Tomohiko Hatada

Dynamic analysis of structures with Maxwell model

A numerical method has been developed for the dynamic analysis of a tall building structure with viscous dampers. Viscous dampers are installed between the top of an inverted V-shaped brace and the upper beam on each storey to reduce vibrations during strong disturbances like earthquakes. Analytically, it is modelled as a multi-degree-of freedom (MDOF) system with the Maxwell models. First, the computational method is formulated in the time domain by introducing a finite element of the Maxwell model into the equation of motion in the discrete-time system, which is based on the direct numerical integration. Next, analyses for numerical stability and accuracy of the proposed method are discussed. The results show its numerical stability. Finally, the proposed method is applied to the numerical analysis of a realistic building structure to demonstrate its practical validity.

Measuring Relative-Story Displacement and Local Inclination Angle Using Multiple Position-Sensitive Detectors

We propose a novel sensor system for monitoring the structural health of a building. The system optically measures the relative-story displacement during earthquakes for detecting any deformations of building elements. The sensor unit is composed of three position sensitive detectors (PSDs) and lenses capable of measuring the relative-story displacement precisely, even if the PSD unit was inclined in response to the seismic vibration. For verification, laboratory tests were carried out using an Xθ-stage and a shaking table. The static experiment verified that the sensor could measure the local inclination angle as well as the lateral displacement. The dynamic experiment revealed that the accuracy of the sensor was 150 μm in the relative-displacement measurement and 100 μrad in the inclination angle measurement. These results indicate that the proposed sensor system has sufficient accuracy for the measurement of relative-story displacement in response to the seismic vibration.

New Directions of Health Monitoring for Building Structures

The concept of structural health monitoring (SHM) has appealed the attentions of structural engineers. However, most of the proposed schemes for SHM do not seem “friendly” to the practicing engineers in terms of the used data or employed methods. In this regard, the direct sensing of inter-story drift displacements could open the door to the construction of “practicing engineers friendly” SHM schemes. The authors‘ group developed non-contact types of inter-story drift displacement sensors. Several schemes based on the drift displacement sensing are discussed, which do not involve heavy researchers-oriented processes.

Relative-story displacement sensor for measuring five-degree-of-freedom movement of building layers

We have developed a novel relative-story displacement sensor capable of measuring the 5-degree-of-freedom movement of building layers for structural health monitoring. Three pairs of infrared-light emitting diode arrays and positionsensitive detector units were used for simultaneously measuring the relative-story displacement, the inclination angle of the lower layer, and the torsion angle between two adjacent layers. For verification, laboratory tests were carried out using a shaking table, a motorized micrometer and a rotation stage. In the static experiment, it is verified that the local inclination angle and the torsion angle can be measured as well as the relative-story displacement using the sensor system. The resolution of the sensor system in the displacement measurement, that in the inclination angle measurement, and that in the torsion angle measurement were evaluated to be 0.10 mm, 34.4 μrad, and 14.6 μrad, respectively. In the dynamic response experiment, the accuracy of the sensor system was experimentally evaluated to be 0.20 mm in the relative-displacement measurement, 110 μrad in the inclination angle measurement, and 90 μrad in the torsion angle measurement, respectively. These results indicate that the developed sensor system has a sufficient accuracy for the structural health diagnostics of buildings.