Frangible Coupler Designs

Transpo Industries manufactures a series of breakaway systems for ground-mounted sign supports, marketed under the trade name Break-Safe. The Break-Safe system uses frangible couplers and is available for U-channel, both concrete footing and direct burial; 3-in to 4.5-in (75-mm to 115-mm) round pipe; 3-in to 5-in (75-mm to 127-mm) square

tube; and wide-flange and standard beam shapes. Schematics of Transpo Industries concrete base and the direct burial system for back-to-back U-channel are presented in Fig. 7.47. Figure 7.48 shows the Break-Safe system for square-tube and round-pipe supports [33].

The Break-Safe has a number of advantages over slip base designs. One advantage is that the critical torque requirements of the slip base bolts are eliminated by the use

of frangible couplings. There are retrofit kits available, for wide-flange and standard beam supports, that use the existing slip base anchor to convert to a frangible coupler design. Another advantage of the Break-Safe system is that the concrete base installa­tions do not require a protruding stub. This decreases the probability of snagging the undercarriage of an impacting vehicle, and damage to the anchor system itself. The protruding stub is eliminated by bolting the frangible coupling into anchors placed in the concrete footing. Proper assembly requires that the anchors be accurately placed for each type of support system. Accurate anchor placement requires the use of an installation jig similar to Fig. 7.49 [33]. The anchor spacings, dimensions A and B in Fig. 7.49b, vary with the type and size of sign support being installed. Frangible and load concentration couplers (Fig. 7.22) usually perform satisfactorily when struck from any direction (they are multidirectional).