预应力钢骨超高强混凝土梁抗弯性能非线性分析

为全面了解预应力钢骨超高强混凝土梁的受力性能,采用ANSYS对预应力钢骨超高强混凝土梁在静力荷载作用下的抗弯受力过程进行数值模拟分析,并与试验结果进行比较。结果表明,该模型所得的开裂荷载、极限荷载、钢筋屈服荷载以及荷载位移曲线与试验结果接近,验证了有限元模型的正确性。模型为预应力钢骨混凝土结构的非线性分析提供了一种较为准确的数值模拟方法。     

预应力CFRP加固钢筋混凝土梁的受力试验

采用预应力碳纤维布(CFRP)、非预应力CFRP加固钢筋混凝土梁与未加固对比梁进行受力试验,分析了预应力CFRP加固钢筋混凝土梁的破坏特征,研究CFRP预应力和混凝土预裂对加固钢筋混凝土梁的裂缝、挠度、混凝土和CFRP应变、开裂荷载、屈服荷载和极限荷载的影响。结果表明:对CFRP施加预应力可充分发挥其高强的特性;预应力CFRP可明显增强加固钢筋混凝土梁的抗弯性能,提高开裂荷载、屈服荷载和极限荷载,提高截面抗弯刚度,增大极限破坏时的挠度和延性,减小裂缝宽度和延伸长度;混凝土预裂将在一定程度上降低预应力CFRP对加固梁抗弯性能的增强作用。     

基于XFEM的预应力混凝土梁裂纹扩展研究

混凝土开裂多是由于混凝土材料中拉应力超过抗拉极限引起的,在工程中常用预应力来增强混凝土整体的抗拉性能。为了研究预应力的施加如何阻止混凝土中的裂纹扩展,基于ANSYS仿真建立有、无预应力的预制裂纹混凝土梁的扩展有限元模型,在相同的荷载施加条件下进行裂纹扩展计算。研究发现预应力的施加可以有效提高混凝土开裂的临界荷载且加剧混凝土开裂的突然性;同时,还会改变裂纹扩展模式,使裂纹随着荷载的增加发生逐段的突变扩展,区别于无预应力混凝土梁中的裂纹连续扩展;在相同荷载作用下,相比无预应力混凝土,预应力的施加显著降低了底部裂纹的扩展长度及裂纹最大张开宽度,有效的控制了裂纹扩展。     

方钢管超高强混凝土短柱轴压性能数值模拟分析

通过有限元软件ＡＢＡＱＵＳ建立方钢管超高强混凝土短柱轴心受压非线性有限元计算模型,研 究了构件受力行为,分析了混凝土强度、含钢率及钢材屈服强度对核心混凝土纵向应力－应变关系以及 构件承载力的影响。结果表明:构件均为强度破坏,方钢管超高强混凝土短柱轴心受压全过程主要分为 弹性段、弹塑性段、下降段、平稳段四个阶段;混凝土强度及含钢率对核心混凝土纵向应力－应变关系曲 线影响较大,钢材屈服强度对其影响不明显;提高混凝土强度、增大含钢率和提高钢材屈服强度均能显 著提高构件承载力,但构件延性随混凝土强度增加而降低,钢材屈服强度对构件延性影响不明显。     

各因素对简支Ｔ形截面钢筋混凝土 梁抗爆性能的影响

利用ＬＳ－ＤＹＮＡ软件建立了简支Ｔ形截面混凝土梁有限元模型,分别对梁整体振动频率、梁钢 筋应力、混凝土破坏程度进行了分析并研究了配筋率对爆炸荷载作用下梁抗爆性能的影响,以及截面高 度与翼缘尺寸的改变对梁抗爆性能的影响。研究发现:爆炸荷载作用下梁的振动频率均小于固有频率; 与增加纵筋配筋率相比,增加箍筋配筋率能更有效地提高梁抗爆性能,增加梁截面高度会使梁振动频率 增大,提高梁抗爆性能;增加翼缘宽度不利于提高梁抗爆性能,但是增加翼缘厚度能减小梁跨中截面挠 度、增大振动频率、增加梁整体刚度,从而有效地提高梁的抗爆性能;跨中截面梁底纵筋最大应力小于钢 筋屈服强度（ｆｙ＝400ＭＰａ）,支座处箍筋应力超过钢筋屈服强度;“提高箍筋配筋率＋增加梁截面高度＋ 增加翼缘厚度”为提高Ｔ形截面梁抗爆性能的最优组合模式。     

玻璃纤维聚合物筋混凝土梁正截面承载力的计算方法

本文以62根玻璃纤维聚合物筋混凝土梁和钢筋混凝土梁的试验结果为依据，分析配筋率对开裂弯矩和极限弯矩的影响。结果表明，配筋率对开裂弯矩的影响较小；当玻璃纤维聚合物筋的配筋率在平衡配筋率和弯剪界限配筋率之间变化时，玻璃纤维聚合物筋混凝土梁的抗弯承载力随着配筋率的增大而增加。最后，讨论了玻璃纤维聚合物筋混凝土梁开裂弯矩和抗弯承载力的计算方法。     

混合配筋超高强混凝土管桩抗弯性能试验研究

为研究 Ｃ105级超高强混凝土对预应力混凝土管桩受力性能的影响,对设计制作的 7根混合配筋预应力混凝土管桩（ＰＲＣ管桩）和 1根预应力混凝土管桩（ＰＨＣ管桩）进行了抗弯性能试验,分析超高强混凝土（Ｃ105）和非预应力钢筋配置等对 ＰＲＣ管桩受弯性能的影响。试验结果表明:超高强混凝土ＰＲＣ管桩和 ＰＨＣ管桩均呈现为受弯破坏;ＰＲＣ管桩抗弯承载力较 ＰＨＣ管桩有明显提高,且随非预应力钢筋配筋率的提高而增大,提高幅度约为 32％;非预应力钢筋的配置对开裂弯矩影响不大,但使 ＰＲＣ管桩的裂缝分布范围更广（平均裂缝间距约减小 18％）,变形更加充分,延性得以提高。     

湿热环境下预应力CFRP加固高强混凝土梁的抗弯性能研究

为研究高温、高湿环境对碳纤维布加固高强混凝土梁抗弯性能的影响,在温度为４０℃和温度为２０℃环境下,对ＣＦＲＰ预应力及非预应力加固的２４根梁进行弯曲试验。结果表明:在温度为２０℃的自然环境下,与无ＣＦＲＰ布粘贴的基准梁相比,粘贴非预应力ＣＦＲＰ布加固的试验梁,其开裂荷载提高３５．６％,极限荷载提高３７．６％,并且随着ＣＦＲＰ的施加和预应力等级的逐渐加大,其开裂荷载显著升高;在温度为４０℃的湿热环境下,与无ＣＦＲＰ布粘贴的基准梁相比,非预应力ＣＦＲＰ加固的试验梁,其开裂荷载提高２７．３％,极限荷载提高２９．３％,随着ＣＦＲＰ预应力等级逐渐提高,其开裂荷载呈逐渐增大趋势;与温度为２０℃自然环境相比,在温度为４０℃的湿热环境下,试验梁的开裂荷载与极限荷载呈下降趋势,且随着预应力等级的增大,下降幅度变大。     

两跨三层型钢超高强混凝土框架抗震性能试验研究

为研究型钢超高强混凝土框架的抗震性能,在恒定轴向压力和往复水平荷载作用下对一榀两 跨三层的型钢超高强混凝土框架进行试验研究,观测其破坏形态,得到框架试件的荷载—位移滞回曲 线,分析了型钢超高强混凝土框架的破坏机制、滞回性能、延性、耗能能力、强度及刚度退化等力学性能。 结果表明:本框架试件基本实现了梁铰破坏机制,在试验轴压比高达０．３８的条件下,试件的滞回曲线圆 润饱满,位移延性系数为４．３２～６．０６,极限破坏时的等效黏滞阻尼系数达到０．２９５,框架试件的强度和刚 度退化较为平缓,说明其具有良好的变形性能和耗能能力,即型钢超高强混凝土框架的抗震性能优良。     

基于声发射信号表征混凝土断裂过程的异常现象

混凝土作为一种人工石材,由于浇筑过程的影响,其断裂破坏过程不可避免地存在一定随机性。利用声发射实时动态无损监测技术,分析了带预制裂缝混凝土三点弯曲梁试件裂缝扩展发生偏移和钢筋混凝土三点弯曲梁破坏荷载循环增减等特殊试验现象存在的客观性。试验分析发现,预制裂缝尖端粗骨料的存在,致使裂缝并非沿着预制裂缝直接向前扩展,而是出现绕道扩展的现象;配筋率过大时,钢筋混凝土三点弯曲梁试件的破坏荷载值将维持在钢筋极限屈服强度附近循环变化。可见,钢筋混凝土三点弯曲梁试件的失稳荷载取决于配筋率的高低。研究成果表明声发射技术可为开展混凝土损伤断裂试验提供一种新的研究手段。     

SPATIAL AND TEMPORAL WATER QUALITY VARIABILITY IN AQUATIC HABITATS OF A CULTIVATED FLOODPLAIN

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off‐channel habitats were connected to downstream regions 0.10% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L^?1, the median total phosphorus was 0.29 mg L^?1 and the median total nitrogen was 1.56 mg L^?1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.     

Spatio‐temporal variation of gross CO2 and CH4 diffusive emissions from Australian reservoirs and natural aquatic ecosystems,and estimation of net reservoir emissions

Carbon dioxide (CO₂) and methane (CH₄) diffusive emissions were measured during two field surveys in Queensland and Tasmania, Australia, using the floating chamber method. Bubbling and degassing emissions in 2010 were estimated in Koombooloomba Dam reservoir using only inverted funnels and gas concentrations, respectively. A total of 14 reservoirs and 16 rivers and lakes were sampled from 2006 to 2010. Spatial variation was substantial within each water body, as well as between them. The main drivers of diffusive emission variation were physiographic region and climate, with a clear demarcation being observed between diffusive emissions from tropical Queensland and temperate Tasmania, and between the humid West Coast Range (Tasmania) and dry Central Plateau (Tasmania). Higher CO₂ and CH₄ diffusive emissions were observed during the dry season, when long water residence times would promote organic matter degradation. Estimated total gross emissions, including diffusive, bubbling and degassing emissions, for Koombooloomba Dam reservoir were about 1.5 × 10⁶ t CO₂eq km² per year, or 24 × 10⁶ t CO₂eq per year. This corresponds to a plant emission factor of 3.18 kg CO₂eq MWh^?1. Using an estimate of terrestrial emissions derived from literature data for the Tully River catchment area, rough estimated net emissions from the catchment area are about 44 kt CO₂eq per year, or 5.83 kg CO₂eq MWh^?1, which is in the lower range of the studied reservoirs.     

Serial discontinuities in a Rocky mountain river. II. Distribution and abundance of trichoptera

River regulation in the headwaters and middle reaches of the Gunnison River, Colorado, significantly altered distributions and abundances of Trichoptera fauna. Twenty-five species were collected from mainstream samples, with the greatest species richness occurring at an unregulated, rhithron segment above the central reach dams. At sites immediately below the three hypolimnial-release dams and a reregulation dam, species richness was reduced 35–90 per cent and abundance > 95 per cent. Net-spinning caddisflies were the dominant trichopterans at unregulated sites; Arctopsyche grandis in the upper reaches (218 organisms, 586 mg dry mass m^?2) and Hydropsyche cockerelli, H. occidentalis and Cheumatopsyche pettiti in the lower river (9041 total organisms, 6621 mg m^?2), downstream from the last dam. The observed distributional pattern of low trichopteran densities in dam tailwaters and high hydropsychid densities at sites 60–80 km below the central reach dams is a classic expression of continuum resets and adjustments in response to stream regulation as predicted by the Serial Discontinuity Concept.     

Surveying for Water Resources

Abstract

A professional Land Surveyor (Geomatician) describes the Hydrogeologists' survey requirements of a major water resources assessment for the government of The Sultanate of Oman (1992 to 1996). The need for objective specifications is stated. Specialist terms like geoid, spheroid, Mean Sea Level are explained and how to relate spheroidal levels to the geoid. Methods like traditional survey, satellite survey, and photogrammetry are introduced. The paper encourages coordinated working for the benefit of water resource assessment and recommends employment of the professional land surveyor for major studies.     

The Impact of Economic Development on Water Pollution: Trends and Policy Actions in Malaysia

The paper examines the impact of development activities on water pollution in Malaysia. Hence, the main objective of this paper is not just to examine the trends of development-induced water pollution around the region of the country but to know where the problems are and the policy measures taken by the government. It evaluates the probable causative relationship between problems introduced due to technology employed in water pollution control and governmental policy measures. It examines the relationship between development indicators as sources of pollution and polluted rivers over a period of 12 years. The findings of the paper have shown that despite the policy enforcement actions against the identified sources of water pollution, all the three development indicators (chosen based on those identified sources) still accounted for high percentage of river pollution in Malaysia. The findings of the paper were used to identify the central fact of the location of the problem. Some crucial conclusions of where the problems likely to be, as reflected in the findings, are: (a) the issue of interactive-effects between pollutants that many policy-makers are not aware of. This is when policy measures concentrate only on one source of water pollution; (b) the enforcement strength and/or effectiveness of policy measures themselves; (c) financial constraints to invest in appropriate technology especially sewerage systems for controlling human source of water pollution in the country; as well as those confronting small polluting industries (d) finally, lack of cooperation between government and private business firms to comply with regulatory policies for water pollution control.     

Intangible Flood Damage Quantification

Flooding is a natural disaster that may cause tremendous tangibleand intangible damage to the national economy. The tangible damage assessment, i.e. the monetary value of all direct and indirect physical damages, has already been studied, whileintangible damages have not yet been taken into account. Thisarticle, therefore, is the first systematic attempt to assess bothtangible and intangible damages. The new proposed Anxiety-Productivity and Income Interrelationgship Approach (API) has been developed to quantify the intangible damage in monetary terms. The Bangkok area has been selected as the research area because several severe flood events have occurredthere over the last two decades. The 1983 Bangkok flood caused 6600 million baht in damage, according to estimates by the National Statistical Office (NSO). This article examines the totalflood damage (including the intangible damage) at different flood magnitudes. Case studies with and without flood mitigation projects are studied and compared. Furthermore, thisarticle also discusses the improvements over the conventional approach offered by the new API methodology.     

Seasonal variation in nutrient retention during inundation of a short‐hydroperiod floodplain

Floodplains are generally considered to be important locations for nutrient retention or inorganic‐to‐organic nutrient conversions in riverine ecosystems. However, little is known about nutrient processing in short‐hydroperiod floodplains or seasonal variation in floodplain nutrient retention. Therefore, we quantified the net uptake, release or transformation of nitrogen (N), phosphorus (P) and suspended sediment species during brief periods (1–2 days) of overbank flooding through a 250‐m floodplain flowpath on the fourth‐order Mattawoman Creek, Maryland U.S.A. Sampling occurred during a winter, two spring and a summer flood in this largely forested watershed with low nutrient and sediment loading. Concentrations of NO increased significantly in surface water flowing over the floodplain in three of the four floods, suggesting the floodplain was a source of NO. The upper portion of the floodplain flowpath consistently exported NH, most likely due to the hyporheic flushing of floodplain soil NH, which was then likely nitrified to NO in floodwaters. The floodplain was a sink for particulate organic P (POP) during two floods and particulate organic N and inorganic suspended sediment (ISS) during one flood. Large releases of all dissolved inorganic N and P species occurred following a snowmelt and subsequent cold winter flood. Although there was little consistency in most patterns of nutrient processing among the different floods, this floodplain, characterized by brief inundation, low residence time and low nutrient loading, behaved oppositely from the conceptual model for most floodplains in that it generally exported inorganic nutrients and imported organic nutrients. Published in 2007 by John Wiley & Sons, Ltd.     

浅淡溢洪道改扩建方案与选择

溢洪道改扩建和进行溢洪道方案布置，要择优选取溢洪道进口型式、防冲消能工，以使其工程量省、施工快、运行管理方便     

Experience in the Introduction of Steam-Water-Oxygen Cleaning, Passivation, and Preservation at the TÉTs-23 Cogeneration Plant of the Mosénergo Company

Conditions of the process of steam-water-oxygen cleaning, passivation, and conservation (SWOC, P, and C) of internal heating surfaces of the boiler and the high-pressure feed heater (HPFH) piping over the steam side are presented. The process produces partial cleaning of the internal heating surfaces from scale and yields a corrosion-resistant protective film that hinders corrosion processes both in the operation of the boiler and in the idle period.     

钢筋混凝土三点弯曲梁断裂韧度计算模型

基于虚拟裂缝模型,针对钢筋混凝土试件在三点弯曲作用下开裂截面的受力特征,在合理假定的前提下,给出了一种计算钢筋混凝土三点弯曲梁的失稳断裂韧度的解析方法。然后,应用该方法计算了初始缝高比 α₀（初始裂缝长度与试件高度的比值）分别为0.2,0.3,0.4,0.5的三点弯曲试件的最大荷载和临界有效裂缝长度,进而求得了钢筋混凝土三点弯曲梁的失稳断裂韧度。通过对计算结果与试验数据的误差分析,发现失稳断裂韧度最大误差为4.915%,说明这种方法可以较为准确地预测三点弯曲梁的失稳断裂韧度。在此基础上研究了初始缝高比 α₀对失稳断裂韧度的影响,发现失稳断裂韧度基本上不随 α₀ 变化,失稳断裂韧度可以作为材料常数,应用于裂缝扩展状态的判断。