Author: Pon Dhileepan
Lysaght Zed sections feature one broad & one narrow flange, sized so that two sections of the same size fit together snugly, making them suitable for lapping.
The table below from the lysaght catalogue clearly shows the difference in sizes of each flanges.
The purlin bolts are always placed equidistant from the centre & hence the steel modeller does not have to worry about whether the broad flange of a purlin comes at top or the narrow flange. The broad & narrow flanges will be placed alternatively at the site. This is the case for almost all the times.
But very rarely, there might be additional bolts/holes at the top flange or bottom flange and the steel modeller has to consider modelling the purlins with their exact orientation i.e, whether broad flange of a purlins comes at top or the narrow flange.
For instance, the below design demands for M12 bolts or hook rods from the top flange of the Zed purlin to support the nearby gutter. Hence the modelling has to be precise about the broad flange & narrow flange for each purlin in a continuous row.
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