The truss shown in Fig. 12 is a type of timber truss that corresponds with the Fink type. It is unusual to construct this truss of timber, but the figure shows how trusses for small spans may be built of timber on these lines. The necessary connections and rigidity at the joints are obtained by the introduction of ornamental fish- or tie-plates, as illustrated. The true hammer-beam truss is shown in Fig. 13. This type is used in timber trusses for church construction. The truss proper extends above the line ab, which is the top line of the hammer beam; below this line, the construction may be considered as a brace or corbel. The upper part is FIG. 12 designed to support three purlins and a ridge pole, each of the intermediate purlins being supported by individual struts. The members c and d must be designed for direct stress and, in addition, for a bending stress, due to the fact that their axes do not coincide with the direction of the stress. In trusses of this character, sometimes a hammer beam is made in one piece and extended from wall to wall, while it is not unusual to use a tension member between the points g and h, hiding it by ornamental turned wooden covering. It is not unusual to support hammer-beam trusses of this kind on an arcade, which separates the nave of the church from the side aisle. When this plan is adopted the thrust at the foot of the truss can be carried back to the roof beam, as shown at i, which in turn transmits the thrust to heavily buttressed outside walls. 13. Gothic Trusses.-In Fig. 14 is shown a working drawing of a developed hammer-beam truss. At first glance it is not apparent that this truss is of that type, but further study shows that the members a b, bc, cd, and do are approximations of the curve of the typical hammer-beam truss and that the struts placed at bf and dg simply take the upward thrust of these members and thus eliminate the transverse stresses that would ordinarily occur in the curved me mbers of a hammer beam. The truss shown in the illustration is for a span of 68 feet, which is large for a truss of this character; its interior upper curve is in the form of a pointed arch. The form of the truss involves changes of stresses under unsymmetrical and wind loads, and therefore a combination of struts and tension bars must be used for some of the members. These combination members consist of two small pieces of timber with a tension rod between, as in the case of the member cd, which consists of two 5" × 10" yellow-pine pieces with a 2-inch rod passing between them and terminating in the cast-iron boxes shown. This method of construction is excellent and may be used in many forms of trusses. The cast-iron boxes may be made of any shape desired to accommodate the members meeting at a joint. They are arranged so as to be open toward the interior of the truss in order that no inconvenience is found in tightening the bolts. In some cases, where it is particularly difficult to do this, it may be necessary to use socket wrenches and a special form of spanner. The side webs of these boxes should be placed centrally with the members meeting at the joint; and in order to facilitate erecting, hexagonal nuts should be employed throughout. The purlins are fastened to the upper chord by means of -inch bolts that hold them firmly, while the ridge box is so designed as to conveniently carry the ridge pole that rests on it. Straps, or ties, are used at the ends of purlins meeting at any joint where no casting is provided, so as to secure abutting purlins together. The whole of this truss frame is incased so as to give the building an architectural finish. 14. Timber Trusses of Peculiar Design.—It is frequently necessary to build timber trusses to fulfil unusual conditions. Such a truss is illustrated in Figs. 15 and 16; it is applicable to boat houses, sheds, and barns. The general drawing for this truss is shown in Fig. 15, and in order that the construction of the building may be clear, the plan of the building and the contour of the ground are shown. The building is a large boat house, and therefore the primary object to be attained is that the floor space shall be open, |