Structural Performance Assessment Based on Statistical and Wavelet Analysis of Acceleration Measurements of a Building during an Earthquake

This study introduces the analysis of structural health monitoring (SHM) system based on acceleration measurements during an earthquake. The SHM system is applied to assess the performance investigation of the administration building in Seoul National University of Education, South Korea. The statistical and wavelet analysis methods are applied to investigate and assess the performance of the building during an earthquake shaking which took place on March 31, 2014. The results indicate that (1) the acceleration, displacement, and torsional responses of the roof recording point on the top floor of the building are more dominant in theXdirection; (2) the rotation of the building has occurred at the base recording point; (3) 95% of the energy content of the building response is shown in the dominant frequency range (6.25–25 Hz); (4) the wavelet spectrum illustrates that the roof vibration is more obvious and dominant during the shaking; and (5) the wavelet spectrum reveals the elasticity responses of the structure during the earthquake shaking.

The neighbouring vibrating ‘multiple water-bag’ plasma potential and related aspects

The spatial factor Φ(x) of the vibratory-state MWB (‘multiple water-bag’) plasma potential Φ = Φ(x) exp (- iwt) in the vicinity of its generating electric charge rgr;(x) exp (- iwt) is proved to be the Poisson potential U(x) of ρ plus an error function ξ(x) whose magnitude can be rendered as small as desired, in relation to │Φ(x)│, by locating the recording point sufficiently close to the charge. How close this should be is independent of ρ, but depends quantitatively on the MWB model and the frequency ω, and qualitatively on whether the frequency of the vibrations is greater or less than the plasma frequency. A high vibration frequency reinforces accuracy in the Poissonian approximation. The question as to whether Φ is weaker or stronger than U(x) is tacked. Shielding efficiency is explored in the vibratory state.

CONVERTED WAVES IN REFRACTION SURVEYS OVER MARKERS WITH VARIABLE DEPTH

Converted head waves are observed sufficiently often in crustal and other refraction surveys to raise interesting questions as to their possibilities in interpretation. Some simple cases are examined in which sequences of P, S, and converted head waves are assumed to be observed over a two‐ and a three‐layer medium. Investigation is made of the theoretical requirements in terms of numbers of shot and recording points, and the number of members in the sequence, to allow calculation of layer velocities and thicknesses when there is low to moderate structure on the interfaces. It is found that as few as a single shot and a single recording point, and two, three, or four members of a sequence are sufficient to allow determination of some or all of the P and S velocities in the layers, and the depths to the layers below shot and recording point. How far these possibilities can be realized in practice is dependent on the development of techniques to produce and observe converted waves consistently in refraction surveys. To what extent this can be done is at present little known, and is a matter for future research. If converted waves can be used regularly in refraction work, some operational advantages might result as follows. Because of the decrease in the number of shot and recording points necessary to derive velocities and depths when sequences of head waves are observed, it is possible either to gather usable data with minimum effort, or, if a more elaborate array of points is used, to achieve greater detail regarding the lateral variation in velocity and depth over what would have been obtained from a single wave type.