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 Post subject: Re: Lamppost falling
PostPosted: Sun Jun 26, 2011 8:35 pm 
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Jon Hall from Roch gave a very interesting presentation about structural testing of steel columns at the ILP meeting. Rather than it being a sales plug for his company he kept the talk based on the “peace of mind” that structural testing gives lighting engineers with regard the safety of columns.

Jon had some pictures of failed columns from various parts of the world, and several things were of interest. All the examples he showed had suffered failure at or below ground level. In some cases the failure was corrosion, in others – an aluminium column – there was a fatigue crack around its circumference. An example from the UK had suffered a crack around 300mm below ground level which caused it to fail and fall across a busy road luckily causing no injuries – it was a 10m column. None of these columns appeared to be more than 20 years old. Perhaps it is modern columns which are designed to be more “crash friendly” compared to the over engineered columns of the 1950s which are the real issue?

Not all methods of structural testing can detect flaws right down to the root of the column which is another issue. Thankfully despite 8 million  streetlights in the UK, structural failure is rare.

Unauthorised signage, hanging baskets and banners can all place additional loading on columns. Jon stated that banners are often the worst culprit with many banners generating more windage than the column and lantern combined. One council who wanted to put banners up on columns on a dual carriageway for the Olympics, were advised to have the columns tested for strength first. Several unsafe columns were found. In another instance an electrician called to disconnect the service from an unsafe column found it was so structural weak that he refused to work under it. It was necessary to use a Hiab to support the column whilst the service was disconnected.

The current trend for post top mounting of columns is also have an impact. In high winds, columns with post top mounted lanterns tend to oscillate with the movement being of small amplitude but high frequency. Columns with brackets tend to oscillate more slowly but with larger amplitudes. It is the frequency of oscillation that causes fatigue and it may require additional mass in the column or lantern to damp the oscillation.


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 Post subject: Re: Lamppost falling
PostPosted: Sun Jun 26, 2011 10:57 pm 
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Oooo interesting yet again Phosco.

It's going to be interesting in 10-15 years time when all this new stuff ages.


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 Post subject: Re: Lamppost falling
PostPosted: Sun Jun 26, 2011 11:06 pm 
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... if any of it is around in 10-15 years and hasn't all failed!

Phosco152 wrote:
Jon had some pictures of failed columns from various parts of the world, and several things were of interest. All the examples he showed had suffered failure at or below ground level. In some cases the failure was corrosion, in others – an aluminium column – there was a fatigue crack around its circumference. An example from the UK had suffered a crack around 300mm below ground level which caused it to fail and fall across a busy road luckily causing no injuries – it was a 10m column. None of these columns appeared to be more than 20 years old. Perhaps it is modern columns which are designed to be more “crash friendly” compared to the over engineered columns of the 1950s which are the real issue?


I have had an issue with making columns crash friendly - I fail to see the need when drunk drivers will find something to crash into: lamp post or not. What is the point in spending thousands of pounds designing (or for local authorities: installing) new crash safe columns that are designed to fail and have to be replaced (at more cost) when a vehicle crashes into them? and the most likely cause of these crashes will be people driving whilst intoxicated. Moving columns back from the road edge is fine, makes perfect sense. Installing ones designed to break? No, not in my book. Not when trees, street cabinets, buildings and telephone poles are dotted around and just as likely to be the target of a vehicle crash. And what about this: a car crashes into a crash-safe lamp post - the drunk driver is fine because the column and car absorbed the impact (and the alcohol has relaxed his body so it wasn't tense upon impact); but the column swings over in the opposite direction of the vehicle and lands on another car or a pedestrian... is that safe?

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Unauthorised signage, hanging baskets and banners can all place additional loading on columns. Jon stated that banners are often the worst culprit with many banners generating more windage than the column and lantern combined. One council who wanted to put banners up on columns on a dual carriageway for the Olympics, were advised to have the columns tested for strength first. Several unsafe columns were found.

I have actually heard about that one myself. Up here in York, lamp post banners are very rarely used... the most columns to have banners fitted were the Revo Festival columns which had double banners for Royal Ascot fitted (on the year the normal course was closed and the event moved here).

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In another instance an electrician called to disconnect the service from an unsafe column found it was so structural weak that he refused to work under it. It was necessary to use a Hiab to support the column whilst the service was disconnected.

I hope the HIAB removed the column immediately after it was disconnected!

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The current trend for post top mounting of columns is also have an impact. In high winds, columns with post top mounted lanterns tend to oscillate with the movement being of small amplitude but high frequency. Columns with brackets tend to oscillate more slowly but with larger amplitudes. It is the frequency of oscillation that causes fatigue and it may require additional mass in the column or lantern to damp the oscillation.

Ah, now we have a proper well-founded why boring-as-hell post top lantern/column combos should stop (other than looking incredibly boring and like massive golf clubs turned upside down and stuck into the ground!) - in that they can actually cause premature column failure. Since somebody from Amey was at the meeting, maybe he'll pass that info on and we'll see a return to proper streetlight installations!

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 Post subject: Re: Lamppost falling
PostPosted: Mon Jun 27, 2011 2:32 pm 
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I think it is a bit of a sweeping generalisation to say drivers only crash into things when they are drunk.

What about a 3rd party such as a passenger who would be saved injury if the column was crash friendly/passively safe?

All reasonable measures should be taken to reduce injuries in the event of an accident - ultimately the safest course may be to have no obstructions - lighting columns - at all.

Another factor is that it is pointless making a column stronger than it needs to be, as this only increases cost.

Anyway back on topic, SAPA poles did show videos of their passively/crash safe columns being tested, with a variety of measures being employed from breakaway columns to those that crumple and deform on impact. Similar videos have been posted on the web before.

Of particular note, is the (British Standard ?) requirement that the lantern falls within a 2m radius of the base of the column on impact. You would thought that this would land on the car but in practice the car has moved out of this zone by the time it stops. We were told this is actually quite an engineering challenge as the initial impact causes a percussion shock to travel up the column, often this causes failure of the bracket attachment with the bracket and lantern coming down together, but  if the bracket remains attached, the period and amplitude of the shock change due to the different tube diameters which then result in the lantern being jettisoned from the end of the bracket. Loss of the lantern needs to be in a "controlled manner". Only "generic" lanterns are tested rather than all the various different possible types by the way...


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 Post subject: Re: Lamppost falling
PostPosted: Mon Jun 27, 2011 6:01 pm 
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Near to where I live there is a few columns which have been replaced because someone has ploughed their motor into them, one column was even replaced twice within a 2 year period.

Out of the three that were smashed into only one original suvivor remains, a top entry Stanton coloumn.

This shows the replacements, the one closes to the camera had to be replaced after two years. The previous one was a mid 90's concrete which was lost in an incident 4 years ago.

The suvivor .

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 Post subject: Re: Lamppost falling
PostPosted: Sun Nov 13, 2011 10:25 pm 
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Has anyone ever found knocked down columns that have been left where they came to rest?
I have found 2 concrete columns on two sites that have been knocked down and never picked up, both are still there today after 40 odd years.  :)


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 Post subject: Re: Lamppost falling
PostPosted: Sun Nov 13, 2011 11:28 pm 
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Are these private sites or public roads?

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 Post subject: Re: Lamppost falling
PostPosted: Sun Nov 13, 2011 11:47 pm 
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mazeteam wrote:
Are these private sites or public roads?

Both are on public roads so i don't know why they have'nt been picked up, one is a stantion type 7 that has been there so long a tree has grown around part of it!


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 Post subject: Re: Lamppost falling
PostPosted: Sun Nov 13, 2011 11:57 pm 
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Well that is quite a suprise! I thought they'd be on private grounds. I take it the lanterns are long gone...

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 Post subject: Re: Lamppost falling
PostPosted: Mon Nov 14, 2011 12:36 am 
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Location: Cleveleys nr Blackpool
On Fleetwood Marsh there was a long line of felled and poor condition CU Avenue columns which dated back to when the area was used as railway sidings (the railway there closed in 1970). Some used to be standing with the bracket and rusty remains of a lantern attached in the early 90s but last time I checked (2007) they were all lying on the floor broken.

On a public road in Poulton, there was a full Stanton 10 column complete with overarm bracket and Thorn Beta 4 MBF lantern lying on the pavement in the late 80s and early 90s for at least 5/6 years. Even more mysterious is that it was never replaced at the time. Last time I checked though there was a fairly new looking Stainton column with 2600 fitted nearby and the Stanton was long-gone.


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