Deconvolution interferometry has been receiving increasing attention in structural system identification and health monitoring, due to its robustness when applied to real structures and data, sensitivity to damage and smaller sensitivity to effects of the supporting soil. At its current stage of development, deconvolution interferometry is applied to detect vertically propagating waves, associated with lateral deflection of the structure as a whole, identify their velocity along the height, and detect changes in velocity possibly caused by damage.
The first part of this study presents results for vertical wave velocities in a set of 16 instrumented buildings in California, identified by an algorithm, developed earlier by the authors for rapid assessment of the structural integrity following an earthquake using data from accelerometers. This algorithm fits a piecewise uniform shear beam in the observed response by matching, in the least squares sense, pulses in impulse response functions. The preliminary set of buildings analyzed comprises mid-rise and high-rise concrete and steel frame structures, which are classified by height, structural material and lateral force resisting system. For this study, an equivalent uniform shear beam is fitted, with the objective to get insight into the distribution of values of the equivalent velocity over different types of structures. The results show that the dependence of the identified wave velocity is the strongest on the type of lateral resisting system (i.e., if shear walls are present), and the weakest on the building height.
The second part of this study presents an application of the wave method for structural system identification to localize earthquake induced damage in a full-scale slice of a 7-story reinforced concrete (RC) shear wall test structure. The method considers buildings as vertical waveguides consisting of stacked slices of a Timoshenko Beam (TB). The method identifies the shear and longitudinal velocities of vertically propagating waves in the slices (layers) by fitting the observed impulse response functions computed from recorded response similar to how we have done so previously for the shear beam model. A methodology that can robustly and accurately detect damage and its location in a structure will be useful for post-earthquake rapid damage assessment of buildings, specifically in tall buildings. For this study, a 4-layer TB (representing each story or a group of two or three stories, respectively) is fitted into the recorded acceleration response of the test building. The 7-story test building was shaken by four earthquake motions with increasing intensities. The four earthquakes induced light damage (first event) up to severe damage (fourth event) to the structure progressively. Ambient vibration tests were performed following each earthquake representing the post-earthquake state of the building. We qualitatively ranked structural damage incurred by each story of the building as light, moderate or severe according to available on-site damage inspections. The layered Timoshenko Beam was identified by fitting the recorded ambient vibration responses at the building’s floors. The aim was to monitor reductions in the estimated beam’s shear and longitudinal wave velocities at each layer (i.e., floor) which were shown to be sensitive to damage. These reductions are compared with actual extent of damage observed at different stories of the building. The results show that: 1) The reducing trends in the estimated wave velocities are consistent with the true extent of damage during each earthquake. It is shown that the most significant reduction in the calculated velocities occurred after the last earthquake shaking which is consistent with on-site observations, 2) The most significant reduction in wave velocities among the beam’s layers occurred at the first story which is consistent with the surveyed overall damage along the height of the building, This also shows that the fitted TB can accurately identify the location of most significant damage, 3) In addition, the identified layered TB shows that the extent of shear and bending deformations of the layers vary along the height of the building, with top layers (i.e., 3rd to 7th stories) deforming more in bending while the bottom two layers (1st and 2nd stories) deforming predominantly in shear.
|Commitee:||Terzic, Vesna, Calabrese, Andrea|
|School:||California State University, Long Beach|
|Department:||Civil Engineering & Construction Engineering Management|
|School Location:||United States -- California|
|Source:||MAI 82/4(E), Masters Abstracts International|
|Subjects:||Civil engineering, Engineering|
|Keywords:||Wave methods, Shear Beam Model, Timoshenko Beam Model|
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