安装有防屈曲支撑建筑的地震模拟与经济性分析

结合防屈曲支撑拟静力实验的研究成果,用ABAQUS有限元软件模拟一栋建筑的地震反应。比较原设计结构与减少梁柱面积但安装有防屈曲支撑的减缩结构这2种方案下的地震响应,使两者的层间位移角相近并满足规范要求,进而做经济性对比。结果表明,防屈曲支撑可以有效地减小结构地震响应,并且先于梁柱破坏,保护主体结构安全;安装防屈曲支撑的结构在满足设计要求的同时,还可以节省建筑成本,缩短施工工期。     

OBSERVATION OF SEDIMENT LOAD IN THE RIVER WITH THE THILTMETER (WITH THE TILTMETER OF ZÖLLNER SUSPENSION

SUMMARY

One of the most important factors for the study of various problems of river-improvement and river-utilization is the measurement of amount of sand and gravels transported by water.

However, to this date, no definite methods of the measurement have been discovered. The author found a new method of this measurement using a tiltmeter (with horizontal pendulum of Zöllner suspension).

Applying this method, it is able to measure sediment load (bed load and suspended load) both at the time of low-water and flood. Also through this method, it is possible to observe and self-register variation of the rate of sediment transportation continuously in such a case as other methods are not useful.

The test observation at Sukumo-gawa, Hakone-machi, Ashigara-gun, Kanagawa-pref, from September 1953 to November 1954 performed by the author of this articel was successful.

Thus, this method has been put in practical use at upper stream of Katashina-gawa in Tone-river system, Gumma-pref, since July 1956.     

防屈曲支撑的有限元模拟及滞回性能分析

结合防屈曲支撑拟静力实验的研究成果,本文采用有限元软件ABAQU S对其进行了数值模拟分析。在模拟过程中,应用金属Com b ine本构模型设置内芯钢板材料属性。该模型是对传统双线性本构模型的改进,模拟结果很好地符合了实验结果,同时验证了防屈曲支撑具有良好的减震耗能性能,其在轴向加载达到7倍屈服位移时,依然能保持良好的滞回特性。通过对模型中橡胶无粘结层的合理设置,研究了内芯钢板在失稳变形中无摩擦滑移与能量缓冲转化的形变特点。分析表明,当外包约束强度和刚度足够时,内芯钢板在受轴向压力时只发生多波微幅弯曲失稳;随着内芯钢材与外包有效约束间隙的增大,支撑的失稳波幅也随之增大,支撑承载力与耗能能力显著降低。     

疏林草原榆树天然更新研究进展

疏林草原是由稀疏乔木以及灌木和草本植物组成的植被类型,其生态系统结构和功能有一定独特性。目前榆树疏林草原面积减少,榆树种群更新不良可能是重要原因。从种群特征、草树关系、微生境、人类活动等4个方面对榆树种群更新进行总结。主要结论是:随年龄增长,榆树种群表现为由集聚到随机的分布趋势;榆树与草本植物通过占据不同生态位实现共生;植被盖度与微生境、人类活动、围封对榆树更新影响很大。还未见报道的问题有:个体成对现象;种子入侵草地空斑;风蚀和沙埋过程对榆树更新的影响;榆树更新的最佳围封年限。最后,指出榆树疏林研究的未来两大方向是榆树疏林与全球环境变化,榆树疏林与沙地植被恢复。     

Large amount of fluid migration around shallow seismogenic depth preserved in tectonic mélange: Yokonami mélange,the Cretaceous Shimanto Belt,Kochi, Southwest Japan

Studying subduction zone fluid at shallow seismogenic depths is important to understand the nature of fault rocks at the updip limit of the seismogenic zone because fluid–rock interactions affect heat and mass transfer, and fault strength. In this study, we conducted detailed analyses of distribution of shear veins, and estimation of pressure–temperature conditions for shear vein formation for the Yokonami mélange, Shikoku, Southwest Japan, which is tectonic mélange zone in an on‐land accretionary complex. We found a seismogenic fault at the upper boundary of the Yokonami mélange, indicating that the Yokonami mélange was active at seismogenic depth. The field‐transect distribution of shear veins was examined. The frequency, the total and mean thicknesses of the shear veins were about 3.7 per meter, about 10 mm per meter, and about 3 mm per shear vein, respectively. Quartz within the shear veins shows elongate‐blocky textures, suggesting precipitation from advective flow. The pressure and temperature conditions for shear vein formation were examined by fluid inclusion analysis, ranging 175–225°C and 143–215 MPa, respectively. The temperature is almost consistent with the paleotemperature determined from vitrinite reflectance, suggesting that the shear veins were formed at up to the maximum depth. The depth might be consistent with that where the seismogenic fault was formed. On the basis of the pressure and temperature conditions and the distribution of shear veins, we estimated the minimum volumetric ratio of fluid to host rocks, assuming that the shear veins had precipitated from advective flow. The estimated amount of fluid is about 106 m³ per cubic meter of host rocks. The results suggest that a large amount of fluid migrates through mélange zones at shallow seismogenic depths. This fluid possibly originates from the dehydration of clay minerals from underthrusted sediments and an altered subducting slab.     

Submerged forest off Nyuzen, Kurobegawa alluvial fan, Toyama Bay, Central Japan

Remnants of a submerged ancient forest have been found on the continental shelf of NW Japan off the Kurobe alluvial fan in Toyama Bay. The remains, standing tree stumps and roots, are located at depths between 20 and 40 m and ages of 8,000 years B.P. to 10,000 years B.P. have been determined by the ¹⁴C method. Alnus and Salix are the most commonly preserved genera and the trees grew on the now sub-merged seaward margin of the alluvial fan. Pollen analysis permits an estimate of palaeo-temperatures 2°C to 4°C lower than at present. Diatoms give some indication of salinity variations at the time of forest development and suggest brackish water, possible lagoonal conditions. The distribution of the stumps and roots suggests that there were probably two separate forests which were overwhelmed by rising sea-level and flash flood deposits. The present day submarine exposures may be due to recent submarine erosion related to the seaward movement of flood waters which passed from the fan into the upper reaches of the Toyama submarine canyon system.