Wind Panel Loading (Pro)

Introduction

The Wind Panel Loading function when applied to a frame, automatically calculates and applies the weighted external pressure coefficients “Cpe” to be used with each wind loaded panel for each wind direction specified.

The value of Cpe is dependent on the wind surface angle to the horizontal, the angle between the wind direction and the normal to the wind surface and the wind zone depending on the position of the member within the wind surface and the building as a whole, the typical wind zones from BS 6399 Pt2 are:

A-D and H-K for walls and inclined walls

A-G and X-Y for flat roofs, and

A-J and K-S for monopitch and duopitch roofs.

EC design uses similar lettered zones around a building.

Adjustments are automatically made for corner angles, funnelling effects 0.25b to 1.00b, re-entrant corners and both narrow and wide recesses.

The program will dynamically change all Cpe values for any changes you make to wind directions at any time. All angular values and all member zoning locations are dynamically determined by the program. To ensure maximum flexibility you will however be able to overwrite some or all of these values.

Once a site has been identified in UK or Ireland from the site data maps or wind pressure site data has been manually entered for sites outside the British Isles, the program combines the site dynamic wind pressure with the local Cp values to determine the actual wind pressure on each panel of the building for each of the specified wind directions. These pressures are distributed on to the individual members of the frame as local loads prior to analysis of the frame.

Applying Wind Loading Panels to a Frame

The wind loading is applied to the frame through a series of steps;

1.Specify the wind directions and internal pressure and suction coefficients.

2.Set up the wind loading cases automatically.

3.Select globally wind loaded members on which the wind load reduction will apply.

4.Select the wind site from the UK and Ireland map to obtain local data.

5.Apply the wind panels to the walls and roofs of the building model.

6.Identify ‘bracing’ or non-directly wind loaded members, eg, wall or roof bracing.

Wind Directions

Up to 8 wind directions on the frame can be considered using the load groups W1 to W8. The direction of the wind is defined based on the angle with the frame’s global X axis. For example W1 to W4 could be used to define four principal wind directions, 0, 90, 180 and 270 degs for a rectangular shaped building. The angle between the frame Z axis and magnetic North is specified in the ‘Angle to North’ text box. If the ‘Draw Global Axis’ icon is on, then the global axis symbol at the bottom right of the screen graphically indicates the North direction in relation to the frame global axis.

Tip – you can double click on the ‘Ang. With X’ label to automatically introduce the principal axis values. Similarly, double clicking on the ‘Int Pres Co.’ or ‘Int Suc Co.’ labels will introduce basic coefficients of 0.2 for internal pressure and 0.3 for internal suction. Note that you don’t need to place a minus sign in front of the 0.3 since it has been designated as a suction coefficient.

There are several wind methods available in the design codes. The particular method you wish to use can be selected in the ‘Method’ box.

There is also an option here to use the ‘User Defined’ method. In selecting this option, a table opens up to enable you to enter your User Defined Values for the site. These will be used as the dynamic wind pressures for the various heights of your building. Note that the dynamic wind pressure ‘q’ is entered in units of Newtons per metre squared (N/m2), not kN/m2 as would often be the case. This is so the values line up with those used internally within the site data module. Wind reduction factors can be added for various wind diagonal lengths.

There is also an option to 'Use maximum wind pressure in all directions' which is useful if you do not know the orientation of the building at a preliminary design stage.

With a canopy you can use the overall values from the codes or use the local zone values. Leave the box unchecked to use the overall values from BS6399, tables 13 & 14 or EN 1991-1-4 tables 7.6 & 7.7.

Determination of Cs and Cd factors for wind.

The structural factor CsCd takes into account the effect on wind actions from the non-simultaneous occurrence of peak wind pressures on the surface (Cs) together with the effect of the vibrations of the structure due to turbulence (Cd). For further detailed information see section 6 of EC1-1-4 and associated National Annex.

In the wind loading input area the CsCd factor can be directly entered by the user or, alternatively, the program can evaluate the CsCd factor based on the building type. Select the type of building from the droplist in the MasterKey Wind Loading panel. The program will calculate the CsCd based on the UK NA.

Wind Load Case Generation

Wind loading cases can be automatically generated for all wind directions and local/overall wind situations (wind diagonals in the BS code). These include dead, live and wind combinations in both ultimate and service conditions.

See Auto Generation of Load Cases on how to generate these wind loading cases. This will generate a set of load cases which includes the W1 to W8 wind directions. There will also be a full set which will include the internal pressure coefficient. These will show a ‘P’ load group instead of the ‘W’ load group in all these combinations. Similarly there will be another set including the internal suction coefficients shown as the ‘S’ load group.

Wind Load Reduction Members (Wind Diagonals)

In EuroCode wind design, individual members can be specified for local or overall wind effects. (Wind diagonals are only relevant in British Standard design and have a similar function).

This option has the effect of designing the members which are locally loaded by wind (such as cladding members) for a larger wind pressure than members which are globally loaded by wind, e.g. vertical bracing members.

By default it is assumed that all frame members are being designed for local wind effects. If there are members in your frame that you want to be only considered for overall wind, eg, bracing members, you can place these members in the Wind Load Reduction groups.

Select ‘Wind load reduction on globally wind loaded members’.

On the frame, click on the members on which the wind load reduction will apply.

Note that the overall wind effect factor is the CsCd (user specified per wind direction) multiplied by the lack of correlation factor (automatically determined). The CsCd factors are set in the wind directions table. Also ensure that wind loading cases set as ‘Overall Wind Loading’ in the load combination area are in place.

In BS design the wind diagonals are picked from the frame and given a wind diagonal dimension - this value can be an average dimension to cover a number of elevation diagonal lengths. It works in a similar way to the EC method above.

Wind reduction factors can also be applied to the local wind on selected members which take wind from a large area, for example, portal rafter members where the wind area could be (say) 20m long by 7m wide giving a local ‘a’ diagonal value of 21.2m, rather than the default value of 5m. For further information on how to apply to local members only select this technical note.

Selecting the Wind Site Data

You can select the site data from the Wind Site map by clicking on the button in the right hand panel or from the Loads > Wind Panel Loading (Pro) > Site Data Wind Analysis menu.

Once in the site data you can select the particular site for your building by;

1.Picking the site location from the GB site map

2.Picking the site location from the Irish site map

3.Manually inputting the national grid reference NGR

4.Inputting the site’s Eastings and Northings

You can examine the wind pressure values calculated by scrolling to the bottom of the output screen. You will see that wind pressure values are determined for the different heights in the structure, for each wind direction specified and also for each wind diagonal.

Select File> Exit MasterKey Wind Analysis, to take you back into your model. The dynamic wind pressures for the site will have been automatically applied to your model on exiting the Wind Analysis.

For a building outside of the Britain Isles click on the ‘Set Default Site’ button in the Site Data tab, then enter the relevant site data as described in Site Data Wind Analysis – Background section below.

For additional information on the site data, local obstructions, fetches and topography see Site Data Wind Analysis – Background section.

Setting Up Wind Panels

Basics

The Wind Loading facilities in the Loads menu enable the application of an area load in the direction normal to any planar surface. Similar to area loading, the wind loading is controlled by wind loading panel groups. Each wind loading panel group defines one planar surface and contains the following information.

4.All the wind panels in the planar surface

5.Up to 8 different wind load intensities on the surface, using wind load groups W1 to W8, representing eight different wind directions. Each group applies a uniform load intensity to its surface.

3.The side of the surface on which the wind loading is applied

4.The load distribution characteristics on the surface, i.e. one way or two way spanning.

The wind zones and coefficients of external pressure are automatically calculated for each wind direction on each surface. The dynamic wind pressure is then calculated by the MasterKey Wind Analysis module to arrive at the wind loading on the surface.

When we access the Wind Loading with a file where no previous wind loading has been applied, an empty wind load group is present. Each wind loading group applies to one planar surface. Each planar wind loaded surface of the building should have a separate group.

The Basic Rules of Wind Loading;

3.Each wind load group applies a uniform wind load intensity normal to a planar surface

2.A wind load group can only apply to one planar surface

3.All the members that define the panels in a planar surface should be added to the wind load member group. This is different from the gravity area loading application method where only the loaded members are added to the group. The wind loading calculations determine which members of the panels are loaded and which are not according to the direction of span.

4.Unlike the gravity area loading method, bracing members do not need to be defined in a special bracing group, rather they are simply not added to the wind loading group and therefore do not affect the distribution of wind area loading.

5.A member can belong to more than one wind load group.

6.A panel must have three or four straight sides. A straight side of a panel can be made up of any number of individual elements.

Wind Loading side panel

All the utilities required to set up wind panels are contained in the right hand panel. We will take a quick look at their functions.

Switches on the wind loading module

Gives access to the Wind Diagonals input screen

Gives access to the Bracing Members input screen

Gives access to the Wind Directions screen

Takes you to the Wind Site Data area

Allows you to add or remove items

Find panels

Add a new group

Clear current group / clear all groups

Delete current group / delete all groups

Pick panel or members to create wind surface

Fast select panel / automatically create all panels

One way or two way spanning panel

Direction of span of panel, horiz, vertical or shortest direction

Rotate the span direction to an angle or align with a member

There are a few tick box options relating to the wind panels;

Wind on both sides (Parapet)/(Canopy) – if a panel is outside the envelope of a building, eg, a canopy or wall parapet, the program will assess the coefficient of force for that panel, taking account of wind being applied to both sides of the panel.

Note that canopy panels should be applied along each side of a building separately as individual rectangular shaped panels. Do not apply a single panel around the whole circumference of a building roof as this will adversely affect the coefficients used.

Close open sided wind panels – automatically closes open panels.

Swap direction of red normal lines – the red lines perpendicular to a panel indicate the external face. If required you can swap the direction of the red normal lines so they are in the opposite direction.

Create panels from all selected members.

Ignore Wind Loads on Dummy Members – dummy members are sometimes used to close panels. Any wind spanning on to a dummy member is split half and half between its ends and applied as point loads to the structure. You can choose to ignore the wind on dummy members where relevant.

The wind zones, coefficients of pressure and dynamic wind pressures are automatically calculated within the wind analysis module when the panels are applied to the envelope of the building. Therefore the Load/Cpe table will remain blank. You can override the automatically calculated values, if required, by typing in your own values for any of the Cpes, zones, funnelling effects and angles between surfaces (beta angle).

Note that gravity dead and live loads can also be added to panels within the Load/Cpe table. This is especially useful, for example, on multi-faceted roofs, saving you having to add area loading panels to these area and so saving double working.

Update all panels for their interaction

Reset titles for each panel automatically

Draw all wind loading panels

Colour code wind loading per surface/intensity

Copy brief to clipboard

Paste brief from clipboard

See below for further information on combining panels and resetting titles.

Adding Wind Panels

Switch to the Add/Remove button and then choose a selection mode. You can either;

6.Pick individual panels off the frame. As you move the cursor over the frame individual panels will be outlined in cyan. These can be added to the current group. Panels that have already been placed in a wind panel group will have a dark blue outline to distinguish them from unpicked panels. Add a new group for a new planar surface.

2.Pick individual members off the frame. All the members around the perimeter of a panel should be selected. The outline members will show in red. Once the outline has been closed the panel should highlight in colour. The red lines perpendicular to the members of the surface indicate the side that the program sees as the outside face of the panel.

Note – in both the above options you can also window around panels/members to include them.

3.The fast selection of wind panels option not only allows you to pick a panel, but will automatically add a new group each time a panel is picked speeding up the process.

4.Use the Auto All option to allow the program to attempt to automatically apply wind panels to the envelope of the whole frame. You must ensure the perimeter of the frame has been split into rectangular and triangular panels for this function to work well. Dummy members may need to be added in locations to facilitate this.

Ideally you want the complete external envelope of the building to be closed in by wind panels. Hence the program, when assessing the wind zones, can distinguish between the interaction of adjacent panels and so produce the most accurate wind loading around the building for each wind direction being considered.

Check the application of the wind loading around the building using the Wind Load display buttons in the top toolbar – see chapter on Getting Started. Show the panels and their pressure values for each wind direction. Positive values will be external pressures (usually coloured yellow) and negative values will be external suctions (usually coloured green).

Combining panels

You can combine panels so that 2 or 3 or more panels in an elevation or roof can act together. However, these panels must all be in the same planar surface.

For example, if a side elevation has a part of the elevation spanning vertically and part spanning horizontally, these would have to be defined as 2 separate panels. Since they are in the same elevation you want them to interact to give their true wind zones and relevant Cpes. Thus you would combine these 2 panels.

Whilst in one panel, click on the ‘Select Panels to Combine with’ button and then click on the second panel. Both panels should highlight in colour but only one panel will show the red perpendicular lines (indicating the outer surface). When the program examines the envelope of the building these 2 panels will be considered to act as one, even though their span directions are different.

Update all panels for their interaction

After adding new panels you can have the program update the interaction of all the panels. In doing this the program will reassess the interaction of the various panels around the building envelope and will update the zones and Cpe values.

Reset titles

Each panel title can be entered by the user or alternatively you can let the program set its own titles. Allowing the program to set the titles automatically means that the panel interaction has been automatically assessed and a relevant title based on its orientation and position within the structure attributed to each panel. The title will have an ‘@’ symbol in front of it.

After alterations or additions to the panels, the panel titles can be updated by clicking on the ‘Reset Titles’ button.

Bracing Members

You can access the bracing members option from the button in the top right panel or from the Loads > Wind Panel Loading (Pro) > Bracing Members menu.

These bracing members are members in panels that are not directly loaded with wind loading, eg, bracing members in a roof or external wall panel.

1.Click on the +/- button to pick members.

2.Select the members that are to be bracing members.

Viewing Wind Loads

Wind Loading panels can be displayed graphically using the Wind Load icon. The Direction drop list will allow you to select which wind direction you wish to view the wind intensities for. W loads are due to wind intensity based on Cpe values, P loads will also include the internal pressure coefficients and S loads will also include the internal suction coefficients.

On the graphical display of the wind you can show the ‘Cp’ values across the model, or alternatively the actual wind pressures ‘Q’ or wind zones ‘W’ applied.

Wind loading on members can be displayed using the Frame Loads icon in the top toolbar – see section on Viewing Loads on how to use this function.

Site Data Wind Analysis – Background

The MasterKey Wind Analysis Site Data is based on a third party piece of software that integrates seamlessly with MasterFrame (Pro). In the Site Data interface there is the main map of the UK or Ireland alongside a more detailed local map. There are also 2 circular diagrams based on the chosen site location, one indicating your structure surrounded by 30 degree segments and the distances to sea, country and town displayed in blue, green and red. The second diagram indicates the distribution of wind pressure around your structure. Below the main maps, the calculations are displayed.

Choosing a Site Location from the Wind Data Map

A location is chosen from the MasterKey Wind Analysis site data map for Great Britain or Ireland, or if outside these areas a default site can be set up to generate the wind pressures for a particular location. Pick a site directly off the map or enter the site grid references, if known, to get exact site information. (Note - grid references can be obtained from various internet sites, for example, www. multimap.com, based on the site address or post code.) You can also enter the eastings and northings, if known.

Accurate wind and topographical information is contained within the Wind Map database. This information is used by the program to obtain the wind pressures on a structure as it varies with height and orientation. Several wind diagonal lengths can be taken into account. The user can choose which analysis method to employ.

Site Data interface

The Site Data tab enables you to enter a title reference and select which map type to be the main graphic. You can choose between the GB site or Irish site maps. The grid references are shown here and can be manually changed if you know the exact grid references for your particular site. The basic wind speed and site altitude are given. The data for a particular site can be saved as an independent file for future re-loading (Save/Load Site to file). If the site is outside Great Britain or Ireland, you can set up a file containing a default (overseas) site, using the Set Default Site button. The site information for an overseas site is manually entered in the following tabs, so that the wind pressures can be accurately calculated.

The Site Data tab also allows you to specify the orientation of your building relative to the North, so as to ensure accurate application of the wind loading to the individual faces of the structure.

Obstructions Interface

If there are obstructions in the vicinity of the structure being examined, these can be taken into account by specifying the height of and distance to the obstructions at intervals of 30 degrees around the building. These are normally automatically entered from the in-built database, but can be overridden if desired.

If the orientation of the building is known, the UK Sd factors can be used to reduce the wind pressures around the building. If the orientation is not known or is outside the UK or Ireland, the Sd factors should be set equal to 1.

Sea/Country/Town Interface

Fetch distances and category types are automatically included when a site is selected from the Great Britain/Ireland map. For a site outside Great Britain/Ireland, the values can be entered manually for each orientation.

Topography Interface

The local topography can be taken into account resulting in modification of the wind loading. This can be done using the internal data within the wind map or altered manually.

There is an option to use the site altitude only to evaluate the wind loading ignoring the effects of local topography.

Report (Output) Interface

On the Report (Output) tab, the user can select which method to employ for the calculation of the wind loads – Standard, Hybrid, Directional or Designer’s Guide. Having settled on the appropriate method, the screen and printing output options can be selected. The basic wind speed automatically selected from the map may be changed if desired, as can the start and length of the season under consideration. Building floor levels and wind diagonal lengths can be changed from the defaults if necessary (note – when used in conjunction with MasterFrame (Pro), these values are automatically taken from the model). Select the risk period from the droplist. Finally the graphics scale and number of segments can be varied. The wind pressure diagram can be viewed for each wind diagonal length a, if applicable.