Load Combinations

The various types of loads (dead, floor, roof, etc.) are to be combined in proportions that are prescribed by the building codes. For example, in Section 1605 of the 2021 IBC, you'll find that the service level of dead and floor loads must be combined at full value, i.e., D+L (ASCE 7-16 2.4.1.2). If a snow load may also be present on that member, you must additionally consider the combination of dead, floor, and snow loads, which is specified in ASCE 7-16 2.4.1.4: D+0.75L+0.75S. The member must be designed to "resist the most critical effects resulting" from all possible combinations of loads in the proportions prescribed by the code.

RedSpec™ combines input loads in proportions that depend on the building code and the type of member, as delineated in the following tables. The load duration factor (LDF) used in the resistance is the factor associated with the shortest-term load in the combination.