in the ISU WiST Lab to offer improvements to the system and techniques used for data acquisition and analysis and to contribute new model building methods for future testing. The system verification involved design and construction of bridge deck section models, acquiring displacement time histories from wind tunnel testing, analyzing the acquired data with an improved version of the ILS System ID software, and finally comparing obtained flutter derivatives through an assortment of means. The parametric study involved comparing flutter derivative data between stable and unstable bridge decks, longer and shorter section model lengths, and solid-streamlined versus slotted-streamlined bridge decks. These studies helped to illustrate the importance of bridge design for stability and model design for proper analysis. For the comparative study, bridge models were tested in two separate single DOF cases (vertical and then torsional) and a two DOF case (vertical and torsional). In all eight flutter derivatives were extracted, four being direct flutter derivatives. The direct flutter derivatives were compared between the single DOF cases and the two DOF case as well as with data from outside sources to establish further confidence in system operation

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Dr. Stronck, professeu

A comparative and parametric study of experimentally obtained flutter derivatives of four bridge decks - streamlined and bluff shapes

Predicting instability for flexible structures has always been a crucial activity in the science of aeroelasticity. Instability for actual structures, such as bridge decks, can be predicted by extracting flutter derivatives from a wind tunnel section model study. A variety of methods have been employed to extract flutter derivatives including free-vibration, forced-oscillation, and computational fluid dynamics. A recent technique developed in the Iowa State University Wind Simulation and Testing Laboratory (ISU WiST Lab) utilizes a three degree-of-freedom (DOF) free-vibration suspension system for data acquisition and the Iterative Least Squares method incorporated with System Identification (ILS System ID) software for data analysis. Validation of this technique was critical for establishing confidence in the obtained flutter derivatives. Another important aspect of wind tunnel testing is the ability to develop realistic models capable of providing means to obtain reliable pressure and/or force data while maintaining rigidity and minimal weight. The purpose of this research was to scrutinize the free-vibration technique used in the ISU WiST Lab to offer improvements to the system and techniques used for data acquisition and analysis and to contribute new model building methods for future testing. The system verification involved design and construction of bridge deck section models, acquiring displacement time histories from wind tunnel testing, analyzing the acquired data with an improved version of the ILS System ID software, and finally comparing obtained flutter derivatives through an assortment of means. The parametric study involved comparing flutter derivative data between stable and unstable bridge decks, longer and shorter section model lengths, and solid-streamlined versus slotted-streamlined bridge decks. These studies helped to illustrate the importance of bridge design for stability and model design for proper analysis. For the comparative study, bridge models were tested in two separate single DOF cases (vertical and then torsional) and a two DOF case (vertical and torsional). In all eight flutter derivatives were extracted, four being direct flutter derivatives. The direct flutter derivatives were compared between the single DOF cases and the two DOF case as well as with data from outside sources to establish further confidence in system operation.</p