Comparison of wind speed hill shape multipliers calculated by seven different national and international standards

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Nayyerloo, M.; King, A.B.; Flay R.G.J. 2015 Comparison of wind speed hill shape multipliers calculated by seven different national and international standards. Lower Hutt, N.Z.: GNS Science GNS Science report 2014/52 56 p.

Abstract: Wind flow is strongly influenced by hilly terrain, with both valleys and hill crests experiencing higher wind speeds than flat terrain. Increased wind speeds over hilly terrain are a potential hazard to buildings and above-ground infrastructure located on hilly terrain. In New Zealand, hilly terrain is common and at locations far from any wind measurements design wind speeds are frequently estimated by applying the AS/NZS1170.2 Loadings Standard. A relevant question is – “How accurate is it?” In an attempt to answer this question, the New Zealand Wind Engineering Research Consortium, with representatives from the National Institute of Water and Atmospheric Research Limited (NIWA), Opus International Consultants Limited (Opus), the Institute of Geological and Nuclear Sciences Limited (GNS), and the University of Auckland, has been formed and funded by the Natural Hazards Research Platform ( The consortium has undertaken series of experiments comparing measured wind speed-ups over the rugged Belmont hills in the Wellington area of New Zealand, wind tunnel test measurements and speed-ups from numerical modelling, with wind estimates from the AS/NZS1170.2 Loadings Standard to evaluate how accurate the loadings standard design wind speeds are. This report summarises methods and procedures adopted by seven national and international standards to estimate hill shape wind speed multipliers, and compares the resulting multipliers for a section of the Belmont Hill as a typical example of New Zealand’s hilly terrain. The overall aim is to understand best practice around the world regarding hill shape effects on design wind speeds to provide the necessary information for provision of improved design wind speed procedures to reduce the vulnerability of New Zealand’s built environment to wind damage. (auth)