[A lintel is the stone which covers a door or window opening, and which, therefore, acts as a beam. They are often designated by stonecutters by the term "cap."] When it is necessary to use rather a long lintel in a stone wall the ashlar above the lintel may be arranged so as to relieve the lintel of some of the weight, as shown in Fig. 94. If the wall above the lintel is of brick a relieving arch may be turned, but this generally detracts from the appearance of the building, and the best way to strengthen the lintel, when the length does not exceed 6 feet, is to let it rest on a steel angle bar the full length of the cap, as shown in Fig. 95. When the width of the opening is more than 6 feet the lintel should be supported by steel beams, as shown in Figs. 96 and 97. A single beam, as in Fig. 96, may be used where only the weight of the lintel and its load is to be supported, and two or more beams where the whole thickness of the wall and also the floor joist must be supported.
When the lintel is the full thickness of the wall, and any steel support is undesirable, the strength of the lintel may be increased, if of a stratified stone, by cutting the stone so that the layers will be on edge, like a number of planks, placed side by side. The ancient Greeks and Romans often cut their lintels in this way, and apparently for this reason.
In placing windows in a brick or stone-wall the designer should be careful to arrange them so that they will not come under a pier. This is not apt to happen in the front of a building, but it sometimes happens on a side or rear wall, where the windows are placed to suit the interior arrangement and without regard to the external effect.
If a door or window must be placed under a pier or high wall steel beams should be used to support the wall above and also the lintel. Many broken lintels are evidence of a too frequent neglect of this precaution.
Another point that should be carefully considered in laying out the stonework is building the ends of caps and sills into piers. If the pier extends through several stories the joints will all be slightly compressed and the masonry will settle some, and if the ends of the caps and sills of the adjoining windows are solidly built into the piers they are very apt to be broken as the pier settles.
Fig- 97. - 3/8-inch Steel Plate Riveted to Beams.
The best arrangement is to keep the caps and sills back from the face of the pier, and either build pilasters against the pier to receive the caps and sills, as shown at A, Fig. 98, or else build the ends of the stones into the pier in such a way that they can give a little. When the cap is back from the face of the pier this can easily be done.
Lintels should have a bearing at each end of from 4 to 6 inches, according to the width of the opening. It is better not to build the ends into the wall more than is necessary to give a sufficient bearing.
Composite Lintels. - Very often it is desired to place a stone lintel over a store window 10 or 12 feet wide. To procure such a lintel in one piece is, in many places, impracticable, and it is therefore necessary to build the lintel up in pieces. When such is the case at least three stones should be used, and the end joints should be cut as shown in Fig. 99. Cutting the stones in this way binds them together better, and also gives the appearance of being self-supporting. A greater number of stones, say five or seven, may be used if preferred, but the joints should be cut in the same way. Such lintels should always be supported by steel beams, either as shown in Fig. 96 or Fig. 97.