THRUST BLOCK CALCULATION- PIPE 40MM X 90 ELBOW FITTING
Density of concrete
Grade of the concrete
Minimum characteristic strength of steel
Working pressure
F.O.S(NFPA 13 A.10.6.2.1c)
Design Pressure
Slope of the pipe
Internal angle of friction
Allowable bearing pressure
Density of soil
Diameter of Pipe
Area of the pipe
Depth of pipe from Ground level
=
=
=
=
=
=
=
=
=
=
=
=
25
31
420
6.5
1.5
9.75
90
30
200
18
40
0.001257
0.9
kN/m3
Mpa
Mpa
bar
bar
Degrees
Degrees
kN/m2
kN/m3
mm
m2
m
650 kPa
(From MEP)
975 kPa
0.04 m
General Equation for Hydraulic Thrust of Horizontal Bends
NFPA 13 A.10.8.2 (p13-336)
Horizontal force
=
=
Vertical reaction
=
=
Total Reaction
=
=
Thrust Block Dimensions
PA(1-cosθ)
1.77421 kN
PA sinθ
1.095344 kN
2PA sin(θ/2)
1.732034 kN
A
A
=
0.12
m
B
=
0.12
m
C
=
0.25
m
D
=
0.25
m
Depth
=
0.3
m
Volume
=
0.0103
m3
Weight
=
0.2575
kN
Friction Coeff =
0.5 ( As per Soil report)
Base area =
0.05405
m2
Least side dim for lateral check =
0.25
Side area =
0.075
m2
Check for Bearing
D
B
C
m
Since the working pressure is considered for the calculation of the thrust forces, the vertical reaction above can be
considered to check the bearing.
Vertical reaction on soil(V)
= Vertical reaction + (Friction Coeff. * Weight of Concrete)
(Base Resistance)
= 1.224094 kN
Area of the base of Thrust Block
= 0.05405
m2
Pressure under the base
= 22.64743 kPA
Observed pressure less than SBC, OK
Check for Lateral Stability
Due to the change of the angle, there are vertical and horizontal forces. The horizontal forces are generated in the direction of the pipe.
In this calculation, it is considered that the pipe will not be taking any force.
Horizontal force on pipe (SLS)
=
1.774210399 kN
Ground resistance = Force due to lateral force difference + base resistance
Ground resistance = (σp-σa)Af +τbAb
Calculate the active earth pressure coefficient = (1-sinθ)/(1+sinθ)
Ka = (1-sin30)/(1+sin30)
Ka
=
Calculate the passive earth pressure coefficient = (1+sinθ)/(1-sinθ)
0.33
Kp = (1+sinθ)/(1-sinθ)
Kp
=
3.00
Since the forces are applied on the concrete block and pipe, consider pressure in the middle of the pipe.
Active pressure (σa) = Kaγh
=
5.403311029 kPa
Passive pressure (σp) = Kpγh
=
48.570219 kPa
Side surface area = pipe +thrust block
=
0.075628319 m2
Net pressure acting on the Pipe
=
43.16690797 kPa
Resistance force from soil
=
3.264640666 kN
Base Resistance force
=
1.224093607 kN
Applied horizontal force
=
1.774210399 kN
(Each side (Af/2))
Applied force < Resistance force, hence stable
The factor of safety against sliding
=
2.530 >>>
1.5
Safe in sliding