Patch Loads (prior to 2019)

Patch loads are applied in a similar fashion to line loads. Patch loads can be placed over an area loading panel or a number of panels. The resulting forces due to their load will be resolved, according to the direction of span, to the supporting boundary members.

The corresponding patch load diagram depicts what each of the four fields – A, B, C and D – represent. The red line along the bottom indicates the selected member from which you specify the patch load start and end points.

The fields B and C together represent the starting corner of the patch load, measured from the start of the selected member, in the XZ plane. Fields A and D represent the opposite corner of the patch load, measured from the start of the selected member, in the XZ plane. Note that A and B start from the centre line of the selected member.

Notes

If your patch load, or part of it, lies beyond the bounds of the area loading panels, the portion of load beyond the boundary members will not be taken into account

Opening the Patch Load Editor

1.Open the Area Loading Editor

By default, the Area Loading Editor should open on the “Area Loading Panel Groups” tab. The Patch Loads button is the fourth button to the right of it.

1.Click the Patch Loads button

Adding a Patch Load

1.Open the Patch Loads Editor

2.Click the Add New Group button to create the group

3.Provide a title for your new patch load group

4.Click the Add/Remove Items button

5.Click on a member from which you want to apply the patch load

6.Specify a start point for your patch load by providing a value in the B and C textboxes

7.Fields A and D represent a length from the start point of the member to the end point of the patch load – provide a value for both to establish your patch load definition

8.Under the Load Intensity area, you have the option to specify up to four different types of load and their magnitudes

a)You can rotate through the available load group letter denominations

b)Apply a value to each load group denomination using the adjacent textbox and separating values with a semi-colon (;)

9.With the patch load defined, you can click other members onto which this patch load definition will apply

          Notes

The nodal coordinates can be useful when determining your start point and the length and width to the end point of the patch load. To switch them on:

•From the Nodes and Coordinates category in the menu, enable node coordinates in the X and Z directions

When applying a load intensity, the specified load will apply to the group number specified under the alternate load groups area

•For example, if you set the load group letter denomination fields to D, L, A, G, and you have set the corresponding alternate load group number to “Load Group D3 L3” (i.e. load group number 3), the load intensity values will apply to D3, L3, A3, G3 only

Snow Drift Loading

On the roofs of buildings it is often necessary to consider snow drift loading either in roof valleys or behind parapets, for example. The snow drift is usually triangular in shape, starting from a max depth and reducing to zero part way up the roof pitch. Whilst triangular loading is not available within the area loading options, an alternative approach would be to add patch loading in strips across the roof. Each strip would have a higher intensity until the maximum value is reached, a series of stepped loads rather than a true triangular load.

How to develop this loading?

Create a patch (strip) load along the lowest point of the valley and give it the highest intensity of snow drift loading, eg, a live load of 3.0 kN/m2. Select one of the members to be the reference member from which the dimensions start.

Create another patch load to produce the second strip up the roof altering the dimensions where necessary and the snow load intensity, eg, a live load of 2.0 kN/m2. Create a third patch load further up the roof and give it the lowest intensity, eg, 1.0 kN/m2.

Finally, repeat the procedure for the opposite side of the valley to produce loading similar to that shown below.

Picture of patch snow loading strips decreasing in intensity up the roof slope.