Nonlinear substructuring control for simultaneous control of acceleration and displacement in shake table substructuring experiments

Structural Control and Health Monitoring

Kajiwara

2023

Self Cite

This study introduces enhancements for nonlinear substructuring control (NLSC) to achieve simultaneous control of acceleration and displacement in shake table substructuring experiments with severely damaged structures. Although shake table control is greatly affected by a specimen placed on its top and its nonlinear characteristics, accurate control, even with nonlinear characteristics, is essential for experimental purposes. The NLSC was developed for a dynamically substructured system (DSS) scheme involving nonlinear substructures, and its first application to a shake table experiment was performed on a one-storey steel frame. In the experiment, NLSC realised simultaneous control of table acceleration and displacement with a slight nonlinear characteristic within the frame, although its performance degraded as the nonlinearity became stronger. To address this degradation issue, this study introduces two techniques for enhancing NLSC shake table substructuring experiments. One is a composite filtering technique to minimise noise-contaminating displacement data fed back to the table control so that the error feedback action in NLSC can be fully utilised. The other involves a new linear model that is assumed to be more highly damped than the actual system to enhance the stability robustness of NLSC against nonlinear characteristics. After a series of numerical examinations, this study experimentally examined the enhancements on actual shake table experiments using a steel frame. Using the NLSC with the enhancements, a substructuring experiment was successfully conducted; moreover, the NLSC realised simultaneous control of the table acceleration and displacement with nearly 100% accuracy, even with severe nonlinear characteristics.

“…In the previous studies on NLSC [53,54,56], the following controllers have been efective in minimising the error in equation ( 12) particularly when ∆τ � 0:…”

Section: Controller Design Of Nlscmentioning

confidence: 99%

“…Analysis. When G(s) is given somehow, the stability of the NLSC shake table substructuring experiment is governed by the feedback signals [56], which are described by…”

Section: Stabilitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Enhancements of Nonlinear Substructuring Control for Shake Table Experiments on Severely Damaged Structures

Structural Control and Health Monitoring

Kajiwara

2023

Self Cite

“…NSBC utilises a nonlinear signal, which is obtained from the outputs of a controlled system and its linear model under the same input signal. Its effectiveness for nonlinear system control has been demonstrated using shake table experiments 36,37 and dynamical substructuring experiments 38,39 . When NSBC was applied to a shake table experiment with a steel structure, a seismic acceleration record with 100% accuracy was realised even when the structure displayed severe nonlinear characteristics owing to the yielding of its structural components 36 …”

Section: Introductionmentioning

confidence: 99%

Nonlinear signal‐based control for shake table experiments with sliding masses

Earthq Engng Struct Dyn

Ikago

Guo

et al. 2023

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This study introduces the first application of nonlinear signal‐based control (NSBC) to shake table experiments with sliding masses. NSBC utilising a nonlinear signal was specifically developed for nonlinear system control. In shake table experiments with a steel structure, it realised a seismic acceleration record on the table with near 100% accuracy even when the structure displayed nonlinear characteristics due to yielding of its components. Regarding the severity, sliding is stronger than yielding because of the rapid shifts of stick and slip states. Sliding is utilised for structural damage mitigation in seismic isolation systems, which are prominent devices in earthquake engineering. However, when sliding occurs on a shake table, it significantly jeopardises the table control. Thus, this study investigates the performance of NSBC to shake table experiments involving the phenomenon. First, this study examines the effectiveness of NSBC via numerical simulations on a shake table with a sliding interface, demonstrated by the Karnopp model, with a friction coefficient of 0.2. Subsequently, a linear model is designed based on the stability analysis of NSBC to assess stability margins obtained from different models. Experiments are performed by placing masses weighing approximately twice the table weight on sliding interfaces with friction coefficients of 0.2–0.4. In these experiments, NSBC with a reasonable linear model design realised expected acceleration records with sufficiently high accuracies, whereas inversion‐based control failed. This study verifies the effectiveness of NSBC for shake table experiments with sliding masses.

“…This controller acts on the nonlinear signal obtained from the outputs of a controlled system and its linear model subjected to the same input signal. The effectiveness of the feedback action on nonlinear structural dynamics has been demonstrated by dynamic substructuring experiments (Enokida and Kajiwara 2017a;Enokida and Kajiwara 2017b) and shake table experiments (Enokida 2022b). In its application to a single-axis shake table with a steel structure (Enokida and Kajiwara 2019), NSBC realized a seismic acceleration record with an accuracy of approximately 100.0%, despite the structure on the table exhibiting severe nonlinear characteristics owing to the yielding of its structural components.…”

Section: Introductionmentioning

confidence: 99%

Numerically disturbed shake table experimentation to examine nonlinear signal-based control

Ikago

Kajiwara

2022

Front. Built Environ.

Self Cite

This study introduces a numerically disturbed experimentation to address the shake table control degradation commonly observed in shake table experiments. This degradation is caused by nonlinear characteristics, such as seismic damage, in the experiments; however, observing such nonlinear characteristics is a major purpose of these experiments. In the proposed numerically disturbed experimentation, a structure is numerically simulated, and its structural responses are fed back as the disturbance signal to the table in the physical domain via real-time interaction. This enables us to examine the control performance of a shake table with a structure, without having to place an actual structure on it. This experimentation is beneficial in cases wherein new control methods are applied for shake table control because the control performance can be examined safely and efficiently under various structural conditions by using numerical simulations. The proposed experimentation was applied to the shake table control examination of nonlinear signal-based control (NSBC), which has a nonlinear signal feedback action for nonlinear structural dynamics, as well as inversion-based control (IBC), which is a common feedforward method. In the numerically disturbed experiments, NSBC accurately realized a seismic acceleration record on the shake table with severe nonlinear characteristics, whereas IBC exhibited control degradation due to nonlinear characteristics. Similar results were obtained using actual shake table experiments with a steel structure. Therefore, the proposed numerically disturbed experimentation can be an alternative to shake table experiments using structures.