基础工程课程设计-低桩承台基础设计(桩径1.5m)

基础工程课堂设计低桩承台基础设计学生姓名：nilfarochinel班级：桥5一、拟定承台平面尺寸钻孔灌注桩属于摩擦桩中的钻孔桩，根据规范要求，其中心距不应小于桩径的2.5倍，此处，横、纵向桩中心距均取桩径的2.5倍即：横、纵向桩的中心距为1.5*2.5=3.75m根据规范，为了避免承台边缘距桩身过近而发生破裂，并考虑桩顶位置允许的偏差，边桩外侧到承台边缘的距离，对于桩径大于1.0m的桩不应小于0.3倍桩径并不小于0.5m。故：承台长承台宽二、进行基桩的平面布置桩的排列形式采用行列式，基桩布置如图1所示三、拟定桩长并验算单桩轴向受压容许承载力承台每延米自重：土层Ⅰ中桩每延米自重：土层Ⅱ中桩每延米自重：设：第二层土中桩长为根据要求，一般应将桩底至于岩层或坚硬的土层中，已得到较大的承载力和较小的沉降量，若在施工条件允许的深度内没有坚硬土层的存在，应尽可能选择压缩性较低、强度较高的土层作为持力层，要避免是桩底坐落在软土层上或离软弱下卧层的距离太近，以免桩基础发生过大的沉降。显然，土层Ⅱ相对于土层Ⅰ更适合成为持力层。桩底所承受的最大竖向荷载最大值为：计算时取以下数据：桩的周长，，,,所以承载力：解之的取因此拟定桩长为：桩端以上各土层的加权平均重度值为：桩端处土的承载力容许值：因为,所以取单桩轴向受压承载力容许值的计算：桩底所承受的最大竖向荷载因为,不满足要求，所以需重新拟定桩长。取=17m。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：桩端处土的承载力容许值：因为,所以取单桩轴向受压承载力容许值的计算：桩底所承受的最大竖向荷载因为,满足要求。此时拟定的桩长为：四、判断是否为弹性桩当时，故桩的计算宽度为：平行于水平力作用方向的桩间净距为地面线以下桩的计算埋入深度，且。所以计算可得：符合要求故整个深度的地基系数比例系数m取第一层土的m，惯性矩抗弯刚度桩的入土深度，故按照弹性桩计算。五、桩顶荷载分配并校核桩顶刚度系数值的计算：式中：，即：已知：取用4。查附表17、附表18、附表19得：,由下式可得：计算承台底面原点0处位移,低桩承台要考虑桩—土—承台的共同作用。即：其中计算作用在每根桩顶上的作用力竖向力：水平力：弯矩值:校核单位宽度水平抗力：单位宽度弯矩值：水平力校核：竖向力校核：弯矩值校核：显然，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竖向最大荷载：因为,不满足要求，所以进行重新计算。取=25m。桩端以上各土层的加权平均重度值为：桩端处土的承载力容许值：因为,所以取单桩轴向受压承载力容许值的计算：因为,满足要求。重新确定桩长为七、单桩内力及位移计算与验算（1）桩身弯矩Mz以及桩身最大弯矩Mmax计算1）由于，故可以采用无量纲法即：无量纲系数AM,BM分别由附表查的，Mz计算如下表：MZ计算列表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）桩身最大弯矩Mmax最大弯矩位置确定（2）桩身剪力Qz计算无量纲系数AQ,BQ分别由附表查的，Qz计算如下表QZ计算列表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计算无量纲系数Ax,Bx分别由附表查的，Xz计算如下表XZ计算列表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）转角位移计算无量纲系数分别由附表查的，计算如下表φZ计算列表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、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.计算该处轴向受压荷载时，根据《公路桥梁通用设计规范》（JTGD60—2004）第4.1.6，恒载分项系数取1.2。则1）纵向钢筋面积按《公路桥规》规定全部纵向钢筋配筋率按0.2%配置现选用12根Φ20的HRB335级钢筋：桩身采用C25混凝土，。计算偏心距增大系数因为长细比:所以偏心距增大系数：其中:,取;，所以：计算截面实际偏心距根据《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTJD62-2004)求轴向偏心距：其中即：以下采用试算列下表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，当时,与实际值最为接近，故取0.88作为计算值。截面承载力复合轴力复合:弯矩复合：轴力和弯矩均满足要求。裂缝宽度验算根据《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTJD62-2004)第6.4.5条，圆形截面钢筋混凝土偏心受压构件，当按作用短期效应组合计算的截面受拉区外缘钢筋应力时可不必验算裂缝宽度。式中：则：说明在桩身弯矩最大截面外缘钢筋处于受压状态，可不必进行裂缝宽度验算。钢筋布置如图：九、群桩基础承载力和沉降量验算1.桩底持力层承载力验算由《公路桥规》可知，摩擦型群桩基础桩间中心距小于6倍桩径时，可将桩基础视为实体基础。当偏心受压时，应满足下列条其中：式中：桩端平面处的最大压应力（kPa）；承台底面包括桩的重力在内至桩端平面上的平均重度；桩的长度（m）；承台底面以上土的重度；