SEI/ASCE7-02 load combinations (Allow. Stress)

[warrenw]

With reference to vertical steel stacks or steel derricks. If there is only dead load and wind load, can you still use the 0.75 load reduction for the wind loads when using allowable stress design?
In the past we would calculate the wind loads(unfactored) and apply a 1/3 increase to the allowable stresses according to AISC.
I was under the impression that with ASCE 7-98 you applied a 0.75 load reduction to the wind load only and no increase in allowable stress. Which gave you about the same results.

Now as I look at the new ASCE7-02 section 2.4 - Combining nominal loads using allowable stress design - combination #5 for my case it breaks down to Dead load + Wind (all other loads not applicable). The 0.75 load reduction seems to be used in combination #6 but not in combination #5. But it does state no increase in allowable stresses shall be used with these load combinations.
Is the 0.75 reduction allow???
Warren

 

[etompos]

Section 2.4.1 of ASCE 7-02 clearly states that increases in allowable stress shall not be used with the load combinations, except where the material strength is time dependant, which it is not for steel.

The 0.75 load combination factor is only to be applied where TWO or more loads act concurrently. In the case you mention, it does not apply.