118 CIVIL WORKS GUIDELINES FOR MICRO-HYDROPOWER IN NEPAL
Sum of horizontal forces that act at the bend
ΣH-F10X
1. Expansion case 53.18 - 22.85 = 30.33 kN
2. Contraction case 16.66 - 22.85 = - 6.19 kN
Sum of vertical forces that act at the bend
Σv- F10y - WB
1. Expansion case
345.26 - 5.28 - 354.64 = 14.66 kN
2. Contraction case
320.44 - 5.28 - 354.64 = 39.48 kN
Pbase = 320.44/6 [1 + (6x0.06/3)] = 59.8 N/m2
In both case Pbase < Pallowable = 200kN/m2
... the structure is safe against sinking.
Check if the block is safe against sliding:
1. Expansion case
ΣH < µΣV
µ = 0.5 for concrete/masonary on oil
53.18 kN < 0.5x.45.26 kN
53.18 kN < 160.22 kN OK.
Now draw a force diagram on the block as shown in Figure 7.7.
Check if structure is safe against overturning:
1. Expansion case
Take sum of moments about point 0 with clockwise moments as
positive:
ΣM@0 = 30.33x2.15 + 22.85x0.6 + 354.64x1.41-14.66x1.0 =
564.30 kN-m
( )d =
ΣV
ΣM
= 564.30/345.26 = 1.63 m
2. Contraction case
ΣH < µΣV
Since ΣH < µΣV in both cases the structure is safe against sliding.
... The anchor block is stable. The calculations could be repeated
to justify using a smaller, more economical block.
e = 3/2 - 1.63 = 0.13m
eallowable = Lbase/6 = 3/6 = 0.5 m
... e < eallowable
2. Contraction case
Take sum of moments about point 0 with clockwise moments as
positive:
ΣM@0 = -6.19x2.15 + 22.85x0.6 + 354.64x1.41-39.48x1.0 = 460.96
kN-m = 460.96
( )d =
ΣV
ΣM
= 460.96/320.44 = 1.44 m
e = 3/2 - 1.44 = 0.06 m
Recall that eallowable = 0.5
... e < eallowable
Figure 7.7 Force diagram on the anchor block
Since < eallowable for both cases, the structure is safe against over
turning.
Check if the structure is safe on bearing capacity:
Note that for stiff clay allowable bearing pressure is 200kN/m2
(Table7.3).
1. Expansion case:
( )Pbase =
ΣV
Αbase
1 + 6e/Lbase
Pbase = 345.26/6 [1 + (6x0.13/3)] = 72.5 N/m2
2. Contraction case:
( )Pbase =
ΣV
Αbase
1 + 6e/Lbase