离岸深水全直桩码头结构承载特性及简化计算方法研究

发布时间：2018-04-25 22:17

本文选题：离岸深水全直桩码头 + 软土地基　；参考：《天津大学》2016年博士论文

【摘要】：随着运输船舶趋向大型化发展,新建港口码头的位置向离岸、深水区推进,离岸深水区浅层地基土体多为饱和软粘土。全直桩码头结构是适用于软土地基上离岸深水域的新型高桩码头结构型式。然而,该结构型式与传统含斜桩或叉桩的高桩码头结构型式不同,其承载机理、破坏模式与传统高桩码头存在较大差异;结构所处离岸深水区波浪荷载强度更高,波浪循环荷载作用引起的土体循环软化效应显著;离岸深水全直桩码头桩身较长,结构柔度较大,结构基本周期与波浪力、撞击力荷载周期接近,结构动力响应特性、风暴潮浪与结构相互作用等问题突出;在长期波浪循环荷载作用下,离岸深水全直桩码头结构循环累积变形特性尚不清楚。针对以上问题,结合某离岸深水港设计方案,对离岸深水全直桩码头结构承载机理、破坏模式、水平荷载作用下结构稳定性影响因素(考虑土体循环软化效应)、水平荷载作用下结构静、动力简化计算方法以及循环荷载作用下结构循环累积变形简化计算方法等问题进行了系统的研究,主要研究内容、研究方法及研究成果阐述如下:1.借助大型商用有限元分析软件ABAQUS建立了离岸深水全直桩码头结构-地基相互作用的三维弹塑性有限元模型。采用荷载控制方式,结合加载系数及理想塑性流动概念,分析了波浪力、撞击力水平荷载及竖向荷载作用下结构受力、变形及水平荷载作用下沿桩身弯矩与桩侧土压力分布情况。研究了离岸深水全直桩码头结构承载特性及破坏模式,结合桩身弯矩和桩侧土压力分布情况,建议了采用“塑性铰”破坏模式作为判断水平荷载作用下离岸深水全直桩码头结构极限状态的标准。2.通过有限元软件接口子程序将饱和软粘土地基循环强度与Mises屈服准则相结合,基于拟静力分析建立离岸深水全直桩码头结构考虑土体循环软化效应的计算模型,对波浪荷载作用下饱和软粘土地基土体循环软化效应进行模拟。采用有限元法分析了土体循环软化效应对结构稳定性的影响情况,进而探讨了桩基入土深度、桩壁厚度、土性条件、土体循环软化效应及剪胀角对离岸深水全直桩码头结构水平极限承载力的影响情况。3.通过有限元法验算m法、P-Y曲线法和NL法计算离岸深水全直桩码头结构的适用性,得出基于m法的简化计算方法适用于小位移情况;基于P-Y曲线法和NL法的简化计算方法在小位移及大位移情况均与有限元计算结果吻合较好,验证了静力简化计算方法的有效性。结合“塑性铰”失稳判别标准,基于P-Y曲线法、NL法建立了一种通过桩身极限弯矩与设计荷载作用下桩身最大弯矩之比确定离岸深水全直桩码头结构水平极限承载力的简化方法。4.采用模态分析法研究离岸深水全直桩码头结构自振特性,得出了结构基本周期较长,与波浪力、撞击力荷载周期接近,结构动力响应突出的结论。进一步通过计算发现离岸深水全直桩码头结构动力响应可按单自由度系统位移动力放大系数理论公式进行简化计算。在此基础上,基于P-Y曲线法、NL法建立了离岸深水全直桩码头结构动力响应简化计算方法,通过与动力有限元计算结果对比,验证了该动力响应简化计算方法的有效性和可行性。5.根据循环荷载作用下软粘土循环累积变形随循环荷载作用次数的变化趋势与静力荷载作用下土体蠕变随时间的变化趋势相类似的特点,将循环荷载作用次数看作时间度量单位,建立了基于蠕变理论的软粘土循环累积变形计算模型,建议了采用拟静力弹塑性有限元方法计算土体循环累积变形情况。为说明该方法计算全直桩码头结构循环累积变形的可行性,借助ABAQUS有限元软件,利用其接口子程序实现对室内已有的循环三轴试验结果进行数值模拟,结果显示二者基本重合。最后采用该方法研究了循环荷载作用下离岸深水全直桩码头结构的循环累积变形特性。
[Abstract]:As the transport ships tend to be large and large, the position of the new port wharf is moved to the offshore and deepwater areas, and the shallow foundation soil in the offshore deepwater area is mostly saturated soft clay. The structure of the full straight pile wharf is a new type of high pile wharf suitable for the deep offshore waters of the soft soil foundation. The structure of high pile wharf is different, its bearing mechanism and the failure mode are different from the traditional high pile wharf; the wave load intensity of the offshore deepwater area is higher, and the cyclic softening effect caused by the wave cyclic loading is remarkable; the pile body of the offshore deepwater full pile wharf is long, the structure flexibility is larger, the basic structure period and wave of the structure are also. The wave force, the impact force load cycle is close, the structural dynamic response characteristic, the storm wave and the structure interaction are outstanding. Under the action of long term wave cyclic loading, the accumulative deformation characteristics of the offshore deepwater full pile wharf structure is not clear. In view of the above problems, the offshore deep water full straight pile code is used in combination with a offshore deepwater port design scheme. The bearing mechanism of the head structure, the failure mode, the influence factors of the structural stability under the horizontal load (considering the soil cyclic softening effect), the static structure under horizontal load, the simplified calculation method of dynamic force and the simplified calculation method of the cumulative deformation of the structure under cyclic loading are systematically studied. The main research contents are studied. The methods and research results are as follows: 1. with the help of the large commercial finite element analysis software ABAQUS, a three-dimensional elastoplastic finite element model of the structure foundation interaction of offshore deepwater full pile wharf is established. The load control method is used to analyze the wave force, the horizontal load of the impact force and the vertical load, combining the loading coefficient and the ideal plastic flow concept. Under loading, the bending moment of the pile and the distribution of soil pressure on the pile side under the action of load, deformation and horizontal load. The bearing characteristics and failure modes of the offshore deepwater full straight pile wharf structure are studied. The "plastic hinge" failure mode is suggested to be used as a judgement of the horizontal load, which is combined with the pile bending moment and the distribution of soil pressure in the pile side. The standard.2. of the structure limit state of the bank deepwater full straight pile wharf combines the cyclic strength of saturated soft clay foundation with the Mises yield criterion by the finite element software interface subroutine. Based on the pseudo static analysis, the calculation model of the soil cyclic softening effect of the offshore deep water full pile wharf structure is established with the saturated soft clay under the action of wave load. The effect of soil cyclic softening is simulated. The influence of soil cyclic softening effect on structural stability is analyzed by finite element method, and then the influence of pile penetration depth, pile wall thickness, soil condition, soil cyclic softening effect and dilatancy angle on the horizontal ultimate bearing capacity of offshore deepwater full pile wharf structure is discussed. .3. is used to calculate the applicability of M, P-Y curve method and NL method to calculate the structure of offshore deepwater full pile wharf through the finite element method, and the simplified calculation method based on M method is suitable for small displacement cases, and the simplified calculation method based on the P-Y curve method and the NL method are in good agreement with the finite element calculation results in the small displacement and large displacement cases, and the static force is verified by the finite element method. Based on the P-Y curve method and the NL method, a simplified method for determining the horizontal ultimate bearing capacity of offshore deep water full pile wharf is established based on the P-Y curve method and the maximum bending moment ratio of the pile body under the effect of the designed load. The method of modal analysis is used to study offshore deepwater. The self vibration characteristics of the structure of the full straight pile wharf are obtained. The conclusion is that the structure of the structure has a long basic cycle, and the wave force, the impact load cycle of the structure is close to, and the dynamic response of the structure is prominent. On this basis, based on the P-Y curve method and NL method, a simplified calculation method for dynamic response of offshore deep water full straight pile wharf is established. By comparing with the results of dynamic finite element calculation, the validity and feasibility of the simplified calculation method of the dynamic response.5. is verified by the cyclic loading action of cyclic loading of soft clay under cyclic loading. The variation trend of the number of times and the trend of soil creep under the static load is similar to the change trend of time. The number of cyclic loading times is regarded as the unit of time measurement, and the calculation model of cyclic cumulative deformation of soft clay based on creep theory is established, and the calculation of cyclic cumulative variation of soil mass by the quasi static elastoplastic finite element method is proposed. In order to illustrate the feasibility of calculating the cumulative cyclic deformation of the whole straight pile wharf structure by this method, with the help of ABAQUS finite element software, the results of the indoor cyclic three axis test are simulated with its Interface subroutine, and the results show that the two are basically overlapped. Finally, the method is used to study the offshore deepwater under cyclic loading. The cyclic cumulative deformation characteristics of the full straight pile wharf structure.

【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：U656.1

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