Welding THE TOWER: A brief guideline to the welding processes and techniques applied in the fabrication and erection of the structural steel for the Torre Mayor Building.

Ramon S. Fernandez

Pascual Contreras Toro

Authors Ramon Fernandez is Technical Development Manager for Corey S.A. de C.V. He is a Civil Engineer from the Autonomous University of Guadalajara. Since 1988 he has been involved in the pioneering quality assurance project in Mexico based on ISO9000 standards. He designed and directed the project that in 1996 allowed to Corey S.A. de C.V. became the first fabricator in Latin America certified in the AISC Quality Certification Program in the complex buildings category including the sophisticated Paint endorsement. He have developed quality assurance systems and inspection plans for some of the most important structural steel projects in the last 7 years in Mexico and in projects for Argentina, Chile, El Salvador, Puerto Rico and the United States, including the inspection processes based on FEMA requirements used for the fabrication of columns for the new International terminal of the San Francisco Airport. Since 1991 he has been involved in the research and teaching of alternative NDT procedures, welding processes, metallurgy, fabrication automation, and software development. Ramon Fernandez is an ASNT Level III Certified NDT Inspector, AWS CWI Welding inspector and ISO9000 Quality System certified Auditor. Pascual Contreras Toro in the Welding Processes Development Chief for Corey S.A. de C.V. He is a Professional Mechanical Technician from the Polytechnic Institute of the University of Guadalajara. He has been involved in welding processes for more than 28 years. He specialized in welding processed in La Rochelle France. He was the Quality Control Manager for Concarril (the Mexican fabricator of subway wagons) and District Manager for Hobart. He has been involved for more than 18 years in the research and teaching of alternative welding processes and techniques including welding automation, production and maintenance welding.

Summary The Torre Mayor Building represents a major milestone in the construction industry history of Mexico. Large, heavy and thick elements, complex connections and geometry and the most strict requirements in the industry for quality and safety implies challenges to whom welding processes cannot be absent The accumulated knowledge learned in the Mexico City, Northridge and Kobe earthquakes about seismic behavior of welded connections is incorporated in the development of this project. The 1985 earthquake in Mexico City and its aftermath of damages implied radical modifications to local construction codes in the city. Torre mayor is the first project of this magnitude developed since this new construction code is enforced. In this paper we describe the welding processes developed to fabricate and erect the structural steel for this project and how proper selection of welding equipment, consumables and joint design can help to keep project advance on schedule. Less than 4 miles from the original site where the capital of the Aztec empire was established, in an small island within a lake where they found an eagle devouring a serpent, our crew and staff is erecting and welding the tallest building in Latin America in conditions where only eagles dare to live.

Figure 1. Actual stage of construction as in late March, 2002.

Welding THE TOWER: A brief guideline to the welding processes and techniques

applied in the fabrication and erection of the structural steel for the Torre Mayor Building.

Ramon Salvador Fernandez Orozco

Pascual Contreras Toro

There are no small numbers when we try to explain the size and scope of a project like Torre Mayor.

The building represents an important milestone in the construction industry in Mexico. The structural steel comprehends 16,500 metric tons in 57 levels.

THE CHALLENGE IN NUMBERS

Welding consumables for both, shop-fabrication and field erection, amount a total tonnage of 258 metric tones (169 metric tones for shop welding and 89 metric tones for the field). In erection welding we estimate that there will be distributed approximately 45% electrode and 55% FCAW wire for semiautomatic welding

To have an approximate idea of the amount of welding wire that will be used in this project, if we extended all the wire to form a single unit it accounts for 1.9 times the earth circumference.

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Figure 3 The Torre Mayor structure Wireframe

Figure 2 SMAW electrode tack welding of elements in site.. Along the project electrode use FCAW

wire

The estimated amount of man-hours devoted to welding, using SMAW electrode and FCAW wire for the project totals 155,000 men-hours, this is equivalent to a person working for 17.7 years 24 hours a day, 365 days per years.

To have a measure of the advantage of using semiautomatic processes, we will use a similar analogy to evaluate.

If only SMAW electrode is supposed to be used in the project we estimate that a total amount of 434,500 men hour is required to complete the project. This is equivalent to a person working for 49.6 years 24 hours a day, 365 days per years. This is 2.8 times the amount of time.

More than 45 welding power sources (multi-process, constant voltage, 650 amperes of capacity al 100% duty cycle) in two shifts are used for shop welding in two shifts. 50 similar power sources are being used for field welding.

RECENT TENDENCIES IN THE STRUCTURAL STEEL MARKET IN LATIN AMERICA AND ITS IMPACT IN WELDING TECHNOLOGY

Along many years, and with an increased emphasis since the 1985 earthquake in Mexico City (Reinforced now worldwide as a consequence of the Northridge and Kobe Earthquakes), the primary steel sector in Mexico has strengthened its effort in diffusing the advantages of steel as structural material. But essentially, the fabrication of structural steel had been using the same procedures used in the last three decades.

Due to NAFTA and other trade agreements that opened the frontiers of Mexico to the competition with companies in Canada and in the Unites States, Mexican structural steel fabricators established contact with fabricators and suppliers in other countries to evaluate available new technologies and also provided additional resources to create or adapt design and fabrication procedures to the Mexican structural steel market reality. The intention was to offer to the local market

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quality, cost, punctuality in the delivery and safety conditions similar to of any manufacturer worldwide, and also to initiate export projects.

These tendencies could summarize to:

1. The incorporation of automation processes (Numerical controlled equipment) in the fabrication of steel structures that formerly were reserved only to other sectors of the industry. Through these equipment it is possible to obtain the necessary flexibility to manage complex forms in the structure, important reductions in the execution time and production costs thus as a uniform quality.

2. Use of concurrent engineering structural steel detailing software.

3. Use of the most recent welding technology, processes, equipment and consumables equal to the North American market.

4. The recognition of the need and advantage of designing welding procedures specifications fitted specifically to each welding positions, welding environment, availability of welding equipment and the need of seismic resistance conditions.

5. Development of quality assurance systems in the processes of design, fabrication and erection that until a few years ago were reserved to other sectors, as the industry of energy generation. (Based on AISC and ISO9001 Guidelines)

6. Cooperative work with the structural designers to develop connections more efficient to fabricate and erect at the site.

7. Provide solutions to the increasing demand of safety and reliability from our customers through the diffusion in the fabrication processes of NDT inspection procedures; reserved in the past to other type of products.

Elimination of the disadvantages that traditionally have been attributed to structural steel related to the elevated cost of the maintenance to prevent corrosion and the susceptibility to suffer harmful damages in the case of fires that have been surpassed in great measure with the advances achieved in the use of new materials and processes of paint application and fire retardant materials.

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FABRICATION WELDING

Shop welding is basically performed by the Submerged Arc Welding process (SAW) and Flux Cored Arc Welding process (FCAW).

For welding fillet welds and flat groove joints SAW process is the most efficient process. The AWS A5.17 EM13K-F7A2 combination of welding wire and electrode is a high deposit (from 15 to 20 kilograms per hour) with excellent mechanical properties and impact resistance that complies and exceeds the requirements established for the project.

The electrode of choice for FCAW welding is AWS A5.20 E70T-1, this is a high deposit –impact resistant- excellent mechanical properties electrode. This wire is used with a protection atmosphere of carbon dioxide (CO2) that provides also a reduced spatter surface easier to clean.

Preheating and interpass temperature are key elements to avoid delayed cracking of welds. Because of the thickness of materials involved in this project the enforcement of proper care for this conditions are a priority for all our welding staff and inspectors.

Figure 4. FCAW Welding of a 102 thick bracing connection plate including a portion of column.

Apropiate weld joint design and procedures allowd us to reduce welding time 71%.

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Figure 5. A 740 pound per feet W section column for the Torre Mayor in the fitting

area. Thick material (over51 and up to 152 mm) are common in this project.

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Figure 6 Example of complexity of welding connections and the challange of height

ERECTION WELDING

Due the complexity of geometry and a combination of different welding positions there is no single consumable solution for field welding.

Low Hydrogen AWS A5.1 E7018 SMAW electrode is always the best option for field welding restricted access joints in all positions.

FCAW Wire AWS A5.20 E71T-8 is a better option to electrode if there is no the access restriction but the out-of-the-flat-position condition prevails.

In areas where proper wind protection is available FCAW Wire AWS A5.20 E71T-1 is an even better option for an out of the flat position condition due to an increased deposit rate.

Preheating and interpass temperature are key elements to avoid delayed cracking of welds. Because of the thickness of materials involved in this project the enforcement of proper care for this conditions are a priority for all our welding staff and inspectors.

The picture in the right of this paragraph shows the human scale referenced to the size of the connection and elements involved in this project

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Figure 8. Dimensional inspection of structural elements for the Torre Mayor

Figure 7. - Self-shielded FCAW welding of columns in site. Note the arrengement of 8stacked welding power sources to provided service to a similiar number of welders.

Near one hundred of this equipment are in use for this project

QUALITY CONTROL IN THE TORRE MAYOR BUILDING.

Dimensional accuracy is one of the priorities in order to reduce to a minimum the adjustments required while a structural element is being erected. Elements are dimensional verified along fitting prior to welding and once the piece is already welded and finished.

For this project, fabrication and erection processes incorporate inspection guidelines requirements including ultrasonic inspection of 100% of the complete penetration welds.

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Figure 9 - Corey use the most recent technology in ultrasonic NDE of field welds

The inspection plan for Torre Mayor emphasizes the use of automation. As an example, automatic welding equipment usage is promoted through the increase of Non Destructive Inspection requirements if manual welding methods are chosen.

In this project, to have welds in materials with thickness of up to 6 inches is commonplace. This represents for us the necessity to design alternative ultrasonic inspection methods for partial penetration welds not covered by AWS-D1.1, which is the standard welded construction code for this project.

CONCLUSIONS

Once we have revised the basics of the welding processes involved in this project we can construe some important facts that can be translated to the execution of similar future projects:

• The Torre Mayor is a project with no parallel in the recent history of construction in Mexico, and is a proof of the cooperation between companies in Canada, The United States and Mexico.

• A close collaboration between structural designers, detailers, fabrication and erection personnel and the welding specialist in the design of connections for the project to simplify both fabrication and erection which means important savings in time, allocation of resources and, finally, money.

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Figure 9 A mixt (welded-bolted) connection that allows streamline erection while providing the advantages of a welded

connection

• As we shown, in this project we are applying the same welding technology available in any world-class quality company.

• Continuous training, supervision, feedback and motivation to the welding crew are a key element for the success and performance of all welding process.

REFERENCES

Chapultepec Tower, Mexico City. Ahmad Rahimian and Enrique Martinez Romero. 1998 AISC NSCC Proceedings.

Impact of recent developments in non-destructive Inspection and information technology on the quality assurance of structural steel in Mexico. Guidelines for future action and pending agenda Ramon S. Fernandez Orozco, 2000 AISC NASCC Proceedings.