Square Steel Tubes

Square steel-tube sign supports are used in many localities. They provide four flat sur­faces for mounting sign panels, facing different directions, without special hardware as required by some support types. Square-tube supports can be purchased from a number of manufacturers and are available with %s-in (11-mm) holes or knockouts at 4-in (25-mm) centers on all sides [26, 27, 28]. The square tubing is available in!4-in (6.4-mm) incre­mental sizes from 1.5 in X 1.5 in (38 mm X 38 mm) to 2.5 in X 2.5 in (64 mm X 64 mm). Maximum sign areas for various square-tube sizes and strengths are illustrated in Table 7.5.

Square tubing can be driven directly into the ground using a drive cap with sledge or power equipment. The performance of the support assembly upon impact, and sub­sequent repair, are enhanced by using an anchor base. Three common methods of installing a single square-tube sign support are presented in Fig. 7.13. Figure 7.13a shows a direct burial installation. Square tube up to a maximum size of 2.25 in X 2.25 in (57 mm X 57 mm) has been approved for installation by direct burial. The perfor­mance of square-tube sign supports upon impact is more predictable, and easier to repair, by the use of an anchor base system [29]. Figure 7.13c shows an anchor base system where a 36-in-long (900-mm) piece of square tube, one size larger than the anchor piece, is driven into the ground. This anchor piece is left protruding 1 to 2 in (25 to 50 mm) above the ground to permit bolting of the signpost. The signpost is inserted 6 to 8 in (150 to 200 mm) into the anchor piece and bolted in place. Figure 7.13b shows a device similar to the anchor base installation except that it uses an outer stiff­ener sleeve one size larger than the 36-in-long (900-mm) anchor base piece. The stiffener sleeve provides a double-walled thickness that reduces damage to the anchor piece. Upon impact, the post yields at the top of the anchor assembly, normally leaving it undamaged as in Fig. 7.14.

Square steel tubes with perforations on all four sides have been found to provide acceptable crash performance for sizes as large as 2.5 in X 2.5 in (64 mm X 64 mm) when embedded directly into the soil. They are acceptable in both strong and weak soil when embedded to a depth of 48 in (1220 mm). Repairing direct-embedment supports,

however, is more difficult than repairing the yielding breakaway system. The V-loc system from Foresight Industries can also be used as an anchor system for square-tube supports.

Figure 7.15 shows anchor systems for square tubing that are manufactured by Unistrut Corporation. Figure 7.15a shows a heavy-duty breakaway anchor for use with 2-in and 2.5-in (50-mm and 64-mm) square tubes. It consists of a /L-in-thick (4.8-mm) wall that eliminates the need for a stiffness sleeve and allows the signpost to break away on impact without damaging the anchor wall. Figure 7.15b shows an anchor post that can be driven directly into extremely hard or rocky soil conditions. It is made

from 1/4-in X 4-in (6.4-mm X 102-mm) steel angle section that can help stabilize the sign assembly in soil conditions that provide poor resistance to lateral and torsional forces. Figure 7.15c shows a stabilization anchor sleeve that helps adjust for inconsistent roadside gradients. The anchor rods help resist the environmental loads that can cause the signpost to lay over or twist in soft or shoulder dropoff conditions. The stabiliza­tion sleeve is installed over an anchor piece and the two rods inserted at a 45° angle to increase stability.

Figure 7.16 presents a soil stabilization anchor manufactured by Xcessories Squared [30]. The stabilizer is attached with a corner bolt, through the lower slots, to an anchor piece of square tube. The tops of the stabilizer piece and anchor are aligned and the

assembly is driven into the ground until only 2 in (50 mm) remains above the ground surface. After the bottom end of the signpost is inserted 8 in (200 mm) into the anchor assembly, it is secured with a corner bolt from the back side, through the stabilizer, anchor, and signpost.