Gable Columns

Data for the gable columns can be entered under the Gable tab.

The span number, distance and section size for each column can be entered, taking into account the in-bay and global symmetry to reduce the number of entries. If the Global Symmetry and In-Bay Symmetry buttons are being used, but you do not require the gable columns to be symmetrical, you can enter the distance to the gable column, followed by NN, YN, or NY to switch off the symmetries. For example, entering 7.5 NY for the X dimension would place a gable column as 7.5 metres from the left portal column. The N indicates that the column should not be mirrored globally, but Y indicates it should be mirrored in this span.

The beta angle for the column can be altered. The major axis of the column is assumed to be at 90 degrees to the main frame columns. The beta angle is changed by entering “1” in the beta field, to rotate it by 90 degrees (p/2), “2” to rotate by 180 degrees and so on.

The base level of the gable column can be altered if required. For drafting purposes, specify the top and bottom plate thicknesses.

If the gable end frame is to be designed as a beam and post rather than an end portal, the rafter ends can be set as pinned.

Tip - If you set the top plate thickness to a negative value, for example, -20 mm, the column will be separated from the rafter by that amount and will also assume a vertical slot type top connection. This means the gable column will not support the rafter, but will take horizontal wind load and transmit wind forces only into the rafter. Thus a gable frame can be entered as a full or half-bay portal frame, acting with portal action and not just as a beam and post type scenario.

You can omit a set of gable columns from the North or South ends using the last two data entry columns. Note that in the diagram below, the columns have been omitted from the north end in span two by typing “n” in the appropriate cell.

The main frame at each gable defaults to the same section sizes as the portal frames. To change the gable frame rafters and columns from these defaults, alter the values in the 'Change South Gable' and 'Change North Gable' to 'Y'. You can opt to have the South and North gables with the same section sizes - enter 'Y' in the 'North as South' data cell. Entering 'N' means the gables can be different.

Now move to the Columns tab to change the gable main columns section. Select the S Gable button to move to the south gable, altering the section sizes in the different spans. Do the same for the north gable.

Move to the Spans tab to alter the rafter sections for both the south and north gables.

Gable end bracing can be added by selecting the 'Gable Bracing' button on the 'Gable' tab. For further details on bracing see the Bracing tab info.