huangyhg

design of girts
i am aware of the fact that the increase of allowable stresses for wind is no longer allowed. but when designing girts the only loads are the dead load of the siding, the dead load of the girt, and wind. thus your load combination is dead + wind. but it appears to me that you should be allowed the increase due to the fact that the wind load is not constant. the asce says "unless it can be demonstrated the such an increase is justified by structural behavior caused by rate or duration of load". does any one have an opinion on this? has anyone used the increase for designing girts?
load duration factors normally apply to wood but not to steel.
duration has no relevance for steel. timber is the only structural material that has increased strength with shorter duration.
the reason why the 1.33 factor used to apply was not because of load duration, it was because of wind gusts not occurring on the front and rear faces at the same time.
the 1.33 factor was dropped as the new wind code includes a gust factor to account for this.
'the wind load is not constant'- it only takes an instant for an overload to collapse a building.
the only load-time-duration effects seen by steel are for very very short loads, tiny fractions of a second such as blast loading. wind loading does not count for this and so no increase for load duration is permitted for steel.

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