Numerical Modeling of Massive Timber Piles Supporting Double-Span Stone Arch Bridge Damaged in 2011 Great East Japan Earthquake

Abstract

Tokiwa Bridge is a double-span stone arch bridge constructed in 1877 in Tokyo designated as a national cultural artifact. Tokiwa Bridge is supported by a timber pile foundation consisting of hundreds of tapered pinewood piles installed in the clayey layer. This feature of the foundation is different from that of stone arch bridges in other areas where the spread foundation is set directly on the rock. Tokiwa Bridge was damaged in the 2011 Great East Japan Earthquake and is currently undergoing seismic retrofit designed to improve its seismic performance while preserving the original timber pile foundation of the bridge. The authors are providing technical support for this project by evaluating the seismic performance of Tokiwa Bridge before and after the ongoing retrofit construction. Although the seismic performance of Tokiwa Bridge should be evaluated through dynamic analysis targeting the whole bridge system, it is difficult to model all the piles due to the limitation of numerical capacity and its complexity. In this study, therefore, a reasonable model was developed for the piled foundation that would not consider piles individually and treat timber piles as an area of hypothetical ground improvement, since the pile arrangement is irregular and the piles are of inconsistent size, shape, and condition. By comparing the results of these results to an analysis considering individual timber piles under pushover analysis conditions the applicability of the numerical model was confirmed.