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MANHOLE CASTINGREFERENCE GUIDE

TABLE OF CONTENTSMaterials . . 2Load Bearing. 3Key Dimensions of Round Frame and Cover. 3Key Dimensions of Inlet Frame and Grate. 4Frame Designs. 5Grate Designs. 6Curb Inlets or Combination Inlets. 7MaterialsWatertight Frames and Covers. 8Airport Castings. 8QUICK REFERENCEManhole Features.9-10All the iron provided in a product should have a minimumrecycled material content of 85%. All manufacturers shouldprovide material certifications on product that includescountry of origin and material quality and if requested, shallprovide load test data on the casting.NATIONAL PRECAST CONCRETE ASSOCIATIONWith nearly 1,000 member companies, NPCA serves asthe voice of the precast concrete industry in the UnitedStates and Canada. The industry includes a diverse mixof companies, from small single-plant manufacturersto multinational vertically integrated companiesthat operate in many sectors of the constructionindustry. NPCA provides an array of services to thesemanufacturers that include technical engineeringsupport, the industry’s largest certification program,safety programming, educational courses and a suiteof print and online publications. In addition to servicesto members, NPCA provides specialized technicalinformation to owners, contractors, engineers anddesigners on precast concrete products.Gray IronIron conforming to ASTM A48, Class 35B, as noted insection 7.1.1 and 7.1.3 of AASHTO M306. Class 35B exhibitsthe best corrosion and wear resistance properties as wellas the desirable quality of high compressive strength.Therefore it makes a good load bearing street hardware.35,000 psi minimum tensile strength iron is furnished.Ductile IronIron conforming to ASTM A536. Ideal material forconstruction castings when standard gray iron castingsdo not have the load bearing capabilities. Ductile Iron hasgreater strength characteristics than structural carbon steelwithout the corrosion characteristics of steel. It is usuallyused in areas subjected to loads greater then H20 loadings.Also because it has excellent compressive strength it isoften recommended as a cost effective approach to mateductile iron lids or grates with gray iron frames.Copyright 2012 by National Precast Concrete Association (NPCA); allrights reserved. No part of this manual may be reproduced in any formwithout permission in writing from the National Precast ConcreteAssociation.1320 City Center Dr., Suite 200, Carmel, IN 46032800-366-7731 precast.orgSteel GratesMaterial shall be hot rolled steel confirming to ASTM A36.Galvanizing is recommended for all steel frame, grates& covers, conforming to ASTM 123. Steel grates can becompatible with cast iron frames.2

Load BearingQUICK REFERENCELight DutyThese castings are suitable for a wide range of non-trafficlocations. Castings labeled light duty are recommended forsidewalks, terraces, landscape applications, and very lightduty vehicular traffic, such as golf carts or lawn mowers.2.5 over 16,000 lbs requirement of H20 and HS20. This loaddesignation is appropriate for general traffic applications.Extra Heavy Duty (Airport and PortAuthority)Heavy Duty AASHTO M306 HighwayLoadingCastings listed in this category can accommodate wheelloads of 100 psi or greater. They are considered for airportsand any place where concentrated loads might be applied.These castings can also accept proof loads from 100,000 to200,000 lbs, which meets the design loading associated withthe FAA wheel loading.According to AASHTO M306 castings must meet a minimumof 40,000 lbs proof load on a 9” x 9” load test area. Afterthe test, the cover grating or frame is inspected for cracks ordeformation. This specification allows for a safety factor ofKey Dimensions of Round Frame and CoverQUICK REFERENCEClear OpeningBase Flange OpeningClear opening is the diameter of the smallest openinglocated near the top of the frame. It is also known as the “C”dimension.Base flange opening is the opening at the bottom of the frame. It isalso known as the “D” dimension.The cover diameter is the diameter of the lid. It is also knownas the “A” dimension.length from the outermost part of the flange directly across to theother outermost side. It is also known as the “E” dimension.Frame flange diameterCover Diameter Frame flange diameter is the diameter of the whole frame or theCover ThicknessCover thickness is the thickness of the lid at the perimeter. Itis also known as the “B” dimension.Frame HeightThe frame height is the height of the frame. It is also knownas the “F” dimension.3

Key Dimensions of Inlet Frame and GrateQUICK REFERENCEClear OpeningClear opening is the length of the opening located near thetop of the frame. It is also known as the “C” dimension.Grate DiameterThe grate diameter is the diameter of the lid. It is also knownas the “A” dimension.Grate OpeningThe width of the opening between bars in thegrate. It is alsoknown as the “G” dimension.Grate ThicknessGrate thickness is the depth of the grate at the perimeter. It isalso known as the “B” dimension.Frame HeightThe frame height is the height of the frame. It is also knownas the “F” dimension.Base Flange OpeningBase flange opening is the opening at the bottom of theframe. It is also known as the “D” dimension.Frame Flange DiameterFrame flange diameter is the diameter of the whole frameor the length from the outermost part of the flange directlyacross to the other outermost side. It is also known as the“E” dimension.4

Frame DesignsQUICK REFERENCEBottom & Top FlangeA bottom flange is a flange that is located at the base of the frame. A top flange is a flange that is located at the top of theframe, and is typically installed in a concrete slab application.Reversible FlangeA reversible flange can be either on the top or bottom of the frame depending on how the lid is placed on the frame. Top flangeis also known as the slab type and the bottom flange is also known as the built up type.Mud RingA mud ring is cast into the frame on the bottom below theflange so the frame centers properly on the manhole cone.Manhole Frame with Mud Ring5

Grate DesignsQUICK REFERENCEDiagonalGrateVane GrateThe vane grates allows better hydraulic efficiency.The designer mustbe aware of the ADArequirements beforeusing this grate.SinusoidalSinusoidal grateshave a “S” typeappearance.Vane Grate with Cross BarsVane grates, which have better hydraulic efficiency, areangled toward the flow of water. The vane grate offerslongitude bars that are friendlier toward bicycles.BeehiveBeehive grates are usedwhere clogging of a flatgrate is prevalent andunacceptable. This grateis not recommendedin traffic areas orpedestrian areas.Hydraulic EfficiencyThe hydraulic efficiency of a grate is its rated ability tointercept storm water. Hydraulic tests prove that theVane style grate, properly installed, will accept as muchas 20% more water than any of the conventional gratestyles.Americans with Disabilities Act GrateADA style grates are available in various shapes and sizes. Thesegrates are designed for pedestrian applications. Grates placedon pedestrian walkways must follow certain laws required bythe Americans with Disabilities Act which set guidelines thatmanufacturers follow. These guidelines specified that grating mustbe conscience of narrow-tiredbicycles and wheelchairs andpractice proper caution forpedestrian safety on walkways.Grating placed in these areasmust have spaces or holesno greater than ½ inch in onedirection. If they are placed inthe direction of travel then theymust be placed so that the longdimension is perpendicular tothe travel. The act dictates that designers carefully consider thesafety of the type of grating selected for various applications.Cross section of vane-style gratein testing flume showing hydraulicperformance at 2 cfs.6

Curb Inlets or Combination InletsQUICK REFERENCEAdjustable HeightCurb boxes can be adjusted to the right curb height. Thepicture above shows how the adjustment is accomplished.Adjustable HeightCurb Inlet, Back, Frame and GrateA Grate WidthB Grate LengthC – Frame Height (Front)D Frame Height (Back)E Hood AdjustmentF Flange Frame Width or DiameterG Flange Frame Length or DiameterH Curb WidthCurb or combination inlet with adjustable heightEnvironmental MessagingInlets can be furnished with environmental notices, such as the one below, which address’ specific drainage situations andNPDES messaging requirements.7

Watertight Frames and CoversQUICK REFERENCEWatertight AssemblyWatertight castings are gasket sealed with a bolted cover.These manholes are suitable for low pressure, gas or steamtight applications.Water-resistant manhole frame and bolted lidPressure Tight BoltingPressure tight bolting, very similar to watertight bolting, aresuitable for low pressure applications up to 20 p.s.i.Frost ProofIf a manhole is frost proof it has an extra inner cover, such asthe one below. The typical inner cover has a neoprene gasketaround the edge and a locking bar with tightening screw.When the locking bar is tightened the gasket creates anextremely tight seal to the sides of the frame which does notallow frost, debris, and other containments inside.Frost-proof frame, solid lid and innter lidAirport CastingsQUICK REFERENCEAirport castings are for heavier, dual-gear aircraft. Airport series products are capable of withstanding a minimum load of100,000 pounds and in many applications, more than 200,000 pound proof load. All of the grates and covers are bolted to theframe as called for by the FAA Advisory Circular AC150/5370-10A. All airport castings must pass a load test required by theAASHTO M306.Airport VerticalBar GrateAirport HatchAirport ManholeFrame and GrateBolted Trench Drain Assembly8

Manhole FeaturesQUICK REFERENCEFlange AnchorBolt HolesVentedVented covers are covers that have strategically placeholes in the top of them that allow venting of the manholestructure.Allows the frame to besecured to the concretecone.Pick Hole Options(Open, Closed, etc.)An open pick hole is a pick hole completely open to the interiorof the manhole. A closed pick hole is accessible to workersopening the lid but also continues towards the center andhides within the lid making the manhole concealed to theoutside. Closed pick holes are water resistant.Custom Logo andSpecial LetteringMost foundries have thecapabilities to make a customlogo that can be placed on topof the cover. Along with thelogo, special custom lettering isan option. Minimum quantitiesmay be required.Open PickHoleClosed PickHoleClosed Pick BarSecurity BoltingSecurity Bolting is an option that is available on most covers & some grates. Some ofthe most common bolting schemes include stainless steel hex head bolts and flat headslotted screws. The following security bolted options are available as well as cam deviceswhich eliminate bolts.Cam Lock Device9

Gasketed LidsA Gasket that is placed on the bottom of a cover or lid where the lid bears on theframe helps create a seal. This gasket can help prevent surface water leakage intothe manhole. The gasket fits firmly and securely within the covers precisely machinedgroove. The gasket material can consist of a variety of material with good sealingqualities, abrasion resistance and a low compression set. “T” seal gasket is shownbelow. Other options are available.“T” Seal Gasketed DetailHinged ProductsSome covers or grates can be hinged for easier lifting.Common types of hinges are concealed hinges, which areflush with the lid surface, and butt hinges, which are raisedabove the lid surface. Hinged assemblies are available onsquare, rectangular and round unitsHinged Manhole AssemblyButt-hinged Frame and LidConcealed Frame and LidLift Assist Hinged CoversA hinged cover with a lift assist can be operated by anindividual, eliminating the need for an additional liftingdevise.10Hinged Manhole Cover

Iron conforming to ASTM A48, Class 35B, as noted in section 7.1.1 and 7.1.3 of AASHTO M306. Class 35B exhibits the best corrosion and wear resistance properties as well as the desirable quality of high compressive strength. Therefore it makes a good load bearing street hardware. 35,000 psi minimum tensile strength iron is furnished. Ductile IronFile Size: 1MBPage Count: 10