In order to achieve a durable, high strength, structural steel (weathering steel) in the unpainted condition, some requirements for designing, fabrication, construction, site climate condition, inspection and maintenance need to be taken into consideration.

Weathering steel, or to use its technical title of “structural steel with improved atmospheric corrosion resistance”,  is a high strength, low alloy, structural steel. In suitable environments it can be used in an unpainted condition which results in very low maintenance costs and an economic bridge solution.

The design of weathering steel bridges should be undertaken in accordance to the relevant parts of AS/NZS 5100.6. However, there are several requirements – mostly related to detailing and suitability of environment, which relate specifically to weathering steel, are outlined in this publication.

HERA Report No. R4-97:2020 – New Zealand Weathering Steel Guide for Bridges

This steel design guide for bridges in New Zealand has been prepared to provide guidance to industry on the required aspects of site suitability, design, fabrication, construction, inspection and maintenance for the appropriate use of weathering steel in bridges in New Zealand.

‘Weathering steel’ is a high strength, low alloy, structural steel that, in suitable environments, can be used in the unpainted condition. Weathering steel develops a tightly adherent rust layer or ‘patina’, which significantly retards the corrosion rate of weathering steel compared with conventional structural steel, while also providing a versatile high strength structural steel.

However, to realise the full capability of weathering steel in bridges requires attention to some aspects of the design, fabrication and construction of the bridge and the consideration of the climatic conditions at the site.

With attention to these details, bridge life spans of a 100 years, or more, can be accommodated with weathering steel.

Gain access to this report by following this link to our reports and resources page.

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What does this mean for you?

This design guide for bridges in New Zealand has been prepared to provide updated guidance to industry.

It focuses on the required aspects of design, fabrication, construction, site suitability, inspection, maintenance and rehabilitation for the appropriate use of weathering steel for bridges in Aotearoa.

The ‘New Zealand Time of Wetness’ and the ‘New Zealand First Year Microclimate Corrosion Rate Maps’ provided in this document assist the users to use this guideline for their projects.

For our valued Platinum ‘Ordinary’ members – we’re pleased to provide the e-version of this updated guideline for free!

If you have any specific question related to this publication for your project, please get in touch with myself via email at or by mobile +64 21 198 8701.

Update shared by our Manager Structural Systems, Kaveh Andisheh.