本文關(guān)鍵詞：水平循環(huán)及偏心荷載作用下群樁性狀模型試驗(yàn)研究　出處：《浙江大學(xué)》2014年博士論文　論文類(lèi)型：學(xué)位論文

  更多相關(guān)文章： 群樁基礎(chǔ) 水平循環(huán)荷載 偏心荷載 扭轉(zhuǎn)荷載 模型試驗(yàn) 離心機(jī)試驗(yàn) 群樁效應(yīng) 荷載耦合效應(yīng) 荷載循環(huán)效應(yīng) 混凝土群樁 斜樁 ABAQUS

【摘要】：近海工程項(xiàng)目通常體型巨大、結(jié)構(gòu)高聳,其下部基礎(chǔ)除了要承擔(dān)上部結(jié)構(gòu)的自重荷載外,還長(zhǎng)期受到風(fēng)、波浪、水流等水平循環(huán)荷載的作用。群樁基礎(chǔ)在該循環(huán)荷載作用下不僅容易產(chǎn)生累積變形,極端條件下甚至可能發(fā)生破壞。另一方面,大型結(jié)構(gòu)在承受水平荷載時(shí),由于荷載作用方向的隨機(jī)性,傳遞至下部群樁基礎(chǔ)的荷載在某些情況下還可能存在一定的偏心距。這意味著基礎(chǔ)將同時(shí)承受水平和扭轉(zhuǎn)荷載的作用,從而產(chǎn)生復(fù)雜的受力和變形響應(yīng)。目前人們對(duì)群樁基礎(chǔ)在水平循環(huán)及偏心荷載作用下承載性狀的認(rèn)識(shí)存在很多的不足,因此有必要結(jié)合近海工程的特點(diǎn)對(duì)上述問(wèn)題展開(kāi)系統(tǒng)深入的研究。 本文通過(guò)1g大比尺模型試驗(yàn)以及離心機(jī)模型試驗(yàn),分別研究了高承臺(tái)群樁在水平循環(huán)及偏心荷載作用下的受荷性狀。本文開(kāi)展的主要工作及相應(yīng)的研究成果如下： (1)采用鋼管及混凝土分別設(shè)計(jì)并制作了大比尺的單樁及群樁模型,利用浙江大學(xué)大型土工物理模型試驗(yàn)系統(tǒng)開(kāi)展了一系列加載試驗(yàn),對(duì)水平循環(huán)及偏心等復(fù)雜荷載條件下的群樁受力和變形性狀進(jìn)行了系統(tǒng)的研究。全部模型試驗(yàn)包括：1×2鋼管群樁水平偏心加載試驗(yàn)、2×2混凝土群樁水平偏心加載破壞試驗(yàn)、3×3鋼管群樁水平循環(huán)加載試驗(yàn),以及相關(guān)的單樁加載試驗(yàn)。 (2)基于3×3鋼管群樁水平循環(huán)加載試驗(yàn),分析討論了群樁水平剛度、基樁內(nèi)力及荷載分配等響應(yīng)隨荷載循環(huán)的變化規(guī)律,并引入了循環(huán)效應(yīng)系數(shù)以評(píng)估循環(huán)荷載對(duì)樁基水平承載性狀的影響。研究結(jié)果表明,樁基的水平剛度隨荷載循環(huán)次數(shù)的增加而減小,且先期循環(huán)加載歷史會(huì)影響樁基后期的水平加載剛度；各級(jí)循環(huán)加載中,單樁及群樁的樁頭峰值荷載隨循環(huán)次數(shù)增加依次表現(xiàn)出穩(wěn)定型、發(fā)展型和破壞型等三種不同的衰減形態(tài),反映了樁周土體由彈性到塑性再到破壞的發(fā)展過(guò)程；群樁中各排基樁分擔(dān)的荷載比例隨著循環(huán)次數(shù)增加不斷變化,其中前排樁分擔(dān)的荷載逐漸增大；由于承臺(tái)的約束作用,基樁軸向循環(huán)拉壓受荷,導(dǎo)致群樁伴隨水平循環(huán)加載過(guò)程產(chǎn)生嚴(yán)重沉降；荷載循環(huán)效應(yīng)對(duì)群樁水平受荷性狀的影響要比單樁大得多。 (3)基于1×2鋼管群樁水平偏心加載試驗(yàn),分析了群樁的整體變形以及基樁內(nèi)力等響應(yīng),并通過(guò)ABAQUS有限元模擬,討論了不同偏心距大小及基樁布置形式對(duì)群樁水平偏心受荷性狀的影響。試驗(yàn)結(jié)果表明,水平偏心荷載下群樁中各基樁的內(nèi)力存在較大的區(qū)別,離加載點(diǎn)近的基樁承擔(dān)的荷載更大；受水平與扭轉(zhuǎn)荷載耦合效應(yīng)影響,群樁中基樁的抗扭承載力較單樁顯著提高；基樁樁頭扭矩及水平剪力共同抵抗水平荷載偏心引起的附加扭矩,且基樁剪力對(duì)抵抗群樁扭轉(zhuǎn)的貢獻(xiàn)隨荷載的增加不斷增大。數(shù)值計(jì)算結(jié)果顯示,水平荷載偏心距對(duì)群樁整體變形的影響相對(duì)較小,但對(duì)基樁的內(nèi)力影響較大；基樁布置形式顯著影響群樁的水平和抗傾覆剛度,但對(duì)群樁的整體扭轉(zhuǎn)響應(yīng)影響較小。 (4)基于2×2混凝土群樁水平偏心加載破壞試驗(yàn),揭示了群樁的漸進(jìn)破壞過(guò)程,配合數(shù)值分析研究了各基樁的內(nèi)力隨加載的變化規(guī)律,并對(duì)混凝土群樁在水平偏心荷載下的破壞過(guò)程及機(jī)理進(jìn)行了總結(jié)。研究結(jié)果表明,較高的加載高度、上部結(jié)構(gòu)的自重以及樁身混凝土的開(kāi)裂等因素加劇了群樁在水平偏心荷載下的傾覆破壞；群樁在加載初始階段基本處于彈性狀態(tài),各基樁的水平剛度較大；當(dāng)荷載超過(guò)一定的臨界值后混凝土基樁先后出現(xiàn)開(kāi)裂,群樁剛度隨之降低,變形相應(yīng)增大；上部結(jié)構(gòu)自重荷載引發(fā)的P-△效應(yīng)使前排基樁承受的軸向荷載迅速增加,最終前排角樁出現(xiàn)軸向偏壓破壞,群樁及其上部結(jié)構(gòu)隨之發(fā)生整體傾覆。 (5)利用浙江大學(xué)ZJU-400土工離心機(jī),開(kāi)展了砂土中群樁承受水平及偏心荷載的系列模型試驗(yàn),著重對(duì)比研究了直樁群樁與斜樁群樁在不同荷載條件下的變形及承載特性。試驗(yàn)結(jié)果表明,斜樁群樁的水平及扭轉(zhuǎn)承載力均顯著大于直樁群樁；水平偏心荷載下斜樁群樁中各基樁的樁頂位移差異較直樁群樁更大；斜樁群樁通過(guò)基樁軸向受荷可以更有效地抵抗水平荷載。數(shù)值計(jì)算結(jié)果表明,基樁斜度對(duì)群樁水平承載性狀的影響較大,群樁水平剛度隨基樁斜度的增加而增大。 (6)提出了考慮多向荷載共同作用的群樁分析模型；在剛性承臺(tái)的假設(shè)下推導(dǎo)了群樁整體剛度矩陣的表達(dá)式；同時(shí)考慮不同方向的群樁效應(yīng)以及基樁各向荷載之間的耦合效應(yīng)影響,討論歸納了基樁各向剛度的計(jì)算確定方法；總結(jié)了多向荷載共同作用下群樁分析的一般流程,并給出了相應(yīng)的分析實(shí)例。
[Abstract]:Offshore engineering projects are usually large, high-rise structures, the lower base in addition to bear load of upper structure, has long been the wind, wave, flow and horizontal cyclic loading. In the pile foundation under cyclic loading is not only easy to deformation, damage may occur even under extreme conditions. On the other hand large, the structure under horizontal loads, due to the randomness of the loading direction, the load transfer to the lower part of the pile group foundation may also exist certain eccentricity in certain circumstances. This means that the foundation will also bear the horizontal and torsional loads, resulting in stress and deformation response of the complex. At present people understanding of pile foundation bearing capacity under horizontal cyclic and eccentric loads has many deficiencies, so it is necessary to combine the characteristics of the offshore engineering system An entry study.
Based on the 1g large scale model test and centrifuge model test, the load characteristics of high cap pile group under horizontal cyclic loading and eccentric load are studied respectively. The main works and corresponding research results in this paper are as follows:
(1) the steel and concrete were designed and manufactured a large scale single pile and pile group model, using Zhejiang University large soil physical model experiment system to carry out a series of loading tests on the level of circular and eccentric complex loading conditions of pile force and deformation properties were studied systematically. Including all model test: 1 x 2 level steel pipe piles eccentric loading test, 2 * 2 concrete pile group horizontal eccentric loading, 3 * 3 steel pipe pile group horizontal cyclic loading test, and the single pile loading test.
(2) based on the 3 * 3 steel pipe pile group horizontal cyclic loading test, discussed the pile stiffness, pile internal force and load distribution of the response changes with the load cycle, and the cycle effect coefficient to evaluate cyclic load bearing properties influence on the pile. The results show that the level of pile stiffness the degree of decrease with the increasing of the number of loading cycles, and cyclic horizontal loading loading history will affect the later pile stiffness; various cyclic loading, single pile and pile head load in the peak showed stable with the cycle number increasing, development and destruction of type three kinds of different forms of attenuation, reflection the pile of soil from elastic to plastic to the development process of destruction; the proportion of load of each row of pile group to share with the number of cycles are constantly changing, the load of the front pile sharing increases by bearing; Due to the constraint role of the platform, the axial cyclic tension and compression of the pile will cause serious settlement of pile groups accompanied by horizontal cyclic loading. The effect of load cycling on pile group's horizontal load is much larger than that of single pile.
(3) based on the 1 * 2 level steel pipe piles eccentric loading test, analyze the whole deformation of pile and pile internal force response, and through ABAQUS finite element simulation, discussed different eccentricity and pile layout size affected by the bearing characters of pile group horizontal eccentricity. The experimental results show that the force level of eccentric load the pile of pile group under the existence of great difference, from the loading point near the pile bear larger; due to horizontal and torsional load coupling effect in pile group pile, the torsion bearing capacity of single pile is increased; the additional torque pile head torque and horizontal shear resistance common horizontal load eccentricity the shear resistance of pile and pile group with torsion increases with the increase of the load. The numerical results show that the horizontal load eccentricity of the pile deformation is relatively small, but the effect on the internal force of foundation piles The layout of the pile significantly affects the level of the pile group and the anti overturning stiffness, but it has little influence on the whole torsional response of the pile group.
(4) 2 * 2 concrete pile group horizontal eccentric loading based on revealing the progressive failure process of pile group, the internal force of pile changes with load were studied with numerical analysis, and the concrete pile failure process at the level of eccentric load and mechanism are summarized. The research results show that high the loading height, weight of the upper structure and the pile of concrete cracking and other factors exacerbated the level of pile group under eccentric load overturning failure; pile group in the initial stage of loading in elastic state, the pile's horizontal stiffness is bigger; when the load exceeds a certain critical value of concrete pile has crack, pile group the stiffness decreases, the deformation increases; P- delta effect caused by the weight of the superstructure load to bear axial load in front of pile increases rapidly, the final front corner pile axial bias damage group The pile and its superstructure will be overturned as a whole.
(5) by the Zhejiang University ZJU-400 geotechnical centrifuge, carried out in sand pile under horizontal and eccentric load series model test, focuses on the comparative study of straight pile and pile group pile characteristics under different loading conditions of deformation and bearing. Test results show that the inclined pile horizontal and torsional bearing capacity were significantly higher than straight pile; the pile in pile group under eccentric load level of the pile top displacement difference than the straight pile more; inclined pile by pile axial load can effectively resist horizontal load. The numerical results show that the pile inclination on the pile horizontal bearing behavior of great influence pile group, horizontal stiffness increases with the increase of pile inclination increases.
(6) the analysis of pile group interaction model considering multi direction load; the rigid cap under the assumption that the expressions of the whole pile group stiffness matrix; coupling effect between different directions at the same time considering the effect of pile group pile and anisotropic load, discusses and induces a method for determining the pile stiffness calculation of anisotropy; summary the multi load flow analysis of pile groups under, and gives the corresponding examples.

【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類(lèi)號(hào)】：TU473.1

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