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181.
新亚欧大陆桥新疆段环境灾害时空分维特征研究 总被引:1,自引:0,他引:1
基于区域自然灾害发生的随机性和不确定性 ,运用分形、混沌理论 ,对新亚欧大陆桥新疆段近 38年的环境灾害受损次数进行了时空分维特征研究。结果表明陆桥新疆段受损状况不仅在时间序列上具有自相似性 ,其容量维 Df在 0 .830 2~ 1 .437之间 ,而且在空间序列上也具有自相似性 ,存在明显分维结构 ,其信息维 D1在 0 .0 997~ 0 .1 2 72之间。灾害严重区段的容量维值较大 ,并且容量维值越大 ,灾害事件中等级的复杂程度就越高 ,这一特征将有助于认识灾害发生规律和动力学特征。 相似文献
182.
Energy dissipating restrainers for highway bridges 总被引:1,自引:0,他引:1
Recent destructive earthquakes have demonstrated the vulnerability of highway bridges to collapse due to excessive movement beyond the available seat widths at expansion joints. This paper investigates the efficacy of using energy dissipating restrainers at expansion joints for preventing collapse of highway bridges in the event of a severe earthquake. The restrainer consists of a nonlinear viscous damper and an elastic spring connected in parallel or in series. Two-dimensional finite element analysis using bilinear hysteretic models for bridge substructure joints and nonlinear gap elements for expansion joints is performed on example bridges with one or two expansion joints. The analytical study demonstrates that the energy dissipating restrainers are effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints, without significantly increasing ductility demands in the bridge substructures. 相似文献
183.
The local scour around bridge abutments has been an active research topic for many decades. But very few studies have been conducted regarding the impacts of ice cover on the local scour phenomenon aro... 相似文献
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186.
Hoon Sohn Mark Dzwonczyk Erik G. Straser Anne S. Kiremidjian Kincho H. Law Teresa Meng 《地震工程与结构动力学》1999,28(8):879-897
Damage detection techniques have been proposed to exploit changes in modal parameters and to identify the extent and location of damage in large structures. Most of such techniques, however, generally neglect the environmental effects on modal parameters. Such environmental effects include changes in loads, boundary conditions, temperature, and humidity. In fact, the changes due to environmental effects can often mask more subtle structural changes caused by damage. This paper examines a linear adaptive model to discriminate the changes of modal parameters due to temperature changes from those caused by structural damage or other environmental effects. Data from the Alamosa Canyon Bridge in the state of New Mexico were used to demonstrate the effectiveness of the adaptive filter for this problem. Results indicate that a linear four-input (two time and two spatial dimensions) filter to temperature can reproduce the natural variability of the frequencies with respect to time of day. Using this simple model, we attempt to establish a confidence interval of the frequencies for a new temperature profile in order to discriminate the natural variation due to temperature. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
187.
Immersed tunnel is an important part of the Hong Kong-Zhuhai-Macao Bridge (HZMB) project. In immersed tunnel floating, translation which includes straight and transverse movements is the main working mode. To decide the magnitude and direction of the towing force for each tug, a particle swarm-based translation control method is presented for non-power immersed tunnel element. A sort of linear weighted logarithmic function is exploited to avoid weak subgoals. In simulation, the particle swarm-based control method is evaluated and compared with traditional empirical method in the case of the HZMB project. Simulation results show that the presented method delivers performance improvement in terms of the enhanced surplus towing force. 相似文献
188.
Pile groups are frequently used to support bridge decks. Scour in the vicinity of piles is the main cause for the bridges failure. In this research, to address the effects of uniform and nonuniform pile spacing on the equilibrium scour depth, laboratory experiments were carried out under steady clear-water conditions. For this purpose, scour depth produced by pile group with various pile spacing and arrangement was investigated using a laboratory flume. Flume bed was covered by uniform sediments with a median size of 0.9?mm and 0.2?m thickness. Flow discharge and velocity as well as scour depth were recorded in each experiment and the data were analyzed. The results showed that the pile spacing influences the local scour depth and with increase in uniform and transverse (perpendicular to the flow) spacing, the maximum scour depth was reduced. The pile spacing variation in line with the flow has a minor effect on scour depth. In addition, the pile spacing perpendicular to the flow was with the most influences on scour depth. The results of this research can be used by engineers to optimize the design of bridges. 相似文献
189.
港珠澳大桥地处伶仃洋的湾口水域,东、西人工岛分别位于伶仃洋大濠深槽两侧。人工岛水域水深流急,潮流正面冲击人工岛,易造成人工岛海域水下地形发生大的变化与调整,最终形成以人工岛为中心的局部滩槽新格局。在大桥工程设计阶段,采用伶仃洋二维潮流泥沙数学模型,对人工岛建设后的伶仃洋水沙环境和水下地形冲淤进行了模拟计算。模型预测结果表明,人工岛对伶仃洋水域的水沙环境影响集中在人工岛上、下游各5 km水域内,人工岛呈冲刷趋势,岛体上下游形成以岛为中心的梭状淤积体。人工岛建设10年前后的水下地形冲淤变化结果表明,人工岛建设引起的海床冲淤变化趋势与数学模型预测结果基本一致,此为当初采用的数学模型预测效果提供了良好的佐证。 相似文献
190.
为探明工程建设后东海大桥风电场水域鱼类群落结构特征,作者利用等级聚类和多元统计等方法对该水域鱼类种类组成、优势种及群落结构进行分析。春、秋季共发现18种鱼类,隶属6目9科15属;鲈形目鱼类所占比例最高(50%),其中又以虾虎鱼科鱼类最高(44.4%)。春季优势种为短吻红舌鳎(Cynoglossus joyneri)、棘头梅童鱼(Collichthys lucidus)、矛尾虾虎鱼(Chaeturichthys stigmatias)和孔虾虎鱼(Trypauchen vagina),秋季优势种为棘头梅童鱼、龙头鱼(Harpadon nehereus)和凤鲚(Coilia mystus);棘头梅童鱼为春、秋季共同优势种。等级聚类和非度量多维标序排序表明,东海大桥风电场水域鱼类群落可分为春季和秋季2个组群,相似性检验(ANOSIM)显示2个组群差异极显著(R=0.851,P0.01)。生物与环境相关分析(BIOENV)表明温度和盐度是影响东海大桥风电场水域鱼类群落结构的最主要环境因子,两者结合因子与鱼类群落的相关系数为0.791。本研究发现,东海大桥风电场水域是棘头梅童鱼、凤鲚、龙头鱼等多种鱼类的育幼和索饵场所,群落结构具有典型的季节特征。 相似文献