In transportation and bridge construction, vehicle load distribution formulas are pivotal, ensuring safety and economic efficiency for both structures and vehicles. At Xe Tải Mỹ Đình, we understand the importance of mastering specialized knowledge about trucks. This article delves into vehicle load distribution formulas, based on the national standard TCVN 11823-3:2017, to provide readers with a comprehensive overview and practical applications.
Vehicle Load Distribution Formulas According to TCVN 11823-3:2017 Standard
TCVN 11823-3:2017 serves as the guiding principle in bridge design in Vietnam, detailing load and load factor standards. Section 6.1.2.6 Distribution of wheel loads through soil cover is particularly crucial when considering the impact of vehicle loads on underground structures like box culverts and pipe culverts.
Wheel Load Distribution Through Soil Cover for Culverts
The standard specifies that if the soil cover above the culvert is thicker than 2400mm and greater than the culvert span (for single-span culverts) or greater than the distance between the inner surfaces of the two culvert sidewalls (for multi-span culverts), the effect of vehicle live load can be ignored.
However, when the soil cover is thinner, the distribution of wheel loads needs precise calculation. The formula and distribution method depend on the soil cover thickness and the type of culvert.
Case of Soil Cover Less Than 600mm
For soil cover less than 600mm, the vehicle live load is distributed directly onto the top slab of box culverts or reinforced concrete pipe culverts as specified in clause 6.2.10 of TCVN 11823-4. Notably, for reinforced concrete pipe culverts with soil cover from 300mm to 600mm, the design must be based on a soil cover thickness of 300mm, reflecting caution in ensuring safety.
Case of Soil Cover Greater Than 300mm (Non-Concrete Pipe Culverts) or 600mm (Other Culverts)
When the soil cover is thicker than the above levels, the live load is considered to be uniformly distributed over a rectangular area. This area is determined based on the wheel contact area dimensions (according to clause 6.1.2.5) and the Live Load Distribution Factor (LLDF) specified in Table 8 of the standard.
Formula for calculating the load distribution rectangular area (ALL):
ALL = lw * wwWhere lw and ww are the length and width of the live load distribution footprint at depth H (soil cover thickness), respectively.
Table 8 – Live Load Distribution Factor (LLDF) on buried structures
| Structure Type | LLDF in the transverse or parallel direction to the span |
|---|---|
| Concrete pipes with soil cover of 600 mm or more | 1.15 for diameter ≤ 600 mm, 1.75 for diameter ≥ 2400 mm, linear interpolation in between |
| All other types of culverts and buried structures | 1.15 |
Formulas for determining the distribution width (ww) and distribution length (lw):
These formulas vary depending on the vehicle’s direction of travel (parallel or perpendicular to the culvert span) and the soil cover depth (H) compared to the interaction depth of the wheel axle load (Hint-t or Hint-p).
-
Vehicle direction parallel to the span of the culvert:
- Interaction depth of wheel axle load (Hint-t):
Hint-t = 1220 + Di- When H < Hint-t:
ww = wt + LLDF * H + 0.060 * Di- When H ≥ Hint-t:
ww = wt + sw + LLDF * H + 0.06 * Di -
Vehicle direction perpendicular to the span of the culvert:
- Interaction depth of wheel axle load (Hint-p):
Hint-p = 2440 + Di- When H < Hint-p:
lw = lt + LLDF * H- When H ≥ Hint-p:
lw = lt + sa + LLDF * H
Where:
wt: tire width (510mm)lt: tire length (250mm)sw: wheel spacing (1800mm)sa: axle spacing (mm, varies depending on design vehicle)Di: inner diameter or clear span of the culvert (mm)LLDF: Live Load Distribution Factor (from Table 8)H: soil cover thickness (mm)
Formula for calculating vertical live load pressure (PL):
PL = (P * (1 + IM/100) * m) / ALLWhere:
PL: vertical live load pressure (MPa)P: live load on the road surface (total interacting wheel load) (N)IM: impact factor (from clause 6.2.2)m: lane factor (from clause 6.1.1.2)ALL: load distribution rectangular area (mm²)
Heavy truck driving on a bridge, illustrating load distribution on the structure.
Practical Applications of Vehicle Load Distribution Formulas
Accurately applying vehicle load distribution formulas not only ensures compliance with technical standards but also offers several practical benefits:
- Safe structural design: Formulas help engineers precisely determine the loads acting on bridge and road components, enabling the design of structures with sufficient load-bearing capacity, ensuring safety for both the structure and users.
- Optimization of building materials: Accurate load calculations prevent over-design and material waste. Structures are designed adequately, ensuring safety while saving construction costs.
- Assessment and quality control of structures: Vehicle load distribution formulas are crucial for evaluating the actual load-bearing capacity of bridges and roads, serving quality control and maintenance efforts.
- Management of transportation loads: Understanding the formulas helps state management agencies establish appropriate vehicle load regulations, preventing overloading of bridges and roads, and protecting transportation infrastructure.
- Applications in freight transport: For truck transport businesses like Xe Tải Mỹ Đình, mastering load distribution formulas helps optimize cargo loading, ensuring even load distribution, preventing damage to vehicles and goods, and complying with legal regulations.
Conclusion
Vehicle load distribution formulas are an indispensable part of bridge and road design standards, especially crucial for ensuring safety and economic efficiency. Understanding and accurately applying these formulas, based on TCVN 11823-3:2017, is the responsibility of engineers, managers, and those directly involved in the transportation sector.
At Xe Tải Mỹ Đình, we are committed to providing useful and in-depth information about trucks, contributing to enhancing knowledge and skills for the Vietnamese transportation community. We hope this article has provided readers with a clearer and deeper understanding of vehicle load distribution formulas and their practical applications.
References:
- TCVN 11823-3:2017 Design of highway bridges – Part 3: Loads and Load factors.
