考虑摩阻力和轴向荷载影响的边坡锚固框架简化有限元计算

Simplified finite element computation of slope anchor frame considering influence of friction resistance and axial loads

目前,边坡锚固框架常被等同于平地上的十字交叉地基梁,视为仅受交叉结点处锚杆拉力在框架轴线的垂向分量的平面弯曲变形构件,按Winkler弹性地基梁法计算其内力,没有考虑在框架底土摩阻力和框架轴向荷载影响下,其实则为拉压与弯曲或斜弯曲组合变形构件,导致现行计算结果与实际存在偏差。为此,以某黄土路堑边坡为例,采用经平板载荷试验数值验证的室内外试验土工参数,首次建立考虑摩阻力和轴向荷载影响并将锚杆作用按等效力简化的边坡锚固框架内力计算有限元方法。同时,由黄土的变形模量换算出Winkler法对应杆系有限元模型参数,按现行算法分别建立平地框架实体与杆系有限元模型以分析Winkler法存在的问题及其结果与相应边坡框架模型简化有限元计算的差异。结果表明:平地模型Winkler法与相应实体有限元法所得框架竖肋弯矩图很相似,但前者弯矩最大值较后者偏大,二者横梁弯矩差别较大;将边坡上组合变形的框架等同于平地上平面弯曲框架所得内力与实际会存在很大偏差。

At present,slope anchor frames are often regarded as,a plane bending member to merely sustain the component of the tensile force of the anchors perpendicular to the axises of the frame at the intersections,same as the cross foundation beam on a flat ground.Their internal forces are calculated using the Winkler elastic foundation beam method.They are actually a combined deformation member,sustaining bending combined with tension or compression deformation or skew bending when the influence of skin friction from the soil at the bottom of the frames and axial loads are ignored.As a result,there exists a deviation between the calculated results and the real values.For this purpose,taking a cutting slope of loess as an example,a finite element method for computing the internal forces of slope anchor frames was originally established.The action of anchors is simplified as an equivalent force and the influence of the skin friction and axial loads is considered.Meanwhile,the corresponding parameters in the link finite element model based on the Winkler method were converted using the deformation modulus of the loess.The current method was used to analyze the existing problems of the Winkler method as well as the result differences from those by the simplified finite element model of the slope anchor model,the solid finite element and link finite element models for a frame on the flat ground were,respectively,established.The results show that for the models on the flat ground,the bending moment diagrams of the vertical ribs by the Winkler method were quite similar to those by the solid finite element method,but the maximum moment of the former was greater than that of the latter.The bending moment of the horizontal beams were significantly different.It is also shown that there will be a significant deviation from the actual internal forces when the frame with combined deformation on a slope is regarded as a frame with plane bending on a flat ground.