求助

4．基础抗冲切验算
计算公式：
按《建筑地基基础设计规范》（GB 50007－2002）下列公式验算：
Fl ≤ 0.7•βhp•ft•am•h0 (8.2.7－1)
Fl = pj•Al (8.2.7－3)
am = (at＋ab)/2 (8.2.7－2)
pjmax,x = F/S＋M0y/Wy = 158.00/8.40＋20.00/5.74 = 22.28 kPa
pjmin,x = F/S－M0y/Wy = 158.00/8.40－20.00/5.74 = 15.32 kPa
pjmax,y = F/S＋M0x/Wx = 158.00/8.40＋155.00/2.87 = 72.77 kPa
pjmin,y = F/S－M0x/Wx = 158.00/8.40－155.00/2.87≤0, pjmin.y = 0.00 kPa
pj = pjmax,x＋pjmax,y－F/S = 22.28＋72.77－18.80 = 76.26 kPa
pjmin,y怎么会小于0?满足规范要求吗,规范没有提到?