This paper is concerned with robust strategies to perform a model-based damage detection of multistory buildings effectively. Theoretically, the model-based damage detection can be reasonably carried out through vibration monitoring and system identification. The change in modal properties due to damage is identified accurately by time series model if structural vibrations are measured appropriately. Then, the reduction of local stiffness is estimated correctly from the change in modal properties by using sensitivity equations. However, in practice, it is not an easy task to pinpoint the location and extent of local damage because of noise contamination, system nonlinearity, estimation error, model uncertainty and so on. To overcome these problems, several robust strategies are presented in the model-based damage detection of multistory buildings. The basic idea consists of decreasing the number of physical parameters to be estimated, increasing the number of modal properties with good accuracy, enhancing sensitivity to damage and reducing noise and nonlinear effects. The effectiveness and limitations of these strategies are discussed through a series of shaking table tests of two small-scaled test structures.
Authors propose a method to identify the mass matrix of a large building structure by using a small active dynamic damper, or equivalently, an active tuned mass damper. We modify the acceleration feedback algorithm, which was once developed for improving the dynamic damper's performance, with a different objective. The advantage of the dynamic damper is its size: it is so small that there is a possibility that we could create an extra-small device for measuring the mass of a large structure. We review the physical meaning of the acceleration feedback, and then we use a single-degree-of-freedom model to explain how to operate the device to examine the weight of a primary structure. Then, we extend this method to a multi-degree-of- freedom model so that we can measure its effective modal mass with respect to the location where this device is placed. The identification of the mass matrix of a large structure can be completed as we shift the observing points and determine the associated effective mass. Several numerical studies are also carried out to certify the proposed method.
This paper presents damage detection tests of five-story steel frame with simulated damages. We discuss pre-analytical study and results of experiments. Fiber brag grating (FBG) sensors, accelerometers, strain gauges and laser displacement meters are installed in this test frame. We assume damages by removing studs from only one story, loosening bolts of beams, cutting part of beams and extracting braces from only one story. From the results of pre-analytical study, we can estimate which story is damaged from the change of natural period and mode shape to some extent. We applied flexibility method which is one of a damage identification methods using modal properties. We also apply flexibility method to results of experiments. In some cases we can estimate which story is damaged, and in other cases we cannot. We also applied a method using multiple natural frequency shifts. Making use of the change in five natural frequencies due to damage, the location of damaged stories can be pinpointed. In both methods, we cannot identify damaged story in some cases. Some methods other than methods using modal properties have to be tried to apply in such cases.
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