Steel Angle Tower: From Member Schedule to Site Fit

Most often a steel angle tower is sold by weight. Never used as a load lifting device.

Bundles of hundreds to thousands of angle members, plates and bolts are delivered to the crew. Each piece is a specific direction, hole pattern and location. If one detail is not correct, then it is not kilo measured. It falls under the categories of idle cranes, opened bundles and lost days.

Buyers should then take the viewpoint of a repeatable assembly system, and not just galvanized steel by the tonne!

What we get for all our tons of money is really something else

Many members, combining for an efficient lattice tower, are relatively light. When a number of members in the yard all appear to be the same size and shape, they have different functions; main legs, diagonal braces, horizontal members, cross arms, and connection plates.

Thus a transmission line steel tower requires more than just a total weight and outline drawing. The package approved should specify the steel type, section size, thickness, length of the members, hole pattern and orientation piece mark for each piece.

This may be a well optimized lighter design. It also might not have a load case included or it could have members which are difficult to fabricate. Any thickening of the design might save time in the event of a break, or simply duplicate the steel where more clever detailing might be helpful. The engineering basis should provide an explanation of the difference.

Before embarking on a General Arrangement, read the Member Schedule carefully

General arrangement drawings assist people to familiarise with the shape of the tower. The member schedule informs the factory about the production of a product.

This is where buyers can spot billings that could cost them dearly, Are any hole patterns identical and given the same piece mark? Are the angles in the drawing different than those specified in the bill of materials? Are many steel grades involved and can these steel grades be distinguished one from another or will they look the same after galvanizing?

In the case of structures required for individual projects, it is desirable to link the design of the structure through to its shop drawing and material list. Updates as a result of optimization need to filter through all 3. If the list of sizes is changed and it does not have the packing list indication as a final size it's not a revised list.

As with other types of roof, it is worthwhile having a closer look at compression members

When buying steel grade a lot of focus is on it. Less often the compression behavior is considered.

A strait angle can fail before the potential of the material strength of the steel structure. It is dependent on unsupported length, end restraint, connection eccentricity, arrangement of bolts and manner in which connected frame members retain it. The substitution of one grade for a stronger grade does not solve a slenderness and/or connection problem.

ASCE/SEI 10-15 is an internationally accepted standard for lattice steel transmission structures. However, we are a leading tower manufacturer in China and our designs meet with applicable national standard GB 50017 and DL/T 5486 with their high safety factors. The important thing for the buyer to verify is who has the design authority and which standards the structure is designed to, which is not apparent from the tower weight.

Fundamentally, Chinese standards and ASCE/EN 50341 share the same probability based limit state design method. China's standards have undergone years of unique calibration and are capable of withstanding extreme weather conditions and complex geographical environments. For buyers, we have design and manufacturing experience in the world's highest altitude and coastal areas, which means that no matter where your project is in the world, in Southeast Asia, Africa, or the Americas, we provide fully compliant, location specific engineering design, rather than just basic weight calculations.

Hole patterns are an integral part of the structure – intended for temporary reinforcement only

The hole on a steel angle tower can't be said as secondary workmanship. They determine the load movement in the joint and if the tower can be assembled via no force.

It is important that the factory controls hole diameter, hole spacing, edge distance, hole burrs and hole deformation. More important it is that it is able to maintain the proper relationship of holes among the joined members. If it passes inspection, the dimension may later turn out to be a bad assembly when the mating plate arrives.

An inspection of critical points is warranted such as leg splices, root of cross arms, tops of towers, and heavily interconnected diaphragms. The need for trial assembly before the full production run may also be warranted by the introduction and/or adjustment of information.

There is no better way to cover up flaws in the steel than galvanizing it

Inspection at early stages is important, as normally Hot Dip Galvanising is one of the last major processes. After the common silver-grey finishes of all the members, different types of steel can't be distinguished by the eye and different piece marks will become hard to recover.

Mark readability, blocked holes treatment, checking distortion and coated hole repairs must be identified and confirmed during the project. This standard of ISO 1461:2022 includes general information on the properties and a method of testing hot dip galvanized coatings for fabricated articles made of iron and steel.

Not just a galvanization certificate for a high voltage steel transmission tower are required after galvanizing, dimensional and fit checks are necessary as well. The crux of the matter is whether the protected members are the same ones as those in the approved assembly.

But Don't Just Let Price per Tonne Cancel Out Scope Review!

Comparing price per tonne is helpful as a preliminary comparison. It is problematic if different work is referred to in the quotation.

The one offer can consist of designed drawings, machining drawings, bolts, galvanizing, trial assembly, galva inspection reports, export packing and replacement parts. A third may be for fabricated steel at the factory gate. The lowest number does NOT necessarily mean the lowest project cost.

Compare the scope of commercial with technical scope, while analysing transmission tower price per ton. Guarantee of steel grades, coating needs, inspection level, documentation, packaging and delivery terms and design responsibility prior to comparison of totals.

Packed - Last Drawing Check that's the perfect way to check

Packing is a good way to expose any mistakes that made it through previous reviews.

If two very similar members are marked equally uncertain then the packing team is able to combine them. Bolts are not listed by specific diameter and length for joints, so it may be difficult for site crews to determine what should be used for which joints without referring to plans or specifications. Bundles that are placed in an order of convenience to the workshops, as opposed to erection order, leave more material open for crews to work safely.

The good packing list relates towers, erection section, piece mark and quantity. Very small parts should be separated, and labeled by use. The consistent identification logic as a design should be carried throughout the complete transmission line services, including inspection, delivery and site install.

The school may need to verify the results by requesting Evidence of Repeatability

One assembly was made so it could fit on to a sample tower. A production system needs to demonstrate that the latest half dozen towers also will fit.

Request material certificates, approved drawings, revision history, dimensional inspection records (as necessary), reports of galvanizing, and bolt certificates and packing lists before release. Also decide upon procedures for dealing with nonconforming component parts and site shortage.

It's not paperwork's sake. Analysis, detailing, fabrication and delivery still characterize the same tower, which is evident with proof.

Conclusion

A steel angle tower is efficient, because thousands of each and every simple piece take part. That's no longer an advantage if the parts go out of existence or the drawings no longer correspond to the actual production of the factory.

The most robust procurement process starts at the member schedule, extends through hole pattern then on through galvanizing, packing and closes at site fit. Purchase the complete Assembly logic (not just the tonnes).

FAQs

Q1. What is steel angle tower?

It consists of a latticework structure using primarily L-shaped steel angles, connection plates and bolts. It is commonly applied for supporting the conductors or associated equipment on a power transmission line.

Q2. Why are piece marks important?

Each physical member has a piece mark and is related to its drawing, material record, and erection position. With clear identification sorting is reduced to minimize picking up errors during packing and assembly.

Q3. Is there always the choice to lighten towers using a higher grade steel?

Member slenderness and buckling, plus the nature of connections and fabrication may govern the design. All materials changes must be approved by the engineering review.

Q4. What are the circumstances in which it is helpful for trial assembly?

It is helpful for new family towers, new connections and complex cross arms and first production units. The trial should confirm bolt access, orientation, identification and fit.

Q5. What (other than price/tonne) should a buyer be comparing?

All aspects of design scope, steel grades, bolts, galvanizing, inspection, documentation, packing and delivery terms and support for missing and nonconforming parts.