(活)+0.15×25KN/M3(板自重)+0.05×20KN/M3(面层)]=6.25KN/M2
荷载计算
98.47KN/M×7.5/2=369.26KN
45.4KN/M×7.5/2=170.25KN
(8.4+3.13+6.25KN/M2×3.5)×7.5/2×1/2=250.54KN
累计:790.05KN
根据土质情况,柱体设Ф1200MM,R=600mm,R’=550mm,A=1130400mm2,桩体长10M,混凝土采用C25,Fam=13.5N/mm2,配筋采用18Ф22,As=6839mm2,Fy=310N/mm2,摩擦角∮=30o,土重度r=18KN/M3,h=5.67m,t=4.33m。
(2)人工挖孔桩验算
土压力产生的最大弯矩计算:
故基坑上侧为公轴,按重荷载计算,折成p=50KN/m2,如图:
由式:h’=p/r=50/18=2.778m
r’=r(h+h’)/h=18(5.67+2.778)/5.67=26.819KN.M3
Ka=tg2(45°-φ/2)=tg2(45°-30°/2)=0.333
Kp=tg2(45°+φ/2)=tg2(45°+30°/2)=3
EA=h×r×Ka+p×Ka=5.67×18×0.333+50×0.333=50.636KN/M2
μ=eA/(Kp-Ka)r=50.636/(3-0.333)18=1.055m
a=2h/3=2×5.67/3=3.78
L=h+μ=5.67+1.055=6.725m
则:ΣE=L×(h×r/2)×Ka+p×h×Ka
=6.725×(5.67×18/2)×0.333+50×5.67×0.333
=208.683KN/M
Xm=2ΣE/(Ka-Kp)r=2×208.683/(3-0.333)×26.819=2.416m
Mmax=ΣE(L+Xm-a)-(Kp-Ka)rXm3/6
=208.683×(6.725+2.416)-(3-0.333)×26.819×2.416×(1/6)=950.636KN.M
(3)人工挖孔砼灌注桩弯距验算
将式:
afcmA(1-sin2πa/2πa)+(a-at)fyAs=0
at=1.25-2a
整理后,令b=fyAs/fcmA
得a=[1/(1+3)]×(1.25+sin2πa/2π)
已知:b=310×6839/13.5×1130400=0.139
a=0.413
则:at=1.25-2a=0.424
代入公式:
M=(2/3)fcmRrsin3πa+fyAsRs(sinπa+sinπat)/π
=[(2/3)×1.35×1130400×600×sin374.34°/3.14]+[310×6839×550×sin74.34°+sin76.32°]/3.14
=2454.56×106N.MN=2454.56KN.M>950.636KN.M
所以满足要求
(4)人工挖孔桩护壁厚度验算
已知:桩径r=1200mm;深度H=10m,壁厚t1=150mm;水容重rw=10KN/M3;其他数据见钢筋验算,地下水暂按地面下3m,不考虑粘聚力。
最深段的总压力为:
p=rhtg2(45°-/2)+(r-rw)(H-h)tg2(45°-/2)+(H-h)rw
=18*3*tg230°+(18-10)(10-3)tg230°+(10-3)*10
=106.667N/M3
用C20砼,fc=10N/MM2,D=1.8m;安全系数K取1.65,
则壁厚:t=kpr/2fc
=1.65*106.667*120/2*10*100=10.56>t1=15cm
所以满足要求
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