图7－50 两柱脚下的冲切破坏锥体
①按图7－50，对每个柱分别进行冲切验算。 对B柱：hc?bc?0.6m
a0x1?1.0?0.3?0.225?0.475m
a0x2?1.8?0.3?0.225?1.275m?h0，取a0x2?0.92m a0y?0.7?0.3?0.225?0.175m
Fl?FB?3338kN
冲垮比 ?a0x10x1?h?47520?0.516 09 ?a0x20x1?h?920920?1.0 0 ?0y1750y?ah?920?0.19?0.2 取?0y?0.2 0冲切系数：?0.720x1???0.2?0.720.516?0.2?1.006
0x ?0.720x2?1.0?0.2?0.6
?0y?0.720.2?0.4?1.8 所以
31
[?0x1(a0y?bc)??0x2(a0y?bc)??0y(2hc?a0x1?a0x2)]fth0 ?[1.006?(0.175?0.6)?0.6?(0.175?0.6)?1.8?(2?0.6?0.475?0.92)]?1100?0.92 ?5987kN??0Fl?3338kN对C柱：bc?0.6mhc?0.9m
a0x3?1.2?0.225?0.45?0.525m
a0x4?1.6?0.225?0.45?0.925m?0.92m 取a0x4?0.92m a0y?0.175m
FL?Fc?5444kN
0.5250.525?0.571 ?0x4??1.0 0.920.920.1750.175 ?0y??0.2 ?0.19?0.2 取?0y?0.920.920.72冲切系数：?0x3??0.934 ?0x4?0.6
0.572?0.2冲垮比：?0x3? ?0y?1.8 所以：
[?0x3(bc?a0y)??0x4(bc?a0y)??0y(2hc?a0x3?a0x4)]fth0?7114kN??0Fl?5444kN
② 对双柱联合的承台，除考虑在每个柱脚下的冲切破坏锥体外，尚应按下图考虑在两个柱脚的公共周边下的冲切破坏情况。
图7-51双柱脚的公共周边下的冲切破坏锥体
32
由图7-51知，hc?0.3?0.45?3.0?3.75m
bc?0.6m
a0x1?0.475m
a0x2?0.925m?0.92，取a0x2?0.92m a0y?0.175m
冲切力：Fl?FB?FC?3338?5444?8782kN 冲跨比：?0x1?0.516，?0x2?1.0，?0y?0.2 冲切系数：?0x1?1.006，?0x2?0.6，?0y?1.8 所以：
[?0x1(bc?a0y)??0x2(bc?a0y)??0y(2hc?a0x1?a0x2)]fth0
?[1.006?(0.6?0.175)?0.6?(0.6?0..175)?1.8?(2?3.75?0.475?0.92)]?1100?0.92
?17463kN??0Fl?8782kN满足要求。
2) 角桩对承台的冲切
图 双柱下的角桩冲切
冲切力：Fl?Njmax?Nmax?对桩1
G861?979.4??893.3kN N10a1x1?0.475m a1y1?0.175m
33
c11?c21?0.45?0.45/2?0.675m
冲跨比：?1x?a1x1?0.516 h0
?1y?a1y1h0?0.19?0.2，取?1y?.2
冲切系数：?1x?0.480.48?1.2 ?0.670，?1y??1y?0.2?1x?0.2所以：[?1x(c21??1y1/2)??1y(c11??1c1/2)fth0?1625kN??0Fl?893.3kN 对桩2：
a1x2?0.925m?0.92m，a1x2?0.92m a1y?0.175m
c11?c21?0.45?0.45/2?0.675m
冲跨比：?1x?1.0， ?1y?0.2 冲切系数：?1x?0.4，?1y?1.2
[?1x(c22?a1y2/2)]fth0?1687.0kN??0Fl?893.3kN 满足要求。
3) 斜截面抗剪验算：将承台沿长向视作一静定梁，其上作用柱荷载和桩净反力值下图7-53c、d，可知柱边最不利截面为I—I和I’—I’，另一方向的不利截面为II—II（图7-53）。
34
对I—I截面：
剪力：V?2Njmax?1786.6kN
m a2x1?0.925剪跨比：?2x?a2x1??1.4 ?1.005?h0??0.30.120.12??0.09
?2x?0.31.005?0.3剪切系数：?2x?3所以：?fcb0h0?0.09?10?10?2.3?0.92?1904kN??0V?1786.6kN
对于I’—I’截面：
剪力：V?11976.6kN
m a2x1'?1.2?0.225?0.525剪跨比：?2x?0.525?0.571 0.92 35