| One of the most important problems in the field of geotechnical engineering is prediction of bearing capacity and settlement of pile foundations of structures, especially for port infrastructures which play a significant role in sustaining an economy. In a shipbuilding industry, pile structures, such as a foundation of overhead cranes, are subjected to a repeated loading under daily function. Many researches have already been conducted to investigate the effects of a daily workload on an overhead crane foundation located on the reclaimed Shanghai sand ground. However, the effect of repeated loading on a reclaimed Shanghai soils located has not been fully understood.The overall objective of this research is to investigate the behavior of crane foundation under the crane load function. This includes experimental and analytical verification. Recently, the study for model test result on this repeat-loading settlement has been conducted. In this thesis, scope of research is mainly aimed at analysis to confirm these experiment results done before through elasto-plastic finite element method. The result of whole numerical analysis is grasped from the nonlinear analysis technique by two-dimensional finite element method using the subloading tij model (Nakai & Hinokio 2004) as an elastoplastic constitutive model. This model can describe typical stress deformation and strength characteristics of soils such as the influence of intermediate principal stress, the influence of stress path dependency of plastic flow and the influence of density and/or confining pressure. Finally comparisons of observed result and computed result are discussed.The main contents in this thesis are as follows:1. First chapter presents the general background of research. With the continuous prospering of the world ships market, Chinese ships industry unceasingly expands the development. In order to enhance the ships product technology content and the attachment value the State Commission of Science and Technology for National Defense Industry carried out "the High-tech Ships Scientific Research Plan", and also vigorously advances the innovation of ship shape and the implementation brand strategy. For these reason, recently three huge ship building bases are being under construction in China. In spite of these progresses day by day in the ships industry, ship factory still lacked crane facilities. To determine the weight caused by daily work experimental space was constructed in the shipbuilding base, and finally we got a result; minimum is several hundred ton; maximum is over one thousand. Pile foundation of crane is withstanding not only outside loading from daily work, but also itself static load. Moreover, it also must withstand the circulation load caused by the crane loading and unloading.One of the most important considering points of bearing load characteristics is the repeated loading ratio, and another characteristic is the certain circulation load the frequency. According to the major results from recent studies, present research also still could not investigate the behavior of crane foundation under cyclic load function. Therefore, there are urgent needs to conduct a research for a crane foundation behavior under repeated loading. However, in the present design handbooks and the standards in china, there are no special considers of circulate loading leading to settlement problem, moreover in the computation method large number of circulations are not considered. During the actual project, there are huge demands to construct heavy, big, and high, pile foundation in view of the present shipbuilding base, if can be solved well, and it is possible to say that the construction cost will be reduced with the guarantee of project security and significant practical advance. Many researches have already been conducted to investigate the effects of a daily workload on an overhead crane foundation located on the reclaimed Shanghai sand ground. However, the effect of repeated loading on a reclaimed Shanghai soils located has not been fully understood.In this chapter, recent researches were reviewed with specific focus on theoretical methods for pile-ground interaction and model tests under cyclic loading. During the last few decades, several researchers have studied the behavior of shaft piles using both laboratory tests and theoretical studies. From both reviews, it is clear that research history was divided into three parts. First section was stated in 1960s, investigation was focused on the pile type subjected to cyclic loading as preparation period. In the 1960's and 1970's, second stage was outgrowth period by numerical analysis, of which advancements have made complicated cases possible to calculate and also computational efforts required with analytical models described below are the least. In recent years, extensive researches and developments have been undertaken to predict more practical and complicated conditions, such as three dimensions, by using nonlinear constitutive model.Soil-pile interaction is a very complicated phenomenon. This complexity is mostly attributed to the soil, rather than to the pile, and it also involves other phenomena such as soil nonlinearity, soil pile gapping, developing of excess pore pressure. Consequently, there are many analytical models which consider this phenomenon with varying levels of emphasis. In general, it is possible to classify the different analytical-numerical models in three groups (1) Continuum solution, (2) Finite element solution and (3) Discrete models. Finite Element Method was frequently used in engineering practice for solving stress analysis problems of which dimensions, mechanical behavior and constitutive model have been chosen by users. In this research, numerical analysis based on Finite Element Method with elastoplastic constitutive model was performed.2. The second chapter presents outline of model tests where experimental method, equipment, and basic procedure are explained. In this research, model tests for a shaft pile are performed with sand and clay respectively. In advance, characteristic of overhead crane loading was investigated in the practical site research. The size of the model ground is 1.6m in width, 0.9m for sand in height, 1.2m for clay in height. The model pile of 1m in length, outer diameter of 16mm, inside diameter of 12mm (304 stainless steel piles) is set up in the Shanghai sand ground where the penetration depth of the pile is 60cm. Here, scale of tank and pile was decided based on the research Chen Zhu Chang (1989), where boundary affection was discussed deeply.3. The third chapter describes results of laboratory test for investigating the characteristic of soil sample where laboratory test will describe physical and strength behavior of sand and clay used in model test. In the case of sand, the sample from Chongming Island was dried and disturbed for preparation, and then consolidated-drained triaxial test, cyclic triaxial test and isotropic test were performed by using the triaxial measurement system. In order to get a parameter of peak strength Rcs, consolidated-drained triaxial test have been carried out under consolidated drained condition with constant lateral stressσr, whereβis obtained from stress-strain relationship. As for compression index and swelling index, stress path of isotropic consolidation test was illustrated to assume normal consolidation line. After these procedures, finally, the density parameter aAF was determined by Cyclic triaxial compress test with constant lateral stress and q/p amplitude. On the other hand, for clay, sample from experimental tank was prepared under saturated and undisturbed condition, and then consolidated-undrained triaxial test, cyclic triaxial test and isotropic test were performed by using triaxial measurement system. Isotropic consolidation test have been performed to determine compression index. As for the swelling index, one dimensional consolidation test, where clay was subjected to be unload-reload cycle for estimating of the recompression characteristics, were conducted. Moreover, another triaxial test have been carried out under consolidated undrained condition with constant lateral pressure so that a parameter of peak strength ratio was determined.4. The fourth chapter presents the outline of numerical analyses in axi-symmetric condition. Numerical analysis was carried out to confirm the influence of repeated loading on the single pile where three types of soil ground, dry-sand, saturated-sand and clay with different ground depths and ground water lines were performed. This chapter covers the layout of numerical analyses and parameter of soil used in this research. Although model tests are carried out only for getting loading and settlement relations, in numerical analyses both loading and settlement relations and soil stresses in the vertical direction of ground elements are calculated. In this chapter, three types of soil have been used in these analyses for same diameter of apparatus. The scale of these apparatus is made with the similarity of real experiment. Solid elements are used as single pile in finite element analyses.In order to predict properly the deformation and the failure of the ground, numerical analysis should be conducted using a simple and generalized constitutive model for soils. In this study, elastoplastic constitutive model for soils named subloading tij model (Nakai and Hinokio, 2004) is used. This model can describe properly the following typical characteristics of soils, in spite of its small numbers of parameters:(1) Influence of intermediate principal stress on the deformation and strength of soils.(2) Influence of stress path on the direction of plastic flow, and (3) Influence of density and/or confining pressure. To describe the whole characteristics, SMP (Spatially Mobilized Plane) concept was suggested in the first stage. Since the plastic strains are predominant in soil response, Matsuoka-Nakai has established a generalized flow rule, using the SMP, which is an almost independent of path. In the tij model, stress parameters are the functions of stress invariants but the strain increment parameters are the functions not only of the strain increments but also of the stress invariants. Nakai and Mihara proposed a modified stress tensor tij that is the function of ordinary stress and its invariants and whose principal directions are coaxial with the principal directions of ordinary stresses. For the next stage, constitutive model with modified tij was improved to rectify the problem, such as over prediction of volumetric strain and un-stabilization of strain during cyclic loading, the evolution rule of the rotational variable is modified and a subloading surface is introduced. Subloading surface always expands or contracts such that the current state of stress lies on it but can never go beyond the normal yield surface. Both normal yield surface and subloading surface move in the stress space keeping similarity in their shapes. As for the influence of stress path on the direction of plastic flow, it is considered by dividing the plastic strain increment into two components - the plastic strain increment dεijp(AF) satisfying the associated flow rule in tij-space as mentioned above and the isotropic plastic strain increment dεijp(IC) under increasing mean stress - in spite of employing just one yield function and one strain hardening parameter.5. The fifth chapter represents the comparison of numerical analysis and model test where the influence of repeated load range is discussed. Finally, the sixth chapter summarizes the overview of the main conclusions. The comparisons of experimental and numerical result are summarized as follows: During the monotonic loading test, in spite of different soil ground, it is seen that the calculation result overestimates the displacement result of model test. However, initial condition of load-displacement response is totally matched with observed result. As for the cyclic loading test, through all comparison, it is possible to say that the calculation results overestimate the circulation settlement. Meanwhile, initial stiffness indicates an acceptable value for all cases. Consistently, those analysis results show very good agreement with the results of the model tests in qualitatively. In terms of the comparison of three different multiplied patterns, once the load is applied over specific value, the experiment result shows a significant plastic deformation, of which characteristic is properly illustrated by computed result. For this meaning, it is possible to say that appropriate numerical analysis, which is able to describe a one loading test result well, enable us to distinguish where the huge displacement is observed or not.6. In this thesis, model tests and numerical analyses were carried out to examine the effects of a daily workload on an overhead crane foundation located on reclaimed sand ground in Shanghai.The results of these researches are summarized as follows:(1) In spite of different soil properties, it becomes clear through the experimental and numerical study that under smaller circulation load an accumulative displacement is still achieving the limit value, in spite of the long-term function. However, once the circulation load surpasses a stable tolerance, displacement of pile head will be significant large, which causes the construction adverse effect. Moreover, it is clear that the numerical analysis in which typical mechanical behavior of soils is appropriately taken into account, can predict well the behavior of shaft pile under cyclic loading condition.(2) By comparing all calculated results with observed ones, it is clear that the numerical analyses can well simulate the observed behavior about bearing capacity under monotonic loading, qualitatively and quantitatively. The results are quite acceptable for all cases. There were, however, some small differences in the behavior during the later stage of loading.(3) The analysis show very good agreement with the results of the model tests qualitatively. The calculation results, however, overestimate the observed circulation settlement quantitatively.(4) As for the parameters and characteristics of sand and clay, laboratory tests strongly indicate that properties of Shanghai sand and clay are quite similar to those of Toyoura sand and Fujinomori clay.For improvement of this research, the following points are indicated:First, it is possible to say that parameters were not good enough to perform the numerical analysis and still there were many uncertain things in the numerical analysis. Second, it might be a cause of characteristic in constitutive models, having a tendency of plasticity displacement under the subloading surface during the reloading condition. For this reason, without expansion loading, plasticity displacement was continuously increasing whole analysis procedure by subloading tij model of which hardening rule was located as isotropic hardening rule. In order to overcome these issues, kinematic tij model following the kinematic hardening rule was suggested in 1999. This model allows the yield surface to rotate in the modified stress-space and hence expresses the stress-induced anisotropy in the deformation behavior of clay. A subloading surface has also been considered in this model for the smooth transition from elastic to fully elastoplastic state. Also it pertinently expresses the increase of strength and stabilization of strains due to over consolidation or cyclic loading. However, in this research, behavior of shaft pile settlement under the repeated loading was acceptable in spite of these issues.
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