Structural health monitoring systems are being recognized as effective tools to minimize maintenance costs for civil infrastructures. Recently, many damage evaluation methods for the systems have been proposed. In this paper, a novel monitoring system that uses a hybrid sensor and a new damage detection algorithm is proposed. At first, a hybrid FBG sensor for monitoring strain and acceleration is proposed. The sensor consists of an FBG element and a mass to form a vibration system. Performance evaluation was carried out through the strain and acceleration measurement experiments using the prototype sensor. Then, a new damage detection algorithm based upon combined use of natural frequency and strain as damage indexes is proposed. Strain information was used as a substitute for natural frequencies of higher modes. Many damage scenarios for a moment-resistant frame were tested for verifying the performance of this algorithm. The results show that the sensitivities of strain and natural frequency are significantly different. Based on this finding, damage position identification was carried out with the help of support vector machines (SVM). It is confirmed that combined use of natural frequency and strain measurement enhances the performance of the SVMs.

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The purpose of this paper is to evaluate the relationship between average shear-wave velocity of the ground (AVS) and the site amplification factor (AF). A method for computing the relation by using the peak ground motions recorded at nearby station pairs is proposed. The method is applied to the strong motion records during several large earthquakes such as the 2000 Tottori-ken Seibu earthquake and the 2001 Geiyo earthquake. In terms of shear strain in surface soils, the effect of nonlinearity on the relation is examined. On the basis of the results, an empirical equation for predicting the AF in terms of AVS, which considers the nonlinear effect of the ground, is proposed.

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We improved additional correction terms for empirical attenuation relations to represent anomalous seismic intensity of subduction zone. New additional terms for the empirical attenuation relations by Kanno et al.(2005) were determined not only for peak values but also for response spectra. We introduced distance from the volcanic front, instead of the trench axis, to observation site as a new parameter of the correction term, which is reflecting anomalous Q structure beneath northeast Japan, and the distance from volcanic front was a better explanation than the distance from trench. The coverage of the correction terms extended up to longitude 138 degree east. We also inspected dependence on source characteristics between interplate and intraslab events. The dependence of ground motion amplitude on the event category was considerable, even without the focal depth identification.

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