基礎工程課程設計-低樁承臺基礎設計(樁徑1.5m)

基礎工程課堂設計低樁承臺基礎設計學生姓名：nilfarochinel班級：橋5一、擬定承臺平面尺寸鉆孔灌注樁屬于摩擦樁中的鉆孔樁，根據(jù)規(guī)范要求，其中心距不應小于樁徑的2.5倍，此處，橫、縱向樁中心距均取樁徑的2.5倍即：橫、縱向樁的中心距為1.5*2.5=3.75m根據(jù)規(guī)范，為了避免承臺邊緣距樁身過近而發(fā)生破裂，并考慮樁頂位置允許的偏差，邊樁外側(cè)到承臺邊緣的距離，對于樁徑大于1.0m的樁不應小于0.3倍樁徑并不小于0.5m。故：承臺長承臺寬二、進行基樁的平面布置樁的排列形式采用行列式，基樁布置如圖1所示三、擬定樁長并驗算單樁軸向受壓容許承載力承臺每延米自重：土層Ⅰ中樁每延米自重：土層Ⅱ中樁每延米自重：設：第二層土中樁長為根據(jù)要求，一般應將樁底至于巖層或堅硬的土層中，已得到較大的承載力和較小的沉降量，若在施工條件允許的深度內(nèi)沒有堅硬土層的存在，應盡可能選擇壓縮性較低、強度較高的土層作為持力層，要避免是樁底坐落在軟土層上或離軟弱下臥層的距離太近，以免樁基礎發(fā)生過大的沉降。顯然，土層Ⅱ相對于土層Ⅰ更適合成為持力層。樁底所承受的最大豎向荷載最大值為：計算時取以下數(shù)據(jù)：樁的周長，，,,所以承載力：解之的取因此擬定樁長為：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：樁底所承受的最大豎向荷載因為,不滿足要求，所以需重新擬定樁長。取=17m。驗算單樁軸向受壓容許承載力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：樁底所承受的最大豎向荷載因為,滿足要求。此時擬定的樁長為：四、判斷是否為彈性樁當時，故樁的計算寬度為：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：符合要求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=25m。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0.00.0001.000000,00-400,97-400,970.10.300.099600.9997473,24-400,87-327,620.20.600.196960.99806144,84-400,19-255,350.30.900.290100.99382213,33-398,49-185,160.41.200.377390.98617277,53-395,42-117,900.51.510.457520.97458336,45-390,78-54,330.61.810.529380.95861389,30-384,374,920.72.110.592280.93817435,55-376,1859,370.82.410.645610.91324474,77-366,18108,590.92.710.689260.88407506,87-354,49152,381.03.010.723050.85089531,72-341,18190,541.13.310.747140.81410549,43-326,43223,001.23.610.761830.77415560,23-310,41249,821.33.910.767610.73161564,49-293,35271,131.44.220.764980.68694562,55-275,44287,111.54.520.754660.64081554,96-256,95298,021.64.820.737340.59373542,23-238,07304,161.75.120.713810.54625524,92-219,03305,891.85.420.684880.49889503,65-200,04303,611.95.720.651390.45219479,02-181,31297,702.06.020.614130.40658451,62-163,03288,592.26.620.531600.32025390,93-128,41262,522.47.230.443340.24262326,02-97,28228,742.67.830.354580.17546260,75-70,35190,402.88.430.269960.11979198,52-48,03150,493.09.030.193050.07595141,97-30,45111,513.510.540.050810.0135437,36-5,4331,944.012.040.000050.000090,04-0,040,002）樁身最大彎矩Mmax最大彎矩位置確定（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0.001.000000241,220.00173.910.10,300.98833-0.00753238,401,00239,410.20,600.95551-0.02795230,493,72234,210.30,900.90468-0.05820218,237,75225,980.41,200.83898-0.09554202,3812,72215,100.51,510.76145-0.13747183,6818,31201,980.61,810.67486-0.18191162,7924,22187,010.72,110.58201-0.22685140,3930,21170,600.82,410.48522-0.27087117,0436,07153,110.92,710.38689-0.3124593,3341,61134,931.03,010.28901-0.3505969,7146,69116,401.13,310.19388-0.3844346,7751,1997,961.23,610.10153-0.4133524,4955,0479,531.33,910.01477-0.436903,5658,1861,741.44,22-0.06586-0.45486-15,8960,5744,681.54,52-0.13952-0.46715-33,6662,2128,551.64,82-0.20555-0.47378-49,5863,0913,511.75,12-0.26359-0.47496-63,5863,25-0,341.85,42-0.31345-0.47103-75,6162,72-12,891.95,72-0.35501-0.46223-85,6461,55-24,082.06,02-0.38839-0.44914-93,6959,81-33,882.26,62-0.43174-0.41179-104,1454,83-49,312.47,23-0.44647-0.36312-107,7048,35-59,342.67,83-0.43651-0.30732-105,2940,92-64,372.88,43-0.40641-0.24853-98,0333,09-64,943.09,03-0.36065-0.19052-87,0025,37-61,633.510,54-0.19975-0.01672-48,182,23-45,964.012,04-0.00002-0.000450,000,060,06（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0.00.002.440661.6210028,80-10,5418,260.10.302.278731.4509426,89-9,4317,460.20.602.117791.2908824,99-8,3916,600.30.901.958811.1407923,11-7,4215,700.41.201.802731.0006421,27-6,5014,770.51.511.650420.8703619,47-5,6613,820.61.811.502680.7498117,73-4,8712,860.72.111.360240.6388516,05-4,1511,900.82.411.223700.5372714,44-3,4910,950.92.711.093610.4448112,90-2,8910,011.03.010.970410.3611911,45-2,359,101.13.310.854410.2860610,08-1,868,221.23.610.745880.219088,80-1,427,381.33.910.644980.159857,61-1,046,571.44.220.551750.107936,51-0,705,811.54.520.466140.062885,50-0,415,091.64.820.388100.024224,58-0,164,421.75.120.31741-0.008473,750,063,801.85.420.25386-0.035723,000,233,231.95.720.19717-0.057982,330,382,702.06.020.14696-0.075721,730,492,232.26.620.06461-0.099400,760,651,412.47.230.00348-0.110300,040,720,762.67.83-0.03986-0.11136-0,470,720,252.88.43-0.06902-0.10544-0,810,69-0,133.09.03-0.08741-0.09471-1,030,62-0,423.510.54-0.10495-0.05698-1,240,37-0,874.012.04-0.10788-0.01487-1,270,10-1,18（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0.00,00-1.62100-1.75058-6,323,68-2,650.10,30-1.61600-1.65068-6,303,47-2,840.20,60-1.60177-1.55069-6,253,26-2,990.30,90-1.57676-1.45106-6,153,05-3,100.41,20-1.54334-1.35204-6,022,84-3,180.51,51-1.50151-1.25394-5,862,63-3,220.61,81-1.46009-1.15725-5,692,43-3,260.72,11-1.39593-1.06238-5,442,23-3,210.82,41-1.33398-0.96978-5,202,04-3,170.92,71-1.26713-0.87978-4,941,85-3,091.03,01-1.19647-0.79311-4,671,67-3,001.13,31-1.12283-0.70981-4,381,49-2,891.23,61-1.04733-0.63038-4,081,32-2,761.33,91-0.97078-0.55506-3,791,17-2,621.44,22-0.89409-0.48412-3,491,02-2,471.54,52-0.81801-0.41770-3,190,88-2,311.64,82-0.74337-0.35598-2,900,75-2,151.75,12-0.67075-0.29897-2,620,63-1,991.85,42-0.60077-0.24672-2,340,52-1,821.95,72-0.53393-0.19916-2,080,42-1,662.06,02-0.47063-0.15624-1,840,33-1,512.26,62-0.35588-0.08365-1,390,18-1,212.47,23-0.25831-0.02753-1,010,06-0,952.67,83-0.17849-0.01415-0,700,03-0,672.88,43-0.11611-0.04351-0,450,09-0,363.09,03-0.06987-0.06296-0,270,13-0,143.510,54-0.01206-0.08294-0,050,170,134.012,04-0.00341-0.08507-0,010,180,17八、樁身截面配筋設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12根Φ20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計規(guī)范》(JTJD62-2004)求軸向偏心距：其中即：以下采用試算列下表ABCD0.862.30470.53041.87860.96390.2390.2231.070.872.33420.51911.91490.93970.2300.2231.030.882.36360.50731.95030.91610.2230.2231.00由上表可知，當時,與實際值最為接近，故取0.88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，摩擦型群樁基礎樁間中心距小于6倍樁徑時，可將樁基礎視為實體基礎。當偏心受壓時，應滿足下列條其中：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；樁的長度（m）；承臺底面以上土的重度；