Why do wind speeds differ on multi crane sites?

At WINDCRANE, we are asked this question a lot. Why is the wind speed sometimes different on one or two of my cranes when they are all on the same site and within close proximity?

This can be common problem in the construction industry for multi crane sites, especially when a crane operator cannot do a lift safely due to high wind limits and another operator nearby can complete the lift as the wind reading is still safe. This can cause concern that the operator did not want to complete the lift and that is why accurate wind monitoring and records are very important, so that you can have proof of high wind speeds and see when the crane could not be operational.

There are a few reasons as to why the wind speed can be different. Here are a few samples of similar but different data from multi crane sites (cranes on the same site/project) and a summary on what could be the reason.

Data source: WINDCRANE IoT wind management service 2020.

Example 1: This is max. wind speed data recorded from 4 similar size/height cranes based on same site in London.

The max (gust) values vary above and below each other. Often they are similar, but occasionally there are large differences, especially on days of high wind speeds like on Oct 31st. In the chart above we have one crane measuring a wind gust of 42.4 mph and another crane measuring 27.2 mph.
 

Data source: WINDCRANE IoT wind management service 2020.

Example 2: This is max/gust data from 3 similar sized cranes on same project/site.

The speeds have a similar profile but do vary above and below each other. This is most likely to be dependent on how the cranes are slewing/luffing.
 

Data source: WINDCRANE IoT wind management service 2020.

Example 3: This is max(gust) wind speed data and average wind speed data recorded for 2 cranes on the same site:

The average wind speeds (in green and yellow) are very close sometimes and max wind speeds (in red and in blue) fairly close, but sometimes (as in the highlighted area) they are noticeably different. This may be due to steady vs gusty wind or the cranes are slewing in different directions.

To summarise, here are some reasons why the wind speed may be different on nearby/ adjacent cranes:

• Urban high-rise sites will tend to have more wind variation across the site due to funneling, shadowing and turbulence from buildings and structures and this can vary greatly with wind direction.
   
• Open sites with no large structures tend to have more uniform wind flow but this may change over the course of a construction project, for example as a large structure is erected on a previously empty site.
   
• Different slew direction and jib luff angle of cranes. The sensor (anemometer) may actually be shadowed by part of the crane (ideally not), or the sensor may go in and out of the wind shadow of other structures/buildings as the crane slews and luffs.

We hope this article was helpful. If you have any questions regarding wind monitoring or wish to discuss how wind monitoring can provide valuable data to your construction projects, then please contact us.