The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
Spivey, Natalie D. - One of the best experts on this subject based on the ideXlab platform.
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X-56A Structural Dynamics Ground Testing Overview and Lessons Learned
2020Co-Authors: Chin, Alexander W., Truong, Samson S., Spivey, Natalie D.Abstract:The X-56A Multi-Utility Technology Testbed (MUTT) is a subscale, fixed-wing aircraft designed for high-risk aeroelastic flight demonstration and research. Structural dynamics ground testing for model validation was especially important for this vehicle because the structural model was directly used in the development of a flight control system with active flutter suppression capabilities. Structural dynamics ground tests of the X-56A MUTT with coupled rigid-body and structural modes provided a unique set of challenges. An overview of the ground vibration test (GVT) and moment of inertia (MOI) test setup and execution is presented. The series of GVTs included the wing by itself attached to a Strongback and complete vehicle at two mass conditions: empty and full fuel. Two boundary conditions for the complete-vehicle test were studied: on landing gear and suspended free-free. Pitch MOI tests were performed using a compound pendulum method and repeated with two different pendulum lengths for independent verification. The original soft-support test configuration for the GVT used multiple bungees, resulting in unforeseen coupling interactions between the soft-support bungees and the vehicle structural modes. To resolve this problem, the soft-support test setup underwent multiple iterations. The various GVT configurations and boundary-condition modifications are highlighted and explained. Lessons learned are captured for future consideration when performing structural dynamics testing with similar vehicles
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High-Temperature Modal Survey of a Hot-Structure Control Surface
2011Co-Authors: Spivey, Natalie D.Abstract:Ground vibration tests are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicles, thermoelastic vibration testing techniques are neither well established nor routinely performed. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. When high-temperature materials, which increase in stiffness when heated, are incorporated into a hot-structure that contains metallic components that decrease in stiffness when heated, the interaction between those materials can affect the hypersonic flutter analysis. A high-temperature modal survey will expand the research database for hypersonics and improve the understanding of this dual-material interaction. This report discusses the vibration testing of the carbon-silicon carbide Ruddervator Subcomponent Test Article, which is a truncated version of a full-scale hot-structure control surface. Two series of room-temperature modal test configurations were performed in order to define the modal characteristics of the test article during the elevated-temperature modal survey: one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the Strongback (fixed boundary). Testing was performed in the NASA Dryden Flight Research Center Flight Loads Laboratory Large Nitrogen Test Chamber
Spivey, Natalie Daw - One of the best experts on this subject based on the ideXlab platform.
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High-Temperature Modal Survey of a Hot-Structure Control Surface
2010Co-Authors: Spivey, Natalie DawAbstract:Ground vibration tests or modal surveys are routinely conducted for supporting flutter analysis for subsonic and supersonic vehicles; however, for hypersonic vehicle applications, thermoelastic vibration testing techniques are not well established and are not routinely performed for supporting hypersonic flutter analysis. New high-temperature material systems, fabrication technologies and high-temperature sensors expand the opportunities to develop advanced techniques for performing ground vibration tests at elevated temperatures. High-temperature materials have the unique property of increasing in stiffness when heated. When these materials are incorporated into a hot-structure, which includes metallic components that decrease in stiffness with increasing temperature, the interaction between the two materials systems needs to be understood because that interaction could ultimately affect the hypersonic flutter analysis. Performing a high-temperature modal survey will expand the research database for hypersonics and will help build upon the understanding of the dual material interaction. This paper will discuss the vibration testing of the Carbon-Silicon Carbide Ruddervator Subcomponent Test Article which is a truncated version of the full-scale X-37 hot-structure control surface. In order to define the modal characteristics of the test article during the elevated-temperature modal survey, two series of room-temperature modal test configurations had to be performed. The room-temperature test series included one with the test article suspended from a bungee cord (free-free) and the second with it mounted on the Strongback (fixed boundary condition) in NASA Dryden's Flight Loads Lab large nitrogen test chamber
Trombetti Tomaso - One of the best experts on this subject based on the ideXlab platform.
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A bracing system for optimized seismic performance of multistory frame structures
country:MEX, 2017Co-Authors: Laghi Vittoria, Palermo Michele, Gasparini Giada, Trombetti TomasoAbstract:The proposed work presents the seismic performances of a structural system obtained by connecting a moment-resisting frame structure with a vertical elastic truss, known in the literature as Strongback. The Strongback system is able to limit the development of excessive inter-storey drifts thus reducing potential dangerous phenomena such as weak/soft stories. In addition, the Strongback system can be equipped with viscous dampers enhancing energy dissipation properties of the whole structure. In the present paper, an applicative example is developed in order to compare the effectiveness of both the Strongback system and different dampers placements
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Strongback system to enhance the building seismic response of framed structures
country:ITA, 2017Co-Authors: Laghi Vittoria, Palermo Michele, Gasparini Giada, Silvestri Stefano, Trombetti TomasoAbstract:In the present paper the behavior of a special structural system is investigated: the innovative system is composed of a vertical elastic truss, known in the literature as Strongback, which acts as a mast when coupled with frame structures by imposing to the latter one a given lateral deformed shape. The rigid behavior of the Strongback, designed to remain in the elastic field under strong seismic ground motion, imposes a uniform inter-storey drift along the frame height, thus avoiding undesired effects such as soft-storey and weak-storey mechanisms. Therefore, the combined structural systems can be modelled at first approximation as an equivalent Single Degree of Freedom system, thus allowing for a simple analytical description of its response. In particular, in the present work the attention is mainly focused on the mutual actions exchanged by the Strongback and the frame, through infinitely rigid connections at each floor. Assuming a shear-type behavior of the frame, an analytical solution of the static equilibrium equations is found. Finally, some numerical simulations of the seismic response of the frame systems with Strongback systems are developed, both considering shear-type frames and frames with flexible beams
Tomaso Trombetti - One of the best experts on this subject based on the ideXlab platform.
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Seismic Design and Performances of Frame Structures Connected to a Strongback System and Equipped with Different Configurations of Supplemental Viscous Dampers
'Frontiers Media SA', 2021Co-Authors: Michele Palermo, Vittoria Laghi, Giada Gasparini, Stefano Silvestri, Tomaso TrombettiAbstract:The paper investigates the dynamic behavior of structural systems obtained by connecting a moment-resisting frame structure with a vertical rigid truss pinned at the base, known in literature as “Strongback,” and equipped with added fluid-viscous dampers. The Strongback, designed in order to remain in the elastic field under strong seismic ground motion, acts as a mast by imposing to the structure a linear lateral deformed shape. By regularizing the lateral drift profile of the structure, the Strongback limits undesired effects such as weak-storey mechanisms, damage concentration and residual drifts. In addition, when supplemental dampers are inserted in the structure, a considerable amount of energy can be dissipated, thus reducing the peak seismic response. The aim of the work is twofold: i) to provide analytical formulations for the preliminary design of added dampers based on the Generalized Single Degree Of Freedom (GSDOF) concept, and ii) to evaluate the increase in energy dissipation capabilities for selected dampers configurations thanks to the presence of the Strongback. The formulas are developed for different configurations of added viscous dampers: dampers inserted within the frame between all or selected consecutive storeys (inter-storey placement) and dampers located at the base of the Strongback to realize a rigid “dissipative tower.” The effectiveness of the dampers configurations is evaluated through dynamic time-history analyses
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Coupled response of framed structures connected to Strongback
'American Society of Civil Engineers (ASCE)', 2018Co-Authors: Michele Palermo, Vittoria Laghi, Giada Gasparini, Tomaso TrombettiAbstract:In the present paper, the coupled behavior of structural systems obtained by connecting a moment resisting frame structure with a vertical elastic truss, known in the literature as Strongback, which acts as a mast by imposing to the structure a given lateral deformed shape, is investigated. The rigid behavior of the Strongback, which has to be designed to remain in the elastic field under strong seismic ground motion, linearizes the lateral displacement profile of the adjacent frame through an exchange of mutual horizontal actions. The presence of the Strongback should thus help in limiting undesired effects, such as soft-story and weak-story mechanisms. For the proper design of both the truss system forming the Strongback and the frame members, the preliminary evaluation of the actions exchanged between the systems is of fundamental importance. The aim of the work is to develop analytical formulas for estimating mutual actions and internal actions in the frame members for the limiting cases of shear-type frames and pendulum-type frames. Finally, some numerical simulations of frame systems with Strongback systems as subjected to earthquake ground motions are developed, including the cases of frames with flexible beams. It is found that the amplitudes and distributions of both mutual actions and internal actions in the frame are significantly affected by the beamto- column stiffness ratio. In the case of relatively stiff beams, the mutual actions tend to reduce the shear and bending moment at the lower stories, which are rather uniformly redistributed along the height. On the contrary, in the case of relatively flexible beams, large mutual actions and internal actions (shear and bending moments) are concentrated at the lower stories, with the upper stories remaining practically unloaded
Laghi Vittoria - One of the best experts on this subject based on the ideXlab platform.
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A bracing system for optimized seismic performance of multistory frame structures
country:MEX, 2017Co-Authors: Laghi Vittoria, Palermo Michele, Gasparini Giada, Trombetti TomasoAbstract:The proposed work presents the seismic performances of a structural system obtained by connecting a moment-resisting frame structure with a vertical elastic truss, known in the literature as Strongback. The Strongback system is able to limit the development of excessive inter-storey drifts thus reducing potential dangerous phenomena such as weak/soft stories. In addition, the Strongback system can be equipped with viscous dampers enhancing energy dissipation properties of the whole structure. In the present paper, an applicative example is developed in order to compare the effectiveness of both the Strongback system and different dampers placements
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Strongback system to enhance the building seismic response of framed structures
country:ITA, 2017Co-Authors: Laghi Vittoria, Palermo Michele, Gasparini Giada, Silvestri Stefano, Trombetti TomasoAbstract:In the present paper the behavior of a special structural system is investigated: the innovative system is composed of a vertical elastic truss, known in the literature as Strongback, which acts as a mast when coupled with frame structures by imposing to the latter one a given lateral deformed shape. The rigid behavior of the Strongback, designed to remain in the elastic field under strong seismic ground motion, imposes a uniform inter-storey drift along the frame height, thus avoiding undesired effects such as soft-storey and weak-storey mechanisms. Therefore, the combined structural systems can be modelled at first approximation as an equivalent Single Degree of Freedom system, thus allowing for a simple analytical description of its response. In particular, in the present work the attention is mainly focused on the mutual actions exchanged by the Strongback and the frame, through infinitely rigid connections at each floor. Assuming a shear-type behavior of the frame, an analytical solution of the static equilibrium equations is found. Finally, some numerical simulations of the seismic response of the frame systems with Strongback systems are developed, both considering shear-type frames and frames with flexible beams
