重庆五梁石拱桥的力学性能分析及其保护措施(一)

采用大型有限元软件ANSYS,对古桥的现状及淹没后的各种工况进行了计算分析.依据整体性加固理论,桥栏、桥面采用植筋技术,桥面用掺有固化剂的泥土或砂土做覆土保护对桥体进行整体性加固.同时依就地势做毛石护坡对桥基进行加固,整个桥体涂刷WACKER BS R OH100石材保护剂提高其抗风化能力,延长古桥存在时间.     

苏中地区古桥特色及保护策略探究

苏中地区河网密布,历史上留下了较多有历史文化典韵的古桥梁.研究现存古桥的历史文化与工艺特征从而发掘出珍贵的古文物价值;梳理该地区典型古桥文化特色有水乡文化、盐税文化和宗教文化,归纳总结古桥的病害及破坏形式进而研究提出古桥保护的对策与方法.该研究也为我国类似区域的古桥文物建筑历史文化特色、建造工艺特征、现有病害现况与保护性加固修缮提供可参考的借鉴价值.     

木桁架文物古桥修缮工程关键设计技术研究

广西现存最早的木桁架文物古桥—惠爱桥加固设计中，利用同步顶升液压控制系统技术设置主动临时支撑，实现加固过程的主动支撑和节点连接件更换及加固。采用增设永久附加斜支撑结构方法，改善了木桁架结构主要控制截面内力和变形，实现了文物古桥的快速抢险加固，延续和完整保存了古桥的原始风貌，社会效益和经济效益显著。     

北京大关双曲拱桥加固改造实践

结合大关双曲拱桥加固实例,介绍了该桥的主要病害,同时分析了病害产生原因,并提出了简单合理的加固方案及加固工艺,荷载试验结果表明:该桥加固后满足规范各项要求,使用效果良好.     

三跨连续石拱古桥承载能力的分析研究

以一座历史悠久的三跨石拱桥为背景,进行外观几何尺寸的测量,推算了拱桥的拱轴线形,绘制该古桥平纵横的尺寸图,同时对古桥的现状及缺陷进行了调查和评估,在此基础上,运用现代分析理论,分析计算了该古桥可能的承载力,结果表明该桥若要通行现代的汽车交通,则从安全的角度只能通行2及t以下的小汽车及行人交通。为保护该桥,建议将该古桥作为该县城文化传承和历史记载的一部分,结合街区步行街的规划,加以加固维护和保留。     

潮州湘子桥装饰艺术的美学意蕴

中国是桥梁的国度,中国古桥非常重视装饰艺术,是技术与艺术完美结合的产物.古桥的装饰蕴含丰富的中国传统文化信息,从古桥的装饰上可以看到中国传统的美学意蕴和审美理想,可以看到古桥所在地区的地域风格、艺术特色以及人文精神.潮州湘子桥历史悠久,装饰精美,素有"江南第一桥"的美称,是粤东地区建筑装饰艺术的典范之作.湘子桥的装饰艺...     

小半径曲线钢箱梁桥病害成因与加固措施研究

独柱墩曲线桥受力机制复杂,由于曲率的影响,易产生弯扭耦合作用。曲线桥产生的病害以及病害特征与直线桥有较大不同。依据某立交G线匝道桥的现场检查,阐述了曲线桥常见的病害,并对病害成因进行了分析。针对病害及其成因,结合具体工程,介绍了曲线桥病害处置的加固方案,为今后独柱墩曲线桥的维修和加固提供依据。     

某预应力混凝土T梁桥病害检查与处治

为了研究某预应力混凝土T梁桥开裂病害的原因及病害加固的方法,本文以某高速公路中一座预应力混凝土T梁桥作为研究对象,阐述了该桥的病害情况、检查手段、病害原因及加固手段。研究结果表明,T梁桥加固后5#梁实测动位移分布在0～0.5 mm区间内,振动幅度显著减弱,裂缝受温度及荷载作用下的宽度变化量较小,证明了加固措施的有效性,可为同类T梁桥病害分析及加固处理提供参考。     

现役装配式箱形梁桥的病害分析与加固设计

本文以某现役装配式箱形梁桥为例,介绍了该桥存在的病害及其成因分析,并提出相应的加固方案,然后通过计算验证其加固效果。该桥经过加固后,承载能力得到了提高,病害得到有效处治。     

大运河山东段古桥拱券构造特征及尺度对比研究

山东段大运河上的古桥是世界文化遗产中国大运河的重要组成部分,具有重要的研究意义。本文选取位于山东省境内现存的月径桥、会通桥(临清)、问津桥、迎春桥、水门桥、会通桥(济宁)、太和桥、夏桥、大石桥及漕井桥这十座运河古桥作为研究对象,从类型、尺度关系、材料材料、构造特征以及艺术处理这五个方面对山东运河古桥的拱券进行研究,总结出山东运河古桥拱券的五点地方特征。     

切割分解法拆除装配式旧桥的施工方案

对省道临午线临汾马务桥西至蒲县黑龙关的旧桥切割拆除方案及施工控制进行了分析,提出了切割分解法拆除装配式旧桥的施工方案,为装配式旧桥整体快速拆除积累了经验。     

一座独特的木拱桥

上海青浦区金泽镇建成一座结构独特、造型别致的木拱桥——普庆桥,重现了北宋张择端《清明上河图》中所绘的桥式。本文介绍单孔木结构叠梁拱的结构特点、受力分析和无支架的施工方法,以达到古为今用之目的。     

Arctic Ocean sea ice drift origin derived from artificial radionuclides

Since the 1950s, nuclear weapon testing and releases from the nuclear industry have introduced anthropogenic radionuclides into the sea, and in many instances their ultimate fate are the bottom sediments. The Arctic Ocean is one of the most polluted in this respect, because, in addition to global fallout, it is impacted by regional fallout from nuclear weapon testing, and indirectly by releases from nuclear reprocessing facilities and nuclear accidents. Sea-ice formed in the shallow continental shelves incorporate sediments with variable concentrations of anthropogenic radionuclides that are transported through the Arctic Ocean and are finally released in the melting areas. In this work, we present the results of anthropogenic radionuclide analyses of sea-ice sediments (SIS) collected on five cruises from different Arctic regions and combine them with a database including prior measurements of these radionuclides in SIS. The distribution of ¹³⁷Cs and ^239,240Pu activities and the ²⁴⁰Pu/²³⁹Pu atom ratio in SIS showed geographical differences, in agreement with the two main sea ice drift patterns derived from the mean field of sea-ice motion, the Transpolar Drift and Beaufort Gyre, with the Fram Strait as the main ablation area. A direct comparison of data measured in SIS samples against those reported for the potential source regions permits identification of the regions from which sea ice incorporates sediments. The ²⁴⁰Pu/²³⁹Pu atom ratio in SIS may be used to discern the origin of sea ice from the Kara-Laptev Sea and the Alaskan shelf. However, if the ²⁴⁰Pu/²³⁹Pu atom ratio is similar to global fallout, it does not provide a unique diagnostic indicator of the source area, and in such cases, the source of SIS can be constrained with a combination of the ¹³⁷Cs and ^239,240Pu activities. Therefore, these anthropogenic radionuclides can be used in many instances to determine the geographical source area of sea-ice.     

Plutonium isotopes in seas around the Korean Peninsula

239+240Pu concentrations and 240Pu/239Pu atom ratios in coastal seas adjacent to the Korean Peninsula were determined, during the period 1999 to 2002, to assess the current distribution and to identify sources of Pu isotopes. 239+240Pu concentrations in surface waters ranged from 3.1 to 22.3 mBq m(-3) with higher concentrations in winter than in summer. 239+240Pu concentrations in seawaters around the Korean Peninsula are greater than that in the western North Pacific. 240Pu/239Pu atom ratios ranged from 0.18 to 0.33 with an average value of 0.25+/-0.03, which is significantly higher than the global fallout average. The 240Pu/239Pu atom ratios of the 2000 m deep entire water column in the south western part of the East Sea (Sea of Japan) was comparable to that observed in waters near Bikini Atoll. The higher 240Pu/239Pu atom ratios than that of global fallout may be explained by the hypothesis that the earlier input signal of low 240Pu/239Pu atom ratio (0.18-0.19) of global fallout plutonium in seas adjacent to the Korean Peninsula is being gradually diluted by the high 240Pu/239Pu atom ratio plutonium transported from the tropical Pacific Proving Grounds via prevailing ocean current.     

Rapid dating of recent sediments in Loch Ness: inductively coupled plasma mass spectrometric measurements of global fallout plutonium

The (239+240)Pu activity profile is determined for a sediment core collected from 170-m depth at Loch Ness, Scotland. These measurements use magnetic sector inductively coupled plasma mass spectrometry for rapid determination of Pu activities and (240)Pu/(239)Pu atom ratios. A (239+240)Pu detection limit of 0.1 Bq/kg is obtained for 2 g of acid-leached sediment; (242)Pu is used as a spike isotope. The Pu activity profile exhibits a maximum of 42.7+/-0.3 Bq/kg (239+240)Pu in the 9-10-cm depth interval. The position of this maximum coincides with peaks in the (241)Am and (137)Cs activity profiles. These peak activities are ascribed to the 1963/1964 peak fallout from atmospheric testing of nuclear weapons. The (240)Pu/(239)Pu atom ratios are in the range 0.15-0.20, in agreement with the expected range of 0.166-0.194 for Northern Hemisphere fallout, and do not suggest the presence of other contributing sources. This study demonstrates that ICPMS has considerable potential for rapid determination of the chronology of post-1950 sediments, and also for validating (210)Pb dates where chronologies over longer time-scales are needed.     

无粘性土中水平荷载桩的地基土极限水平反力研究

本文针对前人推导的水平荷载桩地基土极限水平反力Pu的基本假设不尽合理和所得Pu过大、偏于不安全这一现象,对水平荷载桩地基土极限水平反力的形成特征和桩周土的应力状态进行了分析研究.并在此基础上按塑性理论推导获得了无粘性土中圆形截面水平荷载桩地基土极限水平反力Pu的滑移线理论解,其Pu值约为Broms建议值的一半或更小.经与试桩资料对比,本文解答求得的单桩极限水平承载力与实测值非常吻合.     

Characterization of U/Pu particles originating from the nuclear weapon accidents at Palomares, Spain, 1966 and Thule, Greenland, 1968

Following the USAF B-52 bomber accidents at Palomares, Spain in 1966 and at Thule, Greenland in 1968, radioactive particles containing uranium (U) and plutonium (Pu) were dispersed into the environment. To improve long-term environmental impact assessments for the contaminated ecosystems, particles from the two sites have been isolated and characterized with respect to properties influencing particle weathering rates. Low (239)Pu/(235)U (0.62-0.78) and (240)Pu/(239)Pu (0.055-0.061) atom ratios in individual particles from both sites obtained by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) show that the particles contain highly enriched U and weapon-grade Pu. Furthermore, results from electron microscopy with Energy Dispersive X-ray analysis (EDX) and synchrotron radiation (SR) based micrometer-scale X-ray fluorescence (micro-XRF) 2D mapping demonstrated that U and Pu coexist throughout the 1-50 microm sized particles, while surface heterogeneities were observed in EDX line scans. SR-based micrometer-scale X-ray Absorption Near Edge Structure Spectroscopy (micro-XANES) showed that the particles consisted of an oxide mixture of U (predominately UO(2) with the presence of U(3)O(8)) and Pu ((III)/(IV), (IV)/(V) or (III), (IV) and (V)). Neither metallic U or Pu nor uranyl or Pu(VI) could be observed. Characteristics such as elemental distributions, morphology and oxidation states are remarkably similar for the Palomares and Thule particles, reflecting that they originate from similar source and release scenarios. Thus, these particle characteristics are more dependent on the original material from which the particles are derived (source) and the formation of particles (release scenario) than the environmental conditions to which the particles have been exposed since the late 1960s.     

238Pu and 239+240Pu inventory and distribution through the lower Rhone valley terrestrial environment (Southern France)

Because of atmospheric global fallout due to thermonuclear tests performed between 1945 and 1980 and to the American SNAP 9A satellite explosion in 1964, plutonium's long-lived alpha emitter isotopes ((238)Pu, (239)Pu and (240)Pu) can be found everywhere in the environment. In the soils of the lower Rhone valley, over a surface area of approximately 11,000 km(2), existing results allow estimation of the total inventory resulting from this origin of 551 GBq as regards these radionuclides. The Marcoule Nuclear Reprocessing Plant (NRP) has been releasing (238)Pu and (239+240)Pu into the environment for over 40 years in the region and is as such a second likely source for Pu input. This article gives a global review of plutonium distribution in this particular region. It is shown that releases from Marcoule, although accounting for less than 2% of the total Pu inputs into the terrestrial environment, are responsible for localised and measurable Pu enrichments close to the facility (+2.8 GBq), and in the Rhone delta where sediments from the river settled during the past floods (+0.1 GBq). Irrigating with water from the Rhone River also allowed the transfer of approximately 3.8 GBq of (238)Pu and (239+240)Pu to the soils for the whole 1960-1998 period. These inputs, distributed over wide irrigated surface areas, do not induce significant increases of soil Pu-activity levels. In a second section, this study confirms that most of the plutonium existing in the terrestrial environment is accumulated in the soil. Less than 0.1% of the activities exist currently in the plant compartments, and the flows exported by agricultural productions are very low, although we are interested here in a French region where agriculture prevails.     

Distribution of 137Cs, 238Pu and 239+240 Pu in sediments of the southeastern Brazilian shelf-SW Atlantic margin

In this work levels of 137Cs, 238Pu and 239+240 Pu as well as activity ratios of anthrophogenic radionuclides in sediment samples from the southeastern Brazilian shelf are presented. Instrumental gamma spectrometry was used to determine 137Cs and alpha spectrometry to determine 238Pu and 239+240 Pu after a radiochemical procedure. The levels ranged from 0.30 to 1.79 Bq kg(-1) for 137Cs, from 15 to 150 mBq kg(-1) for 238Pu and, from 18 to 117 mBq kg(-1) for 239+240 Pu. There was a bathymetric differentiation in the radionuclides distribution. 137Cs values were generally higher in the samples collected at water depths of less than 100 m. On the other hand, plutonium isotopes exhibit higher values at greater depths. The mean ratio of 239+240 Pu/137Cs obtained was 0.112+/-0.072 which is in agreement with the value reported for the Atlantic from atmospheric fallout of nuclear explosions in the past. The 238Pu/230+240 Pu ratios varied widely (from 0.339 to 2.088) and showed the influence of the SNAP-9A accident in the 238Pu levels for this area. The main goal of this work was to present unpublished anthropogenic radionuclide levels and activity ratios related to the contamination of the southeastern Brazilian shelf.     

Anthropogenic Pu distribution in Tropical East Pacific

The geographical distribution of the anthropogenic radionuclides ²³⁸Pu and ^239 + 240Pu in the Tropical East Pacific in 2003 was studied from the viewpoint of material migration. We measured the contents of Pu isotopes in seawater and in sediment from the sea bottom. The distributions of Pu isotopes, together with those of coexisting nitrate and phosphate species and dissolved oxygen, are discussed in relation to the potential temperature and potential density (sigma-θ). The Pu contents in sediment samples were compared with those in the seawater. Horizontal migration across the Equator from north to south was investigated at depths down to ~ 800 m in the eastern Pacific. The Pu distribution at 0-400 m correlated well with the distribution of potential temperature. Maximum Pu levels were observed in the subsurface layer at 600-800 m, corresponding to the depth where sigma-θ ≈ 27.0. It is suggested that the Pu distribution depends on the structure of the water mass and the particular temperature and salinity. The water column/sediment column inventory ratio and the vertical distribution of Pu may reflect the efficiency of scavenging in the relevant water areas.