Seismic design using an enveloping combination

During seismic design, it is advisable to design independently for each seismic load combination contained in the enveloping combination, rather than directly assigning an enveloping combination. When a load combination is not specified as enveloping, loading is appropriately declared seismic or not seismic. When the load combination is enveloping, however, the enveloped forces at different stations may come from any of the included combinations. As a result, load combinations are not declared as seismic or not seismic. Further, load combination forces lose association.