基础工程课程设计-低桩承台基础设计

一、根本资料

根底工程课程设计----低桩承台根底设计等截面单箱双室薄壁桥墩〔如以下图示。18m，0.75m，0.8m1.5m(4×14)m230底截面中心处的设计荷载为：N=74958kNzH=2895kNx纵桥向弯矩M=38209kN·my〔xyz〕25。承台顶面与地3.5m。地质资料16m〔土层Ⅰ砾石〔Ⅱ。

， m=10000kN/m4,aka土层Ⅱqk

=70kp,fa a0

m=20230kN/m4a设计参数承台及基桩材料重度 =25kN/m3，基桩设计有关参数为：E=2.8×107kN/m2,λ=0.85,m=0.8,K=6c 0 2班级桩径〔m〕纵桥向〔排〕横桥向〔排〕11.2342、41.53431.834二、主墩群桩根底设计要求〔以纵桥向掌握设计〕〔一〕设计计算内容：依据条件拟定承台平面尺寸；进展基桩的平面布置；拟定桩长并验算单桩轴向受压容许承载力；推断是否弹性桩；桩顶荷载安排并校核；确定桩长并验算单桩轴向受压容许承载力；单桩内力及位移计算与验算；桩身截面配筋设计及桩截面强度验算；群桩根底承载力和沉降量验算。〔二〕设计完成后应提交的文件及图表低桩承台群桩根底设计计算书〔应附计算小图；桥墩及根底构造构造图；基桩钢筋构造图。三、设计依据标准及参考书大路桥涵地基及根底设计标准〔JTGD63-2023〕大路钢筋混凝土及预应力混凝土桥涵设计标准〔JTGD62-2023〕王晓谋.根底工程.北京：人民交通出版社，2023叶见曙.构造设计原理.北京：人民交通出版社，2023江祖铭等主编.墩台与根底.北京：人民交通出版社，1994一、拟定承台平面尺寸钻孔灌注桩属于摩擦桩中的钻孔桩，依据标准要求，其中心距不应小于桩径的2.52.5即：横、纵向桩的中心距为1.8*2.5=4.5m1.0m0.30.5m。故：承台长L1802.531800.321801638cmD1802.521800.321801188cm二、进展基桩的平面布置桩的排列形式承受行列式，基桩布置如图1所示：承台每延米自重：N=11.8816.3825-19.=1011.8kN/m0土层Ⅰ中桩每延米自重：1q 1.82(2519.8)13.232kN/m1 4土层Ⅱ中桩每延米自重：1q 1.82(2521.8)8.143kN/m2 4设：其次层土中桩长为h力层。桩底所承受的最大竖向荷载最大值为：N (Nh z

/12N1

3.5/1212.513.232+h 8.143)74958/121011.893.5/1213.23212.58.143hh 8.143计算R时取以下数据：a11桩的周长ud1 . 8 = 5，A d2 1.822.54m2 ，11p 4 40.85,m0

0.8,k2

6,fa0

500kpa,2

(1619.8h 21.8)/(16h)所以承载力：R0.55.65(5512.570h)2.54a(0.85

〔1619.8+21.8h〕(13+h)))N 6707.838.143hh

(16+h)解之的h =2.99m 取h =3.5m因此拟定桩长为：L =12.53.516m桩桩端以上各土层的加权平均重度值为：1619.83.521.8 2

20.16kN/m3桩端处土的承载力容许值：q mr

ka0 2

(h3)0.80.851697.2kPa

500620.16(19.53)由于qr

1697.2kPa>1450kPa,所以取qr

1450kPa单桩轴向受压承载力容许值的计算：Ra

1u22i1

qliki

Aqp r15.65(5512.5703.5)2.54145026317.31kN桩底所承受的最大竖向荷载N (Nh z

/12N1

3.5/1212.513.232+h 8.143)=6735.53kNNhRa

,不满足要求，所以需重拟定桩长。 h 26735.532.5414505512.5/70 5.65 取h=6.5m。验算单桩轴向受压容许承载力桩端以上各土层的加权平均重度值为：1619.86.521.8 20.38kN/m32 166.5桩端处土的承载力容许值：mr

ka0 2

(h3)0.80.85500620.38(22.53)1961.43kPa由于q 1961.43kPa>1450kPa,所以取q 1450kPar单桩轴向受压承载力容许值的计算：Ra

2i1

qliki

Aqp r15.65(5512.5706.5)2.54145026910.56kN桩底所承受的最大竖向荷载N (Nh z

/12N1

3.5/1212.513.232+h 8.143)=6759.96kNN

<R,满足要求。此时拟定的桩长为：L =12.56.519mh a 桩四、推断是否为弹性桩当d1.81.0m时，故桩的计算宽度为：b1

kkf

(d1)L1

4.51.82.7m地面线以下桩的计算埋入深度h1

3(d1)3(1.81)8.4m，且L2.7m0.6h5.04m。所以1

kb2

1b L2 10.6 2 10.6 h式中：b1

--桩的计算宽度〔m〕,b1

2d；d--桩径〔m〕；k桩形换算系数，此题取kf

=0.9；b与水平外力作用方向的一排桩的桩数n有关的系数，此题取b2

11b20.6Lh1=0.5+0.50.6

kb21

2.7=0.76798.4bkk1 f

(d1)=0.76790.8=1.935m1h 2(d1)2(1.81)5.6mh12.5mmmm，10000KN/m41

d40.5153m464EI0.8Ec

I0.82.81070.515311542720kNm25mb1EI100001.935511542720 5mb1EI100001.935511542720桩的入土深度h19m

2.5 8.976m，故依据弹性桩计算。0.2785五、桩顶荷载安排并校核〔1〕桩顶刚度系数、 、 、PP HH MH

值的计算： =PP l0

1h 1AE CA0 01 1

0,h19m, ,A d22.54m20 2 p 4 C m0 0即：

h190000kN/m3，A0

= S2= 4.52=15.90m24 4 =PP l

1h 10 AE CA0 01= 9.5 12.540.82.8107 19000015.90=0.174EI：hh0.2785195.29154,取用4。l 00171819xQ

M

M

1.48375,

=3EIxHH QM =2EIxMHM= EIxMM M

0.0230EI0.0764EI0.413EI计算承台底面原点0处位移a、c、 ,低桩承台要考虑桩—土—承台的共同作0 0 0 naai1

( sin2pp i HH

cos2i

)BFc1 a a

ni1

[(pp

)xHH

sini

cosi

cosi

]BSc1 n[(

sin2

cos2

)x22x

sin )BIc i1其中

i HH

i i i

i MM 1ch ch2

ch30,Fc nn,Sc n n,Ic nn,B

B1,为承台侧面计算宽度i 2 6 12 1c=mh,Bn n

11.88112.88,考虑到各桩直径相等：c

7495.8 35899.430 npp

120.174EI EI(n

x2)Hn

MBIcHBScMMM ppa

i1

MH 1 10 nHH

(nMM

pp

x2)nHH

1

(nMM

n x2)BFcB2IcFcB2Sc22npp 1

BScn221ii1 i1 i 1 1 MHin MM pp

ni1

x2120.413EI0.174EI84.5233.144EIin 120.0764EI0.9168EI,nMH

120.0230EI0.276EI,n22MH

0.841(EI)2BIc0.1395EI,BSc0.0797EI,BFc0.0683EI1代入a0

112670.05EI

1(nHM

BFc)M(n1

BSc)H10 nHH

(nMM

pp

x2)niHHi

1

(nMM

n x2)BFcB2IcFcB2Sc22npp 1

BScn221代入0

EI

i1 i1 i 1 1 MHP、Q、M竖向力：P (c+x)

i i ii PP 0 i

7450.73KN)i=0.174EI(35899.434.51537.97)i

6246.50KN(x

0)

EI EI 5042.27KNQi

aHH0

HM

173.91KNM i MM 0校核

aMH0

=332.81KNmEx

aFc0

Sc76.60kN/m0MEx

aSc0

Ic95.06kN0水平力校核：nQ12173.9176.7012.883074KN2895KNi竖向力校核：ni1

P4(7450.73+6246.50+5042.27)=7495.8KN=N7495.8KNi弯矩值校核：ni1

xPnMii

4(7450.735042.27)4.5+1〔332.8+95.0612.8=42NmM38209KNm明显，校核结果符合要求。六、确定桩长并验算单桩轴向受压容许承载力由上一问可知，单桩桩顶所受到的最大轴向压力N 7450.73kNmax竖向最大荷载：N 7450.7313.23212.58.1436.5=7669.06kNhmaxN

max

a

6910.56kN,不满足要求，所以进展重计算。 7669.062.541450 h取h=11.5m。

2

5.65

5512.5/7010.34m桩端以上各土层的加权平均重度值为：1619.811.521.8 20.64kN/m32 1611.5桩端处土的承载力容许值：q mr

fa0

k2

0.80.85500620.6424.5由于qr

2403.17kPa2403.17kPa>1450kPa,所以取qr

1450kPa单桩轴向受压承载力容许值的计算：Ra

2i1

qliki

Aqp r15.65(5512.57011.5)2.54145027899.31kNN

max

=7669.06kN<Ra

7899.31kN,满足要求。重确定桩长为L =24m桩七、单桩内力及位移计算与验算Mz

M计算max由于h4，故可以承受无量纲法Q即：M 0A MB 624.45A 332.81Bz M 0 M M M

计算如下表：M M zM0Z0ZzzAMBMQAMMB0 MMZ0.00.0001.000000.00332.81332.810.10.360.099600.9997462.20332.72394.920.20.720.196960.99806122.99332.16455.160.31.080.290100.99382181.15330.75511.910.41.440.377390.98617235.66328.21563.870.51.800.457520.97458285.70324.35610.050.62.150.529380.95861330.57319.03649.610.72.510.592280.93817369.85312.23682.080.82.870.645610.91324403.15303.94707.090.93.230.689260.88407430.41294.23724.641.03.590.723050.85089451.51283.18734.691.13.950.747140.81410466.55270.94737.491.24.310.761830.77415475.72257.64733.371.34.670.767610.73161479.33243.49722.821.45.030.764980.68694477.69228.62706.311.55.390.754660.64081471.25213.27684.521.65.750.737340.59373460.43197.60658.031.76.100.713810.54625445.74181.80627.541.86.460.684880.49889427.67166.04593.711.96.820.651390.45219406.76150.49557.252.07.180.614130.40658383.49135.31518.812.27.900.531600.32025331.96106.58438.542.48.620.443340.24262276.8480.75357.592.69.340.354580.17546221.4258.39279.812.810.050.269960.11979168.5839.87208.443.010.770.193050.07595120.5525.28145.833.512.570.050810.0135431.734.5136.234.014.360.000050.000090.030.030.06Mmax

最大弯矩位置确定Q=0C

M 00.533Z Q Q0由C 0.533及h4 ，查附表13，得zQ1.0091

max

1.0091，故Z max

0.2775

3.92m由z 1.0091及h4，查书中附表13，得K=1.780max MM =K M 1.780332.81592.40kNmmax M 0 Q计算zQQAz 0 Q

MB0 Q

Q

92.69BQA,B，QQ Q zQZZzzAQBQQA0 QMB0 QQZ0.00.001.000000173.910.00173.910.10.360.98833-0.00753171.88-0.70171.180.20.720.95551-0.02795166.17-2.59163.580.31.080.90468-0.05820157.33-5.39151.940.41.440.83898-0.09554145.91-8.86137.050.51.800.76145-0.13747132.42-12.74119.680.62.150.67486-0.18191117.36-16.86100.500.72.510.58201-0.22685101.22-21.0380.190.82.870.48522-0.2708784.38-25.1159.280.93.230.38689-0.3124567.28-28.9638.321.03.590.28901-0.3505950.26-32.5017.771.13.950.19388-0.3844333.72-35.63-1.921.24.310.10153-0.4133517.66-38.31-20.661.34.670.01477-0.436902.57-40.50-37.931.45.03-0.06586-0.45486-11.45-42.16-53.611.55.39-0.13952-0.46715-24.26-43.30-67.561.65.75-0.20555-0.47378-35.75-43.91-79.661.76.10-0.26359-0.47496-45.84-44.02-89.861.86.46-0.31345-0.47103-54.51-43.66-98.171.96.82-0.35501-0.46223-61.74-42.84-104.582.07.18-0.38839-0.44914-67.54-41.63-109.182.27.90-0.43174-0.41179-75.08-38.17-113.252.48.62-0.44647-0.36312-77.65-33.66-111.302.69.34-0.43651-0.30732-75.91-28.49-104.402.810.05-0.40641-0.24853-70.68-23.04-93.723.010.77-0.36065-0.19052-62.72-17.66-80.383.512.57-0.19975-0.01672-34.74-1.55-36.294.014.36-0.00002-0.000450.00-0.04-0.05X计算zQ MX 0 A 0 B

6.97104A

3.72104Bz 3EI x

2EI x x xA,B，Xx x zXZZzzAxBxQ03EIA(104)xM02EIB(104)xXZ0.00.002.440661.6210017.016.0323.040.10.362.278731.4509415.885.4021.280.20.722.117791.2908814.764.8019.560.31.081.958811.1407913.654.2417.900.41.441.802731.0006412.573.7216.290.51.801.650420.8703611.503.2414.740.62.151.502680.7498110.472.7913.260.72.511.360240.638859.482.3811.860.82.871.223700.537278.532.0010.530.93.231.093610.444817.621.659.281.03.590.970410.361196.761.348.111.13.950.854410.286065.961.067.021.24.310.745880.219085.200.816.011.34.670.644980.159854.500.595.091.45.030.551750.107933.850.404.251.55.390.466140.062883.250.233.481.65.750.388100.024222.710.092.801.76.100.31741-0.008472.21-0.032.181.86.460.25386-0.035721.77-0.131.641.96.820.19717-0.057981.37-0.221.162.07.180.14696-0.075721.02-0.280.742.27.900.06461-0.099400.45-0.370.082.48.620.00348-0.110300.02-0.41-0.392.69.34-0.03986-0.11136-0.28-0.41-0.692.810.05-0.06902-0.10544-0.48-0.39-0.873.010.77-0.08741-0.09471-0.61-0.35-0.963.512.57-0.10495-0.05698-0.73-0.21-0.944.014.36-0.10788-0.01487-0.75-0.06-0.81〔4〕转角位移计算zQ M 0 A 0B 1.94104A1.04104Bz 2EI

EI AB

分别由附表查的，z

计算如下表φ计算列表ZZzzAQB2EI0 A(104)M0EIB(104)Z0.00.00-1.62100-1.75058-3.14-1.82-4.970.10.36-1.61600-1.65068-3.14-1.72-4.850.20.72-1.60177-1.55069-3.11-1.61-4.720.31.08-1.57676-1.45106-3.06-1.51-4.570.41.44-1.54334-1.35204-2.99-1.41-4.400.51.80-1.50151-1.25394-2.91-1.30-4.220.62.15-1.46009-1.15725-2.83-1.20-4.040.72.51-1.39593-1.06238-2.71-1.10-3.810.82.87-1.33398-0.96978-2.59-1.01-3.600.93.23-1.26713-0.87978-2.46-0.91-3.371.03.59-1.19647-0.79311-2.32-0.82-3.151.13.95-1.12283-0.70981-2.18-0.74-2.921.24.31-1.04733-0.63038-2.03-0.66-2.691.34.67-0.97078-0.55506-1.88-0.58-2.461.45.03-0.89409-0.48412-1.73-0.50-2.241.55.39-0.81801-0.41770-1.59-0.43-2.021.65.75-0.74337-0.35598-1.44-0.37-1.811.76.10-0.67075-0.29897-1.30-0.31-1.611.86.46-0.60077-0.24672-1.17-0.26-1.421.96.82-0.53393-0.19916-1.04-0.21-1.242.07.18-0.47063-0.15624-0.91-0.16-1.082.27.90-0.35588-0.08365-0.69-0.09-0.782.48.62-0.25831-0.02753-0.50-0.03-0.532.69.34-0.17849-0.01415-0.35-0.01-0.362.810.05-0.11611-0.04351-0.23-0.05-0.273.010.77-0.06987-0.06296-0.14-0.07-0.203.512.57-0.01206-0.08294-0.02-0.09-0.114.014.36-0.00341-0.08507-0.01-0.09-0.10八、桩身截面配筋设计及桩截面强度验算由上可知，最大弯矩发生在距离桩顶以下的 3.92m处，该处的弯矩为M592.40kNm.〔JTGD60—2023〕4.1.61.2。则N1.27450.7313.2323.921uqz2 k1.27450.7313.2323.9215.65553.92

8272.24kN

2 按《大路桥规》规定全部纵向钢筋配筋率按0.2%配置A 0.002 d2=0.00509m2g 416Φ22HRB335A 60.816104m2g

f sd桩身承受C25混凝土，f 11.4MPa。cd由于长细比:0I/A0I/A

240.45

53.3317.5l所以偏心距增大系数： =1+ 1 (0)2l1400e/h h 1 20 0e0

MNMmax

592.408272.24

0.0716m,取rs

h rr0 s

0.90.811.71m;h2r1.8me 0.22.7 0e1 h0

0.313，2

l0h

1.021,故取=121 24所以： =1+1 24

( )20.3131=1.949

14000.0716/1.71 1.8Me max0 Nmax

1.949592.40=0.140m8272.24Af CAf Cf”sdcdsd re Bf0cd

Dgf”其中：r0.9m,并设g=0.9,=0.002即：

Bf Dgf” cd

11.4B0.504Dr= 0.9

0 Afcd

Cf”sd A0.56C0.962.58900.40112.20230.74460.1450.1401.030.972.61580.38652.22900.72510.1380.1400.990.982.64240.37172.25610.70610.1320.1400.94ABCDeABCDe0e/e0 00

=0.138mm,与实际值e0

截面承载力复合轴力复合:N Ar2fu cd

Cr2f”sd

2.6158900211.42.22900.029002280=25165.37kN8272.24kNM Brfu 3cd

Dgr3f”sd0.3865900311.40.72510.0029003280=3478.46kNm592.40kNm裂缝宽度验算依据《大路钢筋混凝土及预应力混凝土桥涵设计标准》(JTJD62-2023)第6.4.5外缘钢筋应力 24MPa时可不必验算裂缝宽度。sss 59.42 Ns

e(2.80 s0

1.0)1.65 2式中：

ss

r2f

3r 3cu,kr900mm,0.005,f则：

cu,k

=25MPa,s

1.0,偏心距e0

MNMmax

592.408272.24

72mm 59.428272.24103

(2.801.0721.0)1.65(0.002)233ss

900225 900 =481.65MPa<24MPa钢筋布置如图：九、群桩根底承载力和沉降量验算桩底持力层承载力验算视为实体根底。当偏心受压时，应满足以下条件plh

fA A ap lh

N(1eA)

f其中：

max

A A W R aAabaL0bB0

4d2ltan4iiii式中：

=i1lp、pmax

——桩端平面处的最大压应力〔kPa；——〔kN/m；l——桩的长度〔m；——〔kN/m；L,B——承台的长度和宽度〔m；N——作用于承台底面合力的竖向分力〔kN；——Aab