Specification of design wind speed for cyclone events in India

Abstract

The objective of this study is to determine the best suited extreme value distribution of wind speed for cyclone events in India. As mentioned by Indian code of standard (IS: 875, part III), fitting of wind speed is done by Gumbel distribution. Wind load is proportional to the square of wind speed (v2) and in Eurocode it is suggested that if v2 follows Gumbel distribution, v may follow Reverse Weibull distribution. So naturally the question arises regarding the appropriateness of Gumbel distribution as an extreme value distribution. The design wind speed mentioned by Indian code with 50 years return period is 65 m/s taking a load factor of 1.5 which indicates that the design wind speed based on Gumbel distribution is 85 m/s. Now if any other extreme value distribution (Fre’chet or Reverse Weibull) apart from Gumbel has been found appropriate for Indian cyclone data, it is required to estimate the under or over estimation of design wind speed which is suggested in Indian code. Since wind load is proportional to v2, a little variation in design wind speed will cause a larger variation in design wind load. Moreover, Indian code used only 56 wind speed data due to cyclone for obtaining the parameters of Gumbel distribution. So it is also required to estimate the uncertainties involved in this ensemble size and whether this ensemble size will lead to a stable statistical estimate of design wind speed or not. This paper is intended to find a better wind speed distribution for cyclone events in India and hence to find a more accurate and reliable design wind load. Copyright © 2013 APCWE-VIII. All rights reserved. Published by Research Publishing, Singapore.