主讲人：Satish Nagarajaiah，Professor of Civil and Mechanical Engineering ，Rice University, Dept. of Civil and Enviroment Engineering, Houston, Texas, USA
Devices with displacement dependent stiffness have been explored for vibration isolations. In this seminar a new negative stiffness device (NSD) that can consists of pre-compressed springs and can be shaped as a function of displacement by curved templates is presented. The proposed NSD is made up of a compressed springs attached to rollers, rolling along curved templates that allow adapting the stiffness as a predetermined function of displacement. The NSD configuration is presented in detail, an analytical model is developed and validated using test results. The NSD is tested under harmonic motion to determine its force displacement behavior and then it is connected to a single degree of freedom (SDOF) system with an additional spring with positive stiffness, on a shaking table to determine its vibration characteristics. The combination of the NSD and the positive spring results in a composite nonlinear elastic spring with an initial softening behavior followed by hardening behavior. Frequency response curves obtained from test results are presented to demonstrate the initial softening followed by hardening is presented. The new NSD can be used for vibration isolation studies in future studies.
Satish Nagarajaiah is a Professor of Civil and Mechanical Engineering, at Rice University, Houston, Texas, USA. Dr. Nagarajaiah expertise is in Advanced Protective Systems (Seismic Isolation, Tuned Mass Dampers etc.), Structural Dynamic Systems, Structural Control, Structural Modeling, Structural Identification, and Sensing using Applied Nanotechnology. His research is funded by the NSF, NASA, DOE, Air Force Office of Scientific Research, Office of Naval Research, other State, Federal, Private Agencies and Industries. National Science Foundation has recognized his contributions to adaptive stiffness structural systems by awarding the prestigious NSF CAREER award in 1998 and awarded a large ($1.6M) NSF project with five universities and multiple investigators in which he and his team invented/developed a new adaptive negative stiffness (patented) structural system that significantly enhances protection of buildings and bridges. He and his team received the 2015 ASCE Moissieff Award for their research on innovative adaptive negative stiffness structures. Dr. Nagarajaiah currently serves as the managing editor of the journal of structural engineering [ASCE International journal], editor of the structural control and health monitoring journal [Wiley International Journal] and editor of Structural Monitoring and Maintenance Journal. He is a fellow of Structural Engineering Institute (SEI) of ASCE. He currently serves on the ASCE SEI Board of Governors.