According to ASCE 7-22 [1], several load cases shall be considered for continuous purlin systems, including the following:


  • Dead Load, Sheeting, Purlins, etc. (1)
  • (Unreduced/Reduced) Roof Live Load (1)
  • Balanced Snow Load and Unbalanced Snow Loads (3)
  • Wind from Left side with Negative and Positive internal pressures (2)
  • Wind from Right side with Negative and Positive internal pressures (2)
  • Wind from Front side with NegativeNegative and Positive internal pressures (2)
  • Wind from Back side with Negative Negative and Positive internal pressures (2)
  • Partial Snow Loads, Full balanced snow load on either exterior span, and half the balanced snow load on all other spans (2)
  • Partial Snow Loads, Full balanced snow load on either exterior span, and half the balanced snow load on all other spans (2)
  • Partial Snow Loads, Full balanced snow load on any two adjacent spans, and half the balanced snow load on all other spans. (Number of Bays -1. e.g.: 6-1=5) 





Moreover, when these load cases are combined with other applicable loads, dozens of load combinations may need to be evaluated.



References:

[1] American Society of Civil Engineers. "Minimum design loads and associated criteria for buildings and other structures." American Society of Civil Engineers, 2022.