Industry Standard Pre-Engineered Steel Pole Compared to RUS Requirements

Posted by Brooke Brackett on Jul 17, 2014 8:46:00 AM

Previously called Wood Pole Equivalents, Pre-Engineered Steel Poles are classified by the ground line moment that they can withstand. Using pre-engineered steel poles can be a practical way to minimize cost and time on certain projects. Generally, pre-engineered steel poles are used for distribution type projects rather than transmission lines due to the shorter spans and lower tensions used on distribution lines.

Pre-engineered steel pole design and classification follow a similar philosophy to that found in ANSI 05.1-2002 for wood poles. Per ANSI O5.1-2002, wood pole classifications can be determined by placing a horizontal tip load two feet from the top of the structure and determining the corresponding ground line moment. Pre-engineered steel poles are similarly designed and classified by applying an equivalent horizontal tip load two feet from the top of the structure. The equivalent horizontal tip load is found by multiplying the horizontal tip load found in ANSI 05.1-2002 by the ratio of factors of safety of steel to wood.

Many manufacturers have developed Pre-Engineered Steel Pole Catalogs for line designers to utilize when designing structures.  These catalogs normally include structural characteristics, weights and maximum ground line moments.  Most Pre-Engineered Steel Pole Catalogs take into account some industry wide assumptions as follows:

  1. Embedment depth is taken as 10% of the height plus two feet.
  2. Heights for pre-engineered steel pole catalogs range from 45-120 ft.
  3. Catalogs include Class 3 thru H10. Noting that Classes 1 thru 3 are typically not economical to fabricate using steel unless a round section can be utilized.
  4. Typically the same top diameter and taper are used per class.
  5. No deflection criterion is used.

Using pre-engineered steel poles may be a good option for a project if the owner and/or line designer is confident with the approximate ground line moment calculation on simple line designs or if the line designer is plugging in the structural properties of a pre-engineered steel pole from a catalog into a line design software.  Using pre-engineered steel poles can help give a good idea of the pole sizes the owner and/or line designer will need. This method of design is generally used for single pole structures that are subject to transverse and vertical loads. Engineering judgment must be carefully exercised when using pre-engineered steel poles in applications that can cause forces to be redistributed along the pole length. Also to keep in mind, the owner and/or line designer is typically responsible for determining the applicable loads and loading criteria, geometric configuration, type and degree of structural support, as well as any other required design or performance characteristics for pre-engineered steel poles.

One requirement to look for when considering using pre-engineered steel poles for a project is adherence to the Rural Utilities Service (RUS) Bulletin 1724E-214. If a project is required to adhere to the RUS Bulletin, there may be some deviations from the standard pre-engineered pole industry standards/catalogs to consider. Some of the deviations include the following:

  • Point of Fixity
  • Tip Load
  • Class Designations
  • Deflection 

The table below summarizes some of the differences that may be found between the RUS Bulletin and most Standard Pre-Engineered Steel Pole Catalogs. 

Deviation_Table_

*Class Designations may vary depending on manufacturer. 

 

Using pre-engineered steel poles in line design can be an effective way to minimize cost and time associated with a project. It’s important to note that there may be deviations between a standard Pre-Engineered Steel Pole Catalog and the requirements of certain specifications, and it is ultimately the line designer’s responsibility to review all applicable specifications, pole configurations and loadings to ensure that a pre-engineered steel pole is the right choice for a structure.  

*Content provided by Callie Lohman, PE, Civil Engineer at DIS-TRAN Steel, LLC. 

 

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Headaches Customers and Steel Fabricators Run Into with Production Backlogs

Posted by Brooke Brackett on Jul 9, 2014 10:00:00 AM

We all appreciate on-time delivery. Whether it’s ensuring your new G. Loomis fishing rod is in before your next tournament or Amazon delivering your new sandals before you head to Florida; we all depend on the supplier. 

It’s critical that the supplier is organized, flexible and has an updated production backlog to make sure delivery is as promised, and not late because they have over-committed themselves.

A backlog is the total production that remains to be completed at any given time.  It may also include some tentative work that you are fairly sure you will be awarded, although you may not have an official purchase order yet.   The sold production is prioritized into a production schedule over the coming months depending on size and the promised delivery date. 

detailer

The backlog is important to all of the departments within an organization, all the way from estimating, to engineering/detailing, production, etc., so that each promised job has its required amount of resources available and scheduled before the fabricator promises any additional deliveries. It must be updated constantly as new jobs are won.  Any company who prides itself on customer service and on-time delivery must have a defined backlog that is current and that has been set to achieve 100 percent of promised commitments.

The backlog allows the estimating department to know exactly how much and where any capacity is available in any given month so that they can make their next commitment to a customer on the next project they are bidding on.   It will show any “holes” in the schedule where something may be worked in.  It will also show “premium hours,” such as weekends, that may be available for customers who have a project that requires an expedited schedule where overtime fees are acceptable to meet the required delivery date.

But as easy as filling a backlog might seem from the outside, it can get a little difficult and sometimes frustrating to the customer and fabricator.

Problem #1: If a customer knows that there is a specific size project coming up for them in the future and roughly when they will need it by, but say the market is so busy, that their chances of getting their project by the desired time is slim once the details are finalized. 

Solution: Fabricators can hold production space for customers based on a rough idea of the project scope and often without an exact purchase order for particular projects. If the customer knows when they need it delivered by and can estimate the scope of the project, then the fabricator will bid other projects around it as if the project remains on track.  This is beneficial to both the supplier and the customer. However, if the project schedule changes, this results in challenges for the supplier due to backlog holes.

Problem #2: Backlog holes can sometimes be one of the more frustrating aspects of managing a production backlog.  Holes in production can come from many sources, such as slow bookings, project slipping or approval hold-ups.  A backlog hole is a period when there is not sufficient work scheduled to meet the facilities capabilities. This results in lost revenue for the facility and lost productivity. 

Solution: From a customer’s prospective, this can be beneficial because if their project “needs” fit the supplier’s “wants” they could get their project at a really good price, a really good schedule or both! Make sure to always stay in contact with the supplier’s estimating department because opportunities like this might arise that work for both.

Problem #3: Often during the normal course of a project, various issues can cause the project schedule to slip.  When this happens the project now moves out into the next future open spot in the schedule.  If the backlog schedule behind the slipped project is full, the next available production spot could be several weeks out.  Often, as a customer, it can be hard to understand how only a week delay in the project schedule can result in a month or longer delay in production. But it’s similar to getting out of line for an amusement park ride and then coming back to find the line has taken your spot and now you have to get behind everyone else.  The issue for the fabricator is that the schedule slip could result in an open backlog hole that is unable to be filled, resulting in productivity loss. 

Solution: These cases don’t necessarily happen all the time, but when they do, they can be frustrating for both parties. Frequent open communication between the customer and supplier often goes a long way in alleviating this issue. Strong relationships between the customer and supplier or having an Alliance Partnership definitely doesn’t hurt in times like these, but other solutions like expediting can be arranged. The fabricator can bring in extra crews, work overtime, expedite shipping-anything to help ease the pain of this problem. (Expediting fees might be included though.)

Problem #4: Typical suspects for project scope change are engineering changes or customer revisions, which result in either an increase or decrease in project scope.  When changes become significant, the backlog schedule is impacted either by the production slot being overfilled (for increases in scope) or under filled (for decreases in scope).  The overfilled production slots often result in split deliveries, with some material delivered on the original schedule and the balance delivered at a later time based on the remaining backlog.  If the scope of the project is reduced and the supplier is unable to fill the resulting backlog hole, there will be a financial impact to the bottom line.

Solution:  By doing strong research, or “homework” on the front end, and not changing the project after it’s been ordered can help alleviate this problem. Staying in constant communication with the fabricator during the quote stage can also help iron out issues before they happen.

Problem #5: Another backlog gremlin is when Murphy ’s Law attacks the project with unforeseen fabrication issues.  Most experienced fabricators are able to negate normal production issues with production buffers and preventive maintenance programs.  However, there are times when either a new product type slows typical productivity, or overly difficult fabrication results in an underestimation of required production backlog time.  Despite the supplier’s best intentions, these issues do occur at times.   

Solution: Make sure that the fabricator has adequate capacity and experiencein the industry. Plant tours, sales visits or even just phone calls and emails exchanged can help build relationships and trust.  Developing a relationship with a fabricator who will be open about any fabrication issues can go a long way to ease any construction scheduling delays as well.

The good news is that often most of these backlog issues can be remedied by upfront and direct communication between the customer and the supplier.  With adequate notice, suppliers are usually able to adjust backlogs to suit project delays or scope changes.

  

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Bet You Didn't Know This About the Fourth of July

Posted by Brooke Brackett on Jul 1, 2014 10:41:50 AM

Fourth of July is no joke here in the United States: we take this holiday serious. Now whether that is because of the smell of BBQ cooking, the incredible firework shows, cold beer or the fact that we get to experience all of the above on a paid holiday, that’s up to you to decide, but either way, it’s one of the most patriotic holidays celebrated in the United States.

But before sparklers, yankee doodle-dandy or town fairs were associated with this day, a committee of five men, including Thomas Jefferson, wrote a statement explaining what the resolution of independence was, called the Declaration of Independence, which declared independence from Great Britain in 1776.

4julypic

Pictured on top from left to right are: Jennifer Smith, DT Alliance Coordinator and Shea Rax, DT Steel Drafter. Bottom row includes: Jackie Spain, Technical Service Assist., Brooke Brackett, Marketing Cooridnator and Desiree Hunter, Steel Drafter. 

Although we celebrate our independence from Great Britain on this day, July 4th, the United States was not technically independent yet when the Declaration of Independence was first adopted. When the 13 colonies first settled, they were allowed to develop freely without much interference from Great Britain, but that changed in 1763 when Britain decided to start taking more control over the colonies. Ever heard the phrase “no taxation without representation”?

This saying was derived when Britain decided that the colonies needed to return revenue to the “mother country” and pay for the colonies’ defense. However, the colonies did not agree since they were not being represented in Parliament, and considered it to be tyranny: no taxation without representation.

After Britain continued to tax, the colonies formed the First Continental Congress in order to persuade Britain to recognize their rights. Well, we know how this turned out: they said no and the American Revolution began. After things started to heat up, John Adams, Samuel Adams, Ben Franklin and others called Sons of Liberty, decided that it was time to unite the colonies to stand together against the British government.

During the American Revolution, a second Congenital Congress was formed and it was then that they adopted the final draft of the Declaration of Independence. All 13 colonies stood behind this declaration, which was approved on July 4, 1776. Although we declared independence, the American Revolution was still being fought, which meant the US was not independent just yet. But after the war ended in 1783, the fourth of July became a highly celebrated holiday in the US.

We often get wrapped up more in the “celebrating” rather than actually remembering why. It’s important that, as a country, we all know and understand our history. The section below is an excerpt from the second paragraph of the Declaration of Independence.  

We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes; and accordingly all experience hath shewn, that mankind are more disposed to suffer, while evils are sufferable, than to right themselves by abolishing the forms to which they are accustomed. But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government, and to provide new Guards for their future security.

The Declaration of Independence serves as a reminder to not lose sight of what our forefathers learned, documented and handed down to generations in the hopes that we don’t make the same mistakes again. History isn’t just a class in school, but real life accounts.  

So to make learning a little more interesting, let’s play a quick game of true or false to test your knowledge.

1. Both John Adams and Thomas Jefferson, the only signers of the Declaration of Independence later to serve as Presidents of the United States, died on the same day: July 4, 1826.

True. They both died on the 50th anniversary of the Declaration of Independence.

2. In 1870, the US Congress made Independence Day a paid holiday for federal employees.

False. In 1870 it was declared an unpaid holiday, but then changed to a paid holiday in 1938.

3. Fifty-nine places in the US contain the word “liberty” in the name.

True. Four are counties; Liberty County, Ga, Liberty County, Fla., Liberty County, Mont. And Liberty County, Tex.

4. There were a total of 46 signers to the Declaration of Independence.

False. There were 56.

5. The term “John Hancock,” a synonym for signature, was originated because John Hancock, President of the Second Continental Congress, was the first signer.

True and False. He was the first signer and the synonym was derived from his name, however this came about because his signature was so large that it is still one of the largest and most famous signatures in history.

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How To Slip Joint Fit Up on Hermetically Sealed Steel Poles

Posted by Brooke Brackett on Jun 24, 2014 10:30:00 AM

When preparing specifications for weathering steel transmission pole projects, utilities will often require that the poles be hermetically sealed.  This means that the inside of the poles are sealed from the outside environment through welding.  The rationale behind this requirement is easy to see.  Weathering steel requires a number of wet/dry cycles in order to form the protective oxide coating that prevents further corrosion.  If water is allowed to rest against a weathering steel surface, this oxide coating cannot form and corrosion can be a result.  By eliminating water from inside the pole, this corrosion mechanism is eliminated.  The most common method of hermetically sealing steel poles is through the use of sealer plates that the top and bottom of a slip jointed section.

Problem:  Difficult slip joint fit up on hermetically sealed poles

Sealer plates are often used on weathering steel slip jointed poles to provide a barrier against air intrusion.  A sealer plate is placed at the very top of the lower section while a second sealer plate is placed above the point of maximum slip on the upper section.   These sealer plates can significantly stiffen the sections against deformation.  Often, steel pole sections will not be perfectly round when formed.  In order for the two sections to mate together properly, the sections need to conform to each other.  When sealer plates are present, the tubes are stiffened against deformation which can make it difficult to achieve the proper slip length.

sealer_plate

Solution:  Eliminate the upper section sealer plate

If the top of a section is sealed against moisture there is no way for moisture to travel up the slip joint.  Furthermore, the air gap between the top and bottom section allows any condensation or other moisture that finds its way inside the tube to drain out the bottom.  Following these recommendations will go a long way towards ensuring proper slip joint fit-up, as well as make the contractor's life easier.

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Topics: slip fit pole assembly procedure

10 Tips: How to Save Money When Submitting a Bid to a Steel Fabricator

Posted by Brooke Brackett on Jun 19, 2014 11:25:00 AM

Every structural steel fabricator is different when it comes down to pricing substation and transmission steel structures. But, there are some commonalities that could help save you money when submitting a Request for Quote (RFQ). How do you do that you might ask?

Well, generally, there’s a rule of thumb to consider: the more information you give the Estimating Department, the better price you’ll receive. If very little information is given, it’s harder for the estimating department/engineers to easily go through and pick out requirements, design the structure and then send the RFQ back in adequate time. And sometimes the price might reflect the assumptions that had to be made. 

Different terms used:

  • Request for Quote (RFQ)
  • Request for Proposal (RFP)
  • Purchase Requisition
  • Inquiry
  • Bid Event / BidQuote / Proposal

DTS_Employee

So, if you’ve asked yourself, “what can I do to save money when submitting a bid,” here are five good starting points.

1. Well-Defined Scope of Work- this could include everything from what the fabricator’s responsibility is, to needing the structures galvanized or weathering, delivery process, how hardware should be shipped, etc.  

2. Technical Specifications- this tells the fabricator how you want the structures built, like what kind of steel to use, etc.

3. Commercial Terms- this is more on the legal side, meaning what type of payment or who to invoice, insurance requirements, warranties, damages, etc.

4. Structure/Electrical Layout- this gives the overall dimensions of a structure such as height and width or phase spacing.

5. Enough Time to Bid- it’s important to keep in mind that fabricators typically have a quote backlog already scheduled out. 

Often, in order to send a bid to a fabricator, customers require the fabricator to be on an approved vendor list in order to quote the project.  The approval process usually involves quality assurance / quality control (QA/QC) audit, industry experience, project references, customer references, commercial term agreement, credit approvals, etc. 

Facts That Could Affect Pricing:

6. Weathering steel generally costs less because unlike galvanized steel, it doesn’t get the galvanized coating. (Typically see weathering steel more with transmission structures.)

7. Usually, the more steel ordered at one time could help give you a better price. In this instance, if you had different structures for one substation, instead of ordering separately, try to coordinate to order all the structures together, which could save money on freight and other expenses.

8. Loads with over-length and over-width sections could get costly because you have to get freight permitting depending on the states along the delivery route. Typically, the price for wider structures is greater than longer structures.

9. Expedited lead times can increase price. Since a production backlog is already in place, fabricators would need to expedite engineering, detailing, rearrange product schedule or may have to include some overtime.

10. Special weld inspection requirements and tests that are beyond typical industry standards could raise the price. If the fabricator needs to pull in a third party to inspect, send material off for testing or bring in an expert, it could increase the price.

These are just a few suggestions, and are not meant to be taken as the rule in every situation when dealing with every fabricator. But it is good to know how your project was priced and what affected it so that there are no hidden surprises or confusion.   

So remember: supply ample information, receive accurate price. 

 

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Topics: transmission structures, substation structures, structural steel fabricators, structural steel price, rfq request for quote, engineering estimating software, structural steel

3 Common Steel Structures Found Inside a Substation

Posted by Brooke Brackett on Jun 12, 2014 2:18:00 PM

In order to watch the fourth game of the NBA Playoffs when the Spurs trek into Miami territory to take on The Heat Thursday, June 12, you need a little thing called electricity. (Besides a television)

But before the electricity can travel into your home, it must pass through a substation first. A substation is an assemblage of equipment where electrical energy is passed in order to be stepped up or stepped down.

Transformers inside a substation change the voltage levels between high transmission voltages and lower distribution voltages. The high transmission voltages are used to carry electricity longer distances, like across the country, whereas lower distribution voltages travel to industrial, commercial or residential consumers.

In a T&D system, the major components typically consist of transmission lines, distribution lines, substations and switchyards.

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The three main types of structures found inside a substation include:

1.)    Dead-End Structures

2.)    Static Poles

3.)    Bus Supports/ Equipment Stands

Dead-end Structures are where the line ends or angles off. They are typically constructed with heavier steel in case they are needed to carry heavier tension. The two most common dead-end structures are H-Frame and A-Frame structures.

 H frame graph

A frame graph resized 600

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The second structure, a Static Pole, is a single, free-standing pole that creates a shield to protect all of the equipment inside a substation from lightning. Static poles may or may not have overhead shield wires attached to enhance protection. It depends on the size of the substation as to how many static poles are needed.             

NOTE: Tapered tubular design is typically efficient and economical in dead-end and static pole situations when compared to AISC standard shape structures.

Bus Supports are the most basic structure found inside a substation. Its main purpose is to provide support for rigid bus as it travels though the substation. Rigid bus is stiff and will not move around during weather events. Unlike rigid, flexible bus is typically used in high seismic describe the imageareas in order to be able to move and dampen the seismic forces that occur. 

Electrical equipment can be of significant weight and must meet specific guidelines for structural loads, deflection limits or clearance requirements. Equipment Stands are the structures that the actual equipment sit on.

Examples of some equipment stands include:

  • Potential Transformers (PT) Stands
  • Current Transformers (CT) Stands
  • Coupling Capacitor Voltage Transformer (CCVT ) Stands
  • Lightning Arresters (LA)
  • Switch Stands

When it comes to which type of steel is used, galvanized or weathering, inside a substation, I won’t say that you will never see weathering steel, but it is very rare. Weathering steel is used more in transmission structures than substation. One of the main reasons is because aesthetically, galvanized steel “looks” better inside a substation. Typically a substation is surrounded by a fence, has a metal building inside as well as white rock on the ground surrounding it. So the look of weathering steel, which is usually a dark brown color, aesthetically, goes better with a transmission line running through the woods to blend in versus in a substation.

So, I'm sure you'll be thinking about all of this tonight as the Spurs and Heat battle it out on the court!

 

 

 

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Topics: electrical substations, Voltage, transmission lines, substation, power, distribution lines, switchyards, equipment, static

How to Avoid Weld Symbol Miscommunication with AWS A2.4

Posted by Brooke Brackett on May 22, 2014 3:06:15 PM

Being a fabricator, we see a variety of fabrication drawings. Not only do we fabricate from drawings generated by our own engineering and detailing groups, but we also fabricate from drawings generated by others. These customer supplied drawings can vary greatly from 20 year-old hand drawn steel drawings to highly detailed drawings with 3D images of the connections. Ultimately, the fabrication drawings are the link between the engineer who is designing the structures and the fabricator fabricating the structures.

Having clear fabrication drawings increases the likelihood that the steel being fabricated turns out exactly how the engineer intended. The drawings do not have to be fancy or highly sophisticated in order the get the message across to the fabricator; however, they should contain the needed information and make sure it’s shown correctly. 

Examples of this include:

  • Fabrication Notes
  • Clear Section Views
  • Proper Weld Symbols, etc.

welder 

The use of proper weld symbols is a critical component to the fabrication drawings.  If the weld is shown incorrectly or left up to the interpretation of the welder, then it can make the difference of whether the connection will hold up to the loadings.  One main problem is incomplete or vague weld symbols that could be interpreted different ways.

Some of the different welds include:

  • Fillet Weld
  • Single Bevel Weld
  • Single V-GROOVE Weld
  • J-Groove Weld
  • U-Groove Weld
  • Square Groove Weld

Welding symbols provide a system for placing welding information on drawings and work sites for the purpose of relaying information to fitters, welders, fabricators, inspectors, etc. These symbols quickly indicate the type of weld joint needed to satisfy the requirements for the intended service. AWS A2.4 Standard Symbols for Welding, Brazing, and Nondestructive Examination is the correct standard. It's a great method for communication between the design engineer and the fabricator, but if the fabricator fails to gain a thorough understanding of what the engineer is requiring, then that could result in welds being placed in the wrong location, sized incorrectly, wrong welding processes, etc. 

The engineer on record who designed the structures, also signs-off on the fabrication drawings, and is ultimately responsible for correct weld symbols.  As a fabricator, it’s a good practice to glance over the drawings before they hit the shop floor in order to be proactive and head off any issues.  They should also have trained welders that flag any weld symbols that are unclear so that they can ask for clarification.  However, if it gets to this point it can start affecting the shop production because the welder could be on standby waiting on a response.  For a fabricator, a welder standing around waiting is not a good thing. 

Referencing AWS A2.4 will help guide and protect all parties so that their projects are a success, as well as allow everyone to be on the same page talking the same “language”.

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What Everyone in the Hot-Dip Galvanizing Industry Should Know

Posted by Brooke Brackett on May 8, 2014 11:44:11 AM

If you ever have the opportunity to visit a galvanizing plant and watch firsthand the hot-dip galvanizing process, you would gain a whole new appreciation for the “silver-looking poles”. It’s a fascinating process with so much behind the scenes chemistry going on. 

To bring you up to speed, hot-dip galvanizing is the process of coating fabricated steel by immersing it in to a bath of molten zinc that metallurgically bonds the zinc to the steel.  This practice has been around for over 150 years, and provides maintenance-free corrosion protection for decades

Quick Breakdown:

When the steel enters the kettle at 840 to 850 degrees Fahrenheit, zinc-iron alloy layers start to form. This portion normally represents about 50 to 70 percent of the total coating thickness, with the zinc being the top layer. Directly coming out of the kettle, all steel is extremely bright, despite the coating appearance.

galvanied-1

5 grades of zinc for continuous hot-dip galvanizing:

1. London Metal Exchange (LME) Grade- contains a minimum of 99.995% zinc

2. Special High Grade (SHG)- high purity of zinc containing a minimum of 99.990% of zinc

3. High Grade (HG)-  contains a minimum of 99.95% zinc

4. Intermediate Grade (IG)- contains a minimum of 99.5%zinc

5. Prime Western Grade (PWG)- contains 0.5 to 1.4% lead, and a minimum of 98.5% zinc

zincchartpic-1

There are distinctive looks and markings on the finished galvanized product depending on the grade used. For example, PWG lends itself to a more spangled look, whereas SHG has a more continuous bright coating.

When steel is delivered on-site the first thing that is noticed is the coating appearance. Upon further inspection, if discolored or lumpy areas are noticed, the most common concern is if it’s detrimental to the life span of the coating. But in many circumstances, the look tends to be more serious than the actual effects.

8 Most On-Site Concerns:

1. Bare Spots- Smaller flaws have little effect on the service life of the coating, and can be somewhat self-healing. Some spots may require repair using such methods indicated by ASTM A 780). But, uncoated, unrepairable spots can be grounds for rejection. Some causes of bare spots can be because of inadequate surface preparation, welding slag, rolling defects, sand embedded in castings or oxidized steel.

2. General Roughness-   This is usually due to excessive growth or unevenness of the alloy layers, which can be attributed to the steel’s chemical composition or original surface condition. Heavy coatings are usually rougher than lighter coatings because irregularity of alloy layers tends to increase with thickness. In most cases, a rough coating does not negatively affect the lifespan, as long as adhesion is good. But, there are always exceptions to the rules. For particular pieces where one surface mates with another, rough coatings can be detrimental.

3. Dross Protrusions- Dross is the zinc-iron alloy that settles to the bottom of the kettle. It produces surface protrusions when the dross layer becomes agitated from the dross inclusions. Dross protrusions tend to have little effect on the surface life since the corrosion rate is similar to zinc. However, extensive dross inclusions can be grounds for rejection because they tend to make the surface more susceptible to mechanical damage.

4. Lumpiness and Runs- A lumpy coating results when the withdrawal is too fast or when the bath temperature is too low, not allowing molten zinc to drain back into the bath. Delayed drainage from bolt holes, folds, seams or other pockets where zinc collects is a consequence of the design. When products come in direct contact with others while being withdrawn from the kettle can also cause a lumpy coating appearance. Although it’s not detrimental to the life span, some cases require a smooth finish.

coating_pictures1-1

5. Flux Inclusions- Flux inclusions occur when a layer of zinc-ammonium chloride floats on the top of the molten zinc. When the steel is submerged in the bath, the flux pushes to the side when the steel is pulled back out. Flux inclusions can be caused by several different scenarios, such as a stale kettle flux where it tends to adhere to the steel instead of clearly separating from the surface as the steel is dipped. If the underlying coating is sound, then flux deposits are not reasons for rejection.

6. Ash Inclusions- Similar to flux, ash may be picked up during the dipping of the steel. Zinc ash is the oxide film on the surface of the bath. Ash inclusions can occur when steel requires slow withdrawal from the bath, and has no effect on the service life. If improper skimming of the exit surface of the bath can lead to gross oxide lumps, and can reduce the effective thickness of the coating, which is not acceptable.

7. Matte Gray or Mottled Coating- Usually appears as a localized dull patch or wed-like area on a normal surface, and develops when there is a lack of free zinc layer on the coating surface during the cooling process. A matte gray coating is found mostly on steel with relatively high silicon or phosphorous content, since they are heavier sections that cool slower. Galvanizers generally don’t have prior knowledge of the steel’s chemical composition, and has no control over its occurrence.

8. Rust Stains- Surface rust stains are not cause for rejection if they are caused by seepage from joints and seams after galvanizing or steel being stored under or in contact with rusty steel. Rust stains like this are superficial and should not be confused with failure of the underlying coat.

Whenever a question arises on the advisability of galvanizing a certain weld material, fabrication or steel type, it is best to consult the galvanizer. Most of the issues can be addressed beforehand if all parties stay in contact throughout the process before the steel arrives at the galvanizing plant. Remember to keep these 8 concerns in mind next time you conduct a visual inspection to help avoid delaying projects. 

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How to Make a Transmission Pole Plumb Using Raking or Cambering

Posted by Brooke Brackett on May 1, 2014 2:53:02 PM

Appearance can determine a lot just to the naked eye. Without knowing any specifics, when we look at something we instantly decide if we like it or not, just by its’ appearance. And over the years, we’ve all either heard or actually experienced that the saying “you can’t judge a book by its’ cover” tends to be true more times than so.

The desired appearance of installed structures can determine things like structure diameter, taper and deflection restrictions. Line angles and unbalanced phase arrangements can create loading situations that will cause a structure to deflect noticeably under normal everyday loadings. There are several methods that are used to lessen these effects, but two specific methods for counteracting monopole structure deflections due to line tensions are raking and cambering.

Both methods are used to accomplish the same goal of making the steel transmission pole appear plumb, meaning straight, under normal everyday loadings.  Steel pole structures can be quite flexible.  Depending on the loadings, configurations, etc. a steel pole can have a significant amount of deflection, yet be structurally adequate. 

In lieu of increasing the size and/or stiffness of deflection controlled poles to decrease the amount of deflection, they can be raked or cambered.  This helps avoid concern from the general public who could misinterpret noticeable deflection to appear like the pole is about to fall over. 

Raking- the deflection at the top of the structure is determined, and the pole is tilted a corresponding amount so that the top of the structure is at a specified position in relation to the structure at ground line. (ASCE 48-11)

Cambering- cambering the structure during fabrication to offset the anticipated deflection under load so that it will appear straight and plumb after installation. (ASCE 48-11)

raked_camber

Raking is when the contractor “tilts” the pole in the opposite direction of the expected deflection before the overhead lines are installed.  This can be achieved by adjusting the leveling nuts below the baseplate on the anchor bolts.  The amount of rake is typically based on the expected deflection under the normal everyday loading.  Also, the amount a pole is raked is typically limited to lower values.  For example, if a pole is deflecting less than the allowable deflection under the normal everyday loading, then the remaining deflection is taken out by raking the pole.  After a pole is raked and all lines are installed, the structure will then deflect back towards the upright position appearing plumb. 

Cambering is when the base plate is horizontal but the actual steel pole is curved, kind of resembling a banana. To achieve this method, selective applications such as heating and cooling cycles are used to apply curvature along the length of the pole, which is a specified amount based on the expected deflection under the normal everyday loadings. The contractor then installs the pole so that the pole curves away from the expected deflection.  Once the pole is erected and all overhead lines are installed, the pole will deflect back towards the upright position appearing plumb. 

Specifications sometime require a pole to be raked if the deflection is less than 1 percent of the normal everyday load case, and to be cambered if the deflection exceeds 1 percent.  

If the pole is to be raked, then the pole is designed for all load cases ensuring the structure does not overstress, while at the same time does not deflect more than 1 percent under the normal everyday loadings. 

If the pole is to be cambered, then the pole is designed for all load cases ensuring the structure does not overstress while at the same time not limiting the deflection. 

3 things associated with curving a pole to keep in mind are:

1. Possible additional costs

2. Maintaining the needed curvature during the galvanizing process

3. Limitations of this method on thicker/larger shafts or shafts with a lot of attachments and thru-vangs.

However, in using this method for deflection controlled monopole structures, there could be overall cost savings by allowing more deflection resulting in smaller/ lighter poles.

Last week’s blog topic was about when to use concrete pier foundations over direct embedded foundations, so just to point out an advantage that concrete foundation has over an embedded pole is that the pole can be easily raked with the anchor bolt leveling nuts. Depending on site conditions and equipment in the field, there can be challenges to maintaining the needed rake as backfill is added around the embedded pole.  When raking, the differential of the nuts are not much compared to the entire structure, therefore making it easier for the fabricator and providing more control in the field for the contractors. When a pole is cambered, it can be at times like mixing art and science together.

 

 

 

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Direct Embedded versus Drilled Pier Foundation for Transmission Poles

Posted by Brooke Brackett on Apr 17, 2014 2:00:00 PM

Before I started writing and learning about the utility industry, I honestly never really noticed the difference, nor did I actually know the difference, in transmission poles or how they were installed. Now, a year and eight months later, I catch myself scurrying to get my iPhone out while driving down the highway to take pictures of tapered tubular davit arms or dead-end h-frame structures.

Have you ever paid attention to the way a transmission pole was installed? I’m sure if you’re not an engineer or someone in the utility industry your answer would be no, but for those of you who are, have you noticed the foundation method? Do you know the different methods?

Well, in the ASCE 48-11, Design of Steel Transmission Pole Structures, three specific methods used to place a steel transmission pole into the ground are pointed out:

1. Drilled Shaft Foundation with Anchor Bolts

2. Direct-Embedded Foundation

3. Embedded Casing Foundation

There are also other methods such as spread, pile, rock anchor foundations, etc. that can be used for more specific applications. But the two that I want to focus on are drilled shaft foundation (also known as drilled pier foundation), and direct-embedded.

When deciding on which method is best suited, there are some considerations that should be addressed in initial design as well as restrictions to pay attention to. Things like type of structure, importance of structure, allowable foundation movement or rotation and geological conditions are important and shouldn’t be overlooked.

Direct Embedded Poles:

  • Tends to be more economical over concrete foundation because it essentially just requires digging a hole, dropping the pole into the ground and then backfilling it with rock, concrete or other specified backfill.  
  • Typically used for tangent and light angle structures where the overturning moments are smaller.
  • As loads get larger, embedding a pole becomes less favorable because they are solely using the pressure of the specified backfill to resist the pole from coming out of the ground.
direct embedded transmission pole

Drilled Pier Foundation:

  • After the hole is dug into the ground, a combination of reinforcing steel and anchor bolts are lowered in place followed by concrete.  
  • Typically used in medium to heavy angle structures as well as dead-end steel structures.
  • The massive weight of the concrete that is in the ground is larger in diameter than the pole, so it can engage more soil, as well as have a greater bending force at the base.
drilled pier foundation

 Other things to consider when selecting foundation types include:

  • Soil properties
  • Foundation loads
  • Design limitations
  • Equipment availability and accessibility
  • Environmental restrictions
  • Cost/budget

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Topics: direct embedded versus drilled pier foundation, tapered tubular davit arms, dead-end h-frame structures, ASCE 48-11, design of steel transmission pole structures, drilled pier foundation, drilled shaft foundation, direc embedded foundation, embedded casing foundation, combination of reinforcing steel and anchor bolts

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