Current Wind Code Basis ASCE 7-95
Objective: 50-year return period wind speed resistance without structural damage
No explicit wind drift serviceability criteria
No acceptance criteria on human tolerance to motion
Implicit overstrength for greater events can be low for areas exposed to hurricanes if wind speeds can exceed 1.2 x (50-year value)
Variable dynamic properties for high-rise structures cannot be addressed by fixed prescriptive gust factors
Notes:
Current U.S. code approaches to wind loading are based on a single value of wind speed representing a 50-year recurrence interval. The 50-year wind speed is commonly used for evaluations of both lateral drift and strength. For high-rise buildings it may yield poor reliability for either serviceability or strength objective.
Numerous papers, such as Tallin and Ellingwood (1984), Charney (1990), or Griffis (1993) have described the poor correlation between static lateral drift limits at the 50-year wind force and occupant perception of acceleration building motion. Use of a 50-year wind for limitation of drift-related damage has also been criticized as overly stringent and lacking relevance to typical building occupancy terms. To compound the ambiguity of this procedure, none of the U.S. building codes in existence or under consideration specify or recommend a building wind drift index, and the values used in customary practice range considerably