Resilience of High-strength Steel Wide Flange Beams to Corrosion in Solar Ground Mount Systems

In this study, W6 wide flange beams (6” I-beams) were analyzed for bending strength under installed conditions with corrosive soils. In typical solar installations, foundations are expected to survive a minimum of 25-30 years. Foundation engineers routinely assume some loss of material due to corrosion over the installed lifetime, which reduces the strength of the material. Hot-rolled steel for I-beams in this size today has 50 ksi yield strength, which is the industry standard. The metallurgy for various higher strength materials had been known, and utilized for different applications, but not for W6 I-beams.

The possibility of producing this higher strength material for W6 I-beams would allow for increasing bending strength but come at a price premium over standard 50 ksi material. In this study, the increase in strength vs. cost efficiency of 65 and 80 ksi materials are analyzed for use in solar foundation applications.

Standard sections and calculation methods were used according to the American Institute of Steel Construction [2], [3] to estimate the capacities of the beams. Though the material strengths increase by 30% and 60% for 65 ksi and 80 ksi material respectively, due to buckling factors, the capacities do not linearly increase with the yield strength. On average, after 30 years in standard corrosion conditions, the same beam size’s strength is higher by 26% and 51% compared to the 50 ksi material.

This strength increase allows one to specify lighter foundations in these conditions or have increased safety factors in foundation designs. This study showed that for virtually any situation using heavier Ibeam sections, there is a significant cost advantage to using higher strength material instead. Where applicable, a 10-foot high-strength foundation’s cost savings potential ranges between $2,000- $10,000/MW, depending on the sizes and quantities of the foundations required on a site. In addition, there are other cost reduction potentials in shipping, and onsite logistics using lighter materials. The potential cost savings increases to scale with longer piles.

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