Issue link: http://alpine.uberflip.com/i/684939
What do these values mean? Think of a truss that has been designed using a duration factor of 1.15 which is generally applied to snow loads. Live loads due to snow are typically at their highest shortly after a snow storm. As soon as some of the snow melts or is blown off of the roof, the remaining reduced load will be endured by the structure for an even longer period of time. Multiple Duration Factors and Load Cases applied to the truss. There are typically several instances where combinations of different load types can occur simultaneously on a truss. Attic Trusses and Wall Girders are two common examples of where multiple types of load and multiple duration factors need to be considered. These trusses are analyzed with several load cases. One load case includes all load types that can occur together. The Duration Factor associated with the shortest duration load in the mix is used to check this case. Other load cases might just include one type of live load plus dead load. These cases would each be checked using the Duration Factor associated with the live load included with that case. iModel can calculate the necessary load cases if you use the appropriate loading features of iDesign.