【摘要】：巖石地基的剛度大、承載力高、變形小的特點,使巖石地基上擴展基礎的基底反力和受力特性與土質地基有所不同。按現(xiàn)行規(guī)范進行巖石地基上獨立基礎設計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、基礎跨高比、基礎底部配筋對基礎截面剪力、基底反力分布、基礎裂縫、基礎極限承載力的影響。其主要工作和成果如下:(1)利用有限元軟件計算得到基礎不同截面剪力大小,發(fā)現(xiàn)在基礎中心到柱邊緣范圍內基礎截面剪力值近似呈線性增大,而在柱邊緣到基礎邊緣范圍內基礎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、基礎的跨高比減小,基礎截面剪力最大值減小。(2)分析有限元得到的基底反力結果可以發(fā)現(xiàn)巖石地基上柱下獨立基礎基底反力分布呈現(xiàn)高度的非線性�；追戳Ψ植伎傮w趨勢從基礎底部中心向基礎兩邊減小,在基礎邊緣處又有所增大,基底反力分布曲線近似呈“M”形。相同荷載作用下,隨著基礎跨高比的增大、巖石的彈性模量增大,基底反力向基礎中心集中而變更加的不均勻。(3)分析有限元軟件計算結果,可以得出柱下獨立基礎在軸向荷載作用下首先在基礎底部中心出現(xiàn)裂縫,隨著荷載的增大基礎裂縫沿著對稱軸向基礎邊緣和基礎頂部發(fā)展,最終形成貫通的裂縫。當巖石地基剛度增大、基礎跨高比減小,基礎首次出現(xiàn)裂縫時的荷載有所增大。(4)分析有限元計算結果可以發(fā)現(xiàn)在一定范圍內隨著配筋的增大對鋼筋附近混凝土的應變有一定的約束作用,但對基礎截面剪力和基礎極限荷載幾乎沒有什么影響�；炷翉姸鹊燃壖芭浣畋３植蛔兊那疤嵯�,巖基的彈性模量越大、基礎的跨高比越小,基礎極限承載力越大。(5)有限元計算結果與塑性鉸理論及規(guī)范計算結果進行對比,依據規(guī)范基底反力均勻分布假設,在保證一定安全冗余,利用有限元計算結果擬合提出了關于地基和基礎剛度比、基礎跨高比的基礎截面抗剪驗算公式。
[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.
【學位授予單位】：重慶大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TU470

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