Ryuta Enokida

This study presents a new method for estimating the seismic responses of multi-story structures equipped with a cost-effective earthquake protection system. This system comprises a graphite lubrication interface, targeting a friction coefficient of approximately 0.2, and a feasible restoring force mechanism to suppress residual displacements. It utilizes the concept of sliding systems through conventional and affordable construction materials although it acts like a fixed-based structure until exceeding the threshold level. This multi-story estimation procedure is an extension of the recently developed procedure for estimating the shear coefficient of a single-story sliding structure with a restoring force mechanism. In the new estimation procedure, a multi-story superstructure is firstly regarded as a single-story superstructure to determine the shear coefficient. Then, the shear coefficient is distributed to each story through floor distribution coefficients considering the mass ratios. The contribution of ground motion intensity is also incorporated into the new form for improving accuracy. For this examination, incremental dynamic analyses (IDAs) are performed for three and six-story free-standing structures, both with and without a restoring force capability. The results clarify the reliability of the new estimation, which matched the IDA results within the ±20% error. The improvement in accuracy achieved by incorporating ground motion intensity is also clarified. The multi-story estimation with the improvement can reasonably estimate the seismic response of sliding structures, without dynamic analysis, solely based on structural properties. This greatly benefits the design process. Furthermore, the IDA results clarified the significant benefits of multi-story sliding structures employing graphite lubrication and properly designed restoring force mechanisms in reducing structural damage and suppressing residual sliding displacements.

The three-dimensional full-scale earthquake testing facility, “E-Defense” was constructed using the 1995 Great Hanshin-Awaji Earthquake as a lesson. Until October 2022, this facility has conducted 123 experiments as part of the research and development on earthquake engineering for various purposes (e.g., the clarification of destruction processes, evaluations of seismic structural performances, functional maintenance, collapse margins, and damage control technologies). Even after its commencement, large earthquakes that significantly affected human life and socioeconomic activities occurred such as the 2011 off the Pacific coast of Tohoku Earthquake caused the Great East Japan Earthquake Disaster. These earthquakes revealed some new challenges for disaster prevention and mitigation. Such issues have also been incorporated as subjects to be addressed by the facility. This article introduces the researches and developments using E-Defense, chronologically linking them with the major earthquakes occurred in Japan after 1995. By summarizing the activities, its near-future direction is also briefly indicated.

This study examines nonlinear signal-based control (NSBC) in shake table experiments with sliding structures, which have an isolation effect during an earthquake. NSBC uses a nonlinear signal obtained from the outputs of a controlled system and its linear model under the same input. Owing to the presence of the linear model, NSBC controllers are described by transfer functions, even for controlling nonlinear systems. NSBC achieved excellent control of the shake table in experiments with a specimen having nonlinear characteristics such as yielding of structural components. A sliding structure placed on a shake table significantly jeopardises its control because the nonlinear severity of sliding is greater than yielding, and its compensation has not yet been fully developed. Therefore, this study introduces NSBC into shake table experiments with sliding structures along with its linear model design to enhance their robustness, utilising the analysis stability to evaluate the design. Numerical simulations with a shake table with a sliding structure with a friction coefficient of 0.22 demonstrate the excellent performance of NSBC in table acceleration control. However, inversion-based control (IBC), a basic compensation approach, shows its ineffectiveness. In actual shake table experiments with a sliding structure with a friction coefficient of 0.2, NSBC with a reasonable linear model achieved excellent table acceleration control with almost 100% accuracy, whereas IBC was ineffective. This study clarifies that NSBC can solve the problem of control degradation caused by a sliding structure placed on the table.