The classification of the load-bearing capacity of manhole covers is usually based on national standards or industry norms. It is divided according to the usage scenarios, vehicle loads and material properties, aiming to ensure safety and durability in different environments. The following are the common classification criteria and specific explanations:
1. Based on the load-bearing capacity of the manhole cover itself: This classification is based on the load-bearing capacity of the manhole cover material itself. It is divided into categories such as
I. Classification in accordance with the Chinese National Standard (GB/T 23858-2022)
In China, manhole covers are classified into six grades based on their load-bearing capacity, represented by “kN” (kilo-newton, a unit of force), corresponding to different usage scenarios:
1. Grade A15 (15kN)
– Applicable scenarios: sidewalks, non-motorized lanes, green belts, etc. for light load areas.
– Load-bearing capacity: Can withstand a maximum static load of 1.5 tons (approximately equivalent to a small car traveling at low speed), and prohibits motor vehicle passage.
2. Grade B125 (125kN)
– Applicable scenarios: residential communities, parking lots, small roads, etc. Allows passage of small motor vehicles (such as cars, light trucks).
– Load-bearing capacity: Can withstand approximately 12.5 tons of static load, suitable for daily light traffic.
3. Grade C250 (250kN)
– Applicable scenarios: urban main roads, highways, freight parking lots, etc. Allows passage of medium-sized trucks (such as trucks with a load capacity of 10-15 tons).
– Load-bearing capacity: Can withstand 25 tons of static load, meeting the requirements of medium traffic volume.
4. Grade D400 (400kN)
– Applicable scenarios: areas for heavy vehicle passage, such as expressways, docks, airport runways, large industrial zones.
– Load-bearing capacity: Can withstand 40 tons of static load, capable of handling frequent rolling of large trucks (such as 20-30 ton trucks) or special vehicles (such as fire engines).
5. Grade E600 (600kN)
– Applicable scenarios: areas with extremely heavy loads, such as ports, heavy machinery operation areas, airport runways.
– Load-bearing capacity: Can withstand 60 tons of static load, designed specifically for extremely heavy vehicles (such as container trucks, tanks).
6. Grade F900 (900kN)
– Applicable scenarios: extreme load environments, such as railway tracks, military bases, heavy industrial zones.
– Load-bearing capacity: Can withstand 90 tons of static load, with the highest strength, capable of meeting special heavy load requirements.
II. International Classification System (Taking European EN124 and American ASTM as examples)
1. European EN124 standard
– It is classified into 7 categories based on load-bearing capacity, symbolized as Class A15 to Class F900. It is similar to the Chinese standard, but there are slight differences in some values (for example, Class D400 corresponds to a load of 40 tons).
– Features: It emphasizes dynamic load testing (simulating repeated vehicle rolling), and pays more attention to long-term fatigue performance.
2. American ASTM standard (such as ASTM C90, ASTM A1238)
– It is divided by “load grade”. Common grades include:
– Light Duty: Suitable for sidewalks, with a load-bearing capacity of ? 15 tons.
– Heavy Duty: Suitable for highways, with a load-bearing capacity of ? 30 tons.
– Extra Heavy Duty: Suitable for airports and industrial areas, with a load-bearing capacity of ? 50 tons.
III. Classification by Materials and Structures
Due to the differences in physical properties, the load-bearing capacity of manhole covers made of different materials varies as well:
1. Cast iron manhole covers (malleable cast iron / gray cast iron)
– Advantages: High strength and good toughness, can cover high load levels of D400 and above, is the mainstream choice for highways and heavy-load areas.
– Typical load-bearing capacity: D400 level (40 tons) to F900 level (90 tons).
2. Composite material manhole covers (resin-based, recycled materials)
– Advantages: Lightweight, corrosion-resistant, suitable for light load scenarios.
– Typical load-bearing capacity: A15 level (1.5 tons) to B125 level (12.5 tons), often used in sidewalks and green belts.
3. Concrete manhole covers
– Advantages: Low cost, widely used in the early stage, but brittle and prone to cracking.
– Typical load-bearing capacity: B125 level (12.5 tons) to C250 level (25 tons), suitable for residential area roads.
4. Steel fiber reinforced concrete manhole covers
– Advantages: Combining concrete with steel fibers, strength is superior to ordinary concrete, can reach C250 level (25 tons).
IV. Selection Principles in Practical Applications
Scene priority:
– Sidewalks, gardens: Choose A15/B125 grade, lightweight and economical.
– Urban roads, parking lots: Choose C250/D400 grade, balancing load-bearing capacity and cost.
– Heavy traffic (such as highways, airports): Must use grade D400 or above, and prefer cast iron material.
2. Consideration of dynamic loads:
– Areas with frequent vehicle passage or high speed (such as highways), need to select a grade higher than the static load (if it is expected to bear 30 tons of dynamic load, choose D400 grade).
3. Compliance:
– Engineering standards of various countries have clear requirements for the load-bearing capacity of manhole covers (such as the regulations of the Ministry of Housing and Urban-Rural Development of China that urban main roads must use grade D400 or above), and must strictly follow the standards.
Summary
The classification of the load-bearing capacity of manhole covers is an important criterion for ensuring urban safety. The core logic is “matching as needed” – based on traffic flow, vehicle types, and material characteristics, select the corresponding grade of manhole covers. From light pedestrian walkways to super heavy industrial areas, the grading system ensures a balance between economic efficiency and safety in infrastructure, embodying the scientific concept of “precise load” in engineering design.