“Crafting a Coat” – Modern Steel Construction

Topics: Accelerated, Innovation, News, Prefabricated, Sustainability

Excerpt and image provided by Modern Steel Construction – “Crafting a Coat” – By John Krzywicki (American Galvanizers Association)

Ancient Societies were the first to discover that coating metals with zinc protects them from corrosion. Only in recent decades, though, could engineers predict just how long that protection would last, thanks to the introduction of a new assessment method. That method, the Zinc Coating Life Predictor (ZCLP), was recently refined and made available on the American Galvanizers Association’s website (zclp.galvanizeit.org).

Originally designed as a sophisticated computational model by Gregory Zhang nearly 30 years ago, the ZCLP allows engineers, architects, and other specifiers to estimate the anticipated service life of zinc coatings based on various atmospheric exposure conditions. Factors such as humidity, temperature, sulfur dioxide concentration, and chloride deposition rate play a crucial role in determining the longevity of a zinc-coated structure. By integrating these variables, the ZCLP provides a reliable estimate of when the first coating maintenance might be due.

The ZCLP is web-based and accessible from any device with an active internet connection. It requires no downloads or installations, and thanks to its new responsive design, it works on all devices. The tool requires the user to input six yearly average atmospheric parameters: annual precipitation, sulfur dioxide deposition rate, relative humidity, airborne salinity, air temperature, and sheltering condition (open air, rain-sheltered or indoor). Thus, using the tool begins with data collection.

The ZCLP computes a corrosion rate in the chosen environment and allows the user to calculate a recommended zinc coating thickness based on the desired time to first maintenance. It can also esti mate the time to first maintenance based on a given zinc coating thickness.
Concrete embedment, immersion, offshore, aquatic facility, chemical exposure, galvanic corrosion, treated wood, and soil embedment applications are not represented by the ZCLP.

Additionally, yearly average wind direction can significantly affect corrosion rates for structures within one mile of coastlines. Evaluation of coastal applications can be limited to structures at least one mile inland or sheltered from coastal winds. The practicality of the ZCLP becomes evident when applied to real-world scenarios. Consider an engineer tasked with designing a bridge in a coastal region. The salt-laden air, high humidity, and variable temperatures create a challenging environment for steel structures. By employing the ZCLP, the engineer can make informed decisions regarding the performance of the zinc coating, anticipate maintenance schedules, and ensure structures remain resilient through their intended service life.

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Additional Resources

What are Press Brake Tub Girders?

Press-brake-formed tub girder (PBTG) is a new technology for short span bridge applications. It consists of modular galvanized shallow trapezoidal boxes fabricated from cold-bent structural steel plate (watch fabrication video). A concrete deck is recommended to be precast on the girder and the modular unit can be shipped by truck to the bridge site.

The system utilizes standard plate widths (based on availability) and is optimized to achieve maximum structural capacity, with most of the steel in the bottom flange and increased torsional stiffness. It is a closed system, since the girder is closed at the bottom. It is versatile for multiple-deck options.

The system utilizes Accelerated Bridge Construction practices, since it:
- Can be installed in one or two days
- Is modular, allowing the use of a precast deck
- Is cost-effective―as much as 1/3 less than a standard concrete girder structure
- Is simple to fabricate, requiring very little welding.
The Short Span Steel Bridge Alliance has developed standardized plans using standard plate sizes (60”, 72” 84”, 96”, 108”, 120”). The designs were developed to achieve maximum structural capacity and are available to use in the free-to-use, web-based design tool eSPAN140.

The press-brake-formed tub girder system is open source.

Learn more about press brake tub girders→