Dynamic loading tests and seismic response analysis of a stud-type damper composed of multiple friction units with disc springs

This paper presents an experimental study on the performance of a shear-sliding stud-type damper composed of multiple friction units with high-tension bolts and disc springs. A numerical evaluation of the response reduction effects achieved by the stud-type damper is also presented. In dynamic loading tests, the behavior of stud-type multiunit friction damper specimens was investigated. Three different full-scale damper specimens, which were composed of five, six, or seven friction units with two or four sliding surfaces, were incorporated into loading devices for testing. The stud-type friction dampers demonstrated stable rigid-plastic hysteresis loops without any remarkable decrease in the sliding force even when subjected to repetitive loading, in addition to showing no unstable behavior such as lateral buckling. The damper produced a total sliding force approximately proportional to the number of sliding surfaces and friction units. The total sliding force of the stud-type damper can thus be estimated by summing the contributions of each friction unit. In an earthquake response simulation, the control effects achieved by stud-type dampers incorporated into an analytical high-rise building model under various input waves, including long-period, long-duration and pulse-like ground motions, were evaluated. A satisfactory response reduction was obtained by installing the developed stud-type dampers into the main frame without negatively impacting usability and convenience in terms of building planning.     

Hydraulic properties of and pressure-head dynamics in thick pyroclastic-fall deposits in Atsuma,Northern Japan: implications for the role of water in shallow landslides induced by the 2018 Hokkaido Eastern Iburi Earthquake

Landslides - The 2018 Hokkaido Eastern Iburi Earthquake triggered numerous shallow landslides on slopes covered with thick pyroclastic-fall deposits. The landslides occurred more frequently on...     

A novel index to evaluate discretization methods:A case study of flood susceptibility assessment based on random forest

The selection of a suitable discretization method(DM)to discretize spatially continuous variables(SCVs)is critical in ML-based natural hazard susceptibility assessment.However,few studies start to consider the influence due to the selected DMs and how to efficiently select a suitable DM for each SCV.These issues were well addressed in this study.The information loss rate(ILR),an index based on the informa-tion entropy,seems can be used to select optimal DM for each SCV.However,the ILR fails to show the actual influence of discretization because such index only considers the total amount of information of the discretized variables departing from the original SCV.Facing this issue,we propose an index,infor-mation change rate(ICR),that focuses on the changed amount of information due to the discretization based on each cell,enabling the identification of the optimal DM.We develop a case study with Random Forest(training/testing ratio of 7:3)to assess flood susceptibility in Wanan County,China.The area under the curve-based and susceptibility maps-based approaches were presented to compare the ILR and ICR.The results show the ICR-based optimal DMs are more rational than the ILR-based ones in both cases.Moreover,we observed the ILR values are unnaturally small(＜1％),whereas the ICR values are obviously more in line with general recognition(usually 10％-30％).The above results all demonstrate the superiority of the ICR.We consider this study fills up the existing research gaps,improving the ML-based natural hazard susceptibility assessments.     

Liquid bridge contribution to shear behavior of unsaturated soil: modeling and application to a micromechanics model

Acta Geotechnica - Liquid bridges in unsaturated soils attach to grain contacts and contribute to strengthening microscopic bonding forces, which leads to macroscopic high strength and stiffness...     

Fine‐structures of planar deformation features in shocked olivine: A comparison between Martian meteorites and experimentally shocked basalts as an indicator for shock pressure

We performed shock recovery experiments on an olivine‐phyric basalt at shock pressures of 22.2–48.5 GPa to compare with shock features in Martian meteorites (RBT 04261 and NWA 1950). Highly shocked olivine in the recovered basalt at 39.5 and 48.5 GPa shows shock‐induced planar deformation features (PDFs) composed of abundant streaks of defects. Similar PDFs were observed in olivine in RBT 04261 and NWA 1950 while those in NWA 1950 were composed of amorphous lamellae. Based on the present results and previous studies, the width and the abundance of lamellar fine‐structures increased with raising shock pressure. Therefore, these features could be used as shock pressure indicators while the estimated pressures may be lower limits due to no information of temperature dependence. For Martian meteorites that experienced heavy shocks, the minimum peak shock pressures of RBT 04261 and NWA 1950 are estimated to be 39.5–48.5 GPa and 48.5–56 GPa, respectively, which are found consistent with those estimated by postshock temperatures expected by the presence of brown olivine. We also investigated shock‐recovered basalts preheated at 750 and 800 °C in order to check the temperature effects on shock features. The results indicate a reduction in vitrifying pressure of plagioclase and a pressure increase for PDFs formation in olivine. Further temperature‐controlled shock recovery experiments will provide us better constraints to understand and to characterize various features found in natural shock events.     

Petrological,petrofabric, and oxygen isotopic study of five ungrouped meteorites related to brachinites

Northwest Africa (NWA) 6112, Miller Range (MIL) 090206 (plus its pairs: MIL 090340 and MIL 090405), and Divnoe are olivine‐rich ungrouped achondrites. We investigated and compared their petrography, mineralogy, and olivine fabrics. We additionally measured the oxygen isotopic compositions of NWA 6112. They show similar petrography, mineralogy, and oxygen isotopic compositions and we concluded that these five meteorites are brachinite clan meteorites. We found that NWA 6112 and Divnoe had a c axis concentration pattern of olivine fabrics using electron backscattered diffraction (EBSD). NWA 6112 and Divnoe are suggested to have been exposed to magmatic melt flows during their crystallization on their parent body. On the other hand, the three MIL meteorites have b axis concentration patterns of olivine fabrics. This indicates that the three MIL meteorites may be cumulates where compaction of olivine grains was dominant. Alternatively, they formed as residues and were exposed to olivine compaction. The presence of two different olivine fabric patterns implies that the parent body(s) of brachinite clan meteorites experienced diverse igneous processes.     

The earliest stage of Izu rear‐arc volcanism revealed by drilling at Site U1437, International Ocean Discovery Program Expedition 350

The International Ocean Discovery Program Expedition 350 drilled between two Izu rear‐arc seamount chains at Site U1437 and recovered the first complete succession of rear‐arc rocks. The drilling reached 1806.5 m below seafloor. In situ hyaloclastites, which had erupted before the rear‐arc seamounts came into existence at this site, were recovered in the deepest part of the hole (～15–16 Ma). Here it is found that the composition of the oldest rocks recovered does not have rear‐arc seamount chain geochemical signatures, but instead shows affinities with volcanic front or some of the extensional zone basalts between the present volcanic front and the rear‐arc seamount chains. It is suggested that following the opening of the Shikoku back‐arc Basin, Site U1437 was a volcanic front or a rifting zone just behind the volcanic front, and was followed at ~ 9 Ma by the start of rear‐arc seamount chains volcanism. This geochemical change records variations in the subduction components with time, which might have followed eastward moving of hot fingers in the mantle wedge and deepening of the subducting slab below Site U1437 after the cessation of Shikoku back‐arc Basin opening.     

Duluth Complex apatites: Age reference material for LA–ICP–MS‐based fission‐track dating

Anorthositic series apatites of the Duluth Complex, Minnesota, USA, have high spontaneous fission‐track densities of up to ~10⁷ cm^–2 and a homogeneous age of ~900 Ma, allowing high‐precision fission‐track dating based on LA–ICP–MS U analysis. Absolute fission‐track dating, track‐length measurement and chemical composition analysis were performed to evaluate a cooling history, which is essential for age reference materials. Preliminary inverse modelling for a sample with a shortened track‐length distribution yielded a monotonic cooling history from ~100°C at 925 Ma. The apatites incur an over‐etching problem when employing the commonly used etching protocol involving 5.5 M HNO₃.