Design of Thrust Blocks_London_Ted

8/11/2019 Design of Thrust Blocks_London_Ted

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JOINT RESTRAINTJOINT RESTRAINT

of EngineersKansas City District

PRESSURIZED PIPEPRESSURIZED PIPE

Presented by:

Ted London, PE

US Army Corps of EngineersKansas City District


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How Thrust is Generatedof EngineersKansas City District

Equilibrium


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What changes equilibrium:

Transient Pressure (surge)

Velocit Head

Changing direction of flow

Changing diameter of pipe

Thermal changes


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Changes in equilibrium are developed at:

Vertical bends

Dead ends

Tees

Wyes

Reducers

Fire Hydrants


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Bearin Ca acitof EngineersKansas City District

versus

Passive Resistance

BEARING CAPACITY FAILURE: The thrust generated

exceeds the bearing capacity of the soil times the bearing

PASSIVE RESISTANCE FAILURE: The thrust

generated slides a wedge of soil


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Bearin Ca acitof EngineersKansas City District


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thrust block by bearing pressure (AWWA m23)

Known Internal ressure of EngineersKansas City District

Pipe outside Diamter D 9.050in

Deflection angle 45

Depth to bottom of thrust block h 7ft

Safety Factor Sf 1.5

Soil Bearing B 1500psf

Solve

Internal Area A D

2

4

Unbalanced Force T 2 P A sin

2 180

Ab TSf

B

b

Passive resistance thrust block design is required if the height of the thrust block is

greater than 1/2 * depth.

In the above example, thrust block has a height of 2 and length of 4. 2 ft tall is less than

three (1/2*7)


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thrust block by Passive Resistance (AWWA m23)

Known

Internal pressure P 150psiof EngineersKansas City District Pipe outside Diamter D 9.050in

Pipe Deflection angle 45

Safety Factor Sf 1.5

Soil Bearing B 1500psf

Unit Wei ht of Soil 110 cfSoil Internal Friction angle 30

Cs 0psf

Internal AreaD

2

4

Unbalanced Force T 2 P A sin

2 180

Nd tan 45

2

180

2

Ab TSf

h Nd 2 Cs Nd.5

Ab

In the above example, a height of 2 and length of 4.5 ft. 2 ft tall is less than three(1/2*4.5)


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Tables should have correct bearing



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Ductile Iron Bolted


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Types of Restrained Joints


and

How The Work


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Errors and OmissionsErrors and Omissionsof EngineersKansas City District

Not considering passive resistance

Over-estimating bearing capacity of soil

Use same table over and over without thinking

Poor installation

Not considering saturated soil

required to resist the force


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Results of Errors


sengagemen o p pes

Displacement of soil Wedges

Poor construction blamed in lieu of design

Root cause ma not be determined


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References


AWWA M23: PVC Pipe Design and Installation

AWWA M41: Ductile Iron Pipe and FittingsDuctile Iron Pipe Research Association (DIPRA)

EBAA Iron

American Ductile Iron Pipe Co. (ACIPCO)


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Questions

Design of Thrust Blocks_London_Ted

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