Description
8″ × 24″
Heavy Duty
Frame & Grate
The deepest frame in the 24″ bore family — engineered for installations where substantial grade differential, thick reconstructed pavement sections, or multi-overlay service histories demand maximum vertical clearance in a single casting. Multiple grate styles available: Slotted, Square, and Bike Proof. Bolts and watertight configurations also offered.
Engineering Reference —
8″ × 24″ Assembly
The cross-section below shows the grate profile (top) and frame body (bottom) with all governing dimensional designators. At 8″, this frame height provides the greatest vertical working range in Amercast's 24″ bore lineup — accommodating deep pavement reconstruction, elevated utility collar installations, and multi-lift overlay programs without intermediate grade ring courses.
Specification Data —
All Designators
| Parameter | Dim. | Value (in.) | Engineering Context |
|---|---|---|---|
| Frame Height | D | 8″ | Maximum frame height in 24″ bore family — 2″ taller than 6″ variant, 4″ taller than 4″ variant |
| Grate Outside Diameter | C | 24″ | Nominal opening designation — consistent across 4″, 6″, and 8″ frame height variants |
| Clear Seat Diameter | E | 23.5″ | Interior ledge diameter; grate bearing surface inside frame |
| Frame Seat Diameter | F | 25″ | Precast cone bearing surface — wider than 6″ variant (24″) for added stability at greater height |
| Overall Assembly O.D. | G | 34″ | Outer flange diameter; governs pavement opening size and frame footprint |
| Grate Thickness | H | 1.5″ | Structural depth of grate casting at bearing plane |
| Grate Styles | — | 3 options | Slotted · Square · Bike Proof — specify at time of order |
| Locking Option | — | Available | Bolts and watertight configuration available — contact Amercast for details |
| Material | — | Gray Iron, Class 30 | ASTM A48 / A48M-22 — min. 207 MPa tensile strength |
| Proof Load | — | 40,000 lbf | H-20 × 2.5 safety factor applied via 9″ × 9″ plate per AASHTO M306 |
| Design Wheel Load | — | 16,000 lbf | AASHTO H-20 single-wheel equivalent; rated for full highway traffic service |
| Finish Options | — | Raw / Bituminous | Custom markings and inscriptions available on request |
The Maximum-Height
Frame — When It Matters
Frame height selection is a function of the vertical gap between the finished casting elevation and the top of the precast structure below. The 8″ frame fills the largest possible gap in a single casting — eliminating stacked grade ring courses, reducing mortar joint count, and simplifying long-term maintenance access.
Where pavement reconstruction, deep overlay programs, or elevated utility collars place the finished grade well above the precast cone seat, the 8″ frame bridges the gap in one piece. Standard practice limits precast grade ring stacks — the 8″ frame removes that constraint entirely.
Unlike single-style frames, the 8×24 HD ships in Slotted, Square, and Bike Proof configurations — allowing engineers to match hydraulic capacity, pedestrian safety, and bicycle compatibility requirements to the specific site context without changing the frame specification.
Seat diameter F = 25″ and overall O.D. G = 34″ are designed for direct bearing on standard precast cone sections per ASTM C478. Bolted and watertight variants are available from the same frame body — no secondary casting required.
Gray Iron Under
Extended Frame Geometry
An 8″ frame body imposes a longer cantilever between the grate seating plane and the flange bearing surface than any shorter variant. Under H-20 wheel loading, this moment arm magnifies the bending stress resolved through the frame wall — making wall cross-section geometry, not merely tensile strength, the governing structural consideration.
ASTM A48 Class 30 gray iron addresses this through its pearlitic matrix and Type A graphite flake distribution, which together deliver compressive strength reaching 620–700 MPa — three to four times the minimum tensile value. Under the compressive-dominant nature of vehicle wheel impulse loading, this ratio is the material's most consequential structural characteristic.
Grate style and structural performance: All three grate styles — Slotted, Square, and Bike Proof — are cast to the same H = 1.5″ thickness and H-20 proof-load standard. Style selection governs hydraulic throughput and surface compatibility, not structural rating.
Fully Qualified Across
All Applicable Specifications
Class 30 qualification mandates minimum 207 MPa tensile strength via standardized test bars. Surface integrity requirements prohibit sand adhesion, scale, cracks, and hot tears on visual examination.
→ ASTM A48/A48M-22The current governing standard for municipal castings in highway service. H-20 rating requires a 40,000 lbf proof load — a 2.5× safety factor over the 16,000 lbf design wheel load — with no cracking or deformation exceeding 1/8″.
→ AASHTO M306 OverviewFrame seat diameter F = 25″ is engineered for direct bearing on standard precast concrete manhole sections. No proprietary adapters, shimming, or secondary castings required for compliant installations.
→ ASTM C478 Precast StandardConforms to NJ Administrative Code § 5:21-7.4 — ASTM A48 Class 30 material, H-20 load capacity, and bicycle-safe grate geometry for stormwater inlet applications in public ROW.
→ NJ Admin Code § 5:21-7.4Gray iron is 100% recyclable with no mechanical property degradation across remelting cycles, supporting EPA Sustainable Materials Management objectives for long-service-life public infrastructure.
→ EPA SMM GuidelinesThe Bike Proof grate style meets NJDOT and AASHTO bicycle-compatible roadway requirements, preventing road bike tire entrapment across all approach angles. Slotted style also qualifies when slot long-axis is perpendicular to travel.
→ Amercast 8×24 Product PageThree Configurations —
One Frame Body
The 8×24 HD is unique within the Amercast 24″ bore family in offering three distinct grate patterns from the same frame casting. Style selection governs two independent engineering variables — hydraulic open area and surface compatibility — without affecting the H-20 structural rating or requiring a different frame specification.
For projects with competing constraints (high flow demand + ADA pedestrian access, or bicycle lanes + stormwater capture), the Slotted style with long-axis perpendicular to travel satisfies both simultaneously. Bike Proof is specified where wheel-trapping risk must be eliminated across all bike approach angles.
- Slotted — Elongated rectangular slots. Maximum hydraulic open area. ADA and bike-compatible when slot long-axis is oriented perpendicular to direction of travel.
- Square — Grid pattern openings. Uniform drainage in all directions. Suitable for applications where approach direction is variable or undefined.
- Bike Proof — Geometry engineered to prevent road bike tire entrapment at any approach angle. NJDOT and AASHTO bicycle-compatible roadway qualified.
- Bolted configuration — Available for security-sensitive installations or locations where cover displacement must be prevented.
- Watertight configuration — Available when inflow/infiltration control is required at the casting elevation. Contact Amercast for gasket and seal details.
- Custom markings — "DUMP NO WASTE · DRAINS TO WATERWAYS" and project-specific inscriptions available.
Specifying the 8″ Frame —
Typical Project Scenarios
Road reconstruction projects that restore or increase the structural pavement section — removing existing asphalt and base, regrading, and repaving — can elevate the finished surface by 6″ or more relative to the original manhole rim. The 8″ frame absorbs this differential without raising the precast cone or stacking grade rings, keeping the barrel undisturbed through the paving operation.
Streets that have received successive asphalt overlays over decades accumulate pavement depth that progressively buries existing manhole frames. When rehabilitation finally exposes the original structure elevation, the 8″ frame restores flush-grade installation at the new finished surface without excavating to the cone seat. A common scenario in municipal resurfacing and grade adjustment programs.
Heavy industrial yards, container terminal aprons, and port facilities with thick concrete or reinforced asphalt pavement sections regularly require frame heights beyond 6″ to achieve flush-grade installations. The H-20 proof-load rating and gray iron construction handle the sustained heavy equipment loads characteristic of these environments without accelerated fatigue or deformation.
High-speed, high-volume arterials and DOT-administered highway drainage structures where maximum structural reserve and minimal maintenance intervention are the governing criteria. The 8″ frame's extended height accommodates future overlay cycles without frame replacement, extending the useful service interval between grade-adjustment operations on critical traffic infrastructure.
Ordering & Specification
Reference
- Item Reference8×24-HD
- Description8″ × 24″ Heavy Duty Frame & Grate
- Grate O.D. (C)24″
- Frame Height (D)8″
- Clear Seat Dia. (E)23.5″
- Frame Seat Dia. (F)25″
- Overall O.D. (G)34″
- Grate Thickness (H)1.5″
- Grate StylesSlotted / Square / Bike Proof
- MaterialASTM A48 Class 30 Gray Iron
- Load RatingAASHTO H-20 (M306)
- AvailabilityIn Stock
For project specifications, Division 33 — Utilities or applicable section:
Manhole frame and grate shall be 8″ × 24″ heavy duty round configuration, gray cast iron conforming to ASTM A48 / A48M Class 30, rated to AASHTO H-20 wheel loading per AASHTO M306 (40,000 lbf proof load minimum). Grate style shall be [Slotted / Square / Bike Proof] as noted on drawings. Furnished by Amercast or approved equal.
Related Assemblies &
Frame Height Variants
Entry-level frame height for installations with minimal grade differential. ADA-compliant grate. Same C, E, and H dimensions — D = 4″.
→ View ProductIntermediate frame height for pavement overlay and grade adjustment applications. ADA configuration available. D = 6″.
→ View ProductSame 8″ frame body with bolt-down cover for security or tamper-resistance requirements. Watertight seal option available.
→ View ProductLocking bolt-down cover with rubber gasket for inflow/infiltration control. Stainless steel hardware. For I/I-controlled system design.
→ View ProductCast iron and steel riser rings for height adjustments beyond frame body range. Load-tested, DOT-approved. Domestic A-36 steel or ASTM A48 Class 35B iron.
→ View CategoryFull catch basin frame and grate assemblies for curb-opening and area-drain stormwater interception in roadway and site drainage systems.
→ View Category
