Yoshikazu Kobayashi

Influence of Elastomeric Bearings on Traffic-Induced Vibration of Highway Bridges

Elastomeric bearings (rubber bearings) have been used in highway pseudo-continuous bridges without joints changed from simple girders to reduce the environmental influence of traffic-induced vibration. In addition, elastomeric bearings have been adopted in simple girder bridges for base isolation systems of earthquakeproof structures. Three-dimensional analysis of dynamic response of bridges under moving vehicles is carried out to examine the change of dynamic response in bridges caused by replacing steel bearings with elastomeric bearings. Analytical results are compared with experimental results in urban highway bridges. It is not shown clearly in experiments that natural frequencies are changed slightly in analysis by replacing steel with elastomeric bearings. Although vertical displacements of main girders at the span center do not almost change between steel and elastomeric bearings, horizontal displacement in the bridge axis direction becomes larger with elastomeric bearings. For the evaluation of the experimental acceleration of the ground motion, the dynamic reaction force is analyzed and the dynamic influence is investigated.

Large-scale evaluation of concrete repair by three-dimensional elastic-wave-based visualization technique

The development of elastic wave tomography technique using three-dimensional ray tracing and identification algorithm is discussed. The technique introduces hexahedral elements for isoparametric mapping of irregular structural shapes, for which the distribution of slowness of ray path is computed using simultaneous iterative reconstruction technique. In addition, the three-dimensional computation capability of the technique facilitates detailed assessment of any cross section within the measured perimeter, which is a main advantage compared to the more conventional two-dimensional elastic wave tomography. The newly developed technique was applied for evaluating the repair of concrete piers of a water intake facility by taking the transit time of primary waves (P-waves) as data for reconstruction of velocity distribution of the measured region. In this particular field implementation, multichannel elastic wave tomography measurements were carried out at selected areas on the piers before and after the repair to study the change of velocity distribution. Simple quantitative analysis for improvement of concrete Young’s modulus due to the repair was also examined. Findings obtained from field measurement and analysis confirmed the usefulness of the technique for large-scale in situ implementations.

Three dimensional analysis on lateral flow of liquefied ground and its mitigation by sheet pile walls

Since the design policy of countermeasures to liquefaction is currently prevention of liquefaction, conventional liquefaction analysis aims to predict the possibility of liquefaction at a target site. However, quantitative prediction of ground flow by liquefaction has been studied for new design policy that allows the deformation of liquefied ground if it is not critical. This paper presents a method for prediction of the ground deformation related liquefaction by viscous fluid model. Furthermore, the mitigation effect of a sheet pile wall is assessed by modeling a sheet pile wall as an elastic beam.