Determination of basic mean hourly wind speeds for structural design in Nairobi county

Abstract

Structural Engineers should be able to accurately predict all loads affecting structures. Consideration of wind loads is very important in the s tructural design especially in the design of high rise structures. This, among accurate prediction of other loads affectin g a structure , ensures safe and economic design of structures. Kenyan structural engineers depend on basic wind speeds which were determined over 30 years ago. It is important to periodically review the wind speeds . This is because the wind speeds experienced could change due to changes in land use like deforestation to give way for infrastructure among other causes. Most structures are usually designed for a life period of 50 yrs, thus the basic wind speed will hav e a return period of 50 years. The objective of this paper is to provide the basic wind speed which will be used to design building structures in Nairobi. Wind data was taken from 8 meteorological stations within and around Nairobi County. Terrain and altitude correction factors were also determined for all the meteorological stations. These correction factors were multiplied to wind speeds measured at anemo meter sites to obtain the design wind speeds for a standard open country terrain and standard elevation. This data was then analyzed stati sti cally using Gumbel method to determine the basic wind speed, from which wind pressure affecting a typical structur e can be calculated.