The portion of the principal next the wall is shown in Fig. 280, while the central portion of the truss, with its lantern and skylight, is shown in Fig. 281.

This principal is composed of a tee steel top or compression member and flat bar tie or tension member, while the bracing consists of tee steel struts and flat bar diagonals.

The details of connections of these members are shown in Figs. 282, 283, 284, and 285.

Scale 1½ inch = 1 foot.

Fig. 296. Scale 1½ inch = 1 foot.

Scale¾ inch = 1 foot.

Fig. 297. Scale¾ inch = 1 foot.

The end shoes (in this example of a very simple type) and their seatings upon the walls at either end are shown in Figs. 286 and 287, and also in elevation in Figs. 288 and 289.

The skylight and ventilator are of a type similar to other examples described in this chapter.

The central cast-iron standard is shown in elevation in Fig. 263, and the side standard, carrying the galvanized wrought-iron louvre blades in Fig. 261, the detail of the cast-iron sill forming the lowermost member of the ventilator, and which forms a drip over the junction of the zinc roof covering at this point, being shown in Fig. 267.

Scale 1½ inch = 1 foot.

Fig. 298. Scale 1½ inch = 1 foot.

Scale 1½ inch = 1 foot.

Fig. 299. Scale 1½ inch = 1 foot.

In contradistinction to a principal with flat bar main tie, above described, we may now consider an example of the older fashioned type of truss with round rod ties. The variation in modern practice from this form of tie has been already discussed in the previous paragraphs of this chapter.

In Fig. 290 we have the side elevation of the shoe of a roof principal of this type, with round rod tie and keyed and Cottered connections. The shoe in this case rests upon the upper flange of a lattice girder, and the plan is shown in Fig. 291, which also gives further details of the key and cotter. The arrangement at the wall end of the same principal is shown in Fig. 292.

Scale 1½ inch = 1 foot.

Fig. 300. Scale 1½ inch = 1 foot.

. Scale 1½ inch = 1 foot.

Fig. 301. . Scale 1½ inch = 1 foot.

The bracing ties being also of round rod section, the details of connections become modified accordingly, as compared with a riveted flat bar detail, and are shown in Figs. 294 and 295; the strut, being of a form frequently used in small spans of this type, and consisting of a pair of flat bars kept apart by cast-iron distance pieces riveted through, is shown in elevation in Fig. 296.

Scale 1 inch = I foot.

Fig. 302. Scale 1 inch = I foot.

Scale 1½ inch = 1 foot.

Fig. 303. Scale 1½ inch = 1 foot.

The normal section of valley gutter at AB, Fig. 297, partly-indicated in Fig. 290, is more fully shown in Fig. 250. The flanged connection, made in rust cement and bolted, is shown in elevation in Fig. 251, and the side elevation of the gutter is shown in Fig. 297, which shows the position of the flanged joint of the gutter with respect to the principal, the connection being made a few inches away from the truss, which simplifies detail and offers facilities in erection.

The detail of flanged connection to the wall gutter is shown in Kg. 259.

The roof principal shown in Fig. 216, in connection with the assemblage of columns and traveller girders, etc., there shown, is composed entirely of angle steels, the upper member consisting of two angles, the lower or tension member also of two angles and the bracings of single angles. The connections are all riveted.

The details of this truss are shown in Figs. 298 to 307 inclusive.

Fig. 298 shows the connection of a pair of principals, supported on the upper flange of a lattice girder (shown in detail in Figs. 81 to 101 inclusive), with their shoes and the valley gutter resting upon the backs of the principals. The shoe at eaves gutter is shown in Fig. 299, in plan in Fig. 300, and in sectional elevation in Fig. 301, the general arrangement being indicated in Fig. 302.

Scale 1½ inch = 1 foot.

Fig. 310. Scale 1½ inch = 1 foot.

The detail at apex of principal, showing foot of central cast-iron standard, connection of ridge purlin, etc., is given in Fig. 303.