The difference between two load groups in LRFD

All QuestionsThe difference between two load groups in LRFD
The difference between two load groups in LRFDJohn Gerald asked 4 months ago
In ASCE 7-16 there is a load group like: 1.2D + 1.0E + L + 0.2S but there is also another group like: 0.9D + 1.0E In both the earthquake load is the same, so why use the second one, while the first will create Worse combination with 1.2 instead of 0.9 for dead load? What exactly am I missing?

1 Answers
The difference between two load groups in LRFDStanley Stanley Delapena answered 4 months ago

Dead loads can, in some cases, be beneficial to the integrity of the structure.
For example, suppose you have a beam simply supported with a cantilever and you want to find the envelope of the bending moment. Depending on the length of the cantilever, it is possible that the simply supported part is often under a negative bending moment. So when calculating the envelope of positive bending moment (from dead and live loads), the dead loads actually “cancel” some of the live load results. In such cases, you may then want to use 0.9 instead of 1.2 as the dead load factor.

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