基礎(chǔ)工程課程設(shè)計-低樁承臺基礎(chǔ)設(shè)計

基礎(chǔ)工程課程設(shè)計----低樁承臺基礎(chǔ)設(shè)計一、基本資料1．某跨線橋主橋上部結(jié)構(gòu)為預應力混凝土連續(xù)梁，跨徑組成為（60+100+60）m，橋面凈寬11m，設(shè)計荷載標準為公路Ⅰ級。采用盆式橡膠支座、等截面單箱雙室薄壁橋墩（如下圖示）。2．主墩高度18m，箱壁厚度0.75m，縱隔板厚度0.8m，墩身頂部1.5m及底部2m均為實心段，矩形墩底截面尺寸為(4×14)m2，采用30號混凝土。作用于墩身底截面中心處的設(shè)計荷載為：豎直力Nz=74958kN水平力Hx=2895kN縱橋向彎矩My=38209kN·m（坐標規(guī)定：縱橋向x軸、橫橋向y軸、豎向z軸）3．主墩基礎(chǔ)擬采用12根鉆孔灌注樁群樁基礎(chǔ)，混凝土標號25。承臺頂面與地面平齊，厚度為3.5m。4．地質(zhì)資料自地面向下16m深度范圍內(nèi)為中密細砂加礫石（土層Ⅰ），往下為密實中粗砂加礫石（土層Ⅱ）。地基土的物理力學性質(zhì)指標為:土層Ⅰ：=55kpa，=19.8kN/m3，m=10000kN/m4,土層Ⅱ：=70kpa,=500kpa,=21.8KN/m3m=20000kN/m45.設(shè)計參數(shù)承臺及基樁材料重度=25kN/m3，基樁設(shè)計有關(guān)參數(shù)為：Ec=2.8×107kN/m2,λ=0.85,m0=0.8,K2=6班級樁徑（m）縱橋向（排）橫橋向（排）橋11.234橋2、41.534橋31.834二、主墩群樁基礎(chǔ)設(shè)計要求（以縱橋向控制設(shè)計）（一）設(shè)計計算內(nèi)容：1.根據(jù)已知條件擬定承臺平面尺寸；2.進行基樁的平面布置；3.擬定樁長并驗算單樁軸向受壓容許承載力；4.判斷是否彈性樁；5.樁頂荷載分配并校核；6.確定樁長并驗算單樁軸向受壓容許承載力；7.單樁內(nèi)力及位移計算與驗算；8.樁身截面配筋設(shè)計及樁截面強度驗算；9.群樁基礎(chǔ)承載力和沉降量驗算。（二）設(shè)計完成后應提交的文件及圖表1．低樁承臺群樁基礎(chǔ)設(shè)計計算書（應附計算小圖）；2.橋墩及基礎(chǔ)結(jié)構(gòu)構(gòu)造圖；3.基樁鋼筋構(gòu)造圖。三、設(shè)計依據(jù)規(guī)范及參考書1．公路橋涵地基及基礎(chǔ)設(shè)計規(guī)范（JTGD63-2007）2．公路鋼筋混凝土及預應力混凝土橋涵設(shè)計規(guī)范（JTGD62-2004）3.王曉謀.基礎(chǔ)工程.北京：人民交通出版社，20044.葉見曙.結(jié)構(gòu)設(shè)計原理.北京：人民交通出版社，20045.江祖銘等主編.墩臺與基礎(chǔ).北京：人民交通出版社，1994

平行于水平力作用方向的樁間凈距為地面線以下樁的計算埋入深度，且。所以計算可得：故整個深度的地基系數(shù)比例系數(shù)m取第一層土的m，慣性矩抗彎剛度樁的入土深度，故按照彈性樁計算。五、樁頂荷載分配并校核樁頂剛度系數(shù)值的計算：式中：，即：已知：取用4。查附表17、附表18、附表19得：,由下式可得：計算承臺底面原點0處位移,低樁承臺要考慮樁—土—承臺的共同作用。即：其中計算作用在每根樁頂上的作用力豎向力：水平力：彎矩值:校核單位寬度水平抗力：單位寬度彎矩值：水平力校核：豎向力校核：彎矩值校核：顯然，校核結(jié)果符合要求。六、確定樁長并驗算單樁軸向受壓容許承載力由上一問可知，單樁樁頂所受到的最大軸向壓力豎向最大荷載：因為,不滿足要求，所以進行重新計算。取=11.5m。樁端以上各土層的加權(quán)平均重度值為：樁端處土的承載力容許值：因為,所以取單樁軸向受壓承載力容許值的計算：因為,滿足要求。重新確定樁長為七、單樁內(nèi)力及位移計算與驗算（1）樁身彎矩Mz以及樁身最大彎矩Mmax計算1）由于，故可以采用無量綱法即：無量綱系數(shù)AM,BM分別由附表查的，Mz計算如下表：MZ計算列表0.00.0001.000000.00332.81332.810.10.360.099600.9997462.20332.72394.920.20.720.196960.99806122.99332.16455.160.31.080.290100.99382181.15330.75511.910.41.440.377390.98617235.66328.21563.870.51.800.457520.97458285.70324.35610.050.62.150.529380.95861330.57319.03649.610.72.510.592280.93817369.85312.23682.080.82.870.645610.91324403.15303.94707.090.93.230.689260.88407430.41294.23724.641.03.590.723050.85089451.51283.18734.691.13.950.747140.81410466.55270.94737.491.24.310.761830.77415475.72257.64733.371.34.670.767610.73161479.33243.49722.821.45.030.764980.68694477.69228.62706.311.55.390.754660.64081471.25213.27684.521.65.750.737340.59373460.43197.60658.031.76.100.713810.54625445.74181.80627.541.86.460.684880.49889427.67166.04593.711.96.820.651390.45219406.76150.49557.252.07.180.614130.40658383.49135.31518.812.27.900.531600.32025331.96106.58438.542.48.620.443340.24262276.8480.75357.592.69.340.354580.17546221.4258.39279.812.810.050.269960.11979168.5839.87208.443.010.770.193050.07595120.5525.28145.833.512.570.050810.0135431.734.5136.234.014.360.000050.000090.030.030.062）樁身最大彎矩Mmax最大彎矩位置確定由QZ=0得：由及，查附表13，得，故由及，查書中附表13，得KM=1.780（2）樁身剪力Qz計算無量綱系數(shù)AQ,BQ分別由附表查的，Qz計算如下表QZ計算列表0.00.001.000000173.910.00173.910.10.360.98833-0.00753171.88-0.70171.180.20.720.95551-0.02795166.17-2.59163.580.31.080.90468-0.05820157.33-5.39151.940.41.440.83898-0.09554145.91-8.86137.050.51.800.76145-0.13747132.42-12.74119.680.62.150.67486-0.18191117.36-16.86100.500.72.510.58201-0.22685101.22-21.0380.190.82.870.48522-0.2708784.38-25.1159.280.93.230.38689-0.3124567.28-28.9638.321.03.590.28901-0.3505950.26-32.5017.771.13.950.19388-0.3844333.72-35.63-1.921.24.310.10153-0.4133517.66-38.31-20.661.34.670.01477-0.436902.57-40.50-37.931.45.03-0.06586-0.45486-11.45-42.16-53.611.55.39-0.13952-0.46715-24.26-43.30-67.561.65.75-0.20555-0.47378-35.75-43.91-79.661.76.10-0.26359-0.47496-45.84-44.02-89.861.86.46-0.31345-0.47103-54.51-43.66-98.171.96.82-0.35501-0.46223-61.74-42.84-104.582.07.18-0.38839-0.44914-67.54-41.63-109.182.27.90-0.43174-0.41179-75.08-38.17-113.252.48.62-0.44647-0.36312-77.65-33.66-111.302.69.34-0.43651-0.30732-75.91-28.49-104.402.810.05-0.40641-0.24853-70.68-23.04-93.723.010.77-0.36065-0.19052-62.72-17.66-80.383.512.57-0.19975-0.01672-34.74-1.55-36.294.014.36-0.00002-0.000450.00-0.04-0.05（3）水平位移Xz計算無量綱系數(shù)Ax,Bx分別由附表查的，Xz計算如下表XZ計算列表0.00.002.440661.6210017.016.0323.040.10.362.278731.4509415.885.4021.280.20.722.117791.2908814.764.8019.560.31.081.958811.1407913.654.2417.900.41.441.802731.0006412.573.7216.290.51.801.650420.8703611.503.2414.740.62.151.502680.7498110.472.7913.260.72.511.360240.638859.482.3811.860.82.871.223700.537278.532.0010.530.93.231.093610.444817.621.659.281.03.590.970410.361196.761.348.111.13.950.854410.286065.961.067.021.24.310.745880.219085.200.816.011.34.670.644980.159854.500.595.091.45.030.551750.107933.850.404.251.55.390.466140.062883.250.233.481.65.750.388100.024222.710.092.801.76.100.31741-0.008472.21-0.032.181.86.460.25386-0.035721.77-0.131.641.96.820.19717-0.057981.37-0.221.162.07.180.14696-0.075721.02-0.280.742.27.900.06461-0.099400.45-0.370.082.48.620.00348-0.110300.02-0.41-0.392.69.34-0.03986-0.11136-0.28-0.41-0.692.810.05-0.06902-0.10544-0.48-0.39-0.873.010.77-0.08741-0.09471-0.61-0.35-0.963.512.57-0.10495-0.05698-0.73-0.21-0.944.014.36-0.10788-0.01487-0.75-0.06-0.81（4）轉(zhuǎn)角位移計算無量綱系數(shù)分別由附表查的，計算如下表φZ計算列表0.00.00-1.62100-1.75058-3.14-1.82-4.970.10.36-1.61600-1.65068-3.14-1.72-4.850.20.72-1.60177-1.55069-3.11-1.61-4.720.31.08-1.57676-1.45106-3.06-1.51-4.570.41.44-1.54334-1.35204-2.99-1.41-4.400.51.80-1.50151-1.25394-2.91-1.30-4.220.62.15-1.46009-1.15725-2.83-1.20-4.040.72.51-1.39593-1.06238-2.71-1.10-3.810.82.87-1.33398-0.96978-2.59-1.01-3.600.93.23-1.26713-0.87978-2.46-0.91-3.371.03.59-1.19647-0.79311-2.32-0.82-3.151.13.95-1.12283-0.70981-2.18-0.74-2.921.24.31-1.04733-0.63038-2.03-0.66-2.691.34.67-0.97078-0.55506-1.88-0.58-2.461.45.03-0.89409-0.48412-1.73-0.50-2.241.55.39-0.81801-0.41770-1.59-0.43-2.021.65.75-0.74337-0.35598-1.44-0.37-1.811.76.10-0.67075-0.29897-1.30-0.31-1.611.86.46-0.60077-0.24672-1.17-0.26-1.421.96.82-0.53393-0.19916-1.04-0.21-1.242.07.18-0.47063-0.15624-0.91-0.16-1.082.27.90-0.35588-0.08365-0.69-0.09-0.782.48.62-0.25831-0.02753-0.50-0.03-0.532.69.34-0.17849-0.01415-0.35-0.01-0.362.810.05-0.11611-0.04351-0.23-0.05-0.273.010.77-0.06987-0.06296-0.14-0.07-0.203.512.57-0.01206-0.08294-0.02-0.09-0.114.014.36-0.00341-0.08507-0.01-0.09-0.10八、樁身截面配筋設(shè)計及樁截面強度驗算由上可知，最大彎矩發(fā)生在距離樁頂以下的3.92m處，該處的彎矩為.計算該處軸向受壓荷載時，根據(jù)《公路橋梁通用設(shè)計規(guī)范》（JTGD60—2004）第4.1.6，恒載分項系數(shù)取1.2。則1）縱向鋼筋面積按《公路橋規(guī)》規(guī)定全部縱向鋼筋配筋率按0.2%配置現(xiàn)選用16根Φ22的HRB335級鋼筋：樁身采用C25混凝土，。計算偏心距增大系數(shù)因為長細比:所以偏心距增大系數(shù)：其中:,取;，所以：計算截面實際偏心距根據(jù)《公路鋼筋混凝土及預應力混凝土橋涵設(shè)計規(guī)范》(JTJD62-2004)求軸向偏心距：即：以下采用試算列下表ABCD0.962.58900.40112.20120.74460.1450.1401.030.972.61580.38652.22900.72510.1380.1400.990.982.64240.37172.25610.70610.1320.1400.94由上表可知，當時,與實際值最為接近，故取0.97作為計算值。截面承載力復合軸力復合:彎矩復合：軸力和彎矩均滿足要求。裂縫寬度驗算根據(jù)《公路鋼筋混凝土及預應力混凝土橋涵設(shè)計規(guī)范》(JTJD62-2004)第6.4.5條，圓形截面鋼筋混凝土偏心受壓構(gòu)件，當按作用短期效應組合計算的截面受拉區(qū)外緣鋼筋應力時可不必驗算裂縫寬度。式中：則：說明在樁身彎矩最大截面外緣鋼筋處于受壓狀態(tài)，可不必進行裂縫寬度驗算。鋼筋布置如圖：九、群樁基礎(chǔ)承載力和沉降量驗算1.樁底持力層承載力驗算由《公路橋規(guī)》可知，摩擦型群樁基礎(chǔ)樁間中心距小于6倍樁徑時，可將樁基礎(chǔ)視為實體基礎(chǔ)。當偏心受壓時，應滿足下列條件其中：式中：樁端平面處的最大壓應力（kPa）；承臺底面包括樁的重力在內(nèi)至樁端平面上的平均重度；