螺纹桩截面几何特性研究

为了便于螺纹桩在工程应用中的设计计算，文中基于螺纹桩截面内半径、螺牙间距、螺牙高度以及螺牙厚度4个控制变量，推导了螺纹桩截面面积、周长的计算公式，建立了螺纹桩截面惯性矩的计算方法，在工程应用的尺寸范围内，分析了4个控制变量对截面几何特性的影响规律，并将螺纹桩与圆桩进行了对比分析。结果表明，螺纹桩截面面积和周长随内半径、螺牙厚度和高度的增大而增大，随螺牙间距的增大而减小，面积增大比周长显著。其中，内半径对截面面积和周长的影响最为明显，当内半径由0.2 m变化到0.5 m时，面积增大了4.4倍，周长增大了1.3倍。螺纹桩与相同截面积圆桩的周长比为1.00~1.05，与相同截面周长圆桩的面积比为0.91~0.99。所以，相同桩长和相同混凝土用量时，螺纹桩的周长仅比圆桩大0~5%。螺纹桩截面存在关于截面对称轴的主惯性矩I_yc和垂直对称轴过形心的轴线的主惯性矩I_xc，且I_xc比I_yc高13%~72%。两主惯性矩随螺纹桩内半径指数增大，随螺牙厚度以相反趋势增大，随螺牙高度线性增大，随螺牙间距线性减小。相较于圆桩，主惯性矩I_yc较小，主惯性矩I_xc较大，但当螺牙厚度小于0.06 m时主惯性矩I_xc小于相同截面周长圆桩惯性矩。

Geometric characteristics of the cross section of screw pile

In order to facilitate the application of the screw pile in civil engineering, this paper deduces the expressions of the cross-sectional area and perimeter of the screw pile, and establishes the numerical calculation methods of the inertia moment based on four key sectional parameters (inside radius, screw pitch, height and thickness of thread). Then, the section geometric characteristics of the screw pile influenced by sectional parameters are discussed and compared with those of the circular pile within the scope of the size in engineering application. The results show that the screw pile cross-sectional area and perimeter increase with the increase of inside radius, height and thickness of the screw thread, but decrease with the increase of screw pitch. What''s more, area increases more significantly than perimeter. The inside radius plays the most important part in influencing the cross-sectional area and perimeter. When the inside radius varies from 0.2 m to 0.5 m, the area increases 4.4 times and the perimeter increases 1.3 times. The perimeter ratio between the screw pile and the circular pile with the same sectional area is 1.00 to 1.05, and the area ratio between the screw pile and the circular pile with the same sectional perimeter is 0.91 to 0.99. Therefore, the perimeter of screw pile is only 0% to 5% larger than that of the circular pile with the same pile length and the same amount of concrete. The screw section has two main inertia moments:I_xc relative to symmetry axis of section and I_yc relative to axis perpendicular to symmetry axis and intersects with centroid of section, and I_xc is 13% to 72% larger than I_yc. They increase exponentially with inside radius, increase in contradictory trend with thickness of the screw thread, increase linearly with height of the screw thread, and decrease linearly with screw pitch. Compared with circular piles, the main inertia moment I_yc is smaller, while the other one I_xc is larger. However, compared with the circular pile with the same perimeter, the main inertia moment I_xc is smaller when thread thickness is less than 0.06m.