1. Introduction to Mechanical Analysis of Dynamic Loads

Loading and securing cargo in freight wagons requires taking into account a number of physical parameters related to the dynamic loads that occur during rail traffic. Loads resulting from acceleration, braking, centrifugal forces generated during track curves and vertical interactions (the so-called “wagon floating”) require precise structural analyses for the correct distribution of the load. Local overloads in the wagon structure, resulting from incorrect weight distribution, can lead to material fatigue or deformation of load-bearing elements (in particular frames and wheelsets), which increases the risk of damage to the infrastructure and the possibility of derailment.

2. Technical regulations governing the loading and securing process of cargo

2.1. International normative regulations (UIC, RID)

The loading process in rail transport is precisely regulated by the standards of the International Union of Railways (UIC) and RID regulations, which define the permissible dynamic loads, requirements for the arrangement of the load, as well as the technical parameters of the lashings. The UIC “Loading Guidelines” document provides detailed guidelines on the protection factors, maximum dynamic forces acting on loads and the structural requirements of freight wagons in terms of the load capacity of frames, wheelsets and braking systems.

According to UIC 571-4, the permissible maximum dynamic load is 4 g for freight wagon axles, which means that the wagon structure must be able to withstand four times the weight of the load during hard braking. These forces must be taken into account in the selection of lashing methods, which shall ensure a minimum coefficient of friction of 0.4 for the contact surface between the load and the wagon floor.

2.2. National standards (PN-EN 12195-1)

At the national level, the PN-EN 12195-1 standards specify in detail the minimum lashing forces depending on the type of load and its mass characteristics. This standard regulates the forces resulting from acceleration and deceleration (main X and Y vectors) by specifying formulas for the calculation of clamping forces for different transport scenarios. These calculations are based on the dynamic coefficient (CF) and the coefficient of static and dynamic friction, which directly affect the number and arrangement of attachment points.

PN-EN 12195-1 also specifies the strength of the materials used for fastening (e.g. belts, chains) and introduces the need to use fastening equipment in accordance with technical requirements. The minimum breaking strength of class L lashing straps is specified at 5,000 daN, which corresponds to the ability to hold a load of up to 50 tons under acceleration conditions exceeding the standard permissible operating standards.

3. Application of cargo securing techniques under dynamic
load conditions

3.1. Clamping forces and their distribution

The cargo securing process requires precise calculations to ensure the structural stability of the cargo and the appropriate distribution of internal forces. According to UIC guidelines, the lashing forces must be distributed in such a way as to minimize torsional moments and lateral forces (especially in platform cars, where lateral forces act on the external load-bearing points of the car). In the case of open-construction wagons (e.g. flatcars), loads are mainly transferred by lashing points in the form of clamps or metal rods, which must be able to absorb the forces preventing the movement of the load when cornering.

3.2. Lashing straps and V-systems

The most commonly used restraint systems are lashing straps, which are made of high-tensile polyester (min. 7,500 daN). These belts are used in parallel or cross configuration, depending on the specifics of the load and stabilization requirements. The cross configuration of the belts allows for an even distribution of lashing forces, which minimizes lateral vectors acting on the load during railway maneuvers.

Wedge systems are used for irregularly shaped loads, e.g. cable drums, pipes or large-size machines. Made of metal or wood, these wedges are designed with compressive strength requirements in mind to counteract lateral displacement. According to the standards, the minimum force acting on the wedge should be at least 2 kN to ensure stability during sudden braking.

3.3. Fastening chains and steel struts

For heavy loads, lashing chains made of high-strength alloy steel are used in accordance with EN 818-2. These chains must have a minimum breaking strength of 10,000 daN and are used in simple lashing point configurations or multiple systems that allow forces to be evenly distributed over the entire length of the wagon. Steel struts, used to stabilize irregularly shaped loads, must meet the requirements for resistance to compressive and tensile forces (usually >30 kN).

4. Loading technical specifications for different types of wagons

4.1. Loading criteria for covered wagons (G)

Covered wagons must be loaded taking into account the axial and lateral loads, which are directly transferred to the wagon frame. The vertical loads resulting from the load weight must be evenly distributed over the floor surface of the wagon and the maximum permissible floor load, according to EN 12663, must not exceed 5 t/m². In addition, loading moisture-sensitive cargo requires the use of wagon door seals to prevent moisture from entering the cargo area.

4.2. Specificity of loading on platforms (K, R, S)

Railway platforms intended for the transport of ISO containers must be equipped with mechanical interlocking systems which, in accordance with ISO 1161 guidelines, provide a minimum locking force of 30 kN for each of the four container lashing points. For loading machines and vehicles, side struts are additionally used to minimise torsional torsional torques on the platform structure during acceleration and braking.

4.3. Loading and securing of cargo in tanks

When transporting liquids in rail tankers, it is crucial to control the pressure inside the tanks. According to RID guidelines, each tanker must be equipped with a system of safety valves that open at pressures in excess of 1.5 bar. The tanks are designed from corrosion-resistant materials such as stainless steel EN 1.4301 with tensile strength up to 600 MPa. The tightness of valves and venting systems must be checked regularly to prevent possible leakage during transport.

5. Shipper’s responsibility and control procedures

The shipper is directly responsible for the compliance of the loading process and securing the cargo with technical standards. Each loading must be documented by means of technical reports, which contain data on the distribution of the load, the lashing methods used and the calculation of the forces acting on the load. The carrier is required to carry out an inspection before the train sets off to verify compliance with UIC and RID standards.