Intensity Of Earthquake Motion Research Articles

Experimental study on seismic responses of tuned mass damper-applied real-scale piping system via shaking table tests

To secure the nuclear power plant (NPP) safety, it is essential to improve the seismic performance of piping systems. Accordingly, to achieve this purpose effectively, applying a tuned mass damper (TMD) to the NPP piping system has been attempted, but this is mostly limited to numerical analysis studies. Therefore, this study aimed to prove the TMD effect of reducing seismic responses of the real-scale NPP piping system through shaking table tests. As a result, it was confirmed that the TMD suppressed target and higher-order mode responses of the piping through the shaking table tests. In particular, the response control effects of the target mode and the higher-order mode were more pronounced when the earthquake motion intensity was larger. The application of the TMD showed reducing relative displacement responses in the harmonic motion excitation by about 80%-90%. This reduced peak relative displacement and normal stress responses by 33%-42% and 25%-37% on average, respectively, under random vibration excitation. Under the seismic excitation, peak relative displacement and normal stress responses were reduced by 7%-14% and 5%-27% on average, respectively. Finally, piping and piping-TMD finite element analysis models were successfully created and validated based on the shaking table test results.

Shaking table test and numerical analysis of nuclear piping under low- and high-frequency earthquake motions

A nuclear power plant (NPP) piping is designed against low-frequency earthquakes. However, earthquakes that can occur at NPP sites in the eastern part of the United States, northern Europe, and Korea are high-frequency earthquakes. Therefore, this study conducts bi-directional shaking table tests on actual-scale NPP piping and studies the response characteristics of low- and high-frequency earthquake motions. Such response characteristics are analyzed by comparing several responses that occur in the piping. Also, based on the test results, a piping numerical analysis model is developed and validated. The piping seismic performance under high-frequency earthquakes is derived. Consequently, the high-frequency excitation caused a large amplification in the measured peak acceleration responses compared to the low-frequency excitation. Conversely, concerning relative displacements, strains, and normal stresses, low-frequency excitation responses were larger than high-frequency excitation responses. Main peak relative displacements and peak normal stresses were 60%–69% and 24%–49% smaller in the high-frequency earthquake response than the low-frequency earthquake response. This phenomenon was noticeable when the earthquake motion intensity was large. The piping numerical model simulated the main natural frequencies and relative displacement responses well. Finally, for the stress limit state, the seismic performance for high-frequency earthquakes was about 2.7 times greater than for low-frequency earthquakes.

Effects of pulse-like earthquake motions on a typical subway station structure obtained in shaking-table tests

A series of large-scale shaking table tests on a typical subway station structure were carried out for pulse-like earthquake motions. The propagation of earthquake motions in soils is explored. The effects of velocity pulse parameters (i.e., pulse shape, pulse frequency (fp), and pulse duration (Tpd)) on dynamic responses of the structure are analyzed from the viewpoint of the dynamic characteristics of soils. It is found that the site amplifies the frequency components of dynamic excitation in specific frequency bands (i.e., the amplification frequency band, AFB). With an increase in earthquake motion intensity, the AFB gradually moves towards low frequencies. Additionally, the bandwidth gradually narrows. The velocity pulse increases the amplitude of the first-mode shear deformation of soils and thus the seismic internal force response of underground structures. In addition, the effect of a one-sided pulse in terms of increasing the first-order shear deformation amplitude of soil is more pronounced than the effect of a two-sided pulse. Pulse-like earthquake motions with long pulse duration and multiple pulse cycles may trigger remarkable resonance-like phenomena of soils and further aggravate soil and structure responses when the main pulse frequencies are located in the AFB of soils.

2006年ジャワ島中部地震で被災したインドネシア伝統木造建築物の耐震性評価

This paper reports the results of the analysis for traditional wooden houses at Kotagede near Yogyakarta which damaged by 2006 Central Java Earthquake based on field survey, static loading test for mock test frames and evaluation of seismic motion intensity. Major findings are as follows: (1) In the field survey, structural and vibration characteristics are clarified. (2) In the experiment, horizontal resistance force is influenced by beam-to-column joint specifications. (3) Using proposed modeling method for the traditional frameworks, earthquake motion intensity at Kotagede is estimated at PGA=250cm/s2 based on the seismic performance evaluation of damaged houses.

Effects of Site Classification on Platform Value of Response Spectrum

Regarding the design response spectrum in the code for seismic design of buildings as target spectra，the 28 acceleration histories are formed artificially．They are used as the inputs ground motion in earthquake response analysis．Four site classifications profiles were selected or constructed from practical site profiles．With the use of 1-D equivalent linearization wave motion method that is wildly used at present in site seismic response analysis, the platform values of surface response spectrum for different profiles under different ground motion inputs were calculated．Different platform values of the response spectrum and relational expression which is seven input earthquake motion intensity and site classifications have been given by statistical analysis.

Evaluation of seismic response of soft-storey infilled frames

In this study two single-bay, three-storey space frames, one with brick masonry infill in the second and third floors representing a soft-storey frame and the other without infill were designed and their 1:3 scale models were constructed according to non-seismic detailing and the similitude law. The models were excited with an intensity of earthquake motion as specified in the form of response spectrum in Indian seismic code IS 1893-2002 using a shake table. The seismic responses of the soft-storey frame such as fundamental frequency, mode shape, base shear and stiffness were compared with that of the bare frame. It was observed that the presence of open ground floor in the soft-storey infilled frame reduced the natural frequency by 30%. The shear demand in the soft-storey frame was found to be more than two and a half times greater than that in the bare frame. From the mode shape it was found that, the bare frame vibrated in the flexure mode whereas the soft-storey frame vibrated in the shear mode. The frames were tested to failure and the damaged soft-storey frame was retrofitted with concrete jacketing and, subjected to same earthquake motions as the original frames. Pushover analysis was carried out using the software package SAP 2000 to validate the test results. The performance point was obtained for all the frames under study, therefore the frames were found to be adequate for gravity loads and moderate earthquakes. It was concluded that the global nonlinear seismic response of reinforced concrete frames with masonry infill can be adequately simulated using static nonlinear pushover analysis.

Development of new drain method for protection of existing pile foundations from liquefaction effects

Pile foundation as well as other underground structures could be seriously affected by soil liquefaction during strong earthquakes. Damages on pile foundation due to liquefaction can be reduced by implementation of some soil improvement method. Main objective of present study is developing of drain method that can improve the soil in order to mitigate the destructiveness of liquefaction on superstructure supported by pile foundation. Series of shaking table tests were conducted on 2×2 pile foundation and soil model was improved by drains. Configurations of drains around piles, intensity of shaking were one of the parameters that were changing during the tests in order to investigate the response of pile foundation in improved soil condition. Shaking table tests and performed On-site experiment showed the following effects of the new drain method. (1) When the intensity of earthquake motion is 200 gal or less, generation of excess pore water pressure is reduced and the pile bending moment is decreased, (2) when the intensity of earthquake motion is stronger (300 gal or more), drainage effect prevents disappearance of subgrade reaction, and (3) proposed new type of drain can control excess pore water pressure without clogging.