SPECIAL FRAMING We have, in the preceding pages, considered the framing which enters into a building of light construction, such as an ordinary dwell ing house, but there are certain classes of structures which call for heavier framing, or framing of special character. Among these may be mentioned battered frames, or frames with inclined walls; trussed partitions; inclined and bowled floors; special forms of reinforced beams and girders; the framing for balconies and galleries; tim trusses, towers and spires, domes, pendentives and niches; and vaults and groins. These subjects will now be taken up and dis cussed, and the methods employed in framing such structures will be explained.
Battered Frames. Sometimes it is necessary to build a structure with the walls inclined inward, so that they approach each other at the top, and so that the top is smaller than the bottom. This is the case with the frames which support water tanks or windmills. An elevation of one side of a frame of this kind is shown in Fig. 211 with a plan in outline at C. It will be seen that the corner posts A A are inclined so as to approach each other at the top, and that they are not perpendicular to the sill at the bottom. This means that the foot of the post, where it is tenoned into the sill, must be cut on a bevel, and the bevel must be cut diagonally across the post, from corner to corner, since the post pitches diagonally toward the center, and is set so that its outside faces coincide approximately with the planes of the sides of the structure as indicated in the plan shown in Fig. 212. The girts B, Fig. 211, will also have to have special bevels cut at their ends, where they are framed into the posts.
After a corner post has been cut to the proper bevel to fit against the sill the section cut out at the foot will be diamond shaped, as shown at A B C D in Fig. 212, which shows a plan of one corner of the sill. It will be noticed that the faces A B and A D of the post do not coincide with the edges of the sill A F and A G. If the struc ture is merely a frame and is not to be covered over with the board ing on the outside, it is not necessary that the outside faces of the post should coincide exactly with the planes of the sides of the structure, and in this case posts of square or rectangular section may be used, with no framing except the bevels and the mortises for the girts. If, however, the frame is to be covered in, the post
must be backed in order that it may be prepared to receive the boarding.
The backing consists in cutting the post to such a shape that when the bevel is cut at the foot, the section cut out will be similar to that shown at E B C D in Fig. 212. The backed post must then be set on the sills so that the point E will come at the corner ,1 The face of the post E B N611 then coincide with the face of the sill A F. The post should be backed before the top bevel is cut because setting it back the distance AE may make a difference in the required length between bevels. If the post is of square section before backing it will have, after backing, a peculiar rhombus-shaped section, as is shown at A in Fig. 212. here II IJK shows the original square section, and L I J K shows the section after backing. These sec tions are taken square across the post perpendicular to the edges.
Fig. 213 shows how the foot cut for the inclined post may be obtained by using the steel square. In Fig. 211 it will be seen that the post A slopes toward the center in the elevation there shown, and it likewise slopes toward the center in the other elevations, either with the same pitch or with a different pitch. The result of the two slopes is to cause the post to slope diagonally. It is an easy matter to find the pitch in each elevation since it depends upon the size of the base and top, and the height between them. We then have the two pitches, the combination of which gives the true pitch diagonally; they can, however, be treated separately. The square may be applied to the post, as shown in Fig. 213, with the rise on the blade and the run on the tongue, and a line may be drawn along the tongue. The post can then be turned over and the pitch shown in the other elevation may be laid off on the adjacent side in the same way, with the rise on the blade and the run on the tongue of the square. Thus a continuous line A BCD may be drawn around the post and it can be cut to this line.