ArcelorMittalSustainabilityCircular Economy – Reduce

Circular Economy – Reduce

Reducing the consumption of raw materials is one way to protect the environment. This precept is fundamental to the steel industry which strives for lighter, but stronger sections. As an example, consider a sheet pile section from the 1950's and compare it to a brand new one from 2015. For the same section properties (elastic section modulus), the new AZ 14-770 is 26% lighter than the equivalent BZ IR! These are significant savings.

Now, let's dive a little bit deeper into the design of steel sheet piles. The key parameters for the choice of a section are the section modulus W (elastic or plastic) and the yield strength fy. In the allowable stress design method, the formula is quite simple:

M = Wel * fy

with M = bending moment,
and Wel = elastic section modulus.

Hence, if you increase the yield strength, you can reduce the required elastic section modulus proportionally.

In the 1950's, a steel grade S355, with a yield strength of 355 MPa, was much more expensive than the standard S235, with fy = 235 MPa. Today, steel sheet piles can be delivered with a yield strength up to 460 MPa. Higher steel grades are slightly more expensive than a standard S355GP, but the cost difference is by far offset by the savings that can be made on the weight of the sheet pile section.

Rule: higher steel grades usually allow the selection of a lighter pile, thus reducing the environmental impact of a steel solution.

Additionally, the European design code EN1993-5 allows even to consider the plastic section modulus Wpl for class 2 sections, which means an additional increase of the resistance of a section between 10% and 25%!

Conclusion: innovation in steel and rolling technology, as well as installation equipment, made it possible to reduce the quantity of steel required to execute exactly the same retaining wall by more than 50% in a few decades. Besides, the solutions are cheaper than ever. And this trend will continue at the same pace.
Last modified: January 7, 2019