Enhancement of nonlinear signal-based control to estimate earthquake excitations from absolute acceleration responses of nonlinear structures
Ryuta Enokida
Abstract
This study constructs an inverse method for multi-storey structures with nonlinear hysteretic characteristics commonly used in earthquake and structural engineering. Constructing the inverse methods, which accurately reconstruct an input signal from a response and structural information, has been challenging owing to the severity of the nonlinear characteristics as well as structural complexity. Nonlinear signal-based control (NSBC) can achieve the exact input estimation from a nonlinear structural response when its linear model is exactly invertible. However, its estimation accuracy decreases when the exact inversion of the linear model is impossible, and an approximation is required. This study introduces a controller design consisting of three enhancements of NSBC to realise accurate input estimation even when the inversion requires an approximation; the estimation of an earthquake excitation from acceleration in the absolute coordinates of nonlinear structures is a typical example. The first enhancement is the improvement of a differentiator used to convert an improper inverse model into a proper one. The second is the zero-stiffness design wherein the stiffness of all storeys in the linear model is intentionally set to zero. The third is the addition of inner-error feedback actions to conventional NSBC controllers. The effectiveness of these enhancements is examined via numerical simulations of the input estimations of nonlinear 2/4-degree-of-freedom (2/4DOF) systems shaken by an earthquake excitation. The enhanced NSBC successfully estimates the earthquake excitation with 100% accuracy from one known absolute acceleration response of the nonlinear 2/4DOF systems. Its potential application for estimating earthquake excitations by realising a predetermined response on nonlinear structures is also analysed.