Orography Factor to BS EN 1991-1-4 and UKNA

Calculation of Orography Factor to BS EN 1991-1-4 Appendix A.3 and UK National Annex. Many sites in the UK have at least one wind direction where the wind velocity accelerates towards a crest. The time consuming and complex calcualtion for orography is often overlooked and the resulting peak wind pressure underestimated. From user input of basic terrain and site information, this calculation determines if orography is significant using Table NA.2 from the UK NA, and if so the values of orographic location and orography factor. A passing aquaintance with BS1991-1-4 is assumed, and if the term orography is foreign, this spreadsheet is probably not for you. It is not intended to be used outside the UK, although providing it is does not contradict a National Annex, it will provide the c0(z) factor in accordance with A.3 of the Eurocode.