橋梁高樁承臺(tái)式摩擦樁基礎(chǔ)設(shè)計(jì)計(jì)算

1、橋梁高樁承臺(tái)式摩擦樁基礎(chǔ)設(shè)計(jì)計(jì)算1 .初步擬定樁長(zhǎng)樁基礎(chǔ)采用高樁承臺(tái)式摩擦樁，根據(jù)施工條件，樁擬采用直徑d=1.2m,以沖抓錐施工。樁群布置經(jīng)初步計(jì)算擬采用6根灌注樁，為對(duì)稱豎直雙排樁基礎(chǔ)，埋置深度初步擬定為h=11.31m。樁長(zhǎng)初步擬定為18m,樁底標(biāo)高為49.54m。2 .樁群結(jié)構(gòu)分析2.1 承臺(tái)底面中心的荷載計(jì)算永久作用加一孔可變作用(控制樁截面強(qiáng)度荷載)時(shí)：N407469.85.62.025.043490(kN)H358.60(kN)M4617.30358.602.05334.50(kN)永久作用加二孔可變作用(控制樁入土深度荷載)時(shí)：N46788.009.85.62.025.0495

2、32(kN)2.2 單樁樁頂荷載計(jì)算樁的計(jì)算寬度匕對(duì)于d1.0m時(shí)：b1KfK(1d)式中：Kf樁形狀換算系數(shù)，于圓形截面，取0.9;d樁直徑，取1.2m；K平行于水平作用方向的樁間相互影響系數(shù)：已知：L12m；幾3(d1)6.6m；n2b0.6；對(duì)于L10.6幾的多排樁：Kb2(1b2)二0.8020.6h1所以:1bl0.9 0.802 (1.2 1) 1.59(m)樁的變形系數(shù)EI0.8EcIc式中：一一樁的變形系數(shù)；EI樁的抗彎剛度，對(duì)以受彎為主的鋼筋混凝土樁，根據(jù)現(xiàn)行規(guī)范采用；Ec樁的混凝土抗壓彈性模量，C20混凝土Ec2.55107KPa；d4I樁的毛面積慣性矩，I0.1018(m

3、4)64m非巖石地基水平向抗力系數(shù)的比例系數(shù)，m120000kN/m4;所以，計(jì)算得：0.62(m1)樁在最大沖刷線以下深度h=11.31m,其計(jì)算長(zhǎng)度則為：故按彈性樁計(jì)算hh0.6211.317.02(2.5)樁頂剛度系數(shù)1、2、3、4值計(jì)算一11已知：l06.69m,h11.31m;(根據(jù)公橋基規(guī)鉆挖孔樁米用一)，22d21.222A1.13(m)44Com°h2dAh tan一2412000011.311.357106(kN/m3)2402一，、一一11.31tan-0-21.14m2,易知該值大于相24鄰底面中心距為直徑所得的面積，故按樁中心距計(jì)算面積，故?。篈322804m

4、2411d6.69-11.31d1211loh11.132.551071.3571068.04AEh1.923 1 06 KN m2 0.925EI已知：h h 7.02 (>4), 取 h=4, l-l0 0.62 6.69 4.15(m)查教材橋梁基礎(chǔ)工程附表17、18、19得：xQ =0.05568xm=0.16498m =0.65853所以3EIxQ 0.623 0.05568EI 0.0133EI2_2 _EIxm 0.620.16498EI0.0634EIEI m 0.62 0.65853EI0.408EI計(jì)算承臺(tái)底面原點(diǎn) O處位移a0、b0、0對(duì)于豎直樁，且各樁的直徑相同時(shí)

5、：N 434907836.04b0n 16 0.925EI EIa0n2(n 41xi )H n 3Mi 1n/2、22n 2 (n 41 ) n 3i 116.66EI 358.60 0.3804EI 5334.5 6116.420.0798EI 16.66EI 0.1447( EI )2 EIn 2M n 3H0.0798 EI 5334.5 0.3804 358.60429.57n 2 (n 4n2、221xi ) n 3i 10.0798EI 16.66EI 0.1447( EI )2EI計(jì)算作用在每根樁頂上作用力P、Qi、MnQi 6 54.11 324.66(kN) H 358.6

6、0(kN)豎向力：P10xi0)0.925EI7836.04(EIdc429.571.6)日7884.10(kN)6612.57(kN)水平力：Qi彎矩：Mi2a00.0133EI6116.42EI0.0634EI429.57EI54.11(kN)0.408EI429.57EI0.0634EI6116.42EI212.52(kNm)校核:XRnMi3(7884.106612.57)1.66(212.52)4828.22(kNm)5334.50(kNm)i1nnpi3(7884.016612.57)43490.01(kN)43490.00(kN)i12.3最大沖刷線深度處荷載計(jì)算從單樁樁頂荷載計(jì)

7、算中，已得出計(jì)算最大沖刷線深度荷載所需要的數(shù)據(jù)，計(jì)算如下：彎矩M0MiQil0212.5254.116.69149.48(kMm)豎向力水平力Q054.11(kN)2.4Po7884.101.136.69(2510)7997.50(kN)最大沖刷線深度下沿樁長(zhǎng)度方向彎矩、水平壓應(yīng)力的計(jì)算樁身最大彎矩處及最大彎矩的計(jì)算:由：Qz=0 得：CqM00.62 149.480 1.713Q054.11由 Cq1.713 且 h =7.02 >4取h =4.0 ,查教材基礎(chǔ)工程附表 13得0.813Zmax0.813故Zmax08131.31(m)0.62又由Zmax=0.813及h7.02>

8、;4取h=4.0,查教材基礎(chǔ)工程附表13得Km=1.296MmaxKmM01.296149.48193.73(kNm)最大沖刷線深度下沿樁身長(zhǎng)度方向彎矩、水平壓應(yīng)力的計(jì)算：采用無(wú)量鋼法計(jì)算，由h=7.02>2.5,所以用摩察樁公式計(jì)算：MzQ°AnM°BmQzQoAqMoBqQ5411其中87.27(kN)Q0=54.11kNM0=149.48kNAm、Bm、Aq、Bq的值查教材基礎(chǔ)工程附表3、4、7、8,計(jì)算如下表:zzAmBmAqBqMzQz0.000.00.000001.000001.000000.00000149.4854.110.160.10.099600.

9、999740.98833-0.00753158.1352.780.320.20.196960.998060.95551-0.02795166.3849.110.480.30.290100.993820.90468-0.0582173.8743.560.650.40.377390.986170.83898-0.09554180.3536.540.810.50.457520.974580.76145-0.13747185.6128.460.970.60.529380.958610.67486-0.18191189.4919.661.130.70.592280.938170.58201-0.2268

10、5191.9310.471.290.80.645610.913270.48522-0.27087192.861.151.450.90.689260.884070.38689-0.31245192.31-8.021.611.00.723050.850890.28901-0.35059190.29-16.851.771.10.747140.814100.19388-0.38443186.90-25.141.941.20.761830.774150.10153-0.41335182.21-32.812.101.30.767610.731610.01477-0.43690176.35-39.692.2

11、61.40.764980.68694-0.06586-0.45486169.45-45.722.421.50.754660.64081-0.13952-0.46715161.65-50.842.581.60.737340.59373-0.20555-0.47378153.10-55.032.741.70.713810.54625-0.26359-0.47496143.95-58.282.901.80.684880.49889-0.31345-0.47103134.35-60.613.061.90.651390.45219-0.35501-0.46223124.44-62.053.232.00.

12、614130.40658-0.38839-0.44914114.37-62.643.552.20.531600.32025-0.43174-0.4117994.27-61.533.872.40.443340.24262-0.44647-0.3631274.96-57.814.192.60.354580.17546-0.43651-0.3073257.17-52.104.522.80.269960.11979-0.40641-0.2485341.47-45.024.843.00.193050.07595-0.36065-0.1905228.20-37.175.653.50.050810.0135

13、4-0.19975-0.016726.46-12.366.454.00.000050.00009-0.00002-0.000450.02-0.042.5樁頂縱向水平位移驗(yàn)算:樁在最大沖刷線處水平位移x0和轉(zhuǎn)角0的計(jì)算:由Z=0h7.02>4取h=4查教材基礎(chǔ)工程附表1、2、5、6得:Ax=2.44066A=-1.62100Bx=1.6210B=-1.75058Q0Ax0qAxnB2eiBx54.11一一一3一一0.6232.041070.1018149.482.44066270.6222.041070.10181.6210符合規(guī)范要求0.62230.5710m6mmQo2EI54.112

14、.041070.10181.6210)3.1317.02m>4m,取4,l0l0Ax169.91279A1四BEI149.480.622.041070.1018(1.75058)104rad0.626.694.15可查得:B5117.50091B15.90058x%B”54.110.6232.043.0103m402ei11070.10183.0(mm)MiB國(guó)bi69.91279212.520.6222.041070.101817.5009154.1127(17.50091)0.6222.041070.10180.21103(rad)212.520.622.041070.1018(5.

15、90058)頂?shù)目v向水平位移x1=3.0(mm)水平位移的容許值0.5.302.74cm=27.4mm>x1故樁頂水平位移滿足要求3.樁身截面配筋及截面強(qiáng)度校核3.1 各種參數(shù)及系數(shù)的計(jì)算最大彎矩發(fā)生在最大沖刷線以下zmax1.31m處，該處Mmax193.73kNm計(jì)算樁最大彎矩控制截面的軸向力NjPiqlo12qZmaxqikczmax式中Nj控制截面的軸向力;Pi單樁樁頂最大豎向力，已求出Pi7884.10kN；所以，計(jì)算得:計(jì)算偏心距Mje0£q樁每延米的自重(包括浮力)qik樁周土摩阻力標(biāo)準(zhǔn)值，已知c沖抓錐成孔面周長(zhǎng)，c1.22qik500kPA251016.96kN

16、;1.34.08(m)1NjPiqIo-qZmaxqikcZmax5333.60(kN)193.730.0363(m)36.3(mm)5333.60樁的半徑r=1200/2=600mm,對(duì)于C20混凝土,保護(hù)層取ag80mm,g520mm樁的長(zhǎng)細(xì)比:L0/d10.221.1518%/r520/60015>4.4,所以,0.867應(yīng)考慮偏心距增大系數(shù)2.7e0/h00.22.736.3/11200.2880.01L01.150.011811.21400e0/h0(L0/h)2121(18/1.2)20.28812.428140036.3/1120故考慮偏心距增大系數(shù)后的偏心距為:e'

17、;e02.42836.388.14(mm)3.2 計(jì)算配筋率采用C20混凝土，鋼筋擬采用HRB33祠筋，即：fcd 9.2MPa ； fsd280MPa計(jì)算受壓區(qū)高度系數(shù)，根據(jù)經(jīng)驗(yàn)公式得:fcd Ae0 Brfsd Dgr Ce022 -Nu Ar fcd C r fsdABCDNu(kN)Nj(kN)Nu/Ni0.832.21480.5621.76351.0398-0.012115182.885333.600.970.842.2450.55191.80291.0139-0.011895274.995333.600.990.852.27490.54141.84130.9886-0.011615

18、379.165333.601.010.862.30470.53041.87860.9639-0.011275499.555333.601.030.872.33420.51911.91490.9397-0.010865634.705333.601.060.85時(shí)，計(jì)算縱向力Nu與設(shè)計(jì)值Nj相近，且大于設(shè)計(jì)值。由表中計(jì)算可見(jiàn)，當(dāng)采用試算法列表計(jì)算，根據(jù)規(guī)范，系數(shù)A、BCD查附表所得:且強(qiáng)度不要求配筋.現(xiàn)按構(gòu)造要求取:0.2%。3.3 配筋并繪制基樁構(gòu)造及鋼筋布置圖鋼筋的面積為：1.220.2%2261.94mm24現(xiàn)選用9根18的HRB33璉W筋，鋼筋的面積為：AS=2290mm2;實(shí)際配筋率為：

19、2.02102290Z212004繪制圖形樁基礎(chǔ)正截面配筋圖樁基礎(chǔ)圓截面配筋圖3.4 對(duì)截面進(jìn)行強(qiáng)度復(fù)核在垂直于彎矩作用平面內(nèi)長(zhǎng)細(xì)比l0/d18/1.215,故穩(wěn)定系數(shù)0.83;混凝土截面積為Acd2/41130400mm2,實(shí)際縱向鋼筋面積As2290mm2,則在垂直于彎矩作用平面的承載力為：'Nu0.9(fcdAcfsdAs)0.90.83(9.211304002802290)8247.54kNN(5333.60kN)在彎矩作用平面內(nèi)cBfcdDgfsdrerAfcdCfsd以下采用試算法列表計(jì)算，各系數(shù)查規(guī)范得：ABCD(e0)(mm)e0(mm)(e0)/e00.942.534

20、30.42952.14330.7847106.0788.141.20345290.952.56180.41552.17260.7645101.5688.141.15229280.962.58900.40112.20120.744697.0788.141.10141240.972.61580.38652.22900.725192.6688.141.05133190.982.64240.37172.25610.706188.3188.141.00194150.992.66850.35662.28250.687484.0088.140.9530409有計(jì)算表可見(jiàn)，當(dāng)0.98時(shí)，()88.31mm,與

21、設(shè)計(jì)的e88.14mm很接近,故取0.98為計(jì)算值、在彎矩作用平面內(nèi)的承載力為：22,NuAr匕Crfsd_-2_22.6424(600)9.22.25610.00202(600)2809211.00kNN(5333.60kN)綜上計(jì)算，均滿足要求4.樁基礎(chǔ)驗(yàn)算4.1 按地基土的支承力確定和驗(yàn)算單樁軸向承載力對(duì)于鉆挖孔灌注樁：1 nR-uqiJApmi0fa0k22(h3)2 i1式中：Ra單樁軸向受壓承載力容許值u樁的周長(zhǎng)，u(d0.1)4.084m；Ap樁端截面面積，Ad2/41.13m2；n土的層數(shù)，此處n1；li承臺(tái)底面或局部沖刷線以下各土層的厚度,li11.31m；qik 500kP

22、a ；fa0 樁端處土的承載力基本容許值,fa0100OkPa；h 樁的埋置深度，從一般沖刷線起算，即h 14mk2 地基土容許承載力隨深度的修正系數(shù)，取10.0 ；2樁端以上各土層的加權(quán)平重度,_ _ _310.00kN /m3qik與li對(duì)應(yīng)的各土層與樁側(cè)的摩阻力標(biāo)準(zhǔn)值,m0修正系數(shù),取0.8；修正系數(shù)，取0.70;所以，單樁軸向受壓承載力容許值為:Ra1 n , A-uqiJApm02 i 1fa。 k2 2(h 3)計(jì)算最不利荷載N max故，滿足12878.86kNG 7884.10 6.698093.47kN116.96 1 11.31 16.962Nmax G8093.47kN

23、K R(2.0 12878.86 25757.72kN)所以，單樁軸向承載力滿足要求。4.2 承臺(tái)沖切承載力驗(yàn)算對(duì)于圓形截面樁換算為邊長(zhǎng)等于0.8倍的圓柱直徑的方形樁，即a0.8d0.96m；對(duì)于柱或墩臺(tái)向下沖切承臺(tái)的沖切承載力驗(yàn)算，由于作用于沖切破壞錐體上的沖切力設(shè)計(jì)值為0.故不進(jìn)行驗(yàn)算；對(duì)于柱或墩臺(tái)向下的沖切破壞錐體以外的角樁和邊樁，根據(jù)設(shè)計(jì)采用規(guī)范設(shè)計(jì)值：h02.0 0.11.9m其向上沖切承臺(tái)的沖切承載力按下列規(guī)定計(jì)算:1）角樁0Fld 0.6 ftdh0apx(byay 'axT)apy(bx 萬(wàn)"a px0.8x 0.2a py0.8y 0.2bx、式中：Fld一角樁豎向力設(shè)計(jì)值，F(xiàn)ld7884.10kN；by一承臺(tái)邊緣至樁內(nèi)邊緣的水平距離，根據(jù)上尺寸圖,計(jì)算得bx1.6m、by1.6max、ay 一沖跨，為樁邊緣至相應(yīng)柱或墩臺(tái)邊緣的水平距離，其值不應(yīng)大于h0,這里Baxay0.2h00.38m；y一沖跨比，xax/h00.2,yay/h00.2a pxapy一分別與沖跨比xy對(duì)應(yīng)的沖切承載力系數(shù)。0.80.8a pxp x 0.20.2 0.22;0.8a pypy y 0.20.80.20.2根據(jù)安全等級(jí)為二級(jí)進(jìn)行驗(yàn)算，所以，. ay.0.6 ftdh0apx(by -2)apy(bxax)0.6 1.06 106 1.92 1.6 0.3