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1.
黏土中鱼雷锚抗拔承载力数值分析 总被引：2，自引：1，他引：1
基于Abaqus软件,针对预埋在一定深度鱼雷锚的抗拔承载力进行3D数值分析,探讨了锚型、土体类型、拉拔荷载倾角、拉拔荷载水平分量与锚翼夹角等多种因素对拉拔承载力的影响。计算结果表明:在均质土、正常固结土和两层土体中,带4个锚翼鱼雷锚增加56.22 m2的锚翼侧面积,其拉拔承载力比无锚翼的提高1.9倍以上;当锚翼侧面积相同时,增加锚翼的宽度可以有效提高锚的承载力;拉拔荷载倾角α在30°～45°范围内,可获得较大拉拔承载力;锚翼宽度越大,拉拔荷载水平分量与锚翼间的夹角β对鱼雷锚水平承载力影响越明显;经归一化的V-H包络线公式对工程应用中预测鱼雷锚的承载力有一定参考价值。 相似文献
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目前没有规范给出串锚的水平承载力计算公式,为了利用有限元法研究串锚水平承载力特性,采用相关理论计算以及室内试验的方法来验证有限元法模拟计算的可靠性。实践证明,有限元法具有较高的计算精度。利用有限元分析软件ABAQUS建立了串锚-土体模型,模拟串锚在水平荷载作用下破坏过程,研究了串锚在水平荷载作用下破坏机理,从而得到了串锚水平承载力特性。在相同的工况条件下,串锚的水平承载力与其锚链长度有关,在一定范围内,增加锚链的长度可以提高串锚的水平承载力;串锚的水平承载力不是相应的单个锚的水平承载力相加,其水平承载力小于相应的单个锚水平承载力之和,在进行串锚水平承载力设计计算时应给与相应的考虑。 相似文献
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法向承力锚是一种新型的适用于深海工程的系泊基础,其极限抗拔力是锚在工程应用中的关键指标。尝试用两种不同的方法评估法向承力锚的极限抗拔力,其一是基于塑性上限分析理论;其二是运用非线性有限元数值方法。与已有的经验公式相比,所建立的计算模型不仅可考虑海床土性质,还能反映锚板定位(嵌入深度及角度)以及系缆力角度对锚极限抗拔力的影响。在与已有评估方法进行比较的基础上,还特别对锚板的嵌入深度、角度以及系缆力角度变化对极限抗拔力的影响规律进行了分析,对三种方法的适用性进行了评述。 相似文献
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针对海相软土地区螺旋钢管桩承载力低与腐蚀问题,提出一种新型压力注浆螺旋钢管桩,并设计5根足尺试验桩,进行现场抗拔承载性能试验,研究螺旋叶片直径与排布方式对成桩直径与桩基抗拔承载性能的影响.结果表明,成桩直径与螺旋叶片直径呈正相关,在每节延长段钢管末端设置螺旋叶片利于提高水泥土柱完整性,使成桩直径更为饱满,提高桩基的抗拔承载性能.将试验结果和现行规范抗拔极限承载力计算结果进行对比,计算结果约为实测平均值的94％,在此基础上提出压力注浆螺旋钢管桩抗拔承载力计算参数修正建议,为后续的设计提供参考. 相似文献
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对利用有限元计算分析张紧式吸力锚承载力的方法进行了研究,结果表明:锚土之间接触特性的描述取决于锚的破坏模式;当锚为竖向破坏时,采用临界剪应力摩擦模型描述锚土间接触是恰当的;当锚为水平破坏时,采用库伦摩擦模型描述锚土间接触是恰当的。计算中若采用基于Mises屈服准则的理想弹塑性本构关系描述软土的不排水应力应变特性,且按位移标准确定极限承载力,则弹性模量的取值对确定软土中吸力锚承载力有影响且取决于锚的破坏模式;当锚发生竖向破坏时,弹性模量按约150倍的不排水强度取值是恰当的;当锚发生水平破坏时,弹性模量按约75倍的不排水强度取值是恰当的。探讨了依据软粘土循环强度利用拟静力弹塑性有限元计算,估算平均荷载与循环荷载共同作用下吸力锚平均位移变化趋势的可行性,计算与模型试验结果比较说明,计算得出的拟静力荷载位移曲线能够对锚实际平均位移的变化趋势给出一个恰当的估计。 相似文献
7.
Spar平台吸力式基础极限承载特性数值分析 总被引：2，自引：0，他引：2
以国外某深海Spar平台工程为背景,针对其所采用的细长型吸力式基础的抗拔承载特性进行三维有限元数值分析.分析中充分考虑土体强度、加载位置和加载角度对吸力式基础极限抗拔承载力的影响,本构模型中钢筒基础采用弹塑性模型.分析结果表明,吸力式基础的极限抗拨承载力随着土体强度的增大而增大,倾斜加载时在基础插入土体部分中点左右加载可取得最大的极限承载力,极限抗拔承载力还随着加载角度的增大而增大.吸力式基础存在倾斜加载时桶基础与桶内外土体的共同塑性屈服破坏和垂直加载时桶外土体的局部剪切破坏等两种不同的破坏模式. 相似文献
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重力锚锚固是一种常见的锚固形式。为了能够提供足够的水平承载力,传统型式的重力锚普遍比较笨重,在上拔回收时会产生较大的竖向吸附力,不利于重复利用。针对此问题,设计了一种新型铰接式重力锚,并阐述了其铺设与回收方案。其次采用有限元方法对其整体强度进行了校核,结果均符合规范。最后基于模型试验,对铰接式重力锚在黏土中的运动过程进行了研究,进而确定了其在黏土中的水平承载力和回收时的上拔力。结果表明：相较于传统重力锚,新型铰接式重力锚在确保水平承载性能的基础上,能够大幅减小上拔力,从而有效地降低铺设和回收作业的难度,且可适应多种海底土质,但该锚型仅适用于悬链线式系泊系统。相关研究结果可为实际工程中铰接式重力锚的设计提供参考。 相似文献
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锚泊基础的承载性能直接影响着海洋浮式结构物的稳定性,因而研究新型有效的锚泊基础已成为海洋工程结构设计中的关键问题之一。文中提出了一种基于海洋软土液化特性的伞状锚,充分利用桩端土体增强抗拔承载能力。应用二维颗粒流分析程序,对该新型伞状锚的安装、抗拔承载能力进行了数值模拟,并与普通锚桩进行比较分析,验证其有效性。针对伞状锚与普通锚桩在拉拔过程中的土体破坏机制,从细观角度分析了其抗拔承载能力的提高机制。研究结果表明,对于相同抗拔锚泊设计竖向承载要求,伞状锚所需材料可大为减少,安装难度明显减低,是值得推广应用的新型锚泊基础形式。 相似文献
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In the field of ocean engineering, a beginning has been made in the use of large‐sized suction anchors for safe anchoring of large compliant structures. Suction anchors derive most of their uplift resistance from passive suction developed during the pullout movement. This article describes a set of laboratory tests on model suction anchors of three different embedment ratios to estimate the pullout behavior of suction anchors in soft clays typical of Indian marine clays. Tests were conducted on model anchors installed in soil beds prepared at four different consistencies in a test tank. This study shows the influence of soil consistency and embedment ratio (L/D) on the pullout behavior of suction anchors and on the variation of suction pressure at the top of the soil plug. The test results reveal that the behavior of suction anchors is much better than the behavior of open‐ended anchors from the considerations of both capacity and deformation. The consistent development of suction inside the anchor top confirms the plug formation and significant breakout resistance in the form of suction‐induced reversed end bearing. The results are further analyzed in terms of suction breakout factors. Further, the effect of burial depth of suction anchor on pullout behavior is shown. 相似文献
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Plate anchors are extensively used in civil engineering constructions as they provide an economical alternative to gravity and other embedded anchors. The rate of loading is one of the important factors that affects the magnitude of soil resistance as well as soil suction force. This article outlines the effect of pullout rate on uplift behavior of plate anchors (70 mm diameter) buried in soft saturated clay by varying the pullout rate from 1.4 mm/min to 21.0 mm/min. The variation of breakout force and suction force with embedment depth and rate of pull are presented. A correlation between the rate of increase of undrained strength of clay and anchor capacity with rate of strain has been established. Finally an empirical equation has been proposed that includes the rate of pull in the estimation of breakout capacity of anchors. 相似文献
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Plate anchors are extensively used in civil engineering constructions as they provide an economical alternative to gravity and other embedded anchors. The rate of loading is one of the important factors that affects the magnitude of soil resistance as well as soil suction force. This article outlines the effect of pullout rate on uplift behavior of plate anchors (70 mm diameter) buried in soft saturated clay by varying the pullout rate from 1.4 mm/min to 21.0 mm/min. The variation of breakout force and suction force with embedment depth and rate of pull are presented. A correlation between the rate of increase of undrained strength of clay and anchor capacity with rate of strain has been established. Finally an empirical equation has been proposed that includes the rate of pull in the estimation of breakout capacity of anchors. 相似文献
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As offshore energy developments move towards deeper water, moored floating production facilities are increasingly preferred to fixed structures. Anchoring systems are therefore of great interest to engineers working on deep water developments. Suction embedded plate anchors (SEPLAs) are rapidly becoming a popular solution, possessing a more accurate and predictable installation process compared to traditional alternatives. In this paper, finite element analysis has been conducted to evaluate the ultimate pullout capacity of SEPLAs in a range of post-keying configurations. Previous numerical studies of anchor pullout capacity have generally treated the soil as an elastic-perfectly plastic medium. However, the mechanical behaviour of natural clays is affected by inter-particle bonding, or structure, which cannot be accounted for using simple elasto-plastic models. Here, an advanced constitutive model formulated within the kinematic hardening framework is used to accurately predict the degradation of structure as an anchor embedded in a natural soft clay deposit is loaded to its pullout capacity. In comparison with an idealised, non-softening clay, the degradation of clay structure due to plastic strains in the soil mass results in a lower pullout capacity factor, a quantity commonly used in design, and a more complex load–displacement relationship. It can be concluded that clay structure has an important effect on the pullout behaviour of plate anchors. 相似文献
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An analytical solution has been developed to estimate the horizontal, vertical, and inclined loading pullout capacities of embedded suction anchors in sand. Validation of the analytical solution on pullout capacities has been made through comparisons with the centrifuge model test results. Primary variables for the centrifuge model tests are the depth to the loading point, the load inclination angle, and the addition of flanges. The results indicate that both the horizontal and vertical pullout capacities of the embedded suction anchor in sand increase, reach the peak and then start to decrease as the loading point moves downward. The inclined loading pullout capacity is very much dependent on the load inclination angle and the loading point. The effect of flanges on the pullout capacities is also found to be significant. 相似文献
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This article reports the response of embedded circular plate anchors to varying frequencies of cyclic loading. The effects of time period of loading cycles and pre-loading on movement of anchors and post-cyclic monotonic pullout behavior are studied using a model circular (80 mm diameter) plate anchor, buried at embedment ratio of six in a soft saturated clay. The frequencies of loading cycles have showed considerable effect on movement of anchors. For given duration of loading, higher frequency cycles cause more movement of anchor than lower frequency cycles. Pre-loading reduces the movement of anchors in subsequent loading stages. When anchors are recycled at a load ratio level less than the pre-cycling load, the movement of anchor in recycling phase are very much reduced, but if the recycling is done at a higher load ratio level, the effect is not that much pronounced and the anchors behave as if they were not subjected to any cycling load in the past. Anchor subjected to cyclic loading and then monotonic pullout shows an increase in initial stiffness, whereas the peak pullout load was found to decrease marginally over that of an anchor not subjected to any cyclic loading. For the present test conditions, the relative post-cyclic stiffness of anchors is found to vary from 1.169 to 1.327. 相似文献
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This article reports the response of embedded circular plate anchors to varying frequencies of cyclic loading. The effects of time period of loading cycles and pre-loading on movement of anchors and post-cyclic monotonic pullout behavior are studied using a model circular (80 mm diameter) plate anchor, buried at embedment ratio of six in a soft saturated clay. The frequencies of loading cycles have showed considerable effect on movement of anchors. For given duration of loading, higher frequency cycles cause more movement of anchor than lower frequency cycles. Pre-loading reduces the movement of anchors in subsequent loading stages. When anchors are recycled at a load ratio level less than the pre-cycling load, the movement of anchor in recycling phase are very much reduced, but if the recycling is done at a higher load ratio level, the effect is not that much pronounced and the anchors behave as if they were not subjected to any cycling load in the past. Anchor subjected to cyclic loading and then monotonic pullout shows an increase in initial stiffness, whereas the peak pullout load was found to decrease marginally over that of an anchor not subjected to any cyclic loading. For the present test conditions, the relative post-cyclic stiffness of anchors is found to vary from 1.169 to 1.327. 相似文献
18.
Abstract In the field of ocean engineering, anchors are used for several purposes. This article studies the behavior of a helical anchor embedded in soft marine clay under vertical repetitive loading. Helical anchors are simple steel shafts to which one or more helical plates are attached at regular intervals. The tests are conducted on a model helical anchor installed in a soft marine clay bed prepared in a test tank. Repetitive loading is applied using a pneumatic loading arrangement. Different cyclic load ratios and time periods are adopted. In each test, after the application of repetitive loading, poststatic‐pullout tests are conducted to observe the effect of repetitive loading on anchor behavior. From the test results, it is found that, up to a cyclic load ratio of 55%, there is no reduction in capacity. Instead, there seems to be a marginal increase in capacity and reduction in displacement. The reasons for this behavior are explained in terms of induced changes in strength and deformation behavior of marine clay under repetitive load. However, at higher cyclic load ratios, there seems to be reduction in pullout capacity of the anchor, and the reason for this is explained in terms of strain criteria. From this investigation, it can be concluded that the deep anchor is more suitable to a marine environment than a shallow anchor. 相似文献
19.
Anchors in sand bed: delineation of rupture surface 总被引：4，自引：0，他引：4
Anchors of very large uplift capacities are required to support offshore structures at great water depths. The capacities of plate and mushroom type anchors are generally estimated based on the shape of rupture surface. An attempt has been made in the present investigation to delineate the rupture surfaces of anchors embedded in submerged and dry sand beds at various depths. The results exhibited two different modes of failure depending on the embedment ratio, namely, shallow and deep anchor behaviour. The load–displacement curves exhibited three- and two-phase behaviours for shallow and deep anchors, respectively. Negative pore water pressures recorded in submerged sand also exhibited variation similar to that of pullout load versus anchor displacement. 相似文献