抗拔桩计算公式

抗拔桩计算公式

Nk≤Tuk/2+Gp

Nk = 330kN

Tuk = Σλiqsikuili = 4×0.4×(0.68×35×2.4+0.68×40×2.5+0.72×50×3.5+0.72×72×5.6) = 866.28kN

Gp = 0.4×0.4×14×(25-10) = 33.6kN

Tuk/2+Gp = 1129.32/2+39.58 = 466.74kN＞330kN

满足

·群桩竖向抗拔承载力《建筑桩基技术规范》 5.4.5-1

Nk≤Tgk/2+Ggp

Nk = 330kN

n = 3

Tgk = ulΣλiqsikli /n= 5.2×(0.68×35×2.4+0.68×40×2.5+0.72×50×3.5+0.72×72×5.6) = 938.47kN

Ggp = 1.68×14×(20-10)/3 = 78.4kN

Tgk/2+Ggp = 938.47/2+78.4 = 547.14kN＞330kN

满足

·桩身受拉承载力《建筑桩基技术规范》5.8.7

拉力全部由钢筋提供，已知桩所受轴向拉力N = 330kN。钢筋等级为HRB400。预应力筋抗拉强度设计值为1000MPa，用4根直径为9mm的预应力筋

N≤fyAs+fpyAps

Aps = 4×64 = 256mm²

As = (N-fpyAps)/fy = (330×1000-1000×256)/360 = 206mm²根据《先张法部分预应力方桩》第5页

非预应力筋主筋直径不应小于14mm，A组桩最小配筋率不小于0.6%

根据最小配筋率则所需要钢筋截面面积至少为

As+Aps = A×0.6% = 960mm²

所需非预应力筋的钢筋截面面积为

As = 960-256 = 754mm²

配4根16的钢筋，实配面积As = 804mm²

此时桩身受拉承载力fyAs+fpyAps = 360×804+1000×256 = 545.44kN。