Description
4″ × 24″
Manhole Frame
& Grate
A precision-cast gray iron assembly engineered for sustained performance under full highway live loading. Built to ASTM A48 Class 30B, rated to AASHTO M306 H-20 proof-load protocols, and dimensioned for seamless integration with standard 24″ precast infrastructure networks.
All dimensions are nominal. Consult Amercast engineering for project-specific tolerance requirements and submittal documentation. Dimensional designators follow standard municipal casting conventions (B, C, D, E, F, X).
| Designator | Parameter | Value | Notes |
|---|---|---|---|
| — | Item Number | 1098 | 4″ × 24″ Frame & Grate |
| B | Overall Assembly Diameter | 34″ | Outer flange seat dimension |
| C | Grate Outside Diameter | 24″ | Nominal clear opening designation |
| D | Clear Opening Diameter | 22-3/8″ | Unobstructed bore through grate |
| E | Frame Height | 4″ | Nominal riser height above structure |
| F | Frame Seat Diameter | 24-1/4″ | Bearing surface diameter |
| X | Grate Thickness | 1-3/8″ | Structural depth of grate casting |
| — | Slot Width (Typical) | 1/2″ max | ADA § 302.3 compliance threshold |
| — | Material | Gray Iron, Class 30B | ASTM A48 / A48M-22 |
| — | Proof Load Rating | 40,000 lbf | H-20 × 2.5 safety factor per AASHTO M306 |
| — | Design Wheel Load | 16,000 lbf | AASHTO H-20 single-wheel equivalent |
| — | ADA Compliance | § 302.3 Conforming | Slot orientation perpendicular to travel |
| — | Finish Options | Raw / Bituminous | Custom markings available |
Class 30B
The alloy designation ASTM A48 Class 30B describes a pearlitic gray iron whose mechanical acceptance criterion is a minimum tensile strength of 30,000 psi (207 MPa) when tested via separately-cast "B-type" test bars — a bar diameter calibrated to castings whose controlling wall section falls between 0.32″ and 0.64″, placing the 1098 squarely within this classification tier.
Gray iron's defining microstructural characteristic — the three-dimensional network of Type A graphite flakes distributed throughout the pearlite matrix — is simultaneously responsible for its most operationally advantageous properties. The graphite network acts as a crack-arrest lattice, conferring outstanding vibration damping (10–25× greater than steel), and compressive strengths that are characteristically three to four times the tensile value — a trait that directly underpins the material's ability to withstand the compressive-dominant nature of wheel-load cycling.
- Min. Tensile Strength207 MPa (30 ksi)
- Compressive Strength (typical)~620–700 MPa
- Brinell Hardness187–241 BHN
- Elastic Modulus97–110 GPa
- Damping CapacityHigh (Type A graphite)
- Thermal Conductivity~46 W/m·K
- Density~7.1–7.3 g/cm³
Why Class 30B for municipal castings? The "B" test bar category standardizes the solidification rate used during qualification testing. Because mechanical properties in gray iron are section-thickness dependent — thicker sections cool slower, producing coarser graphite and lower tensile strength — the B-type bar ensures that test results correlate meaningfully to the actual casting's governing wall section. This is a critical distinction overlooked in generic "Class 30" specifications.
Corrosion behavior: Gray iron's graphite flake network forms a passivating graphitic layer on exposed surfaces, imparting meaningful resistance to atmospheric and soil corrosion without supplemental coatings. Amercast offers both raw and bituminous-coated finishes; the latter provides additional moisture isolation in chloride-laden or acidic soil environments.
Recyclability: Gray iron is 100% recyclable with no degradation of mechanical properties across recasting cycles, aligning with EPA Sustainable Materials Management principles for long-lived public infrastructure.
Proof-Load Qualified
The H-20 designation derives from AASHTO's standard highway truck loading model — a two-axle vehicle producing a 32,000 lbf axle load, or 16,000 lbf per wheel contact. Because a grate assembly occupies a footprint that, in practice, accepts only a single tire simultaneously, the single-wheel load governs structural design. AASHTO M306 translates this into a proof-load requirement of 40,000 lbf — a 2.5× safety factor — applied via a 9″ × 9″ bearing plate at the casting's geometric centroid for a minimum duration of one minute. Any crack propagation or permanent deformation exceeding 1/8″ constitutes a failure criterion.
All Applicable Codes
The foundational gray iron casting standard. Class 30B requires a minimum tensile strength of 207 MPa across standardized B-bar test specimens, with surfaces free of sand, scale, cracks, or hot tears on visual examination.
→ ASTM A48/A48M-22 StandardGoverns proof-load testing of municipal castings in traffic service. Mandates a 40,000 lbf proof load for H-20 applications, representing a 2.5× safety margin over the 16,000 lbf design wheel load. The most stringent and current standard for construction castings.
→ AASHTO M306 OverviewSection 302.3 of the 2010 ADA Standards for Accessible Design limits floor/ground surface openings to a maximum of 1/2″ in the dimension perpendicular to the dominant direction of travel. Elongated openings must be oriented with their long axis parallel to travel direction.
→ U.S. Access Board ADA StandardsThis grate and frame assembly is dimensioned for direct seating on standard precast concrete manhole sections conforming to ASTM C478, with 24″ nominal inside diameter. No special adapters required for typical installations.
→ ASTM C478 Precast StandardConforms to New Jersey Administrative Code § 5:21-7.4, which mandates ASTM A48 Class 30B material, H-20 load capacity, and bicycle/pedestrian-safe grate geometry for stormwater inlet applications in public ROW.
→ NJ Admin Code § 5:21-7.4Gray iron castings are fully recyclable ferrous materials. Specifying long-life cast iron infrastructure supports EPA Sustainable Materials Management goals by reducing lifecycle replacement waste and embodied energy over the service horizon.
→ EPA Sustainable Materials ManagementCompliant Grate Geometry
The 2010 ADA Standards for Accessible Design — specifically Section 302.3 — governs openings in floor and ground surfaces traversed by wheelchair users and individuals using mobility aids. The overarching mandate is that no opening shall permit the passage of a sphere exceeding ½″ (12.7 mm) in diameter in the dimension perpendicular to the predominant direction of pedestrian travel.
The 1098 grate achieves compliance through slot geometry: individual slots are oriented with their long axis parallel to the direction of travel, limiting the critical cross-slot dimension to a maximum of ½″. This orientation simultaneously preserves hydraulic capacity — elongated openings oriented correctly provide far greater net open area than equivalent circular perforations while remaining wheelchair-safe.
Field verification of ADA compliance is straightforward: a standard ½″ ball bearing rolled across any grate axis should not fall through any slot or gap. This test, recommended by civil drainage engineers, provides immediate, instrument-free confirmation of § 302.3 conformance.
- Slot width ≤ ½″ (12.7 mm) perpendicular to travel — satisfies ADA § 302.3 sphere-passage test
- Long slot dimension oriented parallel to dominant direction of pedestrian travel
- No abrupt changes in level exceeding ¼″ at frame-to-pavement transition per ADA § 303
- Frame seating surface dimensioned for flush installation with finished grade
- Compatible with sidewalk, plaza, campus, and multi-use path deployments
- Suitable for installation zones governed by PROWAG (Public Rights-of-Way Accessibility Guidelines)
- Surrounding pavement slope not to exceed 1:48 (2.08%) per ADA accessibility provisions
- Bicycle-compatible: long slot axis perpendicular to typical tire contact eliminates wheel-trapping risk
Full Spectrum of Civil Infrastructure
Primary application within AASHTO H-20 roadway corridors — collector streets, arterials, intersections, and highway shoulders where sustained heavy vehicle traffic demands full proof-load compliance. Replaces aging frames in ROW rehabilitation programs without precast structure modification.
Streetscape renovations, ADA transition plan compliance projects, university campus retrofits, transit station plazas, and parks where drainage must coexist with barrier-free pedestrian circulation. The ADA-compliant grate geometry eliminates the need for bolt-down covers or skip-over drainage design workarounds.
Logistics center aprons, loading dock perimeters, warehouse yard drainage, retail development parking fields, and mixed-use site stormwater conveyance. The 34″ overall diameter and 4″ frame height accommodate direct connection to standard catch basin structures without special adapters.
Ventilated access to subsurface utility vaults, telecommunications chambers, electrical duct banks, and water/wastewater structures where the open-grate configuration provides passive ventilation or continuous drainage while maintaining H-20 structural rating. Markings available for system identification.
Specification Data
- Item No.: 1098
- Description: 4″ × 24″ Manhole Frame & Grate
- Material: Gray Iron, ASTM A48 Class 30B
- Load Rating: AASHTO H-20 (M306 proof-load qualified)
- ADA Status: Section 302.3 Compliant
- Availability: In Stock
- Finish: Raw or Bituminous Coating
- Markings: Custom inscriptions available
For project specifications, use the following CSI-style language:
Manhole frame and grate shall be 4″ × 24″ round configuration, Item No. 1098, gray cast iron conforming to ASTM A48 / A48M Class 30B, rated to AASHTO H-20 wheel loading with proof-load qualification per AASHTO M306. Grate shall be ADA compliant per 2010 ADA Standards § 302.3. Furnished by Amercast or approved equal.
