Riki Honda

Ground strain measuring system using optical fiber sensors

It is essential to study the dynamic behavior of the soil to make clear the characteristics of ground behavior during earthquake. However, the relationship between the dynamic characteristics and the strain of the soil is not completely studied, because there is no device to measure the strain of the real ground directly. Therefore, it is necessary to develop the ground strain measuring system which can be applied to the real ground. This study presents a system to measure the ground strain, using the fiber Bragg grating (FBG) sensors. Using optical fiber sensor makes the devices simple in mechanism and highly durable. We improve the strain measuring device which was proposed by Sato et al. and also develop a new strain measuring device based on a different mechanism. Their applicability is studied in the experiments. The results in the experiment indicate that it is possible to measure the ground strain by the presented systems with the same level of accuracy as that of the systems by Sato et al. It is also important to recognize the necessity to improve the accuracy.

Challenges in Build-Back-Better Housing Reconstruction Programs for Coastal Disaster Management: Case of Tacloban City, Philippines

Following typhoon Haiyan in November 2013, the government of the Philippines organized massive housing reconstruction programs that are currently facing complex implementation issues. The present study investigated the mechanisms of three types of housing reconstruction programs (i.e. owner-driven on-site reconstruction, community-driven off-site relocation and contractor-driven off-site relocation) and discussed sustainability challenges by assessing the gaps between community needs and program performance, measured through the level of beneficiary satisfaction. The study conducted semi-structured questionnaire surveys with beneficiary households and key informant interviews with government officials and nongovernment organization representatives in March 2015. Results showed that on-site reconstruction was delayed due to insufficient and poorly implemented assistance schemes relating to reconstruction (e.g. materials, skills training), while off-site relocation was delayed by prolonged land acquisition and subcontracting issues. Disruption of critical infrastructure, such as water utility services, and lack of livelihood opportunities significantly affected the satisfaction levels of respondents with the recovery progress. The study also found that the no-dwelling-zone policy was not strictly enforced as houses were still being rebuilt in high-risk areas near the coast. Finally permanently relocated residents continue to struggle, especially with regard to their source of livelihood, as relocation sites are inaccessible and located away from employment opportunities.

Design Input Motion Synthesis Considering the Effect of Uncertainty in Structural and Seismic Parameters by Feature Indexes

Various aspects of earthquakes and structures have inherent uncertainty, and this consideration is essential for seismic design. It makes the input ground-motion selection for seismic design a difficult task, especially when nonlinear dynamic analysis of the structure is utilized. This paper presents a simple scheme to deal with the problem. First, a set of possible ground motions that reflects the effect of uncertainty is considered. The set is described by feature indexes that take into consideration the effect of ground motions on structural behaviors. Second, the ground motion that represents the set in terms of the feature indexes is synthesized as a design ground motion. A scheme to synthesize a ground motion to represent the set is also presented. The ground motion is synthesized by iteratively modifying its time-frequency characteristics using wavelet functions to improve the values of feature indexes. As numerical simulations, design ground motion for a pier structure is synthesized considering u...

Synthesis of representative wave of spectrum-fitting input motions based on iterative learning procedure

In the synthesis of input motions for seismic design based on the specified response spectra, Fourier amplitude is elaborately adjusted, while little attention is paid to the time characteristics, although differences in the phase characteristics can cause different nonlinear response of structures. To consider this problem, we propose a scheme to synthesise a wave that represents a set of collected spectrum-fitting ground motions, using an iterative learning scheme to integrate their respective characteristics. In the learning process, the characteristics of the wave are updated by adjusting its time-frequency characteristics using wavelet transform. The learning efficiency is monitored by comparing the characteristic effects of the waves on structures before and after the update, at which point the difference is quantified via Kullbuck-Leibler divergence. Numerical results show that synthesised waves cause comparatively large responses on various nonlinear structural members of a target structure, which indicates the effectiveness of the proposed scheme.