Presentations

In controlling a seismic isolation floor in a building during an earthquake, it is important to reduce not only the acceleration of the equipment on the isolation floor but also the relative displacement of the isolation floor to the placing building floor. In this research, to reduce the response of the equipment on the isolation floor, we investigate the effectiveness of a distributed polynomial control of a semi-active damper for an isolation floor. In a design of the control the total sum of kinetic energy and elastic potential energy is minimized, which are calculated using the relative velocity and relative displacement of an isolation floor as a cost function, and the state variables of the equipment are measured by the local sensor. We compared the performances of the proposed distributed polynomial control and a distributed linear-quadratic-Gaussian (LQG) control by conducting numerical simulation and shaking table experiment. As a result, we observed that the proposed control could reduce the absolute acceleration and relative displacement response of an isolated floor more than the distributed LQG control.

In order to synthesize simulated ground motion more properly, we propose models of horizontal components for synthesized wave using the stochastic Green’s function method considering dominant direction. By using aftershock records of the 2011 off the Pacific coast of Tohoku Earthquake, we calculate the mean square value of acceleration and search for the dominant directions. Then, we adopt directions with small angel difference, strike and orthogonal directions, as two directions for the model. In the same manner as Pao and Kawase (2007), optimum values of the duration time and the peak time are obtained by fitting an envelope to the section maximum values of acceleration, and we derive regression equations to estimate the duration time and the peak time, which are parameters of the Boore’s envelope function, using magnitude and hypocentral distance.

To employ neural networks in structural health monitoring, a large volume of training data is required. The data can be obtained by a generative learning method based on high-precision simulation of seismic responses. We investigate appropriate machine learning parameters such as the numbers of layer nodes in a deep neural network and the number of epochs for training. Response records measured in shaking table tests of a steel frame structure are used as training, validation, and test data. Our results show that response data of only the translational component can achieve high accuracy of damage pattern classification. Regarding the length of response data, clear difference is not observed in two durations of 1 s and 2 s. We propose a method to detect unlearned damage pattern data using the Mahalanobis distance.

When an earthquake occurs, the people in and/or contents of buildings may suffer damage due to the sliding or overturning of furniture and equipment or the falling of objects even if the structure of the building experiences no damage. In this study, using numerical analyses, we investigate a model of effective equipment caster wheel control to reduce damage caused by the moving and overturning of equipment during earthquakes and propose a control method to switch the lock and free conditions of the caster wheel. In the numerical analyses, a simulator library of three-dimensional rigid body dynamics is used and two-direction earthquake ground motion is input into a model of a 10-story steel frame building. The horizontal displacement and the falling down of the equipment model are expressed depending on the caster lock condition.

A reliable index is proposed to assess damage severity of a reinforced concrete (RC) beam based on an experiment. The index is fractal dimension of time-history of the fractal dimension of response waveform to impact excitation, which is calculated by the box counting method. The proposed index can evaluate damage level that requires repair with good accuracy. The finite element dynamic analysis shows the proposed index has a potential to evaluate damage level of an RC beam with a different boundary condition from the experiment.