Chemical and mineralogical composition of marine sediments, and relation to their source and transport, Gulf of Carpentaria, Northern Australia

The Gulf of Carpentaria is an epicontinental sea, deeply indented in the north of the Australian continent. A selection of 100 samples of the surficial marine sediments collected on a regional grid were analysed for major chemical elements and mineral phases using wet chemistry, X-ray diffraction, optical and electronic microscopy.The surficial sediments of the Gulf are highly heterogenous and consist of both young and relict mineral and carbonate components. The terrigenous fraction is fluvial in origin and consists mainly of quartz (16–68%), minor feldspars (0–9%) and traces of siderite. The clay species determined include kaolinite, mixed layers of smectite–illite and illite; clays range up to 15% and do not present a clear pattern of distribution. Biologically productive areas of the Gulf, mainly in shallower parts, supply the carbonate component of the sediment. The carbonate material is comprised of aragonite (7–30%), low-Mg (5–30%) and high-Mg calcite (7–28%), and has variable degrees of alteration caused by sediment transport and/or diagenesis. Such processes are partly reflected in the regional distribution of mineral and chemical components throughout the Gulf. The interpretation of the data set was further refined by cluster analysis (Ward's method), which separated eight clusters (provinces) of sedimentary material. The eastern side appears to be the main source of both terrigenous and carbonate sediment, which is inferred to be transported clockwise. During this dispersion, physicochemical and mineralogical changes take place; the sediments become finer grained and characterised by more stable species of carbonates. As a consequence, the center and the northwest sections are clay-rich and contain dominantly low-Mg calcite.Ooids are relict components that have been identified in areas in which they were not mentioned by previous studies, notably in the southeast. These carbonate particles consist of concentric layers of aragonite deposited around a nucleus of angular quartz, most likely of fluvial origin.This study indicates a complex history over a short time frame with sediment supply, biological production and current patterns being the main factors that control the sediment character and its regional distribution within the Gulf.     

Trace element levels in some commercially valuable fish species from coastal waters of Mediterranean Sea, Egypt

Concentrations of 5 trace elements (Cd, Pb, Cu, Cr, Zn) were determined in muscle of fishes collected from two coastal areas of the Egyptian coast of the Mediterranean Sea west of Alexandria (El-Mex Bay and Eastern Harbour). Sardinella aurita, Alepes djedaba, Siganus luridus, Siganus rivulatus, Sphyraena chrysotoenia, and Scomberomorus commerson were collected from El-Mex Bay. While Boops boops, Lithognathus mormyrus, Sparisoma cretense, Serranus cabrilla and Synodus saurus were collected from the E.H. In all fishes zinc was highest (up to 57 mg/kg) followed by Cr, Cu, Pb and Cd. The concentrations of several metals in fishes were significantly different among the species in each area. For all trace element examined, the concentrations decreased significantly with body weight of some fishes. In contrast, a positive correlation with body weight was found especially for Zn and Cu concentrations in 5 fish species and for Pb in 4 fish species. The concentrations of Cd, Pb and Zn were higher in fishes from El-Mex Bay (3.76, 6.49 and 57.21 mg/kg) than those from Eastern Harbour, whereas the opposite trend was observed for Cu and Cr, revealing the direct sources of trace metal pollution present in El-Mex coastal area. Levels of Cr surpassed the Maximum Permissible Concentration in most fish tissues, followed by Pb and Cd in some species. Cu and Zn presented concentrations below the maximum permissible levels in fish tissues.     

桥梁大体积混凝土构件非荷载裂缝数值仿真分析

混凝土的早期裂缝是混凝土工程质量控制的关键因素,是影响结构使用功能、外观质量和耐久性的重要因素。文章以某大桥工程为例,采用Midas建立数值仿真模型计算该桥0#梁段第二施工阶段现浇混凝土水化温度和温度应力,分析此类构件在施工期间产生非荷载裂缝的原因,并通过对比分析该数值计算结果与实际监测数据,验证了该数值仿真分析方法的合理性。     

珠澳口岸人工岛水泥搅拌桩施工质量控制

结合港珠澳大桥珠澳口岸人工岛西北护岸水泥搅拌桩施工,简述水泥搅拌桩施工质量控制要点和方法。水泥搅拌桩施工质量控制的关键为水泥搅拌机型的选择、水泥品牌的选用、水泥掺入量和每延米用量的选配、桩位、桩径和垂直度的控制、施工参数的确定。     

混凝土泵车底盘的专用化设计要素探讨

根据混凝土泵车的作业特点,介绍了混凝土泵车底盘与通用重卡底盘设计的区别,并对混凝土泵车底盘总体布置、动力系统、传动系统、行驶系统、电器系统的专用化设计进行了介绍,便于设计人员掌握混凝土泵车底盘的设计要素。     

高桩码头结构中伸缩缝有关问题的探讨

高桩码头开伸缩缝的宽度及位置以往不为设计、施工部门所重视,致使天津港高桩码头伸缩缝位置构件破损严重。通过对天津港高桩码头伸缩缝工作状况的调查分析,提出了伸缩缝宽度的计算式,可供今后高桩码头伸缩缝改造及《港口工程技术规范》中有关伸缩缝条款的修改时参考。     

Structural behavior and design of high-strength steel welded tubular connections under extreme loading

The present work is motivated by the increasing need for cost-efficient solutions in offshore structural systems for wind energy production and for improvement of their structural performance. The structural behavior and design of high-strength steel welded tubular connections (yield strength higher than 700 MPa) subjected to monotonic and strong cyclic loading is investigated. In the first part of the paper, an experimental investigation is presented on high-strength steel tubular X-joints subjected to monotonic and cyclic loading far beyond the elastic limit of the material, leading to weld fracture. Two grades of weld metal material are employed in the welding process of the specimens. The experimental results indicate that the weld material grade has a significant influence on the deformation capacity of the welded connection under monotonic loading conditions, and its low-cycle fatigue life. The experimental procedure is simulated using advanced finite element models, elucidating several features of joint behavior and complementing the experimental results. Overall, a good agreement is found between numerical simulations and experimental results, in terms of both global response and local strains at the vicinity of the welds. Furthermore, the structural performance of the welded tubular joints under consideration is assessed using available design methodologies in terms of both ultimate strength and low-cycle fatigue resistance, in an attempt to validate an efficient design methodology for low-cycle fatigue. The results from this research effort are aimed at developing the necessary background for the possible use of high-strength steel in tubular steel lattice structures, particularly in offshore platforms for renewable energy production. They can also be used as a basis for the possible amendment of relevant design specifications and recommendations for including special provisions for high-strength steel structural systems.     

八三式铁路轻型军用桥墩快速抢架技术

为提高八三式铁路轻型军用桥墩拼组抢架效率、缩短抢架进程、降低劳动强度,对八三式铁路轻型军用桥墩抢架准备、预案制订、器材出库装载、现场拼组、墩顶加固等各环节进行充分研究,编制了《八三式铁路桥墩抢修应急预案》,设计了器材集装框架化构件,创新了杆件预拼、单元化拼组、墩外拼组顶推横移就位、墩顶螺旋支座加固法等多项技术措施。详细阐述了每种技术措施的施工工艺,为铁路桥墩的快速抢架积累了宝贵经验。     

三维数字空间法与波叠加法结合的近场声辐射计算

传统的波叠加法是边界元法的有效替代方法,其具有计算速度快计算精度较高等优点,但是也有复杂模型的建立较困难,以及对模型适应性较差等缺点。为了克服传统波叠加法的缺点,从而使其能够计算较为复杂模型的声辐射,将三维数字空间方法与传统波叠加法结合,因为三维数字空间方法具有建模迅速,对模型适应性很好等优点。分别采用边界表示法和体积表示法建模,且通过简单算例计算表明,采用这两种方法与传统波叠加法结合计算外场声辐射是完全可行的,并且结果的精确度相对较高,采用边界表示法的效率相对较高。     

南汇东滩促淤工程南区设计波浪要素研究

针对南汇东滩促淤工程所处的位置,选用基于波能平衡方程和波作用守恒方程的近岸风浪谱模型建立波浪传播计算数值模型,对非线性效应影响条件下的波浪要素进行计算研究。研究结果表明,波浪在远距离的传播过程中,受到沿程的风的影响,组成波之间能量交换转移和耗散等非线性效应的影响不可忽略,在南汇东滩海域采用近岸风浪谱数值模型对波浪的传播变形计算较为合适。