Among the jobs that the erector is often called upon to perform is that of patching or repairing pieces that have cracked or broken. [Fig. 2566] represents a case of this kind, the fracture being at d. The principle to be observed in work of this kind is to cause the bolts to force the fractured pieces together, so that the irregularity or crookedness of the crack, as at d in the figure, may serve to lock the pieces together.
Fig. 2567.
Suppose, for example, we were to put on a patch p, [Fig. 2567], and there would be but little to prevent the crack from opening under severe strain, and the patch would stretch, permitting the crack to open and finally causing the bolts to break or sheer off. A preferable plan, therefore, is to put two patches on the sides in the following manner:—
Fig. 2568.
The holes should be drilled through the beam and the plates held against the beam so that their holes may be marked by a scriber passed through the holes in the beam. The holes in the plates should be drilled closer together than those in the beam, so that when driven in they will serve as keys to close the two sides of the crack together, as shown in [Fig. 2568], where it is seen that one side of the bolt bears against the holes in the patch and the other against the holes in the beam. To facilitate getting the bolts in place the plates may be heated so as to expand them.