Issue link: http://alpine.uberflip.com/i/684939
What does L/240 and L/180 mean? The L is equivalent to the length (truss span) in inches and is divided by the denominator to determine the allowable maximum deflection. For example, if you have a 40' roof span and wanted to calculate the maximum deflection allowed for Live Load, you can use the following formula. (X = allowable deflection) The result indicates that the truss is allowed to deflect 2" under Live Load. L/240 = X = (40) (12) / 240 = 2" Similarly, to calculate the allowable maximum Total Load Deflection, use the formula below: (X = allowable deflection) L/180 = X = (40) (12) / 180 = 2.66" The difference between the allowable Total Load Deflection and the allowable Live Load Deflection equals the Dead Load Deflection; therefore, the maximum allowable Dead Load Deflection for this example is 0.66". Creep Creep is a permanent Dead Load Deflection that is a result of wood deflecting, or creeping, under a sustained load over a given time. To compensate, you can adjust the Dead Load Increase Factor. For example, if you select 1.5, the Dead Load Deflection is increased by 50% and then added to the Live Load Deflection to obtain the Total Load Deflection (DLD x creep factor) + LLD = TLD. Remember, you cannot enter a limit in the deflection fields that is larger than 999, so this is an alternative method to add a higher limit when a higher stiffness factor is desired (i.e. girders of any type).