Seismic performance and new design procedure for chevron‐braced frames     

Edoardo M. Marino  Masayoshi Nakashima 《地震工程与结构动力学》2006,35(4):433-452

The paper is concerned with the seismic design of steel‐braced frames in which the braces are configured in a chevron pattern. According to EuroCode 8 (EC8), the behaviour factor q, which allows for the trade‐off between the strength and ductility, is set at 2.5 for chevron‐braced frames, while 6.5 is assigned for most ductile steel moment‐resisting frames. Strength deterioration in post‐buckling regime varies with the brace's slenderness, but EC8 adopts a unique q value irrespective of the brace slenderness. The study focuses on reevaluation of the q value adequate for the seismic design of chevron‐braced frames. The present EC8 method for the calculation of brace strength supplies significantly different elastic stiffnesses and actual strengths for different values of brace slenderness. A new method to estimate the strength of a chevron brace pair is proposed, in which the yield strength (for the brace in tension) and the post‐buckling strength (for the brace in compression) are considered. The new method ensures an identical elastic stiffness and a similar strength regardless of the brace slenderness. The advantage of the proposed method over the conventional EC8 method is demonstrated for the capacity of the proposed method to control the maximum inter‐storey drift. The q values adequate for the chevron‐braced frames are examined in reference to the maximum inter‐storey drifts sustained by most ductile moment‐resisting frames. When the proposed method is employed for strength calculation, the q value of 3.5 is found to be reasonable. It is notable that the proposed method does not require larger cross‐sections for the braces compared to the cross‐sections required for the present EC8 method. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Millennial‐scale stratigraphy of a tide‐dominated incised valley during the last 14 kyr: Spatial and quantitative reconstruction in the Tokyo Lowland,central Japan          下载免费PDF全文

Susumu Tanabe  Toshimichi Nakanishi  Yoshiro Ishihara  Rei Nakashima 《Sedimentology》2015,62(7):1837-1872

Spatial and quantitative analysis of infilling processes of the tide‐dominated incised valleys beneath the Tokyo Lowland during the last 14 kyr was undertaken by using data from 18 sediment cores, 467 radiocarbon dates and 6100 borehole logs. The post‐Last Glacial Maximum valley fills consist of braided river, meandering river, estuary, spit and delta systems in ascending order. The boundary between the estuary and delta systems is regarded as the maximum flooding surface. The maximum flooding surface beneath the Tokyo Lowland is dated at 8 ka in the Arakawa Valley and 7 ka in the Nakagawa Valley. This age difference is due to the migration of the Tone River from the Arakawa Valley to the Nakagawa Valley at 5 ka, and suggests that the widely held view that the global initiation of deltas coincided with the abrupt rise of sea‐level at 9 to 8 ka is true only where there has been steady sediment supply from major rivers. The meandering river system is dominated by sheet‐like sands that were deposited during lateral migration of channels during the Younger Dryas and isolated vertical sands within muds that reflect vertical aggradation of channels before and after the Younger Dryas. The transition between these channel geometries is controlled by a threshold sea‐level rise of 4 to 7 mm yr^?1. Before migration of the Tone River at 5 ka, the tide‐dominated bay in the Nakagawa Valley was filled by upward‐fining laterally accreting muds. The muds accreted from the margin to the axis of the bay. Such lateral accretion of suspended particles derived from outside the bay has been documented in other tide‐dominated coastal environments and is probably common in other similar settings. After the migration of the Tone River, the bay was filled by upward‐coarsening deltaic sediments.  相似文献   

Capelin (Mallotus villosus) spawning behaviour in Newfoundland waters-the interaction between beach and demersal spawning     

Nakashima  Brian S.; Wheeler  John P. 《ICES Journal of Marine Science》2002,59(5):909-916

  相似文献   

Solar wind speed and its acceleration inferred using the interplanetary scintillation method in carrington rotation 1753     

Kazuyuki Hakamada  Masayoshi Kojima 《Solar physics》1994,153(1-2):419-435

Solar wind speeds (SWSs) estimated by interplanetary scintillation (IPS) observations during Carrington rotation 1753 are projected onto the so-called source-surface of 2.5 solar radii along magnetic field lines in interplanetary space. The following two working hypotheses are examined from different points of view: (1) The SWS is a weighted mean along the line of sight to a radio source; the weight for the SWS depends on the distance from theP-point, the closest approach to the Sun on the line of sight. (2) The weighting function has a very sharp peak at theP-point, so that the SWS shows a real solar wind speed at theP-point. In both the two cases, the SWSs projected onto the source surface are further projected onto the photosphere along magnetic field lines in the corona. Footpoints of these field lines are inferred as photospheric source regions of the solar wind. The intensity of the Hei (1083 nm) absorption line (HEI) in the chromosphere corresponding to these photospheric sources is interpolated from observational data. The weighted mean of the HEI is calculated in case 1. The HEI corresponding to theP-point is used in case 2. The SWS is compared with the HEI in both the two cases. It is found that the correlation between the SWS and the HEI is better in case 2 than in case 1. It is further inferred by correlation analysis between the SWS and the HEI that the solar wind is accelerated within 27 solar radii on average. Although the data examined in this paper were limited to just one solar rotation, these results suggest that the SWS estimated by the IPS technique corresponds to the solar wind speed near theP-point and the weighting function along the line of sight may have a very sharp peak near theP-point.  相似文献   

Hydration of rhyolitic glass during weathering as characterized by IR microspectroscopy   总被引：1，自引：0，他引：1  

Tadashi Yokoyama  Satoshi Okumura  Satoru Nakashima 《Geochimica et cosmochimica acta》2008,72(1):117-125

The mechanism and rate of hydration of rhyolitic glass during weathering were studied. Doubly polished thin sections of two rhyolites with different duration of weathering (Ohsawa lava: 26,000 yr, Awanomikoto lava: 52,000 yr) were prepared. Optical microscope observation showed that altered layers had developed along the glass surfaces. IR spectral line profile analysis was conducted on the glass sections from the surface to the interior for a length of 250 μm and the contents of molecular H₂O (H₂O_m), OH species (OH) and total water (H₂O_t) were determined. The diffusion profile of H₂O_m in Ohsawa lava extends beyond the layer observed by optical microscope. The content of H₂O_m in the hydrated region is much higher than that of OH species. Thus, the reaction from H₂O_m to OH appears to be little and H₂O_m is the dominant water species moving into the glass during weathering. Based on the concentration profiles, the diffusion coefficients of H₂O_m(D_H2Om) and H₂O_t(D_H2Ot) were determined to be 2.8 × 10⁻¹⁰ and 3.4 × 10⁻¹⁰ μm² s⁻¹ for Ohsawa lava, and 5.2 × 10⁻¹¹ and 4.1 × 10⁻¹¹ μm² s⁻¹ for Awanomikoto lava, respectively. The obtained D_H2Om during weathering are more than 2-3 orders of magnitude larger than the diffusion coefficient at ∼20 °C that is extrapolated from the diffusivity data for >400 °C. This might suggest that the mechanism of water transport is different at weathering conditions and >400 °C.  相似文献   

A substructure shaking table test for reproduction of earthquake responses of high‐rise buildings     

Xiaodong Ji  Kouichi Kajiwara  Takuya Nagae  Ryuta Enokida  Masayoshi Nakashima 《地震工程与结构动力学》2009,38(12):1381-1399

When subjected to long‐period ground motions, high‐rise buildings' upper floors undergo large responses. Furniture and nonstructural components are susceptible to significant damage in such events. This paper proposes a full‐scale substructure shaking table test to reproduce large floor responses of high‐rise buildings. The response at the top floor of a virtual 30‐story building model subjected to a synthesized long‐period ground motion is taken as a target wave for reproduction. Since a shaking table has difficulties in directly reproducing such large responses due to various capacity limitations, a rubber‐and‐mass system is proposed to amplify the table motion. To achieve an accurate reproduction of the floor responses, a control algorithm called the open‐loop inverse dynamics compensation via simulation (IDCS) algorithm is used to generate a special input wave for the shaking table. To implement the IDCS algorithm, the model matching method and the H_∞ method are adopted to construct the controller. A numerical example is presented to illustrate the open‐loop IDCS algorithm and compare the performance of different methods of controller design. A series of full‐scale substructure shaking table tests are conducted in E‐Defense to verify the effectiveness of the proposed method and examine the seismic behavior of furniture. The test results demonstrate that the rubber‐and‐mass system is capable of amplifying the table motion by a factor of about 3.5 for the maximum velocity and displacement, and the substructure shaking table test can reproduce the large floor responses for a few minutes. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Estimate of Ablation Rate of Glacier Ice under a Supraglacial Debris Layer     

Masayoshi Nakawo  & Birbal Rana 《Geografiska Annaler: Series A, Physical Geography》1999,81(4):695-701

The ablation rate under a debris layer is very difficult to measure directly at debris-covered glaciers, because the surface is highly heterogeneous, and the ablation rate varies tremendously from place to place. Heat budget considerations with a debris layer on top of glacier ice suggested that 'thermal resistance' of the debris layer could be estimated from surface temperature and the heat fluxes at the debris surface, and the ablation rate of the underlying glacier ice from the thermal resistance and meteorological data. The method was tested at the Lirung Glacier in Langtang Valley, Nepal Himalayas, using the thermal band of LANDSAT satellite for estimating surface temperature distribution of the debris top surface. The amount of melt water thus estimated was compatible with the observed discharge data from the glacier basin for periods of the monsoon season in 1985 and the pre-monsoon to the monsoon season in 1996. The investigation also revealed that the amount of discharge was much larger than the amount of precipitation over the basin, and it was suggested that the melt water from the debris-covered glacier contributes significantly to the river flow as a result of the shrinkage of the glacier.  相似文献   

Hydrothermal activity in the Obiro deposit embedded in the Tagawa acidic rocks,Uetsu region,NE Japan     

Yuki Nakajima  Yuya Izumino  Shin‐ichi Kagashima  Kazuo Nakashima 《Resource Geology》2020,70(4):348-361

The Obiro deposit is located in the Tagawa Acidic Rocks (AR), Uetsu region, NE Japan. The Tagawa AR is composed of a volcanic phase of dacitic welded tuff and a plutonic phase of porphyritic granodiorite. Drill core and ore samples were collected from the deposit and examined by XRD, EPMA, and microthermometry. The drill core samples have suffered pervasively from sericite (illite) alteration, whereas pinkish K‐feldspar alteration halo occur close to veins. The results of EPMA and microthermometry is interpreted as that the magnatic‐hydrothermal fluids has changed as follows; the granodioritic magma intruded at about 1.0 kb and 700°C near the water‐saturated granite solidus; after cooling to about 500°C the fluids boiled according to a change in the pressure regime from lithostatic to hydrostatic; mixing with meteoric water led to sulfide mineralization at around 400°C or less. The main reasons for the mineralization in the Obiro deposit are as follows; the oxidized magma intruded at a shallower level, and thereafter hydrothermal fluids were boiled, resulting in a saline fluid. The saline fluid then dissolved metals such as Pb, Zn, Cu, and Bi, and these metals precipitated during cooling accompanied by dilution of the meteoric water and increasing pH, resulting in decreasing solubility.  相似文献   

Steric sea level changes estimated from historical ocean subsurface temperature and salinity analyses   总被引：13，自引：0，他引：13  

Masayoshi Ishii  Masahide Kimoto  Kenji Sakamoto  Sin-Iti Iwasaki 《Journal of Oceanography》2006,62(2):155-170

An historical objective analysis of subsurface temperature and salinity was carried out on a monthly basis from 1945 to 2003 using the latest observational databases and a sea surface temperature analysis. In addition, steric sea level changes were mainly examined using outputs of the objective analyses. The objective analysis is a revised version of Ishii et al. and is available at 16 levels in the upper 700 m depth. Artificial errors in the previous analysis during the 1990s have been worked out in the present analysis. The steric sea level computed from the temperature analysis has been verified with tide gauge observations and TOPEX/Poseidon sea surface height data. A correction for crustal movement is applied for tide gauge data along the Japanese coast. The new analysis is suitable for the discussion of global warming. Validation against the tide gauge reveals that the amplitude of thermosteric sea level becomes larger and the agreement improves in comparison with the previous analysis. A substantial part of local sea level rise along the Japanese coast appears to be explained by the thermosteric effect. The thermal expansion averaged in all longitudes from 60°S to 60°N explains at most half of recent sea level rise detected by satellite observation during the last decade. Considerable uncertainties remain in steric sea level, particularly over the southern oceans. Temperature changes within MLD make no effective contribution to steric sea level changes along the Antarctic Circumpolar Current. According to statistics using only reliable profiles of the temperature and salinity analyses, salinity variations are intrinsically important to steric sea level changes in high latitudes and in the Atlantic Ocean. Although data sparseness is severe even in the latest decade, linear trends of global mean thermosteric and halosteric sea level for 1955 to 2003 are estimated to be 0.31 ± 0.07 mm/yr and 0.04 ± 0.01 mm/yr, respectively. These estimates are comparable to those of the former studies.  相似文献   

Flexible substructure online hybrid test system using conventional testing devices     

Wang Tao  Masayoshi Nakashima 《地震工程与工程振动(英文版)》2013,12(3):341-350

This paper presents a substructure online hybrid test system that is extensible for geographically distributed tests.This system consists of a set of devices conventionally used for cyclic tests to load the tested substructures onto the target displacement or the target force.Due to their robustness and portability,individual sets of conventional loading devices can be transported and reconfigured to realize physical loading in geographically remote laboratories.Another appealing feature is the flexible displacement-force mixed control that is particularly suitable for specimens having large disparities in stiffness during various performance stages.To conduct a substructure online hybrid test,an extensible framework is developed,which is equipped with a generalized interface to encapsulate each substructure.Multiple tested substructures and analyzed substructures using various structural program codes can be accommodated within the single framework,simply interfaced with the boundary displacements and forces.A coordinator program is developed to keep the boundaries among all substructures compatible and equilibrated.An Internet-based data exchange scheme is also devised to transfer data among computers equipped with different software environments.A series of online hybrid tests are introduced,and the portability,flexibility,and extensibility of the online hybrid test system are demonstrated.  相似文献