Risk Evaluation and Disaster Mitigation Research Division
Earthquake Engineering Lab
Associate Professor
Ph. D (Engineering)

Research Subject(s)
My research interests focus on nonlinear control of structural systems, health monitoring of structures subjected to strong ground motions, and development of free-standing structural systems. I am addressing these research subjects from experimental, numerical, and theoretical aspects.
Key Words
Earthquake Engineering / Control Engineering / Nonlinear Dynamics / Stability Analysis / Tribology
Research Activities

An inverse transfer function method or PID control method is one of the most common methods for shake table control. However, these methods are not suitable for controlling a shake table having a specimen particularly when the specimen displays severe nonlinear characteristics caused by yielding or fracture. These nonlinear characteristics significantly deteriorate the control performance. To this problem, we incorporated nonlinear signal-based control (NSBC), which was recently developed by our research team, into the shake table control. In a series of shake table experiments, NSBC was very powerful for controlling the shake table supporting a nonlinear specimen.

We are developing a free-standing structure that serve as a conventional earthquake-resistant structure under low-intensity earthquake excitations and a base-isolated structure under high-intensity earthquake excitations. For the realization with low cost materials, we experimentally investigated the friction coefficient of the interface of steel and mortar as well as the efficiency of graphite lubrication to the interface. The interface without the lubrication became 0.8, which is inappropriately high to the free-standing structure. However, the interface with the lubrication became 0.2. Our experiments revealed that seismic responses of the free-standing structure with the lubrication became nearly 1/10 of the responses of a conventional earthquake-resistant structure.

This study experimentally examined Hybrid Simulation (HS), which has been used since the early development of structuresing experiments in 1960, and Dynamic Substructuring System (DSS) developed in the middle of 2000s. To examine the schemes, we conducted a series of dynamical substructuring tests for a base-isolated structure having rubber bearings. In the tests, a rubber bearing, which is the core part of the base-isolated structure, is physically excited by an actuator. Other parts of the structure are considered by a numerical simulation having a dynamical interaction with the physical part. DSS achieved a reasonable experiment with high stability, while HS was unable to do so. 

Selected Works

R. Enokida, Keynote lecture: A brief history of E-Defense activity, 7th International Conference on Advances in Experimental Structural Engineering, Pavia Italy, September 2017.

R. Enokida, Stability of nonlinear signal-based control for nonlinear structural systems with a pure time delay, Structural Control and Health Monitoring, 26(8), e2365, 2019.

R. Enokida, K. Kajiwara, Nonlinear signal-based control for single-axis shake tables supporting nonlinear structural systems, Structural Control and Health Monitoring, 26(9), e2376 2019.

R. Enokida, T. Nagae, Seismic damage reduction of a structural system based on non-traditional sliding interfaces with graphite lubrication, Journal of Earthquake Engineering, pp. 1-21, January 2017.

R. Enokida, D. Stoten, K. Kajiwara, Stability analysis and comparative experimentation for two substructuring schemes, with a pure time delay in the actuation system, Journal of Sound and Vibration, 346, pp. 1-16, June 2015.

R. Enokida, I. Takewaki, D. Stoten, A nonlinear signal-based control method and its applications to input identification for nonlinear SIMO problems, Journal of Sound and Vibration, 333, pp. 6607-6622, 2014.12.

Selected Memberships
  • Architectural Institute of Japan
Selected Awards
  • AIJ Excellent Master Thesis Award