Approved Single Supports for Multiple-Support Assemblies

There are few single-support systems that can be buried directly and provide accept­able multiple-support performance upon impact. Two such systems are dual 3-lb/ft (4.5-kg/m) U-channel and dual 4-in X 4-in (90-mm X 90-mm) shaped wooden posts. The majority of single-support adaptations to multiple-support assemblies require the use of anchor pieces and breakaway designs. Triple supports consisting of 1.75-in X 1.75-in (45-mm X 45-mm) square perforated tube and triple 2.5-lb/ft (3.7-kg/m) U-channel

NOTE:

RECOMMENDEO TORQUE

ON SUP BASE FLANGED

HEAD BOLT & NUT IS 54 Nm

KEEPER

PLATE

760

kzoo-э!

FIGURE 7.23 Acceptable slip base breakaway device for multiple-square-tube sign assemblies. Dimensions shown as mm. Conversions: 200 mm = 8 in, 760 mm = 30 in,

54 N-m = 40 ft-lb.

are acceptable when installed with an anchor and breakaway design. Manufacturers are developing devices that enable the use of heavier supports for acceptable multiple — support systems. Figure 7.23 presents a slip base breakaway assembly for square-tube supports manufactured by Unistrut Corporation, which is acceptable for three 2.5-in X 2.5-in (64-mm X 64-mm) supports within a 7-ft (2100-mm) path [32]. The bottom subassembly is inserted into a 30-in (760-mm) anchor piece and placed in an 8-in-diameter (200-mm), 30-in-deep (760-mm) concrete foundation.

Multiple supports for large signs are often constructed as slip base designs with galvanized steel wide-flange (W) or American Standard (S) shapes for the sign support. These shapes, depicted in Fig. 7.24, are designated by their depth and unit weight or mass. For example, a W150 X 18 is a wide-flange shape with a depth of 6 in (150 mm) and a unit weight (mass) of 12 lb/ft (18 kg/m).

Multiple-support-sign assemblies that are constructed of W and S shapes are fre­quently designed with frangible or load concentration couplers. The behavior of these designs is similar to slip bases except that, instead of the base slipping from between the bolts, the couplers, which are used in place of the bolts, break at impact.