Narito Kurata

Forced vibration test of a building with semi-active damper system

The authors developed a semi-active hydraulic damper (SHD) and installed it in an actual building in 1998. This was the first application of a semi-active structural control system that can control a buildings response in a large earthquake by continuously changing the devices damping coefficient. A forced vibration test was carried out by an exciter with a maximum force of 100 kN to investigate the buildings vibration characteristics and to determine the systems performance. As a result, the primary resonance frequency and the damping ratio of a building that the SHDs were not jointed to, decreased as the exciting force increased due to the influence of non-linear members such as PC curtain walls. The equivalent damping ratio was estimated by approximating the resonance curves using the steady-state response of the SDOF bilinear hysteretic system. After the eight SHDs were jointed to the building, the systems performance was identified by a response control test for steady-state vibration. The elements that composed the semi-active damper system demonstrated the specified performance and the whole system operated well. Copyright

A high-density earthquake monitoring system using wireless sensor networks

In this paper we present a high-density earthquake monitoring system using wireless sensor networks. For high-precision monitoring, we developed Pavenet OS, which is a hard-realtime operating system for sensor nodes, and acceleration sensor board. Sensor nodes of the system sample acceleration with less than 0.3 us jitter with Pavenet OS. The system provides earthquake engineering researchers the ability to measure vibrations of structures during earthquakes at less cost and higher node density than previous systems.

Dynamic loading test and simulation analysis of full-scale semi-active hydraulic damper for structural control

A semi-active hydraulic damper (SHD) for a semi-active damper system, which is useful for practical structural control especially for large earthquakes, has been developed. Its maximum damping force is set to 1 or 2 MN, and it is controlled by only 70 W of electric power. An SHD with a maximum damping force of 1 MN was applied to an actual building in 1998. This paper first presents the results of a dynamic loading test to confirm the control performance of the SHD. Next, an analytical model of SHDs (SHD model) is constructed with the same concept for two kinds of SHDs based on the test results. Through simulation analyses of the test results using the proposed SHD model, the dynamic characteristics of the SHD can be well represented within practical conditions. Simulation analyses are also carried out using a simple structure model with the SHD model. It is shown that this SHD model can be used to precisely evaluate the control effect of the semi-active damper system and is useful in practical SHD design under the applied conditions. Copyright

Ubiquitous Structural Monitoring using Wireless Sensor Networks

Ubiquitous structural monitoring (USM) of buildings using wireless sensor networks is one of the most promising emerging technologies for mitigation of seismic hazard. This technology has the potential to change fundamentally the traditional monitoring systems. This paper provides an introduction of wireless sensor network technology for USM, and identifies some of opportunities and associated challenges

Active response control of buildings for large earthquakes - seismic response control system with variable structural characteristics

This paper presents two types of active seismic-response control systems with variable structural characteristics, developed with the objective of ensuring that the safety and function of buildings are not impaired by large earthquakes. The systems are characterized by the active seismic-response control of large-scale civil engineering structures during large earthquakes, using only nominal amounts of energy. One system is the non-resonant active variable stiffness (AVS) system. The results of applying this system to an actual building and confirming its effectiveness through seismic observation are given. Additionally, the results from a simulation analysis evaluating the effectiveness of the system if applied to a high-rise building are also included. Then a brief outline is given of the other system, the active variable damping (AVD) system.

A quantitative error analysis of synchronized sampling on wireless sensor networks for earthquake monitoring

Wireless sensor network technology enables low-cost and high-density earthquake monitoring. The earthquake monitoring measures structural vibrations caused by earthquakes. The earthquake monitoring contributes the progress of earthquake engineering and earthquake resistant technology. If we acquire high quality vibration data, we can precisely estimate structural damage. However, the high quality sensing is difficult because of the distribution manner of wireless sensor networks. In [3], we described overview of our earthquake monitoring. In this paper, we focus on a synchronized sampling mechanism in the earthquake monitoring: especially, its design and evaluation. Section 2 discusses what kind of factors cause sensing error in wireless sensor networks, Section 3 propose a synchronized low-jitter sampling mechanism, which minimize sensing error, and Section 4 evaluates the synchronized lowjitter sampling using a shaking table. Finally, Section 5 concludes this work.

Poster: Data-Centric Task Scheduling for Battleship Island Monitoring

This paper presents our results of the acquisition of actual data of collapsing buildings, as part of our work on the Battleship Island monitoring project. Our Battleship Island monitoring system performs its task by acquiring data of images, sounds, and acceleration of collapsing buildings. The system is powered by solar energy. To enable the efficient use of solar-powered energy, this paper proposes a data-centric task scheduling system which consists of the DC-LQ (Data Centric LQ-Tracker) and BLB scheduling (battery-level based scheduling). An evaluation using computer simulation shows that data-centric task scheduling outperforms conventional task scheduling.

Reliability and control performance verification of an actual semi-active structural control system

Publisher Summary A large control force, in the semi-active structural control systems, can be obtained only by adjusting the characteristics of the control device itself with a small external energy supply. This enables a structural control system to be realized that is highly effective over the range from small to large earthquakes, and that is highly reliable and economical. The required function of the control system is realtime control and system management. The former contains control trigger determination, real time computation with several milliseconds and communication between the semi-active hydraulic damper (SHD) and computers. The latter contains measurement of a lot of information, health monitoring of the system, and emergency alarm. A control computer determines the damping force command to the SHD from the buildings response measured by the sensors and outputs it to the communication computer with a sampling time of five milliseconds. One Com-C outputs the damping force command to four SHDs. A management computer monitors the condition of each SHD and communication situation of each computer, and determines whether or not it is normal.