基础工程课程设计(参考范例)

基础工程课程设计

    名:**

    号:**

    级:**

                指导教师:**

一、设计任务书

(一)、设计资料

1、建筑场地土层按其成因土的特征和力学性质的不同自上而下划分为5层,物理力学指标见下表。勘查期间测得地下水混合水位深为2.1m,本场地下水无腐蚀性。 建筑安全等级为2级,已知上部框架结构由柱子传来的荷载。

承台底面埋深:D = 2.1m。

附表一:土层主要物理力学指标

(二)、设计要求:

  1、单桩竖向承载力标准值和设计值的计算;

  2、确定桩数和桩的平面布置图;

  3、群桩中基桩的受力验算

  4、承台结构设计及验算;

  5、桩及承台的施工图设计:包括桩的平面布置图,桩身配筋图,

承台配筋和必要的施工说明;

  6、需要提交的报告:计算说明书和桩基础施工图。

二、桩基持力层,桩型,桩长的确定

根据设计任务书所提供的资料,分析表明,在柱下荷载作用下,天然地基基础难以满足设计要求,故考虑选用桩基础。由地基勘查资料,确定选用第四土层黄褐色粉质粘土为桩端持力层。

根据工程请况承台埋深2.1m,预选钢筋混凝土预制桩断面尺寸为450㎜×450㎜。桩长21.1m。

三、单桩承载力确定

(一)、单桩竖向承载力的确定:

1、根据地质条件选择持力层,确定桩的断面尺寸和长度。

根据地质条件以第四层黄褐色粉土夹粉质粘土为持力层,

采用截面为450×450mm的预置钢筋混凝土方桩,桩尖进入持力层1.0m;镶入承台0.1m,桩长21.1 m。承台底部埋深2.1 m。

2、确定单桩竖向承载力标准值Quk可根据经验公式估算:

 Quk= Qsk+ Qpk=µ∑qsikli+qpkAp

 桩周长:µ=450×4=1800mm=1.8m

 桩横截面积:Ap=0.45²=0.2025㎡

 桩侧土极限摩擦力标准值qsik:查表得:用经验参数法:

 粉质粘土层:=0.95,取qsk=35kPa

 淤泥质粉质粘土:qsk=29kPa

 粉质粘土:=0.70,取qsk=55kPa

桩端土极限承载力标准值qpk,查表得:qpk=2200 kPa

用经验参数法求得Quk1=1.8×(35×8.0+29×12.0+1.0×55) +2200×0.2025=1674.9KN

用静力触探法求得Quk2=1.8×(36×8.0+43×12.0+1.0×111) +1784.5×0.2025=2008.4KN

3、确定单桩竖向承载力设计值R,  并且确定桩数n和桩的布置

       先不考虑群桩效应,估算单桩竖向承载力设计值R为:

       R=Qsk/rs+Qpk/rp

    用经验参数法时:查表rs=rp=1.65

       R1=Qsk/rs+Qpk/rp=1229.4/1.65+445.5/1.65=1015.09KN

用静力触探法时:查表rs=rp=1.60

       R2=Qsk/rs+Qpk/rp=1647/1.60+361.4/1.60=1255.25KN

       Rz=min(R1,R2)= 1015.09 KN

  

四、桩数布置及承台设计

根据设计资料,以轴线⑦为例。

1、⑦轴A柱:Nmax=4239, Mmax=193KN.m,Vmax=75KN.m                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

柱的截面尺寸为:600×600mm;

按照轴力P和R粗估桩数n1为:

   n1=P/R=4239/1015.09=4.18,由于没有考虑弯矩M,基础及承台上土重,以及承台底土分担荷载作用桩数,n=1.1n1=4.6≈5根

由于n1>3,应按考虑群桩效应和承台效应确定单桩竖向承载力设计值R

先取桩数n=5根,桩的布置按梅花式排列,桩距Sa=(3~4)d=(3~4)×0.45=1.35~1.8m,取边桩中心至承台边缘距离为1d=0.45 m

2、⑦轴D柱:Nmax=4159, Mmax=324KN.m,Vmax=79KN.m                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

柱的截面尺寸为:600×600mm;

按照轴力P和R粗估桩数n1为:

   n1=P/R=4159/1015.09=4.10,由于没有考虑弯矩M,基础及承台上土重,以及承台底土分担荷载作用桩数,n=1.1n1=4.51≈5根

由于n1>3,应按考虑群桩效应和承台效应确定单桩竖向承载力设计值R

先取桩数n=5根,桩的布置按梅花式排列,桩距Sa=(3~4)d=(3~4)×0.45=1.35~1.8m,取边桩中心至承台边缘距离为1d=0.45 m。

五桩承台布置图如下:

3、⑦轴B、C柱(因为柱距近,故设置复合桩基):Nmax=8782KN, Mmax=593KN.m,Vmax=165KN.m                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      

⑴柱的截面尺寸为:600×900mm;

按照轴力P和R粗估桩数n1为:

   n1=P/R=8782/1015.09=8。7,由于没有考虑弯矩M,基础及承台上土重,以及承台底土分担荷载作用桩数,n=1.1n1=9.57≈10根

由于n1>3,应按考虑群桩效应和承台效应确定单桩竖向承载力设计值R

先取桩数n=10根,桩的布置排列见图5,桩距Sa=(3~4)d=(3~4)×0.45=1.35~1.8m,取边桩中心至承台边缘距离为1d=0.45 m。承台布置如下图:

五:复合桩基荷载验算

根据上面承台布置,按下式计算复合桩基。

  

1、5桩承台

1).A柱

     

      由,查表8.16:

;      查表8.17:

 得:

    

查表:预制桩 

(1)       按中心荷载计算

    

(2)       按偏心荷载计算

           满足要求。

2).D柱

单桩承载力与A柱相同,但外荷载小于A柱,且承台设计与A柱相同,因此,D柱单桩受力验算也符合要求。

2联合承台

     

      由,查表8.16:

;      查表8.17:

 得:

    

查表8.9:预制桩 

桩基验算:

(3)       按中心荷载计算

    

(4)       按偏心荷载计算

 满足要求。

六、桩身设计

混凝土为C30,轴心抗压强度设计值= 14.3MPa,抗拉强度设计值为=1.43MPa,主筋采用:4Φ16,强度设计值:=310Mpa。其余按结构图集《预制钢筋混凝土方桩》要求。

七:承台设计

承台设计选C30混凝土,轴心抗压强度设计值为=14.3MPa,轴心抗拉强度设计值为

=1.43MPa。

1、五柱承台

A柱:

(1)   柱对承台得冲切

    

        

 

     满足要求。

(2)       角柱对承台的冲切

        

    

     满足要求。

D柱:和A柱受力近似,故可以不验算承台抗冲切。

2、联合承台

  (1)单独考虑每个柱对承台得冲切

B

    

    

    

  满足要求。

C柱   

    

    

    

    满足要求。

(2)考虑B、C柱共同作用对承台的冲切作用

 

    

    

    

   满足要求。

(3)   角柱对承台得冲切作用

冲切力

柱1:   

          

     

     

     

     

       

  满足要求

柱2:   

          

      

     

     

     

       

  满足要求

八、沉降计算

1、五桩承台

A柱:

由于弯矩较小,故可按轴心受压计算。

等效作用面位于桩端平面,等效作用面积为桩承台投影面积,等效作用附加应力近似取承台底平均附加压力。

    (1)基底接触压力:

(2)基底附加应力                                                         :                           

(3)确定地基手压层深度:

故分两层,第一层:4.3m          

第二层:1.715m        

(4)       计算基础中心下地基中的附加应力:

(5)       计算压缩模量:

(6)       软土地区且桩端无良好持力层时,当桩长l≤25m时,ψ取1.7;

   查附表H:

   

  桩基等效沉降系数

(7)       计算A桩基沉降量:

D:柱

由于弯矩较小,故可按轴心受压计算。

等效作用面位于桩端平面,等效作用面积为桩承台投影面积,等效作用附加应力近似取承台底平均附加压力。

    (1)基底接触压力:

(2)基底附加应力                                                         :                           

(3)确定地基手压层深度:

故分两层,第一层:4.3m          

第二层:1.715m        

(4)       计算基础中心下地基中的附加应力:

(5)       计算压缩模量:

(6)       软土地区且桩端无良好持力层时,当桩长l≤25m时,ψ取1.7;

   查附表H:

   

  桩基等效沉降系数

(7)       计算A桩基沉降量:

2、联合承台

B、C桩基可认为是承受沿7轴线方向的偏心。等效作用面位于桩端平面,等效作用面积为桩承台投影面积,等效作用附加应力近似取承台底平均附加压力。

(1)       求基底接触压力:

      

(2)   求基底附加压力

     求出最大附加压力处的沉降和最小附加压力处的沉降,便可求出沉降差(略)

(3)确定地基手压层深度:

故分两层,第一层:4.3m          

第二层:1.715m        

(4)计算联合承台中心沉降:

软土地区且桩端无良好持力层时,当桩长l≤25m时,ψ取1.7;

   查附表:

   

  桩基等效沉降系数

3计算沉降差

(1)A、BC桩基沉降差:

 

(2)BC、D桩基沉降计算:

满足要求。

九、施工图

参考文献:1.《预制钢筋混凝土方桩图集》(97G361)

  2. 建筑桩基础技术规范》(JGJ94-94)

3.《混凝土结构设计规范》(GB50010-2002)

相关推荐