The Technical Expert Group on Masts and Towers (WG4) of the International Association for Shell and Slender Structures held its biennial meeting in Toronto, Canada on September 11 to 15. ICE presented 2 papers to the group dealing with current issues of interest to the engineering community.
“Wind Extremes in Changing Climate” presented our new service which provides site specific extreme wind extremes in a future climate based on Environment Canada regional model runs for the present and future out to the end of the century. This uses the change in 50 year return winds for a given site based on the current 30 year run compared to a future run for 2070-2100. This relative change is applied to the standard site specific derivation based on the past 40 to 50 year airport data to project the extreme wind change from the current to the future period.
The results of applying this method to two sites separated by 400 km in Ontario show a 13% increase at one site and a 4% decrease at the other site, showing the potential error in applying a provincial or even regional average change as would be available from some of the model output maps.
The discussion paper is available at:
https://www.ice-inc.co/wp-content/uploads/2022/10/Wind-Extremes-in-Changing-Climate-IASS.pdf
The second discussion paper “Wind Speed-Up Formulation Testing” presented the results of recent measurements and wind tunnel simulations carried out by Australian Researchers for the case of Belmont Hills in New Zealand.
The objective of the research was to determine how well the various building codes dealt with the wind speed-up caused by a range of hills also called rolling or undulating terrain. The observations as well as the tunnel testing and numerical modeling show that none of the codes tested, which include the Australian, ASCE 7, NBCC S37, European, Korean or Japanese codes, were able to reproduce the observed speed-up by the hills.
Our paper shows that all of these codes assume that the speed-up formulation can only be applied for isolated hills which means that they do not show any speed-up for the second and subsequent hills, whereas the data shows that each of the hills causes a speed-up almost independently of other hills in the range.
The ICE Inc. site specific formulation developed in 2012 and applied in all of our site-specific assessments starts from the original “Simple Guidelines” by Walmsley, Taylor and Lee which included the treatment for a range of hills. Applying our procedures to the Belmont Hills topography shows good agreement with the wind tunnel data.
It is interesting to note that the ASCE 7 2022 version has removed the restriction to isolated hills so that every hill or ridge will need to be evaluated for speed-up. The new ASCE 7 approach will lead to a 30% or greater over-statement of the speed-up effect on subsequent hills in the range.
The discussion paper is available at:
https://www.ice-inc.co/wp-content/uploads/2022/10/Wind-Speed-Up-Formulation-Testing-IASS.pdf