Yozo Fujino

Base isolation system with shape memory alloy device for elevated highway bridges

Base isolation provides a very effective passive method of protecting bridges from the hazard of earthquakes. The proposed smart isolation system combines a laminated rubber bearing with a device made of shape memory alloy (SMA). The smart base isolation utilizes the different responses of the SMA at different levels of strain to control the displacements of the rubber bearing at various excitation levels. At the same time the hysteresis of the alloy is used to increase the energy dissipation capacity.

Pounding of superstructure segments in isolated elevated bridge during earthquakes

Past severe earthquakes indicate that pounding may cause considerable damage or even lead to collapse of colliding structures. The aim of this paper is to present an analysis of pounding between superstructure segments of an isolated elevated bridge induced by the propagating seismic wave. High-damping rubber bearings (HDRBs), used as isolation devices, are modelled by proposed non-linear formulation and the significance of the bearings model for pounding is indicated. The results of the study show that pounding leads to the increase or decrease of the forces acting on piers, depending on the gap size between superstructure segments.

Reduction of pounding effects in elevated bridges during earthquakes

Pounding of adjacent superstructure segments in elevated bridges during severe earthquakes can result in significant structural damage. The aim of this paper is to analyse several methods of reduction of the negative effects of collisions induced by the seismic wave propagation effect. The analysis is conducted on a detailed three-dimensional structural component model of an isolated highway bridge. The results show that the influence of pounding on the structural response is significant in the longitudinal direction of the bridge and significantly depends on the gap size between superstructure segments. The smallest response can be obtained for very small gap sizes and for gap sizes large enough to prevent pounding. Further analysis indicates that the bridge behaviour can be effectively improved by placing hard rubber bumpers between segments and by stiff linking the segments one with another. The experimental results show that, for the practical application of such connectors, shock transmission units can be used. Copyright

An experimental and analytical study of autoparametric resonance in a 3DOF model of cable-stayed-beam

Autoparametric interaction and the associated phenomenon of amplitude saturation are experimentally observed in a physical model of cable-and-beam structure. In this system, the horizontal beam is fixed at one end and supported at the other end by an inclined taut cable. The longitudinal axes of beam and cable are in a vertical plane. Three natural frequencies of the system are approximately of the ratio 1:1:2. This is a combination of two conditions that are very likely to occur in relatively long-span, multi-stay-cable bridges, namely, 1:1 tuning and 1:2 superharmonic tuning. While the beam is vertically excited with sufficiently large force near a primary resonance, the cable vibrates horizontally at half of excitation frequency. The beam also vibrates horizontally at half-frequency, as well as vertically. As the vertical excitation on the bean is further increased in amplitude, the vertical vibration amplitude gets saturated instead of increasing proportionately. A 3DOF analytical model of the structure is also derived, where the finite motion of the cable introduces geometric nonlinearities in quadratic and cubic forms. The system parameters having been carefully measured from the experimental model, steady-state solutions of the coupled nonlinear equations of motion are obtained, by the perturbation method of multiple time scales. Agreement between experimental observation and analytical prediction is very good, both qualitatively and quantitatively. Very good agreement is found also in the case of horizontal excitation of the beam, where effects of linear and nonlinear interaction are apparent.

Effectiveness of semi-active tuned mass dampers under harmonic excitation

The control effectiveness of a semi-active tuned mass damper (STMD) with variable damping under harmonic excitation is studied. An optimal control law governing the variation of damping of the damper is derived using the optimal control theory. A situation in which the damping can be varied within a certain range is included. Employing the numerical technique, the responses of a single-degree-of-freedom (SDOF) structure coupled with an STMD are investigated. The control effectiveness of the STMD is evaluated by comparing the structures transient and steady-state responses with those of the structure coupled with a tuned mass damper (TMD). It is found that, under harmonic excitation, the vibration suppression by an STMD is significantly superior to that of a conventional passive TMD in both transient and steady-state responses. This improvement is equivalent to an increase of the TMDs mass by about four times.

Concrete Crack Detection by Multiple Sequential Image Filtering

This article presents a new robust automated image processing method for detecting cracks in surface images of concrete structures. This method involves two steps: (1) development of an image filter for detecting major cracks using genetic programming (GP), and (2) elimination of residual noise after filtering and detection of indistinct cracks by iterative applications of the image filter to the local regions surrounding the cracks. The proposed method can be used for the accurate detection of cracks in surface images recorded under various conditions. Moreover, the widths of the detected cracks can be quantified on the basis of the spatial derivatives of the brightness patterns. The estimated crack widths are in good agreement with those measured manually. The paper shows how research on structural health monitoring of bridges and structures has received significant attention in recent years.

Active Stiffness Control of Cable Vibration

Changing the tension as a positive use of parametric excitation is studied. An optimal algorithm is obtained from energy analysis and verified by experiment on a scale model

Quantitative health monitoring of bolted joints using a piezoceramic actuator–sensor

The non-destructive evaluation technique using a piezoceramic (PZT) as an actuator–sensor has a potential to efficiently detect structural damage. In this technique, a PZT actuator–sensor patch is bonded on a structure. Through the measurement of its electrical impedance, which is related to the mechanical impedance of the structure being bonded, the change in structural properties due to damage can be detected. This paper presents the use of a PZT actuator–sensor in conjunction with numerical model-based methodology in structural health monitoring to quantitatively detect damage of bolted joints. The structure used in this study consists of two aluminium beams connected by a bolted joint. The damage was simulated by loosening the bolts. To quantitatively monitor the damage, a numerical model of the structure was formulated. A spectral element method (SEM), based on a wave propagation approach, was used to model the structure. A bonded-PZT beam and a bolted joint element were developed by using the SEM. The equations of motion were derived by using Hamiltons principle and then the spectral element matrices were formulated. Experimental results show the effectiveness of this method to detect the damage. By using the proposed model, the loosening of bolts can be quantitatively identified as the change in stiffness and damping at the bolted joint, indicating a high potential of this method in order to quantitatively monitor structural damage.

Vibration, control and monitoring of long-span bridges—recent research, developments and practice in Japan

Abstract This paper discusses vibration, control and monitoring of long-span bridges, in particular, of cable-supported bridges with emphasis on recent research, developments and practice in Japan. Primary stress is placed on the vibration due to motion-dependent forces such as wind-induced aerodynamic forces and its control. Implementation of passive and active control in the long-span bridges in Japan is described. In the last part of the paper, importance and usefulness of vibration monitoring of long-span bridges is discussed with an actual example.

Investigation of semi-active control for seismic protection of elevated highway bridges

Abstract The applicability of semi-active control for seismic protection of elevated highway bridges is investigated through comparison with active and passive systems. A bridge pier–bearing–deck structure is modeled as a linear two-degree-of-freedom system and three design goals are studied: reduction of pier response, reduction of bearing response and reduction of both responses. The passive system is assumed to have a high-damping rubber bearing and linear quadratic regulator (LQR) control is used for the active system. Normalized peak displacements are used to optimize bearing damping and LQR parameters. LQR-based clipped optimal control is used to command a magneto-rheological (MR) damper in semi-active control, where the MR damper is designed according to deterministic analysis of the active system. Numerical simulations show that semi-active control can reach active control performance if the design goal is to reduce bearing response, while it shows similar behavior to the passive system if the design goal is to reduce pier response. All strategies showed similar performance for the reduction of both responses.