Props

Long span portals often use intermediate props to reduce the span and so save on steel.

Props can be added to frames by specifying the span number and distance to the props in each span.

1.Select the section size and alter the base level if necessary.

2.Define the base fixity (it defaults to 0%) – you can alter this to any value between 0 and 100% (fully fixed). Again this is only applicable if the 'As is' option has been selected in the General input tab.

3.Release the top of the prop if required – the connection defaults to fixed.

4.If there is a mezzanine floor in the frame, you can define whether the prop stops at mezzanine level or continues up to the underside of the rafter.

As with most entries in the table, an empty cell will indicate that the parameter will follow the entry in the cell above.

If you have In-bay Symmetry selected, you need only enter data for one side of the frame. The opposite side of the frame will be automatically mirrored. Similarly, if Global Symmetry has been selected, the spans will be mirrored about the centre of the whole frame.

Using these features is demonstrated by the diagram below, were only two entries are required. The first entry places props symmetrically in the first span at 8 metres from either side. These props are then mirrored globally into the third span. The second entry adds props symmetrically into the second span. If the props are in the same position in all spans, you can enter the span number as “1, 2” in the first entry, and the props will be defined for all 3 spans.