【摘要】：巖石地基的剛度大、承載力高、變形小的特點(diǎn),使巖石地基上擴(kuò)展基礎(chǔ)的基底反力和受力特性與土質(zhì)地基有所不同。按現(xiàn)行規(guī)范進(jìn)行巖石地基上獨(dú)立基礎(chǔ)設(shè)計(jì)存在一些不合理之處。本文主要利用有限元軟件研究分析巖石地基彈性模量、基礎(chǔ)跨高比、基礎(chǔ)底部配筋對(duì)基礎(chǔ)截面剪力、基底反力分布、基礎(chǔ)裂縫、基礎(chǔ)極限承載力的影響。其主要工作和成果如下:(1)利用有限元軟件計(jì)算得到基礎(chǔ)不同截面剪力大小,發(fā)現(xiàn)在基礎(chǔ)中心到柱邊緣范圍內(nèi)基礎(chǔ)截面剪力值近似呈線性增大,而在柱邊緣到基礎(chǔ)邊緣范圍內(nèi)基礎(chǔ)截面剪力值呈非線性減小,減小的速度由快變慢最后趨于平緩。剪力最大值出現(xiàn)在柱與基礎(chǔ)交接處所在截面。相同荷載作用下,隨著巖石的彈性模量增大、基礎(chǔ)的跨高比減小,基礎(chǔ)截面剪力最大值減小。(2)分析有限元得到的基底反力結(jié)果可以發(fā)現(xiàn)巖石地基上柱下獨(dú)立基礎(chǔ)基底反力分布呈現(xiàn)高度的非線性�；追戳Ψ植伎傮w趨勢(shì)從基礎(chǔ)底部中心向基礎(chǔ)兩邊減小,在基礎(chǔ)邊緣處又有所增大,基底反力分布曲線近似呈“M”形。相同荷載作用下,隨著基礎(chǔ)跨高比的增大、巖石的彈性模量增大,基底反力向基礎(chǔ)中心集中而變更加的不均勻。(3)分析有限元軟件計(jì)算結(jié)果,可以得出柱下獨(dú)立基礎(chǔ)在軸向荷載作用下首先在基礎(chǔ)底部中心出現(xiàn)裂縫,隨著荷載的增大基礎(chǔ)裂縫沿著對(duì)稱軸向基礎(chǔ)邊緣和基礎(chǔ)頂部發(fā)展,最終形成貫通的裂縫。當(dāng)巖石地基剛度增大、基礎(chǔ)跨高比減小,基礎(chǔ)首次出現(xiàn)裂縫時(shí)的荷載有所增大。(4)分析有限元計(jì)算結(jié)果可以發(fā)現(xiàn)在一定范圍內(nèi)隨著配筋的增大對(duì)鋼筋附近混凝土的應(yīng)變有一定的約束作用,但對(duì)基礎(chǔ)截面剪力和基礎(chǔ)極限荷載幾乎沒(méi)有什么影響。混凝土強(qiáng)度等級(jí)及配筋保持不變的前提下,巖基的彈性模量越大、基礎(chǔ)的跨高比越小,基礎(chǔ)極限承載力越大。(5)有限元計(jì)算結(jié)果與塑性鉸理論及規(guī)范計(jì)算結(jié)果進(jìn)行對(duì)比,依據(jù)規(guī)范基底反力均勻分布假設(shè),在保證一定安全冗余,利用有限元計(jì)算結(jié)果擬合提出了關(guān)于地基和基礎(chǔ)剛度比、基礎(chǔ)跨高比的基礎(chǔ)截面抗剪驗(yàn)算公式。
[Abstract]:The characteristics of large stiffness, high bearing capacity and small deformation of rock foundation make the reaction and stress characteristics of the expanded foundation on the rock foundation different from that of the soil foundation. There are some unreasonableness in the design of independent foundation on rock foundation according to current codes. In this paper, the effects of elastic modulus of rock foundation, ratio of span to height of foundation and reinforcement on shear force of foundation section, distribution of foundation reaction force, foundation crack and ultimate bearing capacity of foundation are studied by using finite element software. The main work and results are as follows: (1) the shear force of different cross-section of foundation is calculated by using finite element software, and it is found that the shear value of cross-section of foundation approximately increases linearly in the range from the center of foundation to the edge of column. However, the shear force of foundation section decreases nonlinear from the edge of column to the edge of foundation, and the speed of the decrease changes from fast to slow and then to flat. The maximum shear force appears at the cross section between column and foundation. Under the same load, with the increase of elastic modulus of rock, the ratio of span to height of foundation decreases. The maximum shear force of foundation section is reduced. (2) the results of foundation reaction obtained by finite element analysis show that the distribution of reaction force of independent foundation under column on rock foundation is highly nonlinear. The general trend of the base reaction distribution decreases from the center of the base to the two sides of the foundation, and then increases at the edge of the foundation. The distribution curve of the base reaction force is approximately "M" shape. Under the same load, with the increase of the ratio of span to height of foundation, the elastic modulus of rock increases, and the reaction force of the basement concentrates to the center of the foundation and becomes more uneven. (3) the calculation results of finite element software are analyzed. It can be concluded that under the axial load, cracks appear in the center of the foundation base first, and along the edge of the foundation and the top of the foundation with the increase of the load, the through cracks are finally formed. When the stiffness of the rock foundation increases, the ratio of span to height of the foundation decreases, (4) the results of finite element analysis show that the strain of concrete near reinforcement is restrained with the increase of reinforcement in a certain range. However, there is little effect on the shear force and ultimate load of foundation section. On the premise that the strength grade and reinforcement of concrete remain unchanged, the greater the elastic modulus of rock foundation, the smaller the ratio of span to height of foundation, and the greater the ultimate bearing capacity of foundation. (5) the finite element calculation results are compared with the results of plastic hinge theory and code calculation. According to the assumption of uniform distribution of reaction force on the basis of the code, and in order to ensure certain safety and redundancy, a formula for calculating the shear resistance of foundation section is put forward by fitting the results of finite element calculation on the ratio of stiffness to stiffness of foundation and the ratio of span to height of foundation.
【學(xué)位授予單位】：重慶大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2016
【分類號(hào)】：TU470

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