Wind Speeds for the Estimation of World Trade Center Towers' Response
William P. Fritz, Fahim H. Sadek, Emil Simiu
Estimates of the World Trade Center (WTC) towers response to wind by two North American wind engineering laboratories differed from each other by almost 40 %. A recent investigation by the National Institute of Standards and Technology determined that those differences were mainly due to discrepancies between the respective estimates of the wind speeds. In this paper we present a procedure for estimating extreme wind speeds near the WTC site that corresponds to a sector-by-sector approach to the estimation of extreme wind effects. We provide details of the data sets and their treatment, as well as details of the estimates themselves, in a manner intended to be thorough, clear, and transparent. Efforts in the direction of clarity and transparency are in our view necessary if estimates of extreme winds and their effects are to meet the need for effective scrutiny by users and building authorities, and if a solid technical basis for a consensus that remains to be developed among standard and professional organizations is to be created in the near future. Our analyses indicate that sectorial extreme wind speeds, and their counterparts in methods based on the up-crossing technique, are sensitive to sampling errors of a type that does not affect estimates of extreme wind speeds considered without regard for their direction. For this reason, estimates based on overly refined schemes for taking wind directionality into account and that disregard the possibility of such sampling errors are in our opinion prone to being significantly in error.