Container Structure and Materials: A

A container may look like just an "iron box," but its structure has undergone rigorous design and testing—it must withstand the pressure of being stacked 12 tiers high, resist the impact of Force 12 winds and waves at sea, and remain sealed 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
                    │  ┌────────────────┐   │
      ┌─────────────┤  │ Container interior │   │
      │  Left side wall     │  │                │   │
      │  (corrugated panel) │  │                │   │
      │             │  │                │   │
      │             │  │                │   │
      │             │  └────────────────┘   │
      │             │       Floor            │
      └─────────────┴──────────────────────┘
    Corner casting← ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ ─ →Corner casting
                                         Door

Structural component	Function	Material
Corner Casting	Connection point for lifting/stacking/securing	Cast steel
Roof Sheet	Waterproof, resistant to stacking pressure	Corrugated steel sheet (1.5–2.0 mm)
Side Wall	Structural support, protects cargo	Corrugated steel sheet (1.5–2.5 mm)
Floor	Carries cargo weight	Hardwood plywood (APG/MDG)
Door	Cargo access	Steel plate + sealing strip
Bottom Rail	Longitudinal support for the container body	C-shaped steel
Top Rail	Longitudinal support for the container body	Profiled steel

II. Detailed Explanation of Each Component

2.1 Corner Casting

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

Position	Function	Load Rating
Four top corner castings	Lifting points during hoisting	Single-point load capacity ≥15 tons
Four bottom corner castings	Load-bearing points during stacking	Single-point load capacity ≥30 tons
Side slots	Lashing and securing (twist-lock connection)	Single-point load capacity ≥10 tons

Three key holes of corner castings:

Top hole: hook connection point, used for lifting
Side hole: twist-lock connection point, used for securing on ships/trailers
Bottom hole: locating pin hole during stacking

Standard basis: The dimensions and strength of corner castings shall comply with the ISO 1161 standard, and the dimensional tolerance for each hole position shall be ≤1 mm.

2.2 Container Doors

Container doors are one of the weakest parts of a container and the components most prone to problems.

Container Door Component	Function	Common Failures
Door panel	Seal the container body	Impact deformation, door cannot close
Door hinge	Door opening and closing	Corrosion causing difficulty in opening and closing
Locking bar	Lock the container doors	Bending, cannot fully lock
Door handle	Operate the locking bar	Breakage
Sealing strip	Waterproof sealing	Aging causing water ingress
Locking mechanism	Secure locking	Jamming or damage

Container door opening angle standards:

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

2.3 Floor

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

Floor Type	Material	Thickness	Load-Bearing Capacity	Advantages and Disadvantages
APG hardwood	Apitong plywood	28 mm	🟢 Strong	Durable but expensive
MDG hardwood	Meranti plywood	28 mm	🟢 Strong	High cost-effectiveness, commonly used
Bamboo floor	Bamboo plywood (new type)	28 mm	🟡 Medium	Environmentally friendly but poor water resistance
All-steel floor	Steel plate (for special containers)	5 mm	🟢 Extremely strong	Limited to special containers such as flat racks

Floor load-bearing standards:

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

Loading tip: When loading with a forklift, the forklift wheels should travel along the direction of the floor longitudinal beams and avoid rolling across the floor transversely—the transverse load capacity is only 30% of the longitudinal capacity.

2.4 Side Walls and Roof Panel

The side walls and roof panel use a corrugated steel plate design; the corrugated structure increases strength while reducing weight.

Part	Steel Plate Thickness	Corrugation Depth	Lateral Force Resistance
Side wall	1.5-2.5 mm	30-50 mm	≥15 tons (at the upper side rail)
Roof panel	1.5-2.0 mm	15-25 mm	Snow load resistance ≥500 kg/m²

2.5 Bottom Rails and Top Rails

Beam Type	Material	Cross-Sectional Shape	Function
Bottom Rail	C-shaped steel	Channel steel	Bear cargo weight and stacking pressure
Top Rail	Special-shaped steel	Rectangular steel tube	Bear stacking pressure and lifting force
Fork Pocket	Reinforced steel plate	—	Provide load-bearing points for forklift transport

III. Comparison of Three Container Body Materials

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

Mainstream Choice: About 85% of dry cargo containers worldwide use steel structures because of low manufacturing costs, easy maintenance, and high recycling value. Aluminum containers are mainly used for refrigerated containers (good heat dissipation and corrosion resistance), while glass-reinforced plastic containers are mainly used in chemical and special scenarios.

IV. Service Life and Scrapping of Containers

Container Age	Status	Use	Maintenance Focus
0-5 years	🟢 New container	High-end customers, food-grade transportation	Normal use, regular inspections
5-10 years	🟡 Good	General commercial transportation	Need to check the floor and container door seals
10-15 years	🟠 Usable	Low-value cargo, inland transportation	Need to focus on rust and structural damage
>15 years	🔴 Old	Under current CSC regulations, the inspection interval is shortened to 12 months	Recommend evaluating repair costs and residual value

Frequently Asked Questions

How can you tell whether a container can still be loaded?

Check three points: whether the container doors open and close smoothly and lock securely; whether the interior floor is damaged or warped; whether the side walls and roof have penetrating rust holes. If any of these three does not meet the standard, request a different container before loading. When picking up the container, also check the next inspection date on the CSC safety approval plate.

Who is responsible if the floor is damaged during loading?

It depends on the loading method and whether there is overloading. A forklift driving across the floor sideways or a concentrated single-point load exceeding limits is a loading operation issue; if caused by corrosion or structural damage to the container itself, the party providing the container is responsible. Taking photos before and after loading as records is the easiest way to allocate responsibility.

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