Structural Design of Heavy Cargo - Box Calculation

Technical Article on the Topic Structural Analysis Using Dlubal Software

Technical Article

New

08/30/2023

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In this article, a heavy cargo box is calculated according to the guidelines of the German Bundesverband Holzpackmittel (HPE). The load cases for Handling by Crane and Sea Transport are calculated.

Introduction

Wooden transport boxes are often used for the transport of machines or individual components. The spectrum of wooden packaging ranges from simple racks for transporting filigree car body components to complete containers of a heavy-lift box.

The German Bundesverband Holzpackmittel, Paletten, Exportverpackung e. V. (HPE), a professional association for wooden packaging, has created a guideline for calculating heavy-lift packaging, which can be purchased by clicking the following link.

The following load cases are analyzed for heavy cargo boxes.

• handling by crane
• transport by truck
• maritime transport

Regulations

The guideline specifies, among other things, the materials and design standards to be used.

• design of structural timber components according to DIN EN 1995-1-1
• design of structural steel components according to DIN EN 1993-1-1
• C24 strength class for softwood according to EN 338
• attachment points for belts

Example

As already mentioned, this article describes the calculation of a heavy cargo box. The box is subdivided into:

• Box bottom consisting of longitudinal skids, transverse skids, end beams, and bottom boards. The end beams are connected by M16 bolts.
• Box walls consisting of beams supporting the cover (so-called vertical supports), which are connected to a plywood cladding by profiled nails.
• Box cover consisting of cover beams that are also connected to a plywood cladding by nails.
• Steel edge protectors are mounted in pairs on the top and bottom of the case at the belt deflection.

Dimensions:

• length 6.44 m
• width 2.64 m
• height 2.94 m

The flexibility from the nails is applied at 5,700.8 kN/m² in ux and uy in the line hinges.

Cross-Sections:

• crossbars and posts - 16/18 cm
• longitudinal bars and skids - 14/20 cm
• OSB cladding - d = 18 mm

In the box's cover, the OSB panels do not have a stiffening function, which is why they are modeled with the "Load Transfer" surface type in that location.

As mentioned, only three load cases in three combinations are analyzed. Thus, the combinatorics is relatively simple.

• 1.35*LC1 heavy cargo of 20,000 kg, distributed on four load application points
• 1.7 *LC2 crane handling of 10 kN/m² on cover
• 1.35*LC3 truck transport of 18 kN/m² on cover

There is something special about load combination 2. The container is held by the upper cables only. Here, the supports are deactivated by means of stiffness modifications. In load combinations 1 and 3, however, the cables are deactivated.

Results

The design of the timber and steel members is performed directly in the respective design add-ons. In the model file below this article, you can find the design checks included in the printout report.

The still-missing design of the fasteners can be done directly with the axial forces in the line hinges (see following image).

Summary

The design according to the German HPE guideline can be carried out easily in RFEM. In case of frequent design checks of this type, it is useful to parameterize the models and to save them in the Block Manager.

Dipl.-Ing. (FH) Bastian Kuhn, M.Sc.

Product Engineering & Customer Support

Mr. Kuhn is responsible for developing products for timber structures, and provides technical support for our customers.

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• Updated 09/04/2023

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