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Light Pole Splice Design
6

Light Pole Splice Design

Light Pole Splice Design

(OP)
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-ligh...

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.



RE: Light Pole Splice Design

Sorry, can't help here.

Perhaps someone else could shed some light on the subject.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com

RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

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

RE: Light Pole Splice Design

2
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.

Quote (USDA)

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

RE: Light Pole Splice Design

(OP)
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.


RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

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..

RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

(OP)
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.

RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

<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

RE: Light Pole Splice Design

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....

RE: Light Pole Splice Design

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?

RE: Light Pole Splice Design

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 ?

RE: Light Pole Splice Design

<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

RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

(OP)
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!

RE: Light Pole Splice Design

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.

RE: Light Pole Splice Design

OzEng,

I have some drawings from Rohn squirreled away, here. I had asked them for a 50' tower at the time, and it is assembled in two sections. Being a tapering tower, the splice mid-way is just a friction-fit of the two sections, wedged together. For your reference, the 18-sided shape has a 30.25" round mounting flange (bolt circle 26.5" x 8 places). The cross-section of the "octo-decagon" is about 22.5" across flats at the bottom. The top of the lower section is 15.903" across flats. The top of the splice is 29' high. The splice overlap is 26" long. The top cross section goes from 16.763" to 11.5" at the very top of the total 50' tower. The wall thickness is 0.25" bottom section, and 0.1875" in the top section.

This is a very beefy tower, and intended for a rather large wind turbine - yours may be smaller, and you've already said your tower is shorter, too. Hope it helps "scale" your ideas. The splice L/D ratio is about 1.6.

Forgive another tangent, please, but may I ask who is supplying the design loads? The turbine manufacturer? There is some speculation (in the wind power grapevine) that this information is drying up. I doubt it's true (considering how the new certification rules help better define these very loads) but the rumour persists. Other concerns are that tower manufacturers are no longer certifying towers for wind turbine use (giving out the drawings that I have in my very hand) - would that be leading your client to seek your help?

STF

RE: Light Pole Splice Design

(OP)
Hi SparWeb - thanks for the info.

I take it there was no 'clamping force' or member preparation specified on the drawings?

FYI - My client is a small 'green' company looking to develop a pole and footing system comprised of 'of the shelf' wind turbines and solar equipment. I have not been able to obtain turbine loadings. My (cyclonic) design loads actually exceed the rated capacity of the turbine so I have adopted a projected area analysis (of unit and blades) with a wind coefficient of 1.0 on the basis that the unit has 'locked up'. I have seen several approaches to this (including taking the full swept area of the blades) and would be interested to hear your thoughts. After inspecting the unit (it has flexible, aluminium blades) I am confident that the blades will either snap off or be bent back during the design event.

Transmissiontowers - I am still struggling with the splice lock device detail ... ASCE 48 states that 'supplemental locking devices shall be used if relative movement of the joint is critical or if the joint might be subjected to uplift forces. In resisting uplift forces, locking devices shall be designed to resist 100 % of the maximum uplift load.' Since I have the potential for uplift across the joint I am intending to design the device for this load.

I have attached a sketch of my understanding on the arrangement (I am not confident I interpreted correctly)
Is the locking device just a 'J' bolt maneuverer inside through the lap splice and tightened as shown?
I have also shown a proposed detail on the opposite side of the sketch for you comment (would have to drill through the nut on site)....

It was my intention not to have any field drilling of the hot dip galvanised poles to avoid having to touch up the steel.

Thanks for the assistance.


RE: Light Pole Splice Design

Quote:

I take it there was no 'clamping force' or member preparation specified on the drawings?

FYI - My client is a small 'green' company looking to develop a pole and footing system comprised of 'of the shelf' wind turbines and solar equipment. I have not been able to obtain turbine loadings. My (cyclonic) design loads actually exceed the rated capacity of the turbine so I have adopted a projected area analysis (of unit and blades) with a wind coefficient of 1.0 on the basis that the unit has 'locked up'. I have seen several approaches to this (including taking the full swept area of the blades) and would be interested to hear your thoughts. After inspecting the unit (it has flexible, aluminium blades) I am confident that the blades will either snap off or be bent back during the design event.

Sorry, no assembly details, it's more of a spec sheet. I have listed all dimensions that I can, short of e-mailing you the file, though I didn't point out some strength details before. They specify 65 ksi steel.

Loads, that's a whole different story. You may be correct about the blades: I've seen some made from bent aluminum sheet that make me want to stand a mile away. If that's what you're talking about, then they probably won't survive the extreme wind event for some locations... leading to a more fundamental question about the turbine! Thankfully you're not asked to address that (but be wary of it anyway). Be that as it may, there are certified types out there now that will take whatever mother nature's got coming.

The NREL have published reports on dynamic load tests from instrumented wind turbines. You can look them up on the NREL website. (try TP 500-38550) I've taken a stab at reducing their numbers a little (long time ago) and found that they agree with theory well enough that you can use simple estimations of the blades' mass-moment of inertia, spin them at the critical max RPM, and then use the gyroscopic effect to determine the pitch moment that the effect will apply. I have worked so far with free-yawing WT's, so I use a slew rate of 180 degrees per second as the worst case, and get significant pitch moments as a result. You can find similar gyro conditions in propellor-powered aircraft design standards.

Thrust is proportional to the lift on each blade, but it takes too much hard slogging to find that. I found equations on Wikipedia that are NOT conservative when compared to a detailed blade-element analysis of the same rotor. Using the blades alone on a "locked up" rotor as your flat-plate area is not conservative either. Using the flat-plate drag on the whole rotor's swept disk is very conservative, not excessively conservative.

Weight is also an obvious load. Wind turbines tend to be heavier than antennas, so it will have a greater effect on the tower, exacerbating over-turning moments at the base.

If the blades do bend back in extreme winds, consider what happens if they strike the tower. This can raise the turbine unit off of its mount, depending on how that's been designed.

STF

RE: Light Pole Splice Design

Your sketch is a little off. The Thomas & Betts splice lock that we use has an "L-Bolt" about 1/2" diameter in the center of a 1.5" steel plug with a groove in the back and a sholder on the front. After you put the 2 shafts together, you drill a 1.5" hole through both shafts and insert the splice lock. The "L-Bolt" is loose and slides past the shafts. When the sholder bottoms out, the L-Bolt is tightened and clamps the SPLOCK in place. The shear force does not go through the L-Bolt, but it is transferred through the 1.5" plug.

If you have uplift and vibration from the wind turbine, I would probably stay away from the slip joint and use flange plates. FWIR, the huge wind turbine columns use an internal flange and an internal staircase to climb the structure.

I found my SPLOCK and have taken a picture of it.

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

RE: Light Pole Splice Design

(OP)
Thanks for your comments Sparweb - i will chase the manufacturer a bit harder. The unit is tiny as far as turbines go (Nheowind 3D 04) and is purported to have minimal gyroscopic effects due to the unusual blade arrangement (try googling it).

I went back and checked the calcs (i didn't do the prelims and have taken over the job) and realized that i was miles off with my 'projected area analysis (of unit and blades) with a wind coefficient of 1.0 on the basis that the unit has 'locked up'' statement. The current basis of design is for the full swept area of the blades with a drag coefficient of 1.3. So at this point i will be revisiting the design with same area with a drag coefficient of 1.0 (which still seems very conservative to me - but should address some of the issues that could arise from the design simplifications).

transmissiontowers - thank you. A picture tells a thousand words! I take it the steel exposed by the drilled holes is treated/painted?

RE: Light Pole Splice Design

Quote (...A picture tells a thousand words! I take it the steel exposed by the drilled holes is treated/painted? )


Yes, you paint after drilling the hole. If you fab the pole sections knowing that the Splock will be used, you put holes in the upper (outer) section and galvanize the poles, then you press the 2 sections together, and then use the hole as a template to drill the inner hole and paint everything. Since it is a bearing connection to transfer the shear between the 2 sections, you cannot use slots. And because of the fab tolerances in the pole sections, you cannot count on pressing the 2 together to line up 2 holes.

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

RE: Light Pole Splice Design

Sounds reasonable to me. Why would horizontal slots be even considered? There seems to be no possible validation for such an idea...or am I missing something?

BA

RE: Light Pole Splice Design

Quote (.... Why would horizontal slots be even considered? There seems to be no possible validation for such an idea...or am I missing something? )


I guess I should have specified Vertical slots are not used because the Splock is a bearing connection. Now if the pole is big enough to put a man inside and the tolerances are close enough to use a friction connection, you could use a vertical slot and have the guy inside hold the bolt head.

I would still recommend a flange connection because of the slip fit irregularities with tapered shaft fabrication and the vibration and uplift possibilities with the wind turbine.

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

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