Influence of Surface Roughness Uncertainties on Design of Structures with Open and Suburban Exposures

Abstract

Following an investigation into the causes of a 40% difference between estimates of structural response to wind by two reputable wind engineering laboratories, the National Institute of Standards and Technology recommended the development of nationally accepted performance standards based on sound technical methods. The development of such standards requires the use of an uncertainty quantification procedure applicable to the response of structures subjected to wind loads. As part of this development, this paper considers the effect of uncertainty in the subjective determinations of the surface roughness lengths at sites with open and suburban exposures. Extensive data developed jointly by the University of Florida, Applied Research Associates, and the National Oceanic and Atmospheric Administration (NOAA)/National Hurricane Center were used in conjunction with analytic and probabilistic tools to quantify the effect of this uncertainty on the estimation of structural response to wind. It was found that neglecting this uncertainty can result in underestimation of the response by as much as 45%. It is recommended that techniques for the objective measurement of surface roughness lengths be used for structural design purposes and that, in the absence of such measurements, the effect of uncertainty in the determination of surface roughness be accounted for in structural design.