Case Study of Cable Tray Deformation

Cable tray deformation is often governed by flexural failure of support structures and deflection under load, with seismic events highlighting critical vulnerabilities in design.

Seismic Fragility Evaluation

A notable case study at a U.S. nuclear power plant examined cable tray deformation under seismic loading. The evaluation focused on non-serrated strut nuts in cable tray supports, which posed potential vulnerability during beyond-design-basis seismic events. Full-scale shake table tests and pull tests were conducted to determine the seismic capacities of cable tray support configurations. Some cold-formed steel sections not represented in the initial tests were subjected to flexural ultimate strength tests, providing empirical data for plastic limit states and realistic ultimate capacities. The study concluded that flexural failure of cold-formed steel supports governed the seismic fragility, with strut nut capacity slightly higher than the steel sections themselves .

Deflection and Load Considerations

Cable tray deformation is also influenced by span length, material, and beam configuration. Simple beam analysis is commonly used to estimate deflection, with a guideline of maximum deflection of 1/200 of the support span for aesthetic and functional purposes. Continuous beam configurations, where trays span multiple supports, typically exhibit half the deflection of simple beams due to load counterbalancing. Steel trays generally show less deflection than aluminum trays because of a higher modulus of elasticity. Reducing support span or using taller, stronger trays can mitigate excessive deflection .

Seismic Bracing Systems

In high-seismic regions, cable trays require lateral bracing to prevent deformation. A case study in Seattle, Washington, demonstrated the use of proprietary steel bracing between layers of ladder-type cable trays. The trays were supported by threaded rods from equipment cabinets, and diagonal bracing was added to resist lateral seismic forces. The design adhered to the 1994 Uniform Building Code and Bellcore GR-1275-CORE criteria, ensuring that trays did not rely on exterior walls or roofs for support .

Design Implications

Effective cable tray design must integrate load and capacity analysis, material selection, and bracing strategies. Properly designed trays improve safety, reduce deflection, and maintain structural integrity under both static and dynamic loads. Empirical testing, such as flexural and pull tests, provides reliable data for evaluating post-yield behavior, complementing theoretical design methods . This case study highlights that cable tray deformation is a complex interplay of material properties, support configuration, and external forces, particularly in seismic zones, and underscores the importance of empirical testing and robust bracing in industrial and critical infrastructure applications.