Question: In ASCE 7-05 Section 2.3, Basic Load Combinations, there is an Exception 2, which states “Where lateral earth pressure provides resistance to structural actions from other forces, it shall not be included in H but shall be included in the design resistance.” 

Would you please clarify the whole statement entirely? Also, what does it mean “it shall not be included in H but shall be included in the design resistance?”  It would be helpful if you can give an example too.

Answer: The corresponding provision in ASCE 7-10 has become:

1. where the effect of H adds to the primary variable load effect, include H with a load factor of 1.6;
2. where the effect of H resists the primary variable load effect, include H with a load factor of 0.9 where the load is permanent or a load factor of 0 for all other conditions.

You may find this new language easier to understand. The ASCE 7-05 requirement could be paraphrased as: “where the effect of H resists the primary variable load effect, include H with a load factor of 1.0.”  ASCE 7-10 has refined that to 0.9 when the soil causing the pressure can be counted upon to be there and 0.0 when it can be eroded.

A good way to think of the requirement is: the load factor on H is 1.6 when it hurts, but the factor is 1.0 (ASCE 7-05) or 0.9 or 0.0, as appropriate (ASCE 7-10) when it helps.

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