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  • 1.  Single Pole Luminaire Structures

    Posted 02-22-2018 08:39 PM
    Recently I have been reviewing some inspection reports on single post luminaire structures approximately 60' high. Does anyone have a way to judge the integrity of the post with an impact point at the base? Some of these are connected to the base with hook anchors, while some have break-away anchorage. The impact points don't appear remarkable, usually 4" diam with 3/8" to 1/2" deep dents. In some cases the luminaire head broke off the top. To me if the impact was enough to fling the head off the top then the pole itself is compromised.
    I have to remind myself of the constant vibration these poles are subject to over the life time. Could the impacted area become an initiation point for a fatigue fracture?
    Without running any analysis on this type of structure, does anyone have experience with the longevity of a pole structure after impact?

    Shahin Ariaey-Nejad, PE, M.ASCE

  • 2.  RE: Single Pole Luminaire Structures

    Posted 02-26-2018 09:54 AM

    I don't think there is a rule of thumb to decide if a pole is good or not after a crush. You have to gather a lot of information and then make your own decision.
    Without calculating, the only way to judge the integrity of the hit pole is the visual inspection and data collection. A visual inspection of several aspects should be made: cracks of the pole welds with the base, rust of the pole material or welding, horizontality of the base plates, cracks in the area of the impact, and if possible the condition of the anchor bolts. Having all this info you have to make your own decision.
    In some way it should be checked if the foundation has cracks or it is broken or it was tipped because the crush. If the pole was installed with the break-away, it is possible that the foundation had not suffered damages because this system allows the pole to be disengaged from the foundation.
    Perhaps it would be good to seek advice from a laboratory specializing in collisions or a poles manufacturer. In terms of fatigue it could be dangerous if resonance occurs. Consult with a manufacturer of poles. The vibration is caused by the wind. It is advisable to review the wind map of the ASCE-7. Most studies in this domain focus the effect of shock on the vehicle and its occupants that of the integrity of the post. If the pole is a metal one, this could be repaired by welding (replacing the affected area or with a metal collar)

    I'm sorry I can't help more, but I hope this somehow will work for you.

    Serban Tiparescu P.E., M.ASCE
    Construction Procedures Manager
    The Woodlands TX

  • 3.  RE: Single Pole Luminaire Structures

    Posted 02-27-2018 10:11 AM
    Hi Serban - I appreciate that there are other aspects (such as foundation, anchorage or weld damage) - but they were found to be in satisfactory condition. The only issue is as an inspector you have to make an assessment on the spot. Is there an issue or not when there is an impact damage at the base of the pole itself? I searched to see if there was any research papers on the topic - to see if any kind of work was done to see the effect of impacts on light masts. I could not find much. I was just wondering if any one else had looked into this kind of research before. The pole obviously survived the impact. Question is when it is subjected to sustained winds and it experiences vibration and vortex shedding, will the impact area an initiation for cracks? And how long will that take?  What action should I recommend to the owner/agency. Those are my concerns.

    Shahin Ariaey-Nejad

  • 4.  RE: Single Pole Luminaire Structures

    Posted 02-28-2018 10:07 AM
    If the pole is damaged, it should be repaired or replaced.  If the decision is to repair, the scope of the repair should be determined by either the manufacturer of the pole or a qualified engineer.  I disagree that a field inspector should feel pressured to make a decision on the spot, in the field.  The inspector's job is to document the condition.  If review by an engineer is warranted, and it appears that such review is warranted, then that review should take place.  It is beyond the scope of a typical field inspector's qualifications to make such a judgement in the field.

    Andrew Holmes P.E., L.S., M.ASCE
    Consulting Engineer
    Melbourne FL

  • 5.  RE: Single Pole Luminaire Structures

    Posted 02-27-2018 10:10 AM
    Having been coordinating the installation of High Mast Poles, up to 140' tall. I have come to learn a lot regarding their design, from in field experience. I do think, that if a pole is struck by a vehicle and shears off the luminaries, then the pole will have to be replaced. Also if the pole is impacted and a dent is formed, then it should also be replaced. Since I'm working in a hurricane zone with high winds, the dent would compromise the structure. Similarly to a dented coke can, with a weight on top.

    David Jorgensen EIT, A.M.ASCE
    Field Engineer
    Pelham AL

  • 6.  RE: Single Pole Luminaire Structures

    Posted 02-28-2018 10:15 AM
    Thanks David. That's what my "instincts" were telling me too. As engineers we like to quantify things - but as an inspector, I know that is not always possible. The trick is to look at the tell-tale signs and formulate a theory with the clues available - a rather benign looking dent and missing luminaire. There were actually two such poles - one with the luminaire completely missing - just some duct tape to cover the pole top, and one pole with the luminaire head wired back on. Both poles had an impact at roughly the same location, a few feet above the base. One can only imagine the displacement needed at the top to fling the heads off -as in a whip lash effect.
    Thanks for the insight.

    Shahin Ariaey-Nejad