Seismic control of damaged structure by pole assignment and intermittent wavelet-based identification

Calculation of the control forces by control algorithms, such as the pole assignment, proportional-integral-derivative, and linear quadratic regulator, is usually based on initial dynamic characteristics of the intact and undamaged structure, which is considered to be in the ideal conditions. However, because of the effect of natural loads and damage due to aging, these features can change during the structure’s life span, eventually leading to incorrect control forces. In this research, to overcome this problem and to get closer to the actual dynamic characteristics and on the other hand, in order to elude the adverse effects of real-time identification, such as elapsed time of detection, induced to the controller, the intermitted wavelet-based identification technique besides the pole assignment control is introduced. Performance of the proposed controller on three- and five-story with different cases of stiffness and two failure scenarios, under far and near-field earthquakes, are examined and compared by non-updated wavelet-based pole assignment, proportional-integral-derivative and linear quadratic regulator controllers. Results show that damaged structure response controlled by the suggested adapted pole assignment method is significantly reduced compared to ones controlled by other control methods.

Identification of Modal Parameters for Reinforcement of Walls in Earthen Ruins

The protection of earthen sites plays an important role in the context of preservation of cultural heritage, especially in the inheritance and promotion of history and culture. The aim of the paper is to present the essential results of an ongoing research on a reinforced rammed earthen wall in Suoyang City (Guazhou, China). The wall vibrations caused by ambient actions were analyzed using the stochastic subspace algorithm to estimate the modal parameters of the wall. The frequencies of the first three orders are 3.566 Hz, 5.003 Hz, and 6.250 Hz, and the corresponding modes are first-order transverse bending, second-order left and right torsion, and third-order vertical bending, respectively. Then, according to the data of elastic modulus obtained in the lab, the finite element calculation is carried out, and referring to the results of field measurement, the revised elastic modulus value is 205.90 MPa. It is worth mentioning that the revised value is significantly improved from the original laboratory value, and it is also indicated that the seismic performance of the reinforced wall has been significantly improved. The present work is expected to provide a theoretical basis for reinforcement, protection, and seismic control of earthen ruins.

Mitigation of Earthquake Responses Using SMA Supplemented Base-Isolation Devices for Benchmark Building

The efficiency of traditional isolation bearings is doubted for near-field earthquakes because these bearings undergo large displacement. A comparative study of different base isolation systems of base-isolated benchmark building is carried out in the present study. The study is based on assumption that buildings are bi-directionally acted upon by near-field earthquakes for assessing their relative performance in seismic control of the benchmark building. The time history variations of important response parameters and evaluation criteria of the benchmark building has been studied for assessing the effectiveness of the isolation systems. The Shape Memory Alloy (SMA) is utilized with elastomeric bearings and friction bearings to study the effectiveness of SMA wires with different isolators. The benchmark building is modelled as a discrete linear elastic shear structure having three degrees of- freedom at each floor level. Time domain dynamic analysis of this building has been carried out with the help of constant average acceleration Newmark’s method and equilibrium of non-linear forces has been taken care by fourth order Runge-Kutta method. The comparative performance of various isolation systems has been studied with uniform and hybrid combinations. The hybrid combination of SMA supplemented bearings works out the better isolation system keeping in view of the percentage reduction in evaluation criteria for smart base-isolated benchmark building. Furthermore, it is shown that, the functionality of SMA wire is not efficient with Lead Rubber Bearing system, as it is able to control displacement but increases the acceleration, base shear, story drift and isolation forces.

Bistable Nonlinear Energy Sink Using Magnets and Linear Springs: Application to Structural Seismic Control

Nonlinear energy sink (NES) has proven to be very effective in reducing the vibration response of structures. In this paper, a magnetic bistable nonlinear energy sink (BNES) that composed of a guided moving mass attached with linear springs and permanent magnets is proposed. To assess the seismic control performance of the proposed BNES, a shear frame model equipped with the proposed BNES is compared with the same shear frame model equipped with an optimized cubic NES and with a linear tuned mass damper (TMD) system. The results show that, in the idealized situation, where the mass and stiffness is clearly defined (no uncertainty), the BNES can achieve similar performance as a thoroughly in-tuned TMD system. Moreover, in the detuned condition, due to broadband high internal resonance capability, the proposed BNES can outperform the linear TMD and the cubic NES. The study demonstrates that the proposed BNES can be used as an efficient passive vibration absorber for structural seismic control.