This study is partly motivated by the need to develop sustainable energy dissipation devices that do not suffer from oil leakage due to failure of their end seals and from displacement limitations; and partly from the need to develop a robust damper that consists only of traditional civil engineering materials (sand and steel) in association with the use of post-tensioned steel rods with which practitioner civil engineers are familiar. Past failures of fluid dampers are both disruptive and costly, therefore not in-line with the current design paradigm of sustainable engineering, where the design and construction of structural systems shall meet acceptable performance levels at present and in the years to come without compromising the ability of future generations to use, maintain, and benefit from them.
The concept, design, testing, and characterization of an innovative, low-cost, long-stroke, fail-safe, sustainable energy-dissipation device, in which the material surrounding the moving piston — with the attached sphere on it — and enclosed within the damper housing is pressurized sand, are presented. The limited dependence of the energy dissipation of granular materials to temperature, renders the sand an ideal dissipative material. The proposed device is simple, robust in harsh environments with either high or low temperatures and delivers a stable force-displacement behavior over a large number of cycles.
This dissertation firstly presents results from cyclic testing on various configurations of the developed pressurized sand damper. This part of the experimental campaign investigates the effects of the key design parameters of the damper, namely the effect of the clearance between the moving sphere and the cylindrical tube and the effect of the overall length of the damper on its force output.
Then, the phenomenological model that represents the rate-independent behavior of the hysteretic pressurized sand damper is developed and proposed. The strong pinching behavior of the pressurized sand dampers is characterized with two phenomenological models, the Bouc-Wen and the newly developed Vaiana-Rosati models. While both models can capture the pronounced pinching of the hysteretic behavior at larger stroke amplitudes, only the Vaiana-Rosati model is capable of producing symmetric force-displacement loops when the input motion is a periodic displacement history with successive peak negative and positive displacements that are not symmetric, or when the input motion is predefined displacement time-histories derived from seismic ground motions.
Subsequently, the application of two pressurized sand dampers, which have been built and assembled at the SMU Machine Shop, to rocking structures is presented. This experimental campaign assesses the seismic response of rocking structures coupled with pressurized sand dampers through real-time hybrid simulations (RTHS). This campaign constitutes one of the two campaigns that are conducted collaboratively with a team from Lehigh University. The RTHSs are conducted in the Natural Hazards Engineering Research Infrastructure (NHERI) Lehigh Experimental Facility at Advanced Technology for Large Structural Systems (ATLSS) Engineering Research Center, at Lehigh University. For this experimental campaign, the sphere appended on the piston-rod of the pressurized sand damper is merely replaced with a bolt and a nut protruding from each side of the piston-rod. The characterization tests of the pressurized sand damper with the bolt/ nut system took place in the Structures Laboratory of the Southern Methodist University (SMU).
The last Chapter of this dissertation concludes with the response of the pressurized sand damper in harsh environments with extremely low and high temperatures, as well as when the sand that is enclosed in the damper housing is wet. This part of the study is the second one that is conducted collaboratively with a team from Lehigh University. The tests of the pressurized sand dampers where the enclosed sand is wet have been conducted in the SMU Structures Laboratory; while those under extreme temperatures have been conducted in the NHERI Lehigh Experimental Facility at ATLSS Engineering Research Center, at Lehigh University. Two different configurations of the pressurized sand dampers have been used for this study of the dissertation.
CIVIL AND ENVIRONMENTAL ENGINEERING
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Kalfas, Konstantinos, "Component Testing and Characterization of an Innovative Pressurized Sand Damper for the Response Modification of Structures" (2023). Civil and Environmental Engineering Theses and Dissertations. 28.