Container Structure and Materials: A Comprehensive Analysis from Corner Castings to Flooring

A container may seem like just an "iron box," but its structure has undergone rigorous design and testing — it must withstand the pressure of stacking 12 containers high, resist the impact of force 12 winds and waves at sea, and maintain sealing integrity within a temperature range of -40°C to +70°C.

I. Overall Structure of a Container

The structure of a standard dry container can be divided into the following main parts:

                    ┌──────────────────────┐
                    │       Roof Sheet     │ ← Corrugated steel sheet, bears rain/snow and stacking pressure
                    │  ┌────────────────┐   │
      ┌─────────────┤  │   Interior     │   │
      │  Left Side  │  │                │   │
      │  Wall       │  │                │   │
      │ (Corrugated)│  │                │   │
      │             │  │                │   │
      │             │  │                │   │
      │             │  └────────────────┘   │
      │             │       Flooring        │
      └─────────────┴──────────────────────┘
     Corner ← ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ → Corner
     Casting                                Casting
                                         Container Door

Structural Component	Function	Material
Corner Casting	Connection point for lifting/stacking/securing	Cast steel
Roof Sheet	Waterproofing, resistance to stacking pressure	Corrugated steel sheet (1.5-2.0mm)
Side Wall	Structural support, cargo protection	Corrugated steel sheet (1.5-2.5mm)
Flooring	Bears cargo weight	Hardwood plywood (APG/MDG)
Container Door	Cargo entry/exit point	Steel plate + sealing gasket
Bottom Rail	Longitudinal support for container body	C-channel steel
Top Rail	Longitudinal support for container body	Special-shaped steel

II. Detailed Explanation of Each Component

2.1 Corner Casting

Corner castings are the most critical structural components of a container — they are the sole load-bearing points for lifting, stacking, and securing.

Position	Function	Load Capacity
Top 4 corner castings	Lifting points during hoisting	≥15 tonnes per point
Bottom 4 corner castings	Load-bearing points during stacking	≥30 tonnes per point
Side slots	Lashing and securing (twist-lock connection)	≥10 tonnes per point

The Three Key Holes of Corner Castings:

Top hole: Hook connection point, used for lifting
Side hole: Twist-lock connection point, used for securing to vessel/trailer
Bottom hole: Locating pin hole for stacking

Standard Basis: The dimensions and strength of corner castings must comply with ISO 1161 standard, with dimensional tolerances for each hole position ≤1mm.

2.2 Container Door

The container door is one of the weakest parts of the container and the component most prone to problems.

Door Component	Function	Common Faults
Door panel	Seals the container body	Impact deformation, door won't close
Door hinges	Door opening and closing	Rust causing difficulty in operation
Locking bar	Secures the door	Bending, unable to fully lock
Door handle	Operates the locking bar	Breakage
Sealing gasket	Waterproof sealing	Aging leading to water ingress
Locking mechanism	Safety locking	Jamming or damage

Door Opening Angle Standards:

Left door: Opens ≥270°
Right door: Opens ≥270°
Both doors opening simultaneously: ≥180°

2.3 Flooring

The flooring bears the entire weight of the cargo and is the component requiring the most attention during container loading.

Flooring Type	Material	Thickness	Load Capacity	Pros/Cons
APG Hardwood	Apitong plywood	28mm	🟢 Strong	Durable but high cost
MDG Hardwood	Meranti plywood	28mm	🟢 Strong	Cost-effective, commonly used
Bamboo Flooring	Bamboo plywood (new type)	28mm	🟡 Medium	Eco-friendly but poor water resistance
All-Steel Flooring	Steel plate (for special containers)	5mm	🟢 Extremely strong	Only for special containers like flat racks

Flooring Load Capacity Standards:

Single wheel load: ≥2,730kg (spacing ≤500mm)
Double wheel load: ≥5,460kg (spacing ≤1,000mm)
Concentrated load: ≥4,000kg (500mm×500mm area)

Container Loading Tip: When loading with a forklift, forklift wheels must travel along the direction of the flooring longitudinal beams. Avoid driving transversely across the flooring — transverse load capacity is only 30% of longitudinal capacity.

2.4 Side Walls and Roof Sheet

Side walls and roof sheet adopt a corrugated steel plate design. The corrugated structure increases strength while reducing weight.

Part	Steel Plate Thickness	Corrugation Depth	Lateral Force Resistance
Side Wall	1.5-2.5mm	30-50mm	≥15 tonnes (at top side rail)
Roof Sheet	1.5-2.0mm	15-25mm	Snow load resistance ≥500kg/m²

2.5 Bottom Rails and Top Rails

Rail Type	Material	Cross-Section Shape	Function
Bottom Rail	C-channel steel	Channel steel	Bears cargo weight and stacking pressure
Top Rail	Special-shaped steel	Rectangular steel tube	Bears stacking pressure and lifting forces
Fork Pocket	Reinforced steel plate	—	Provides load-bearing points for forklift transport

III. Comparison of Three Container Body Materials

Comparison Dimension	Steel Container	Aluminum Container	GRP Container (Glass-Reinforced Plastic)
Weight	Heaviest (2,200kg/20GP)	Light (1,800kg/20GP)	Medium (2,000kg/20GP)
Strength	🟢 High	🟡 Medium	🟡 Medium
Corrosion Resistance	🟡 Requires anti-rust treatment	🟢 Excellent	🟢 Excellent
Repair Difficulty	🟢 Easy (weldable)	🟡 Requires specialized processes	🔴 Difficult
Service Life	10-15 years	12-18 years	8-12 years
Cost	Baseline price	20%-30% higher	15%-25% higher
Market Share	~85% (absolute mainstream)	~10%	~5%

Mainstream Choice: Approximately 85% of dry containers worldwide use steel construction due to low manufacturing cost, easy maintenance, and high recycling value. Aluminum containers are primarily used for reefer containers (good heat dissipation, corrosion resistance). GRP containers are mainly used in chemical and specialized scenarios.

IV. Container Service Life and Decommissioning

Container Age	Condition	Application	Maintenance Focus
0-5 years	🟢 New	Premium customers, food-grade transport	Normal use, regular inspection
5-10 years	🟡 Good	General commercial transport	Need to inspect flooring and door seals
10-15 years	🟠 Serviceable	Low-value cargo, inland transport	Need to focus on rust and structural damage
>15 years	🔴 Aged	Inspection cycle shortened to 12 months under current CSC regulations	Recommended to evaluate repair costs vs. residual value

Data Note: The above structural parameters reference ISO 668:2020, ISO 1161 standards, and container body specification sheets from various shipping lines.

Data as of July 2026.

Found a structural problem with the container during loading? Take photos, record details, and immediately contact Bofeng Logistics to coordinate a container swap. 20 years of experience helps you avoid structural risks during transportation.

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