STUDY ON OUTPUT ERROR OF SUBSTRUCTURAL SYSTEM INDUCED BY LOCAL DAMAGES OF STRUCTURES

In order to make a decision of necessity of evacuation and repair of the buildings after large earthquakes, information about damaged structural member existence and its location are extremely significant. Since damage to the structure is inherently local, when considering the damage detection by sensor information deployed in buildings, the local scale damage detection framework with high density and large number of sensors can be expected high sensitivity to damages, and also identify damage location. Recent technological advancement of small and low-cost MEMS type sensors and wireless data transmission bring such the local damage detection framework into reality. So, we have proposed substructure-based local damage detection method, which assumes a dense array of sensor instrumentation to a structure. The proposed method divides the whole structure into a set of small virtual substructures consisting of beams and columns. Then, detects local damage existence inside of the substructures using the differences between observation output and simulated output, which called output error, at internal node of the substructure. This paper presents the characteristics of the output errors which are induced by structural damages inside the substructure, which used as a damage index of the substructure. From the analytical studies to general types of substructure, the output error of internal node has been formulated as a function of the boundary nodes inputs and internal node outputs itself. This function is composed of only the transfer functions inside the substructure. This means that this function can be configured with only the dynamical characteristics and damage state of the substructure and is independent of the characteristics of the other part of the whole structure, so the output error can be used as a damage index of substructure. Based on these functions, numerical studies to a simple beam and column model have been conducted. The results show that an increase of the output error by structural damages occurs most stable in the rotational direction, especially in the low frequency range which is dominant in vibration of buildings. Therefore, it is desirable to use a rotational direction component of the sensor output to damage detection of substructure. It also shows that the output error will increase when the substructure has multi or heavy damages. Using the seismic response analysis results for the whole structure, the output error of substructure