Keiji Shiba

Active/passive vibration control systems for tall buildings

Three examples of vibration control systems are described. The first is a hybrid mass damper system, which is one type of active vibration control system, as installed on the top floor of a complex triangular building of forty-three stories in order to reduce the response of the building to strong winds and moderate earthquakes. The second is an unbonded brace damper, which is a kind of elasto-plastic damper using low-yield-point steel. It has been installed in a fifteen-story building as an energy absorption member to control severe earthquake motion. The last is a rotational variable damper using an electrorheological fluid. The feasibility of applying this type of damper to a real scale structure as a semi-active control device has been investigated.

Structural health monitoring system using FBG-based sensors for a damage-tolerant building

An example of structural health monitoring system using FBG-based optical fiber sensors for the damage tolerant building structure is presented. The damage tolerant building is equipped with several passive dampers for absorbing earthquake input energy, and the structural health monitoring system is focused to monitor performance of these dampers. FBG-based optical fiber sensor modules are developed to apply in structural health monitoring system for damage tolerant building structures. The system is verified on static measurement and dynamic measurement in earthquake.

Damage Evaluation for Concrete Structures using Fiber Reinforced Composites as Self-Diagnosis Materials

Health monitoring techniques that utilize structural materials with the ability to diagnose their own condition, so-called self-diagnosis materials, have been under development. The authors have developed two types of electrically conductive fiber reinforced composite to diagnose cracks in concrete structures: a high sensitivity detection sensor and maximum strain memory sensor. Three points bending tests on pre-notched reinforced concrete beam under the cyclic loading is presented using these two self-diagnosis materials, with attention towards the relationship between crack width of the concrete beam and electric resistance. Moreover, effects of volume fraction of carbon particle on memorizing maximum strain are investigated. It has been proved that both self-diagnosis materials are highly effective to detect the cracks in the concrete. And present strain can be obtained by the proposed fiber reinforced plastic composites. Although volume fraction of carbon particle has significant influence on the characteristics of memorizing maximum strain, maximum strain of the concrete structures can be memorized using the appropriate self-diagnosis materials.

Fiber-reinforced composites as self-diagnosis materials for concrete structures

The authors have developed an electrically conductive fiber reinforced composite that its electrical resistance changes almost in proportion to strain. This material was tested for its tensile and bond behaviors. As a result, it was discovered that this material applied for the strengthening of concrete structures is highly effective to diagnose cracks in the concrete.

Film sensor using carbon particles for monitoring integrity of steel structures

The authors have developed such sensors which can be applied to steel structures for health monitoring. The sensor is manufactured by placing copper foils (electrodes) on polymer film and splaying the electrically conductive material on the surface. The electrically conductive material is composed of resin and carbon particles. Carbon particles form a continuous link each other. The strain due to the deformation of the steel members influences the electrical resistance. We can evaluate the strain of the steel members by measuring changing rate of the electric resistance, and then estimate the damages of the steel members. A strain monitoring system with this sensor enables low cost, because it does not need special equipment except for an electrical resistance meter. The authors carried out experimental tests on steel structure specimens with the film sensor attached. The specimens were beam-to-column connections of steel structures buildings subjected to alternative cyclic deformation correspond to input by severe earthquakes. Based on the tests, we investigated the performance and applicability of the sensor for the members of steel structures. As the test results, it turned out that the sensor is able to be used for strain detecting of steel structures.

Seismic Control Effect for Nonlinear Benchmark Building Using Passive or Semi-Active Damper

We study the control effect for a 20-story benchmark building and apply passive or semi-active control devices to the building. First, the viscous damping wall is selected as a passive control device which consists of two outer plates and one inner plate, facing each other with a small gap filled with viscous fluid. The damping force depends on the interstory velocity, temperature and the shearing area. Next, the variable oil damper is selected as a semi-active control device which can produce the control forces by little electrical power. We propose a damper model in which the damping coefficient changes according to both the response of the damper and control forces based on an LQG feedback and feedforward control theory. It is demonstrated from the results of a series of simulations that the both passive device and semi-active device can effectively reduce the response of the structure in various earthquake motions.Copyright