Wind loading is inextricably linked to location. Knowing factors such as the altitude of a sign’s location, whether it is near the coast or in an urban setting, are crucial for making sure appropriate wind conditions are taken into account when designing the structure. If you don’t input the parameters for your own area you will have only broad-brush environs available. These are taken from the UK advice to the Standard (the National Annex to BS EN 12899-1:2007), and include England inland (yes, the whole of England) and Scotland inland (good enough from the lowlands to the highlands). If you provide information such as terrain type and altitude, you can use a much refined and often significantly lower wind loading to test your structures. This will, of course, result in significantly more economical installations.
- To define your own environs (general locality), click on the menu item ‘New Environs…’.
Note - The environs is the area, such as town or county, that will be used as a basis for providing the wind load for each proposal. The exact loading will depend on local factors such as the precise location within the environs, and other local wind conditions.
- In the tabbed, Environs Wizard you can start by providing a name, and description. You may, for example create one called ‘My Local Authority (urban)’ for the urban areas in your area, and one called ‘My Local Authority (rural)’ for the rural areas, and/or make it clear that there are significantly different terrain types or altitudes using the description.
- The next step simply enables you to provide the actual location within the UK or Ireland, for example England or Scotland. This may be more important later on, however, if you are happy to use the European Standard that covers wind loading on structures – BS EN 1991-1, Part 4 (or Eurocode 1) – this information will be used for reference only.
If you show the map you can indicate the rough centre of your area. Again, if you use Eurocode 1 for your wind loading then this coordinate will be used as a basis for the exact location of your proposals and a basic wind speed set, but you will need in any case to give a precise location for each proposal also.
Note - It is not possible to give a location for the environs (locality) to the nearest metre by design. The full 12 figure coordinates are given for indicative purposes only.
- On the next tab you can enter the altitude for your environs. Few localities are uniform and have varying altitudes so you can enter an average. This has less of an effect on the overall wind loading than terrain type and class so doesn’t need to be very accurate.
- The ‘Terrain’ tab provides for you to specify the type of terrain that the environs is made up from. Classes II and III are the most commonly used for traffic signs in rural and urban situations respectively.
- The ‘Terrain 2’ tab provides some options to state whether various conditions exist in your environs. However, just because you select that the environs includes significant orography (hills or escarpments) doesn’t affect the basic wind loads until you specify, for a specific proposal, that the sign assembly will be placed at the top of a hill, ridge, cliff or escarpment.
Tip - Always place a tick in the ‘Has Significant Orography’ box so that you can specify hills, escarpments or even small embankments later on when using this environs.
- For most purposes you can ignore the ‘Proximity’ tab so we will do so for this article. Please note that if you are setting terrain class III then an additional proximity tab will appear which again you can ignore for most purposes.
- On the ‘Wind Assumptions tab you have the option of setting a different ‘wind return period’ for all proposals in your new environ. This is not the same as the design life of an assembly, it is a measure of risk. The value suggested for use in the UK – 25 years – is taken from the National Annex to BS EN 12899-1:2007 is given here. Whilst it may seem strange that you can end up using Eurocode 1 for wind load and parts of ‘12899’ for other items, Eurocode 1 is silent on this.
- The last tab gives the option, if available, for you to select the method used for wind loading. EN 12899 will not be available as we have selected (in step 6) that significant orography is included in the environs. This is OK as using Eurocode 1 results in often significantly lower wind loads. It is also possible to specify a fixed wind load if you have been given this by a client or structural engineer for use for all proposals when this environs is selected.
- You can now save and finish to exit the wizard. Select the new environs form the Environs Manager or from the ‘Proposal’ pull-down menu item.