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PRECAST CONCRETE MANHOLES

PRECASTCONCRETEMANHOLESWHY PROVIDE GUIDELINES?Past Problems Was tedious to keep track ofvariables Was easy to make mistakes Wanted: A design tool to reduceproblemsTOPICS Overview on PRECAST MANHOLES Applications Design Procedures andApplicable Standards Watertight Structures Quality InstallationPRECAST CONCRETE MANHOLES Round Structures ASTM C478, StandardSpecification for PrecastReinforced ConcreteManhole Sections PRECAST CONCRETE MANHOLES Rectangle / Square Structures ASTM C913, StandardSpecification for PRECAST ConcreteWater and Wastewater Structures DO NOT Specify a Box Culvertfor a vertical application.

between core and jacket. • The product is immediately stripped and the form is reused. • Products typically cured in a kiln or a combination of ... • Typically used in base slabs and flat slab tops. • Additional bars may be placed around blockouts. • Conforms to ASTM A615.

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Transcription of PRECAST CONCRETE MANHOLES

1 PRECASTCONCRETEMANHOLESWHY PROVIDE GUIDELINES?Past Problems Was tedious to keep track ofvariables Was easy to make mistakes Wanted: A design tool to reduceproblemsTOPICS Overview on PRECAST MANHOLES Applications Design Procedures andApplicable Standards Watertight Structures Quality InstallationPRECAST CONCRETE MANHOLES Round Structures ASTM C478, StandardSpecification for PrecastReinforced ConcreteManhole Sections PRECAST CONCRETE MANHOLES Rectangle / Square Structures ASTM C913, StandardSpecification for PRECAST ConcreteWater and Wastewater Structures DO NOT Specify a Box Culvertfor a vertical application.

2 BoxCulverts are designed forhorizontal installations andloading conditions. Specify ASTM C913 for SIZES Round ASTM C478 Internal Diameter ( ) 36 144 Check with localmanufacturer foravailability of largerdiameter box structuresare easily fabricatedusing universal SIZES Rectangle / Square ASTM C913 24 x 24 to 72 x 72 sizes increase by 6 incrementsMANUFACTURING METHODS Wet-Cast Cast with an inner and outer form. Product cured in the form. Blockouts/hole formers can easily be METHODS Wet-Cast Cast with conventional CONCRETE or self-consolidatingconcrete.

3 Base sections are typically wet-cast. Wet-cast is common for sanitary MethodsManufacturing MethodsMANUFACTURING METHODSDry-Cast (Machine Made) Product is cast utilizing mechanized equipment. Form vibrators consolidate zero-slump concretebetween core and jacket. The product is immediately stripped and the form isreused. Products typically cured in a kiln or a combination oftarps and moisture curing is MethodsManufacturing MethodsMANUFACTURING METHODSDry-Cast (Machine Made) Both round and square structures may be dry-cast. Hole formers may be incorporated, or coring is doneas needed.

4 Surface may appear rough due to ADVANTAGES Readily Available (more than 400 NPCA members supply PRECAST CONCRETE MANHOLES ) Modular Flexible Design May be designed to accommodate existing utilities Produced in a Quality Controlled Plant EnvironmentPRECAST ADVANTAGES Watertight Structures Easily Achieved Resists Buoyant Forces Superior Strength APPLICATIONS Sanitary and Stormwater Sewer Provide access for inspection and maintenance. Monolithic drop MANHOLES available. Stormwater Inlet and Treatment Structures Structure for housing stormwater treatment equipment.

5 Various proprietary treatment systems Pump/Lift Stations Sanitary andstormwater sewerapplications. Accommodate elevationchanges in gravity flowsewer Utility MANHOLES Provide access tounderground utilitiesand/or vaults. Used by electrical,telecommunications, fiberoptics, water and gascompanies. May be referred to as avalve Structure Sizing Round Structures ASTM C478 ASTM C497 Rectangle/Square Structures ASTM C913 ASTM C890 Lifting and Handling Corrosion Mitigation The structure (round or square) must be large enough toaccept the maximum size pipe.

6 The structure size is a function of the number, size,elevation and entry angle of pipes connecting to thestructure. The structural integrity must be maintained by providing aminimum structural leg of CONCRETE between pipe holes. Ageneral rule of thumb is to provide a minimum of 6 inchesas measured from the interior of the CONSIDERATIONS The type of pipe entering the structure and accompanyingconnection method (boot, compression or mortar) must beknown to accurately determine the required hole size andstructure size. Transition sections may be incorporated above a largerbase section to utilize smaller riser sections, which mayminimize overall project CONSIDERATIONS Square and/or rectangular structures are typically usedwhere pipes can intercept at 90 degrees or 180 roadways and some stormwater site drainage systemsemploy these types of structures.

7 Round structures allow more flexibility in the system designand layout. Various sizes of pipes entering at differentangles can more easily be accommodated by a roundstructure, ensuring watertight connections are CONSIDERATIONS When possible, avoid pipes entering into structure joints andcorners, as this may compromise the structural integrity andwatertightness of the structure. However, this practice maybe necessary for certain installations and should be left tothe discretion of an experienced PRECAST concretemanufacturer. Consult your local PRECAST CONCRETE manufacturer andconnector supplier for exact design requirements andproduct CONSIDERATIONSSIZING CONSIDERATIONSR elationships between Inside Diameter( ), Wall Thickness ( ), OutsideDiameter ( ) and Hole Size ( )* forconcrete (in inches) = + = + ( x 2) = + (2 to 4 )* may vary depending on type of pipeand connection used.

8 Diameter maybe 2-4 inches larger than : ? Hole Size for 24 = 24/12 + 1 = 3 = 24 + (3 x 2) = 30 Hole Size ( ) = 30 + 4 = 34 Hole Sizing for Reinforced CONCRETE Pipe (ASTM C76) 24 = 3 = 30 = 34 = 30 Local specifications and designhandbooks may include minimumrequirements and design tables toassist in the sizing of manholestructures. The adjacent table addressesstructure sizing when usingconcrete pipe for storm CONSIDERATIONSF lorida DOT Drainage Handbook: StormDrains (January 2004)Table 4-210 ft8 ft7 ft7 -6 30 DimensionRoundRectangularPipeSizeMinimum Dimensions For StructuresMinimum Angle Between Pipes Entering RoundStructuresSIZING CONSIDERATIONS Pipe opening ( ) is assumedto be: = + + (2 to 4 ) Recommended minimumstructural leg is 6 inches asmeasured from the interior of thestructure.

9 Structure #1 would not providethe minimum structural leg. Increasing the manhole diameterto the next size (Structure #2)provides the required CONSIDERATIONS Required minimum structural leghas not been achieved. A larger diameter manhole baseshould have been specified. Authorities havingjurisdiction may require aminimum amount of concreteabove openings. Skewed pipes entering rectangular structuresSIZING CONSIDERATIONS Watertight connections may be difficult to achieve. Typically done in stormwater structures using mortarjoints.

10 Consider the use of a round structure and flexibleconnector when requiring a watertight structure. Skewed pipes entering rectangular structuresSIZING CONSIDERATIONS Authorities having jurisdiction may provide design tablesaddressing pipe size and maximum allowable skew 54 48 42 36 30 24 18 Pipe SizeThese values are based on 2" of construction tolerance, precaststructures with 8" walls, and CONCRETE pipe 4-3 Florida DOT Drainage Handbook: Storm Drains (January 2004) Transition SlabsSIZING CONSIDERATIONS Allow the use of a larger basesection to accommodate pipesizes and entry angles.


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