Centrifuge Tests and Simple Analyses for Seismic Soil-Structure Interaction

Dynamic centrifuge tests were performed on a superstructure-footing model that was placed on a dry sand surface and subjected to two different input motions having peak accelerations of 60 cm/s2 and 249 cm/s2. Two simple analyses, equivalent linear analysis (SHAKE) and dynamic response of a structure using a sway-rocking model (SR-model) were performed. The following conclusions were drawn: (1) SHAKE and SR-model analyses can simulate the recorded response of the soil and superstructure. However, the shear wave velocity of the ground that can simulate the superstructure response by an SR-model for amax=249 cm/s2 is much smaller than that of the free field estimated using SHAKE. (2) The observed relation of the base friction force with relative displacement between the footing base and the ground surface shows strong nonlinearity when amax=249 cm/s2, which probably results from the large shear deformation of the thin layer beneath the footing

Liquefaction Potential Evaluation Based on Rayleigh Wave Investigation and Its Comparison with Field Behavior

A simplified method is presented for evaluating liquefaction potential of sand deposits using shear wave velocity. Effectiveness of the proposed method is evaluated through field tests at 17 sites in Niigata city where field performance during the 1964 Niigata earthquake is known. A modified version of steady state Rayleigh wave method is used in which the amplitude ratio between vertical and horizontal ground surface motions can be measured in addition to the phase velocity. Based on the measured phase velocity vs. wavelength relationship, shear wave velocity profile is determined using an inverse analysis. The liquefaction potential of each site is then evaluated using the shear wave velocity. The estimated results are reasonably consistent with the actual field behavior during the earthquake, indicating that the proposed method is effective

Mapping dust column density in dark clouds by using NIR scattered light : Case of the Lupus 3 dark cloud

We present a method of mapping dust column density in dark clouds by using near-infrared scattered light. Our observations of the Lupus 3 dark cloud indicate that there is a well defined relation between (1) the H-Ks color of an individual star behind the cloud, i.e., dust column density, and (2) the surface brightness of scattered light toward the star in each of the J, H, and Ks bands. In the relation, the surface brightnesses increase at low H-Ks colors, then saturate and decrease with increasing H-Ks. Using a simple one-dimensional radiation transfer model, we derive empirical equations which plausibly represent the observed relationship between the surface brightness and the dust column density. By using the empirical equations, we estimate dust column density of the cloud for any directions toward which even no background stars are seen. We obtain a dust column density map with a pixel scale of 2.3 x 2.3 arcsec^2 and a large dynamic range up to Av = 50 mag. Compared to the previous studies by Juvela et al., this study is the first to use color excess of the background stars for calibration of the empirical relationship and to apply the empirical relationship beyond the point where surface brightness starts to decrease with increasing column density

Detection of Dishonest Entities

This paper discusses mechanisms to identify dishonest users of services provided by a server in environments where identities of honest users must be kept as their secrets. An anonymous token based mechanism enables the server to identify dishonest users when dishonest events are detected while the users are receiving services, and a homomorhic anonymous token based one enables that even dishonest events can be detected only after the server completed their services and the users had left from the server. A linear equation based encryption algorithm that is used for implementing the above methods is also enhanced

Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands

We have determined the ratios of total to selective extinction directly from observations in the optical V band and near-infrared J band toward the Galactic center. The OGLE (Optical Gravitational Lensing Experiment) Galactic bulge fields have been observed with the SIRIUS camera on the IRSF telescope, and we obtain A(V)/E(V-J)=1.251+-0.014 and A(J)/E(V-J)=0.225+-0.007. From these ratios, we have derived A(J)/A(V) = 0.188+-0.005; if we combine A(J)/A(V) with the near-infrared extinction ratios obtained by Nishiyama et al. for more reddened fields near the Galactic center, we get A(V) : A(J) : A(H) : A(Ks) = 1 : 0.188 : 0.108 : 0.062, which implies steeply declining extinction toward the longer wavelengths. In particular, it is striking that the Ks band extinction is \approx 1/16 of the visual extinction A(V) much smaller than one tenth of A(V) so far employed.Comment: 8 pages, 7 figures, Accepted for publication in Ap

Earth Pressure Acting on Embedded Footing During Soil Liquefaction by Large-Scaling Shaking Table Test

Shaking table tests are conducted using a large-scale laminar shear box to investigate the effects of non-liquefied crust overlying liquefied soils on an embedded footing. It is shown that (1) The total earth pressure before liquefaction is induced mainly by the inertia force of the building. The shear force at the pile heads corresponds to the difference between the total earth pressure and the inertial force; (2) The total earth pressure after liquefaction is induced mainly by the soil deformation. The shear force at the pile heads car responds to the sum of the total earth pressure and the inertial force of the building; (3) The relation between the relative displacement and the total earth pressure is linear before liquefaction. It becomes nonlinear with the development of pore water pressure and the total earth pressure decreases with cyclic loading after liquefaction; (4) The peak value of the total earth pressure for the super-structure with a low natural frequency is larger than that with a high natural frequency. This is probably because the inertial force of the super - structure with a low natural frequency may interrupt the response of the footing that tends to move with the ground

Preliminary Report on the Geotechnical Aspects of the Philippine Earthquake of July 16, 1990

The Philippine earthquake of July 16, 1990 (MS = 7.8), of which epicenter is about 100 km north of Manila city, was one of the most costly single natural disasters in Philippine history. The loss of life of over 1,600 persons resulted. Extensive damage to buildings, roads, embankments, natural slopes, and bridges was observed in a widespread area of approximately 20,000 square kilometers. One of the major causes of the damage was liquefaction of various sandy soils including artificially fills, alluvial deposits of river delta, and sandbars. This paper presents a preliminary overview of damage aspects of the earthquake, with emphasis on liquefaction-induced damage of various structures

Considerations to Damage Patterns in the Marina District During the Loma Prieta Earthquake Based on Rayleigh Wave Investigation

Rayleigh wave investigation is made in the Marina District to study geotechnical factors controlling the damage patterns in the Loma Prieta earthquake. A portable system has been developed for determining a Rayleigh wave dispersion curve based on the measurements of artificially induced ground vibration or microtremor. Five sites are selected along a line crossing the hydraulic fill zone in which structures and/or buried utilities were significantly damaged. An inverse analysis on the measured dispersion curves results in a cross section of shear wave velocity profiles in the District. Site amplification and liquefaction potential of each site are estimated and discussed based on the Vs-profiles. It is shown that soil liquefaction is likely to have occurred throughout the fill zone, and that the predominant period of ground motions in the zone of structural damage is longer than and closer to the natural period of structures with soft first story than that in the non-damaged zone. These results appear to be consistent with the damage patterns in the District, indicating that the proposed investigation is effective for seismic zonation