Cable Tray Wind Load Analysis

Method & Assumptions

Wind loads are calculated per ASCE 7-22 Chapter 26 (General Wind Requirements) and Chapter 29 (Wind Loads on Other Structures).

Velocity pressure at height z:

q_z = 0.00256 × K_z × K_zt × K_e × V²   (lbs/ft²)

Design wind force on tray projected area:

F = q_z × G × C_f × A_f

Parameters:

  • K_z — velocity pressure exposure coefficient per ASCE 7-22 Table 26.10-1 (power-law formula)
  • K_zt — topographic factor (1.0 flat terrain, >1.0 near hilltops or ridges)
  • V — basic wind speed (mph) from ASCE 7-22 Fig. 26.5-1A (Risk Cat II)
  • G = 0.85 — gust factor for rigid structures (ASCE 7-22 §26.11)
  • C_f — force coefficient from tray construction, fill condition, cover condition, or engineer override
  • A_f — projected area = tray width (ft) × span length (ft) × optional exposed-area factor

NEMA tray capacity screening uses traditional load-class definitions. Under the L/100 deflection normalization, allowable uniform load scales with the inverse cube of span. Verify final capacity, width effects, and support spacing with the selected manufacturer's load tables.

Citations: ASCE 7-22 §26 and §29, NEMA VE 1-2017, NEMA VE 2-2006. See Wind Load Assumptions for construction and cover handling.

See also: Support Span Calculator, Seismic Bracing Calculator.

Wind Parameters

From ASCE 7-22 Fig. 26.5-1A (Risk Category II, 3-second gust at 33 ft). Typical values: coastal US 130–160 mph, inland US 90–115 mph. Use the ASCE 7 Hazard Tool for site-specific speeds.

Per ASCE 7-22 §26.7. Most industrial and petrochemical sites are Exposure C. Use Exposure D for sites near large bodies of water.

1.0 for flat terrain (ASCE 7-22 §26.8). Values >1.0 apply near hilltops, ridges, or escarpments. See ASCE 7-22 Fig. 26.8-1.

Installation Parameters

Centerline height of the tray above grade. Minimum 15 ft applied per ASCE 7-22 Table 26.10-1 for K_z computation.

Standard widths: 4, 6, 9, 12, 18, 24, 30, 36 inches. This is the projected dimension exposed to wind (parallel to wind direction).

Distance between tray supports. Use the Support Span Calculator to determine the appropriate span for your cable load. Typical: 8–20 ft.

Schedule mode infers this from each tray's Raceway Schedule type when available. Solid-bottom trays are treated as flat-plate wind surfaces.

Affects the force coefficient C_f. Fully filled trays are treated as solid surfaces; empty open trays allow more wind to pass through.

Solid covers make the tray behave more like a flat plate. Schedule mode uses each tray's cover value when the Raceway Schedule includes one.

Leave blank to use the selected assumptions. Enter a project-specific coefficient only when directed by manufacturer data or engineering criteria.

Multiplies tray width × span for unusually exposed covers, side plates, or project-specific effective area adjustments.

Total vertical cable weight per foot of tray. Use the Support Span Calculator to derive this from the cable schedule. Used for NEMA capacity check only.

NEMA VE 1-2017 load class. Used to check vertical cable load capacity against the tray's rated capacity at the specified span. Verify with manufacturer load tables for final design.

Evaluation Mode