Experimental Research on Shear Behavior of Reinforced Concrete Composite Beams Under Uniformly Distributed Load

An experimental program was carried out to study the shear behavior of the reinforced con-crete composite beam(RCCB)subjected to two-phase uniformly distributed load.A total of 12 reinforcedconcrete composite beams were tested:10 of them were the RCCB subjected to two-phase uniformly dis-tributed load,the other 2 were the comparative reinforced concrete beams cast at the same time as theRCCB subjected to one-phase uniformly distributed load.The interface of precast unit and recast concretewas natural and rough.The test range of the main composite factors:the ratio of precast section depth tocomposite section depth was from 0.35 to 0.65,the ratio of first-phase load moment to precast section ulti-mate bearing moment was from 0.25 to 0.65.Based on the test results,the stresses of the longitudinal rein-forcements and stirrups,the load-bearing properties of the interface,the crack state and the failure charac-teristics of the RCCB under uniformly distributed load are discussed.The effects of the stirrups,the     

深海采矿系统长距离垂直输运管道力学性能研究

深海采矿系统中的长距离垂直输运管道在工作中具有复杂的流固耦合力学特性,在生产作业中其结构安全性和可靠性面临严峻考验。建立深海采矿系统从海底到水面的完整模型,采用集中质量法对于其中的长距离垂直输运管道的环境载荷进行了研究,并将计算结果与模型试验测量值进行对比验证,重点分析管道顶部轴向张力和剪力的大小关系以及变化规律。分析结果表明:在深海采矿系统的长距离垂直输运管道中,轴向张力在结构载荷占主要成分,由波浪引起的结构轴向张力增加会达到管体自重的38%～48%。因此,选择合适的作业工况对降低结构载荷,加强结构安全性能有很大帮助。     

Bilge keel loads and hull pressures created by bilge keels fitted to a rotating cylinder

This paper presents bilge keel loads and hull pressure measurements carried out on a rotating cylinder in a free surface water basin. A flat plate bilge keel and one more complex shaped bilge keel were studied to investigate the geometry effect. The draft of the cylinder was varied to study the effect of the vicinity of the free surface on the bilge keel loads and hull pressures. The rotation axis of the cylinder was fixed to define a pure roll experiment (one degree of freedom).The cylinder was subject to forced oscillations of varying amplitude leading to a KC range of 0.3–16. Using Fourier analysis the first three harmonic coefficients representing the normal bilge keel load were derived. The first harmonic drag and inertia coefficients are in good agreement to existing experimental data obtained for wall bounded flat plates fitted in a U-shaped water tunnel as reported by Sarpkaya and O’Keefe (1996). New insight is gained by the fact that the addition of higher harmonic contributions is essential to capture the time varying bilge keel normal force.The pressure measurements next to the bilge keel are compared to measurements reported by Ikeda et al. (1979). Similar findings are obtained, showing that the pressure on the hull in front of the moving bilge keel is KC independent while the vortex system in the wake of the bilge keel leads to KC dependent hull pressure distributions. The hull pressure jump over the bilge keel correlates well to the force coefficient on the bilge keel. The complex nature of the vortex induced hull pressures is manifested. The empirically derived hull pressure distribution by Ikeda et al. (1979) for the time instant of maximum velocity is shown to correlate reasonably well to the measured data with some conservatism in the absolute value.Although a cylinder is very different from a ship-shaped section, the experiments provide essential insight into the physics associated with roll damping and into the factors that should be included in a roll damping prediction method.     

拉伸与扭转载荷作用下LNG低温复合软管的力学性能研究

LNG低温复合软管结构复杂,且在运行时受风、浪、流等多种载荷联合作用,其在超低温环境下的力学性能直接关系到其能否安全运行。首先参考江苏某软管公司生产的4英寸LNG低温复合软管,建立软管精细化有限元模型,接着对软管在拉伸、扭转两种轴对称载荷作用下的力学性能进行研究,最后就软管结构尺寸对其力学性能的影响展开分析。结果表明：在拉伸及扭转载荷作用下,不同层芳纶布以及同层芳纶布不同材料主方向在对应波峰、波谷处的受力情况不同。芳纶布铺设角度、芳纶布铺设层数、钢丝螺距以及钢丝直径对复合软管力学性能影响显著,分析相应的灵敏度规律从而对结构尺寸做出调整。研究成果可以为LNG低温复合软管的结构设计提供参考。     

海床表层软土对宽浅式筒型基础承载特性影响研究

近海海床表层多为软黏土或淤泥质土,为探究海床表层软土对海上风电宽浅式筒型基础承载特性的影响,以中国广东某海域风电场为背景,通过有限元分析的方法,研究竖向、水平、弯矩荷载作用下软土层厚度和土体强度对基础极限承载力、破坏模式以及筒基土压力分布的影响。研究结果表明:当软土层厚度小于H/2(H为筒裙高度)时,单向荷载作用下宽浅式筒型基础极限承载力随软土层厚度的增加呈线性减小的趋势;当软土层厚度大于H/2后,承载力降低速率逐渐增大。表层软土的存在,使得塑性区范围缩小,软土层内土体塑性破坏更加明显。竖向荷载作用下,随软土层厚度的增大,筒顶承载先减小后增大,筒内侧摩阻力先增大后减小;水平荷载和弯矩作用下,筒侧被动土压力的降低是引起软土覆盖地基中基础承载能力降低的主要因素。     

轴压作用下双金属复合管组合作用与承载力分析

为探究轴压作用下双金属复合海底管道的组合作用与承载性能,对双金属复合海底管道进行了试验研究和理论分析。开展了不锈钢衬管材料性能试验,对比了国际主流不锈钢本构关系模型和试验结果。利用ABAQUS建立了精细化的双金属复合管道轴压试验有限元模型,系统研究了关键参数如复合工艺产生的环向复合应力、钢管初始缺陷幅值等对双金属复合管在轴压作用下力学性能的影响规律。通过对比已有轴压双金属复合管道试验结果,验证有限元模型。基于验证的有限元模型,对轴压作用下双金属复合管道的组合作用以及径厚比和材料强度对承载力的影响进行了分析。结果表明双金属复合管道的轴压极限承载力主要取决于基管的截面屈服荷载,并随着管径和材料强度的提高而增大。并依据分析结果对双金属复合海底管道的设计提出建议。     

中国南海极端风暴海况下固定式平台结构可靠性分析

基于中国南海海域风暴环境条件,研究分析南海海域固定式导管架平台结构整体性和可靠性,以及新建固定式平台结构设计准则。采用海洋环境数据后报方法,得到南海海域1972~2011共40年的风、浪、流联合数据,从中抽取风暴环境条件;利用通用荷载模型,将40年间的风暴环境数据转变成结构的荷载数据,即基底剪力或倾覆力矩;并计算得到风暴环境荷载的短期及长期分布,以及任意风暴下荷载的概率分布;根据结构可靠性模型,结合荷载的长期分布,研究基于结构暴露等级及失效概率的固定式平台结构强度储备比。根据计算,得到了不同暴露等级下中国南海平台的强度储备比,并与墨西哥湾及北海海域进行了比较,为新建平台提供设计参考。     

Fatigue strength assessment of MARK-III type LNG cargo containment system

The aim of this paper is to investigate the fatigue strength of the GTT Mark-III type LNG insulation system. The LNG insulation system consists of several composite layers with various connections; plywood, triplex, reinforced polyurethane foam and mastic. Consequently, the LNG insulation system may include mechanical failures such as cracks as well as delaminations within the layers due to sloshing impact loads and fatigue loadings. In addition, these failures may cause a significant decrease of structural integrity. In this study, a series of fatigue tests have been carried out for Mark-III type LNGC insulation systems at room temperature considering the effect of sloshing impact. The load levels have been determined based on the ultimate strength of reinforced polyurethane foam. The aim of the study is to investigate the typical failure characteristics of the MARK-III LNG insulation system and to obtain the S–N data under fatigue loading. A consolidated single S–N curve is obtained based on a systematic finite element procedure. Future use of the S–N data in fatigue analysis requires that the response analysis is carried out using a finite element model with the same mesh density and material properties. This study can be used as a fundamental study for the fatigue assessment of the LNGC insulation system as well as a design guideline.     

深海采矿车布放回收中脐带缆轴向张力响应特性研究

在深海采矿车布放回收中,准确预报脐带缆在底部自由悬垂边界条件和顶部波浪载荷随机激励等共同影响下的动力响应是关键点之一。基于三维势流理论与集中质量法,结合水面支持船运动和海流联合激励,对深海布放回收中脐带缆的顶端张力等力学特性进行研究。结果表明：在布放回收过程中,轴向张力在结构载荷中占主要成分;由波浪引起的轴向张力极值与均值差距最大可达到54%;轴向张力的频谱存在双谱峰,分别为 0.14 Hz的主峰和0.10 Hz 的次峰;当浪向角为180°时,轴向张力处于峰谷。     

冰脊形成过程的离散元模拟及影响因素分析

冰脊对极地船舶及海洋工程结构的冰载荷设计及冰区安全运行具有重要的影响,其几何形态是重要的考虑因素。为研究冰脊的几何形态,本文基于Voronoi切割算法构造扩展多面体海冰单元,并使其相互冻结形成平整冰;采用离散单元法模拟海冰在相对运动时挤压形成冰脊的动力过程,统计分析脊帆高度、龙骨宽度、龙骨深度、龙骨水平倾角等主要几何参数,并确定这些几何参数间的对应关系。将离散元模拟结果同冰脊现场观测资料对比分析以验证扩展多面体离散元方法模拟冰脊形成过程的可行性。在此基础上讨论冰厚、冰速、海冰强度等因素对冰脊形态的影响。本文采用离散元方法对冰脊形成过程及几何特性的数值分析可为深入开展冰脊的形成机理及其对船舶、海洋工程结构物的冰载荷分析提供参考依据。     

冰脊间遮掩作用对冰?水拖曳力影响的实验研究

为定量研究多冰脊之间的尾流遮掩作用对海冰漂移运动的影响,物理模型试验（试验有限水深为0.45 m）测量了多冰脊拖曳力的衰减变化。冰脊模型选用底角为45°的等腰直角三角形,选取了4种入水深度、9种冰脊间距进行测量。试验得到了前后冰脊拖曳力及其比值在尾流遮掩情况下的变化规律。前冰脊拖曳力与单冰脊情况一致,与冰脊速度的平方保持线性关系;而后冰脊在间距较小时出现了反向拖曳力,随冰脊间距的增大,后冰脊拖曳系数先减小再增大至不变。前后冰脊拖曳力比值的变化规律可以用指数遮掩函数来描述,该遮掩函数与冰脊间距和入水深度有关而与流速无关。通过与现有海冰模式中的遮掩函数对比,研究结论增强了该指数公式的适用性,加强了对海冰动力学模式中遮掩函数的理解。     

黏土中防沉板—桩复合基础地震反应特性研究

为了研究海底防沉板—桩复合基础在地震荷载作用下的动力反应特性,以我国南海深水工程实例为研究对象,利用Flac3D有限差分仿真软件建立了计算模型,土体采用Mohr-Coulomb本构模型,模型底部输入EL Centro地震波,对不同桩长的复合基础进行分析计算.在该特定工程背景下,研究结果表明:随着桩长的增加,防沉板顶部加速度放大系数呈减小趋势;地震荷载下,复合基础发生震陷,沉降量在地震波加速度峰值过后趋于稳定;当桩长为6m时,复合基础的水平振动程度和震陷量最小;由于桩基础把震动能量传输到深部土层中,复合基础周围土体的加速度响应值小于远场土体.在动力时域内,防沉板与桩连接处弯矩最大,需要在此处增设加固装置.     

Effects of the asymmetric riser and bilge keel arrangements on FPSO green water assessment

This article aims to report important findings on how the asymmetric riser and bilge keel arrangements affect the motion response and green water assessment by using a real FPSO conversion project. Recently, the authors have proposed a practical approach for short-term and long-term green water prediction. In this paper, the method has been further extended to include the effect of truncated bilge keel by using Morrison elements. Numerical studies are conducted focusing on the effect induced by asymmetric riser arrangement and truncated bilge keels. Comparisons of short-term and long-term results between different models indicate that the FPSO’s motion is significantly affected by asymmetrically arranged appendages and attachments in a complicated way. The relative wave elevation is also affected by appendages and attachments, but not the same trend as the motion response. The effect of the asymmetric arrangement of risers and bilge keel on long-term relative wave elevation response has been captured by both traditional contour line approach and response-based analysis, but some discrepancy identified between the results from the two methods indicates the limitation of the traditional contour line approach.     

Field and Theoretical Study of the Response of Super-Long Bored Pile Subjected to Compressive Load

In this article, two full-scale pile loading tests were conducted to observe the field performance of the super-long bored piles, and a simplified approach for nonlinear analysis of the load-displacement behavior of a single pile was presented. The field tests on piles indicates that, under the maximum test load, more than 70% of the pile top settlement is caused by the compression of pile shaft. For practical purposes, the pile top settlement can be reduced through improving the pile shaft strength. When the load reaches the maximum test load, the proportion of the load carried by the pile tip is approximately 30%. The super-long pile is functioning as an end-bearing friction pile. The skin friction at shallow depth is fully mobilized and decreases from a peak value with increasing load. However, the skin friction of deeper soil is not fully developed due to less relative displacement. Furthermore, a BoxLucas1 model is used to capture the relationship between unit skin friction and pile-soil relative displacement, whereas a hyperbolic model is used to describe the relationship between toe stress and pile base displacement. Based on the BoxLucas1 model and the hyperbolic model, a load transfer method is used to clarify the response of a single pile, and a computational flow chart is developed. The efficiency and accuracy of the present method is verified using the field tests on piles. The proposed simple analytical approach is economical and efficient, resulting in savings in time and cost.     

Ultimate load capacities of mooring bollards and hull foundation structures

CSRs (Common Structural Rules for bulker and tanker), which came into effect in 2006, invoke the concept of the ultimate strength of hull girders. While numerous studies associated with the ultimate capacities regarding global hull girders and stiffened panels have been carried out, there are few application cases of the ultimate strengths for deck machineries and their supporting structures. In the present study, nonlinear finite element analyses have been performed to obtain ultimate capacities for a size 450 DIN type bollard including hull foundation structures for which elastic strength assessments based on allowable stress analyses were jointly carried out by a Mooring Fitting SWL Standardization Committee consisting of four major Korean shipbuilders (DSME, HHI, HHIC, and SHI) in 2003. The plastic hardening property is identified from a comparison of the results of ultimate strength simulations and a bollard tension tests performed by the committee. It is assumed that the ultimate load is the corresponding load point when the deformation slope of the bollard column reaches the critical slip angle. It is concluded that the reinforcements appear to be effective with respect to the allowable stress criterion, but are not substantially effective from the point of view of ultimate capacities. In other words, structural reinforcements based on allowable stress analyses may noticeably increase production costs, but do not remarkably raise the ultimate capacities.     

基于广义接触模型的离散元方法及其对船体冰载荷的分析

冰载荷是影响船舶结构安全的主要环境载荷,因而确定破冰船的冰载荷特征可用于船体结构设计及船舶安全预警分析。海冰作为典型的脆性材料,可采用单元间具有黏结失效效应的离散元方法模拟其破碎行为。为有效地模拟海冰破碎的渐进过程,采用由局部黏结点组成黏结单元的广义接触模型。为分析该模型中直接决定黏结单元失效的强度参数的影响,采用海冰单轴压缩和三点弯曲试验数值模拟进行分析。通过模型试验确定了失效模型中法向黏结强度、切向黏结强度和Mohr-Coulomb准则中的接触摩擦系数的影响。将该数值模型应用于极地科学考察船"雪龙号"的平整冰区冰载荷分析中,并与船舶整体冰阻力经验公式进行了对比验证。     

海上风电单桩式支撑结构冰激振动及参数敏感性分析

针对渤海湾某风电场的海上固定式风机支撑结构,采用适用于大直径单桩结构的PSI曲线模拟桩土相互作用,并采用SACS软件建立支撑结构的动力分析模型。首先对支撑结构进行模态分析;其次考虑海冰结构的随机振动作用模式,根据适用于渤海湾的随机冰力谱构造随机冰载荷时程曲线,基于半耦合的时域方法,采用SACS软件对支撑结构进行冰激振动分析,输出塔筒顶部加速度、单桩基底剪力及倾覆力矩等响应参数的时程曲线和响应功率谱;最后针对冰厚、冰速和海冰强度等海冰参数对支撑结构的冰激振动进行敏感性分析。研究结果表明,在随机振动模式下,冰载荷及结构动力响应对冰厚和海冰强度较为敏感,在进行冰激振动分析时应合理确定冰厚和海冰强度等参数。     

Temporary-creep and post-creep properties of aquaculture netting materials

Creep in materials and structures may lead to increasing strains, permanent deformations, change in mechanical properties and rupture at loads significantly smaller than the breaking strength. In this paper, we present data on temporary-creep properties, recovery of strain post creep and post-creep tensile properties of a selection of Raschel knitted netting materials. Creep strain in wet netting materials subjected to a creep target load of 10–90% of average force at break for 30 min varied from 1.6% to 3.5%. The rate of creep decreased with time and decreased target load. The recovery of strain post creep was relatively fast and approximately half of the creep strain was elastic. Post-creep tensile testing showed that the length and force at break were not significantly affected by the creep load history. However, due to permanent deformations of the specimens from the creep test, the nominal breaking strain decreased and the stiffness increased with increased creep target load.     

Structural integrity of Ellisolandia elongata reefs: A mechanical approach to compare tensile strengths in natural and controlled environments

Geniculate coralline algae are oases of biodiversity, providing nursery areas and shelter for the species that live amongst their fronds. The key to their success in the inter‐tidal is the ability to withstand hydrodynamic forces. Under culturing conditions most of the physical and ecological stressors such as intense hydrodynamic forces and grazing are extremely reduced, thus affecting species mechanical properties and their response to external threats. The aim of the present study was to investigate tensile mechanical properties of clusters of fronds of Ellisolandia elongata from natural (sheltered and exposed reef) and culturing conditions (after 1 month of culturing). The tensile test showed that the first failure stress (σ_I) was not significantly different between the natural and culturing conditions, indicating that the two reefs (sheltered and exposed) were characterized by the same distribution of pre‐existing, inherent structural flaws. Interestingly, the σ_max (maximum stress before rupture) was significantly different between the two conditions, with the culturing condition being more resistant to average load compared to the natural conditions. The maximum stress before rupture (σ_max) showed the influence of the environment in reducing the strength and elasticity of the fronds.     

玻纤增强柔性管等效简化模型研究

玻纤增强柔性管作为一种新型海底油气输送管道,具有比强度高、柔度大和抗腐蚀性强等特点,因此在深海油气开发中具有非常广阔的应用前景。玻纤增强柔性管主要由内衬层、增强层和外保护层组成,其中增强层的等效模拟是玻纤增强柔性管设计成功与否的关键。根据玻纤增强柔性管的结构特征和材料特性,选取了四种不同的等效简化模型,对比研究了玻纤增强柔性管在轴向拉压荷载、弯曲荷载以及内压荷载作用下的力学性能。将不同简化模型的计算结果与相应的试验数据进行对比,进行等效模型的优选。研究结果表明,在内压载荷和弯曲载荷作用下,基于Halpin-Tsai模型数值结果与试验结果最为接近。在轴向载荷作用下,采用分离式模型或回形模型计算精度更高,若材料达到屈服状态时,则建议采用分离式模型进行模拟。