DIS-TRAN Steel Blog

DIS-TRAN Take2: How to Calculate the Anchor Bolt Embedment of Transmission Poles

Posted by Wendy Gintz on May 7, 2015 1:30:00 PM

It's been awhile, but we are still at it...  Thats, hopefully createing ueseful tips that make your job easier.

AnchorBolt

We have had a sort of series of Take2s referencing Anchor Bolts.  For this edition we will look at calculating the embedment of steel transmission structures.  Please feel free to go back and view the two previous Take2 Blog posts.

     Anchor Bolt Loads
     Anchor Bolt Design

What you will hear about...

  1. What to consider when calculating the embedment.
  2. What resources to use.
  3. A working example
  4. Additional information to consider

   

Thank you for viewing the DIS-TRAN Take2. We look forward to your feed back.  Please leave any comments or questions you may have about transmission pole or anchor bolt design below.

Until next time...

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Tags: transmission structures, transmission poles, design of steel transmission pole structures, anchor bolts

9 Must Haves for a Steel Structure Specification

Posted by Wendy Gintz on Apr 22, 2015 4:30:00 PM

Specification are to Steel Structures like...Cherries are to a Banana Split.BananaSplit

Specifications come in all shapes and sizes.

From the very informal 3 page document to the all-encompassing formidable documents.  The specification is a tool for the Owner (End User) to convey their minimum project requirements to the supplier.  Defined by Wikipedia, it is a set of documented requirements to be satisfied by a material, design, product or service and also a type of technical standard.

In the utility industry we see specifications presented in many different formats.  As a result, it is very important that a specification be clear and easy to follow.  Be careful about providing multiple specifications and documents that start contradicting one another. In these wordle_2situations the Owner’s requirements and overall message can get lost in a sea of documents resulting in different interpretations by the suppliers.  This can ultimately lead to proposals that can’t be compared properly, Owners not getting what they want, or additional unforeseen costs. When it comes to fabricating substation and transmission steel structures there are many variables that need to be relayed during the design, detail, and fabrication phases.  These specifications provide that direction.  Whether you are using an already created specification, updating a previous version or crafting a brand new one, there are certain sections you want to include.  Below are 9 sections that are not to be missed when deciding the content for your specifications. 

  1. Purpose/Scope – This is the heart of the document.  This is the owner’s chance to define the purpose of the document and clearly layout their expectations for the scope of work.  Example: Intended to serve as a system wide guide for structural design of steel structures.
  2. References – This section typically lists out the required design standards and any other applicable documents.   (e.g. ASTM Standards, ASCE Design Stanards, etc.) 
  3. Submittals – This section typically covers the owner’s expectations of any document to be submitted by the supplier.  This includes things like bid proposal requirements listing out the needed forms and design summaries.  It also covers formal design and drawing submittal requirements.
  4. Loading and Geometry – If the scope of work includes design, this section typically covers the minimum information needed by the Structure Designer to design the structures.  This would include things like loading criteria, unique weather conditions and terrain for the service area, and any other usual loading conditions the designer should consider.    This section also covers the different structure types, general layout of the structures, and the types of connections permitted.  (e.g. slip-fit vs. flange, embedded vs. base plated)
  5. Design – This section typically includes any restrictions to the design, material, field erection, fabrication, etc.  Examples of this include anchor bolt circle limits, minimum material thicknesses allowed, deflection limits, aesthetic preferences, weight limitations, etc.
  6. Fabrication – This covers owner’s expectations of workmanship and quality. 
  7. Finishing/Coating – What type of coating is supposed to be used such has galvanizing, painting, sandblasted, etc.
  8. Inspection – This section typically covers the type of inspections and testing required for the project. 

Of course these are just a few of the main sections.  There may be other sections that pertain to your specific product need, corporate formalities and/or industry.  No matter what your final Specification Document instills, it is important that you and those that use them agree on what is expected from a product and/or service.  This form of communication between the two parties can be a key component to a successful project.

How do you communicate your expectations to your vendors?  We would love to hear from you so please leave a comment below and let us know if this information has been useful.

Pole Design References

Tags: substation design, specific standards for structures, Engineering, design of steel transmission pole structures

Direct Embedded versus Drilled Pier Foundation for Transmission Poles

Posted by Brooke Barone on Apr 17, 2014 3:00:00 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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Tags: 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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