**1. Introduction**

The illumination of outdoor recreational areas, roadways, sidewalks, and parking lots is of the utmost importance at night. To illuminate these areas, different forms of poles are used to support an overhead light fixture. Typically, the best choice of material for these poles aluminum due to its corrosion resistance, lightweight, ease of joining, ease of handling and a high strength to weight ratio. Wind loads are often the prominent force that is applied to poles and can cause localized fatigue cracking at different areas interest [1, 2].

Modern fatigue design utilizes a lower bound S-N curve that is typically established from full-scale test data. Specimens usually contain some sort of stress concentration around a point or detail of interest. Stress concentrations usually occur around connections, cutouts, keyways, copes as well as other locations [3, 4]. One possible way to improve fatigue life would be to reduce the impact of these stress concentrations by minimizing abrupt changes in cross-section. This may be done by providing "smooth" transitions between parts. The fatigue behavior of electrical access hand-holes in welded aluminum light poles is largely unknown. The majority of existing data that has been developed was collected from full-scale welded steel poles [5]. In this study, points of interests where these stress concentrations occur are between the pole itself and the welded hand-holes.

NCHRP report number 176 contains results from experiments conducted at Lehigh University on both unreinforced and reinforced hand-holes in welded steel structures. During this experiment, 13 of the specimens contained some form of hand-hole. Different geometries were evaluated during this study. Over the course of the experiments, none of the hand-holes cracked. To provide an estimate of the stress concentration around the hand-holes, finite element models were created. AASHTO Category E' was recommended [6].

Observations have confirmed the existence of fatigue cracking associated with different hand-holes in the field. NCHRP report number 469 describes fatigue cracks found on welded steel structures near and around the hand-holes in several states. These states included New York, California, New Mexico and Minnesota [7]. In Iowa, there was a failure in a high-mast welded pole that was found to contain cracking around the hand-hole. This failure prompted further investigation into other poles and towers, in which multiple contained some form of fatigue cracking. Fatigue cracking was found in welded aluminum light poles mounted on the Mullica River Bridge after a violent storm in 2011 [8]. **Figure 1** depicts a fatigue failure associated with a hand-hole on an aluminum light pole that occurred in the field.

**Figure 1.** *Fatigue crack in welded aluminum light pole hand-hole.*

*Fatigue Behavior of Reinforced Welded Hand-Holes in Aluminum Light Poles with a Change… DOI: http://dx.doi.org/10.5772/intechopen.106342*

Twenty light poles were tested in bending fatigue at the University of Akron. Static tests were conducted in addition to the fatigue tests in an attempt to gain a better insight into how the strain is distributed around the handhole. The results from this study concluded that the hand-hole fatigue test data fell above category D and E design S-N curves [9]. In addition, the University of Akron performed a study on the effect of a change in the diameter of the specimens, from 10 in to 8 in. It was found that this change had a small, but slightly beneficial effect on fatigue life [9].

In comparison to the previous research conducted on the fatigue behavior of welded aluminum light poles, the novelty of this study comes from examination of changes to the welded hand-hole detail that have not been explored. Previous studies [9–11] utilized an identical weld detail but with different diameter specimens. The specimens included typical 10in diameter as well as 8in diameter poles loaded in four point bending. The change in the detail geometry could yield a better fatigue life that could be used in the field. During this study, eight light pole specimens, each with a different hand-hole detail treatment or geometry, were tested in fatigue. Finite element models were developed to improve the understanding of the stress field around the hand-hole.

## **2. Experiments**

#### **2.1 Pole geometry and material properties**

Eight aluminum specimens were tested under cyclic loading to examine the behavior of the modified reinforced hand-hole details (**Figure 2**). Each of the specimens consisted of a 25.4 cm (10 in) diameter extruded aluminum alloy tube with a 0.635 cm (¼ in) thick wall. Each of these 6063 aluminum alloy tubes had two hand-holes with reinforcement welded in place using a GMAW (Gas Metal Arc Welding) process with 4043 filler (**Figure 2**) [3, 12]. Each specimen was 3.66 m (144 in) in length, with the hand-holes paced 1.37 m (54 in) in from each end respectively. Support rollers for the specimens were inserted 15.2 cm (6 in) from either end.

#### **Figure 2.** *The geometry of a welded aluminum hand-hole detail in four-point fatigue testing.*


#### **Table 1.**

*Mechanical properties of the aluminum hand-hole tubes.*

**Table 1** summarizes the minimum mechanical properties of the welded aluminum hand-hole specimens [3, 12].

#### **2.2 Geometry changes to reinforcement**

Each of the eight poles contained two hand holes and each sample a different handhole treatment or modified geometry. The first set of two consisted of the same welded hand-hole detail used in the field. These hand-holes measured 150 mm (6 in) in the longitudinal direction and 100 mm (4 in) in the transverse direction. The other groups of poles had holes that were milled around the inside before welding, utilized reinforcement castings that were milled the outside before welding or a combination of the two. In the milling of both the hole and cast insert, only about a 6.25 mm (¼ in) of material was removed. As the hand-holes are cut with a plasma process, removal of material around the perimeter of the hole is intended to eliminate any hot – short cracking.

#### **2.3 Fatigue tests**

The fatigue setup that was used in the lab may be seen in **Figure 3**. A control system with a 245 KN (55 kip) MTS servo-hydraulic actuator was utilized to apply load to the specimens. A structural load frame capable of support 1335 KN (300 kips) was used to mount the actuator. The specimens were loaded by a spreader beam with supports that were rollers machined to fit the profile of the tube.

Strain gages were used to monitor strains in the specimens. They were mounted around the hand-holes using adhesive. Tests were conducted in load control. The typical location of the strain gages on the specimen may be seen in **Figure 4**. Strain gage placement was the same as the older study conducted and was taken from [9]. Strain gage resistance was 350 ohms and were 3.175 mm (⅛ in) in. Strains were recorded every two hours, intermittently for 10 second using a Micro-Measurements System 8000 data acquisition device.

Specimens had their hand-hole openings facing "downward" during testing. This was to ensure that they were in tension. Failure occurred when the maximum target load on the specimen could not be supported. Not being able to support the target load is an indication that cracking occurred. When a displacement over 10% of the target was realized, the test was shut down. This 10% displacement was set in order to ensure that the specimens would not fail catastrophically, and the damaged detail could be repaired. This repair was in the form of a moment clamp placed over the failed hand-hole. There was a single case where this moment clamp was unable to repair the specimen to continue testing.

Eight poles, each with two hand-holes, were tested at a nominal stress range of 5.4 ksi (37.4 Mpa). Each of these poles were loaded between 227 kg (500 lbs) and 3402 kg (7500 lbs) to provide a direct comparison between all tests. Strain gages were placed

*Fatigue Behavior of Reinforced Welded Hand-Holes in Aluminum Light Poles with a Change… DOI: http://dx.doi.org/10.5772/intechopen.106342*
