The probability of a complete collapse of the shelf is low; however, accidents often occur, particularly from beam failures, as confirmed by our test projects. Let's examine the potential causes of beam collapse.
1. Issues in design, component selection, and material choice
1. Improper material selection: Beams and hanging plates should be made from steel of at least Q235B grade. In low-temperature cold storage, calm steel (C and D grades) should be used.
2. Incorrect specification selection: A double C-welded beam of 120*50*1.5 should be used, but smaller specifications are sometimes chosen.
2. Major defects in component processing quality
1. Cracks in the hanging teeth of the hanging plate: Steel processing can create microcracks that are not visible. The hanging teeth, typically stamped and cold-bent, experience significant strain, potentially leading to larger, invisible cracks at their roots. Although these cracks may not result in immediate failure, they can grow over time due to stress cycles, leading to sudden tooth fractures. For example, a beam collapse we experienced was triggered by eagle claw-type teeth. This does not imply that all such shelf products have quality defects; if material performance and processing meet standards, the teeth should be fine. Testing cannot prevent such accidents, as there is no current quantitative standard for assessing tooth safety. Until new standards are established, regular inspections are recommended. If a defect is identified post-accident, measures such as reinforcement, load reduction, or scrapping should be taken for the entire batch of beams.
2. Weld defects between the hanging plate and the beam: Ideally, the hanging plate should be welded on all four sides, but often only three or two sides are welded. Regardless, qualified designs should not have leaks or cold welds.
3. Installation defects
1. Hanging teeth not fully or partially seated in column holes.
2. Misalignment in overall height or height discrepancies at the ends of the first layer of beams.
3. Missing safety pins or mismatched installation specifications.
4. Improper use or misoperation of components
1. Overloading or concentrated load storage.
2. Collisions during operation causing irreversible deformation.
3. Removal or loss of safety pins during use.
The process of beam collapse due to missing safety pins typically involves: (1) a safety pin at one end of the beam goes missing and is not detected. During storage and retrieval, the hanging teeth at this end may disengage from the column hole without being noticed.
When the goods are released, the beam's hanging end becomes a cantilever, with the other end bearing all loads. This results in a significant bending moment that damages the hanging teeth of the plate and causes noticeable bending. The load then transfers to the column, leading to cracks in the column hole wall. The accident characteristics include: one end of the hanging piece remains undeformed, with only the hanging teeth falling off or deforming vertically, while the connected column is intact; conversely, the other end shows clear deformation, with hanging teeth falling off or deforming horizontally, and the column hole wall is torn.
Additionally, there is no load warning sign, and the maximum allowable load is uncertain. Structural changes, such as layer height adjustments and disassembly or reassembly in different locations, are unconfirmed.
In the event of a beam collapse:
1. Refer to the original drawings, design specifications, and other relevant materials for the accident shelf.
2. Engage a professional third-party inspection unit to conduct thorough assessments, including material analysis, structural calculations, processing quality, and usage status, and provide a detailed accident analysis and inspection report.
3. Implement solutions based on the findings to ensure the product's safe use.
