Iron roofs covering railway stations, sheds, etc., very frequently rest either one or both sides on the heads of iron columns.

The attachment of the foot of the rafter to the head of the column is effected in several different ways; one or two of which will now be described.

Fig. 303 shows the head of a column supporting a small roof. The shoe, s, which receives the foot of the rafter, is cast in one piece with the column. The swan-neck bend, b, receives the water from the gutter, g, and conveys it into the column, which acts as a down pipe.

Fig. 304 is a side elevation, and Fig. 305 is a front elevation, showing the method by which the roof described in page 157 is supported.

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Fig. 303.

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Fig. 304.

Fig. 305. Scale,  inch = 1 foot.

Fig. 305. Scale, inch = 1 foot.

1 Humber's Record of Modern Engineering, 1866.

In this case the chair, s, is a distinct casting, and bolted on to the girder close to the head of the column.

The intervals between adjacent columns are spanned by cast-iron girders, G, the ends of which are swelled out and brought round so as to grasp the head of the column.

On the ends of these girders are cast burrs, b, and round these is a coupling link, c c, of wrought-iron, so as to hold the girders together.

In this case the gutter, g, discharges through the socket d, down the interior of the column.

The socket prevents the chair from being placed immediately on the head of the column ; it is necessarily a little on one side, as shown at s, which theoretically is a bad arrangement, as it causes an extra bending stress upon the girder ; practically, it is so close to the support that this does not very much matter.

Wind Ties are long rods passing from the foot of a principal rafter diagonally across three or four trusses, to which they are secured, until they reach the ridge; they are generally arranged so as to converge in pairs, as shown in Fig. 306, and should be furnished with union or cottered joints, so that they may be adjusted as to length: these joints are not shown in the figure. Details showing the connection of the wind ties to the rafter are given in Fig. 327, Plate VII.

Such tie rods should be fixed to all large iron roofs, to secure them against the effects of gales blowing at an inclination to the length of the roof.

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Fig. 306.

They are hardly necessary when the gables of the building are of solid masonry, but in many cases, even when the roof is not hipped, the gable end is merely filled in with glass, and they are then required.