Light Pole Splice Design 6

[OzEng80]

Hi

I am designing a street light pole that will consist of a tapering octagonal tube with a wind turbine (mounted on the top - 9m), solar panel arrangement and a light pole (about 3/4 way up the pole). The client wants to introduce a splice connection about half way up the pole. I am struggling to determine an appropriate methodology (and detail) for this arrangement. I have observed that pole splices appear to take the following forms (see attached pics):

Telescoping - two pieces are wedged together with the applied force providing a 'clamping' force (through the tapering section). Ingal provides a methodology (and applied force of 2t) in their 'Pole Assembly & Installation For Street Light Poles' pdf at

http://www.ingaleps.com.au/shop/detail/street-lighting-poles/

Bolting - two pieces are telescoped as per above, except two sets (of two) bolts are provided at two (only) of the quarter points. It appears that a nut is welded to the outer (female section) and the bolt is holding the inner (male) section in place by the clamping force of the bolts (the bolts are unlikely to penetrate the male section due to wiring and adjustment issues). I have spent a lot of time looking for a detail/drawing of this to determine if this is a ring or something on the male section that the bolts align with - but i have failed.

I was really hoping for a design methodology for the telescoping detail that allows the determination of a clamping force (and overlap distance) for an applied moment & axial force. I find the bolted arrangement even harder to get my head around (i don't know to justify shear flow through the ends of a few bolts...) - so would welcome any clarification of this at all.

Any guidance or advice would be much appreciated.

Thank you.

 

[OzEng80]

Missing attachment... Sorry.

 

[msquared48]

Sorry, can't help here.

Perhaps someone else could shed some light on the subject.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[hokie66]

OzEng80,
I don't know who makes them, but I saw a big steel monopole today on a HV transmission line. Between Warwick and Toowoomba. Suggest you might call Energex or one of the other transmission companies for reference to suppliers. This one just had the the sections nested together with no bolting...I think. I was driving.

 

[msquared48]

Actually, now that Hokie mentions it, I do recall seeing a picture of a tapered pole with such a lap connection - no bolts - on the Valmont site on the net. Valmont is a major player in the design and manufacture of steel poles for the transmission and wireless industries in the states here.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[BAretired]

I have no experience in this area either, but it appears the splices are typically slip joints. Here is a link to one document which may be of help.

The following is an excerpt taken from the linked document.

5.7 Splices
5.7.1 Poles shall be designed with a minimum number of joints. Field welding shall not be allowed
as part of the design of a new pole. The shaft joints to be made in the field shall be slip joints or
bolted flange joints. Slip joints shall be designed for a nominal lap that will develop the full
required design strength of the pole at that point. The minimum lap shall meet the requirements of
ASCE Manual No. 72. All welds on both sections of the pole, in the area of the splice, shall be
complete penetration welds for at least a length equal to the maximum lap dimension.
5.7.2 Manufacturer shall verify slip joint fit, through dimensional measurement or actual fit-up,
before shipment. Joints should not interfere with threaded inserts, step nuts, ladder clips, or
jacking nuts.
5.7.3 Sufficient jacking lugs and permanent orientation marks shall be provided at all slips joints
to ensure proper alignment and complete overlap of the joint.
5.7.4 The axis of the pole shall not be distorted after the pole is mated. Shims shall not be
allowed to straighten the pole unless approved by the owner. The owner reserves the right to
reject a pole based on the improper mating of a pole splice.

BA

 

[OzEng80]

Thanks for your efforts BA - most promising lead thus far.

I now have a copy of the document that supersedes the ASCE Manual 72 and unfortunately all the references to 'Field connections of Members: slip joints' consist of references to applied loads from manufacturers or designers - no design method has been provided.

It has the following references:

'Experience has shown that an overlap of 1.42 to 1.52 times the maximum inside diameter of the outer section is sufficient to develop the required strength of the connected 12-sided polygonal sections provided there are no significant gaps between the mating sections and the manufacturer's recommended assembly force has been used.'

Not something to 'hang my hat on' but a useful reference (i was surprised at the degree of accuracy).

For the bolted arrangement: 'Bolted Flange Joints' the following information is provided:

The flange bolts should be brought to a snug tight condition. As flange bolts are brought to a snug-tight condition all of the faying surface may not be in contact. Final bolt tensioning should follow a sequence to provide for even tensioning of all bolts and to ensure section alignment. A pair of bolts on opposite sides of the joint should be tensioned followed by a similar pair until all bolts are tensioned. Proper bolt tensioning in flange joints is required because of the cyclic nature of the loading. High strength bolts are susceptible to cracking when subjected to high stress fluctuations and pretensioning of the bolts by the turn of nut or other approved method ensures a more constant bolt stress and prevent bolts failure.

So it appears that these field connections are justified via testing. Not particularly surprising but a difficult sell to a client who can point out the window and say that he wants 'one of those'...

Appreciate your efforts - I will post if i come up with a (decent) solution.

 

[hokie66]

Testing is often the means of justifying designs like this. I doubt that you will find a design method using calculations, as the companies that make these rely on testing.

 

[SAIL3]

not an expert in this area either, however, I have designed a slip joint of round pipe...the interesting fallout from that was when I examined one of the failure mechanisms of the inner and outer pipes that they actually resist each other when trying to fail in their first primary mode of failure ie...the inner pipe tries to oval in one direction while the outer piped tries to oval in a direction 90 degrees to that...that left the focus on the overlap length which gives a stress profile to react the moment in the joint...my conclusion was that if the overlap is sufficient then the area of failure is right next to the end of the joint in the weaker member....not sure the above info is of any help...in your case which is more critical, I would need testing back-up or info from the experts in the field which would have done mucho testing in that area..

 

[ATSE]

TIA 222-G is an applicable code for a typical telecom pole.
Based on earlier ASCE documents, the lap splice for tapered section = 1.5*Diameter. Splice is male-female slip on sleeve.
No welds, no bolts.
The top section doesn't want to jump off.
Some California jurisdictions required 2.5*D. That is, if the lower pipe diameter = 1.5' at the splice, the largest sleeve length = 2.25' to 3.75'.
That's it.
I will take full-scale lab testing and decades of successful use over calculations.

 

[OzEng80]

Thanks ATSE,

I had a look at TIA 222-G and it is similar to other service pole codes (eg AS4676) in that it defines tolerances but not actual distances or means for calculating slip splice lengths. Interestingly it defines that the splices are to be 'pulled together to ensure firm contact' - which is far less onerous than the 2t force required by Ingal.

For my pole (235mm tapering to 95mm) the diameter at the proposed splice is about 165mm. I was thinking of a splice length of about 600mm which is a multiplier of 3.6 x D - which by most(anecdotal)accounts should be conservative.

Your comments about the top section not wanting to jump off is interesting. With my arrangement it is possible to have uplift (from the solar panel), but not without a moment acting at the splice (which would intuitively resist the axial uplift). I was leaning towards defining the slip joint clamping force as the maximum uplift that can act on the solar panel (and the joint).

I would appreciate your thoughts on my approach to the slip joint and clamping forces?

Note that anything i document will have a lot of verbiage relating to 'testing of slip joint to be undertaken by manufacturer'.

Thanks.

 

[oldrunner]

I haven't look at these details for a long time, but I believe that some pole manufacturers actually had tabs on the upper and lower sections which allowed bolts to be installed and the upper section pulled down on the lower section - insuring a tight fit. It could be that the bolts were left in place.

 

[MikeHalloran]

<tangent>

My Dad watched a contractor try to assemble a two-piece flagpole for a school. The joint halves had been machined to a light push fit, and some protective coating applied.

The contractor elected to ignore the prominent warning labels and not remove the protective coating before attempting to push the pole halves together.

A big hammer didn't work.
A bigger hammer didn't work.
Jacking the pole halves against brick walls didn't work either.

I think the contractor got to buy a new pole, since he did manage to get the halves engaged well enough that they couldn't be separated.

</tangent>



Mike Halloran
Pembroke Pines, FL, USA

 

[SAIL3]

in the case I mentioned in the email above I also put a close-off pl in the end of the inner pipe......this eliminated other concerns I had and somewhat controlled the next failure mode as it prevented the inner pipe from an ovaling failure....

 

[racookpe1978]

Hmmmn.

An observation, but not necessarily a valid observation. Critique this.

A light pole, or a street stoplight pole-with-suspended-arm-and-weight cantilever, is held into the concrete by 4x bolts holding down a simple flanged baseplate that is fillet welded to the pole.

Therefore, since all of the stresses and loads at the base are carried through the midpoint of the pole, why can you not use the same flanged-and-bolted assembly techniques at the midpoint of the pole for the splice?

(Granted, the large visible double baseplate splice might be visually unappealing for a flagpole, but for a structural application? Why not?

 

[rb1957]

if you've got a tapering pole (octogonal in this case), can you use a section of it to create an internal splice from one side of the joint to the other ?

wouldn't it "nest" into both tubes neatly ? you could use "liquid shim" to fill any small voids. you could "drive" the splice tube into the smaller (upper?) tube, to get a good seat. then a couple rows of bolts, lick o'paint ? then the lower side of the splice, bolts would probably clamp up across teh tube, not the best thing to do, but this is a street sign.

wind turbine and solar panels ... that pretty much covers the "reusable energy" bases ... maybe a small garden for carbon sequestation ?

 

[MikeHalloran]

<not so tangent>
I'm assuming that you have a way to fabricate a 9m pole in one piece, and you can certainly ship one easily enough, so maybe you could talk the client out of the splice.

I've seen tall power (only) poles with just telescoped tapered polygons secured by gravity and friction, but if the wind turbine is other than toy-sized, that might complicate things a bit.

For instance, you'd want to consider fatigue from aero interactions between blades and tower, and from whatever imbalance is allowed at fabrication time, and from whatever imbalance accrues from dirt and guano and bird strikes. ... and you'd want to consider what fails next, and how it fails, after the turbine loses a blade. ... which may explain sturdy flanges and manymany bolts on wind turbine towers.

</not so tangent>

Mike Halloran
Pembroke Pines, FL, USA

 

[transmissiontowers]

The T-Line industry has used lap splices for years and the 1.5*D is usually acceptable except for guyed poles. The guys can become slack if the 2 pieces slip. You usually use a hydraulic ram to pull the sections together and there is a splice lock that is installed to prevent slipping.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[OzEng80]

Thanks Transmissiontowers - very useful.
What was the lap splice used for the guyed poles?
Can you also please describe the 'splice lock' detail used?

Thanks!

 

[transmissiontowers]

The practical limit for pole sections is limited by the length of the galvanizing tank and is around 60 feet. The press brake that bends the flat plate into the 2 pole halves is also a limit and most shops use two 30 foot presses in tandem. The 2 halves are welded together and then galvanized. If you need a pole longer than 60', you have to lap splice them or butt splice them with flange plates. The plates are expensive compared to the lap splice. ASCE 48 has the requirements for the lap splices, but 1.5D has worked for a long time.

If you have a single pole the lap splice is fine. If you have a two pole structure with a beam between, you can't count on the lap splices engaging the same especially if you have several. (we have poles that are 270' tall with many splices) In the 2 pole case, you use the flange plates to ensure the beam fits and is horizontal. Guyed lap spliced poles are rare and sometimes occur when a pole was installed and later is used to tap a circuit so it has to be guyed. The splice lock is a device that transfers the shear from the top section to the bottom section and ensures that there is no extra slip when the guys load up. They are a round piece of steel about 1.5" diameter and you drill a hole through the lap splice and insert the splice lock. There is a J-bolt in the center that tightens against the inner pole.

The wood pole distribution people guy everything because it is cheaper than a free standing wood, concrete, or steel pole. Sometimes you don't have the space to guy so you design a free standing pole to handle the tap loads.

HTH

_____________________________________
I have been called "A storehouse of worthless information" many times.