The process of designing a steel member in fire is made complicated primarily due to the need to know the temperature of the member at the time of interest. This is in essence an iterative process which requires solving an equation(s) hundreds of times.
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Galvanizers Association with the aid of Steel Construction Institute (SCI) has recently published a design guide which greatly simplifies the design of galvanized steel members in fire, avoiding any need for complex calculations.
The benefit of utilizing galvanized steel members for fire resistance is apparent in structures that require short fire resistance periods, that is, 15 or 30 minutes of fire exposure, where the temperature reached by the galvanized steel members is around 500°C.
Examples of structures that require such fire resistance periods include car parks and single-storey residential/office industrial buildings. There may also be benefit in using galvanized steel for other types of structures, such as single storey industrial buildings or some multi-storey office buildings, where the use of sprinklers may enable a reduction of the minimum fire period to 30 minutes.
An important factor that affects the rate at which the temperature in a steel member increases is the section factor.
In EN -1-2 the section factor is defined as the surface area of the member exposed to a fire per unit length, Am, divided by the volume per unit length, V. Therefore, a beam exposed to a fire on four sides has a higher section factor than an equivalent one exposed on three sides.
This factor has the same effect irrespective of whether the section is galvanized or non-galvanized, as it only depends on the geometric proportions of the cross-section. That is, the larger the section factor, the faster the temperature in the member increases. As a result of this, the largest benefit of using galvanized steel over non-galvanized steel can occur in different cross-sections at different fire exposure times, depending on the section factor of the cross-section.
The figure 1 , opposite compares the rise in steel temperature of galvanized and non-galvanised steel beams for three different Universal Beam sections. The beams are exposed to fire from three sides with section factors ksh [Am⁄V]m of 75 m-1 109 m-1 and 170 m-1, respectively.
The figure indicates that for a fire exposure period of 15 minutes, the galvanized steel sections can achieve 3.5 minutes, 3.5 minutes, and 2.0 minutes longer fire resistance period compared to the equivalent non-galvanized steel sections, respectively.
For a fire resistance period of 30 minutes, the galvanized steel section with a section factor of 170 m--1 (UB 254 x 146 x 43) performs very similarly to the equivalent non-galvanized steel section. This is because at 30 minutes fire exposure, the temperature in the galvanized section is 820°C, which is significantly higher than 500°C. For the section with a section factor of 75m-1 (UB 533 x 210 x 122), however, at 30 minutes fire exposure, there is still a noticeable gain in fire exposure time of 3 minutes.
If the gains in fire exposure time using galvanized steel are translated into increased resistance, the advantages are more pronounced.
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In figure 2 , the resistance is represented by the maximum utilization that can be achieved by the member, calculated as the ratio of the cross-sectional resistance of the beam in the fire situation to the cross-sectional resistance at room temperature. A degree of utilization of 0.7 is indicated by a horizontal line which corresponds to the largest practical value for which a laterally restrained beam can be designed in the fire situation. This is because beams designed in fire for a degree of utilization larger than 0.7 are likely to fail at room temperature.
For sections UB 533 x 210 x 122 and UB 254 x 146 x 43, the maximum utilization that can be achieved by the non-galvanized steel sections decreases below 0.7 at noticeably shorter fire exposures than that of the galvanized sections. For example, for the steel section with the lowest section factor (UB 533 x 210 x 122), at 23 minutes fire exposure, when the maximum utilization of the galvanized section decreases to 0.70, it can carry 70 % more load than the non-galvanized section. At 30 minutes of fire exposure, even though the gain in fire resistance time is low for sections UB 533 x 210 x 122 and UB 254 x 146 x 43 (see Figure 1), they show a modest gain of 9% and 14% in load carrying capacity, respectively.
France
Further supporting studies have been carried out in France. Three sets of standardfire tests were performed at Effectis, France in a joint project by CTICM, Galvazinc and EGGA . In , fire tests were carried out on I and H profile steel columns exposed on four sides. In , further tests were carried out on I and H profile beams exposed on three sides and I profile and hollow section columns exposed on four sides.
Steel powers our world—bridges, buildings, and machinery all rely on its strength. Yet, corrosion is steel’s Achilles’ heel, threatening its longevity. Enter zinc-based coatings: zinc plating and galvanization. These methods shield steel from rust, but which is better for corrosion protection? In this guide, I’ll break down zinc-plated vs. galvanized steel, exploring their processes, strengths, weaknesses, and ideal use cases, backed by industry data and expert insights.
For those seeking a modern alternative, zinc flake coatings combine high performance with sustainability. Applied via dip-spin or spray, they rival galvanization’s corrosion protection without toxic byproducts, as noted in ScienceDirect studies. These coatings are gaining traction in automotive and renewable energy sectors for their eco-friendly process and versatility.
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