Stainless steel
Figure 5: Design Manual for Structural
Stainless Steel, Fourth Edition, 2017
NSC 5
Technical Digest 2018
Figures 3 & 4: Countess Wear Footbridge: Left: Stainless steel cantilevers being lifted into position during a night closure; Right: Stainless
steel parapet posts and handrails
structural tests is now three times larger than what was used to derive the
original stainless steel Eurocode rules. As a result of the availability of these
new research data, it was possible to develop improvements to the rules in the
2006 edition of EN 1993-1-4 and an amendment to the rules was published
in 2015. The new rules permit less conservative design and extend the range
of grades to which the rules apply (the grades listed in the standard did not
reflect current usage). Efficient design methods are essential for stainless steel
because of its high cost relative to carbon steel.
The most significant revision to the structural design rules in the 2015
amendment concern section classification: the limiting width to thickness
ratios have been increased to align with those for carbon steel, except for
internal compression elements. Additionally, less conservative shear buckling
guidance has been included and clearer guidance on how to design cold
worked stainless steel.
A key difference between stainless steel and carbon steel is that there are a
wide range of stainless steel grades, each with slightly different compositions
and hence corrosion resistance. Another significant revision in the 2015
amendment of EN 1993-1-4 was the inclusion of a step-by-step procedure for
grade selection. The procedure involves the following steps:
• Determination of the Corrosion Resistance Factor (CRF) for the
environment
• Determination of the Corrosion Resistance Class (CRC) from the CRF
The CRF depends on the severity of the environment and is calculated as
follows:
CRF = F1 + F2 + F3
where
F1 = Risk of exposure to chlorides from salt water or de-icing salts;
F2 = Risk of exposure to sulphur dioxide;
F3 = Cleaning regime or exposure to washing by rain.
The CRF considers all corrosion risks including pitting, crevice corrosion and
stress corrosion cracking of stainless steels that may affect integrity of load
bearing parts. The assumption in the selection procedure is that no corrosion
of stainless steel will occur that would impact the structural integrity of a loadbearing
component. However, in some instances cosmetic corrosion (staining
or minor pitting) could occur. These effects may be unsightly and unacceptable
where appearance is important but are not detrimental to integrity.
Grades of stainless steel are classified in one of five CRCs, with CRC V being
the most durable (e.g. containing grades suitable for the highly corrosive
atmospheres above indoor swimming pools). The final choice of a specific
grade within a CRC will depend on other factors in addition to corrosion
resistance, such as strength and availability in the required product form. It is
sufficient for the designer to specify the material by CRC and design strength,
e.g. CRC II and fy = 450 N/mm2.
The publication of the amendment rendered all existing resources for
designers relating to the stainless Eurocode obsolete. A new collection of
supporting design resources is being prepared in order to help designers to
use the new rules in the European dissemination project PUREST (Promotion
of new Eurocode rules for structural stainless steel), part funded by the EU’s
Research Fund for Coal and Steel. The 18 month project started in 2016 and
finished in December 2017 and involved partners from Germany, Belgium,
Spain, Portugal, Czech Republic, Finland, Sweden, Poland and Italy. SCI coordinated
the work with support from Imperial College London and Arup.
Activities were mostly targeted at design practitioners and included:
• Updating and extending the Design Manual for Structural Stainless Steel,
• Translating the Design Manual from English into 9 languages,
• Developing online design software and design apps,
• National seminars and recording webinars for distance learning.
SCI published the Fourth Edition of the Design Manual for Structural Stainless
Steel in 2017 6 (Figure 5). It consists of three parts:
• Recommendations, which give the design guidance and essential
information needed by designers concerning grade selection, durability,
material properties, design rules and fabrication
• Commentary, which explains how the design expressions in the
Recommendations were derived and gives background information and
references
• Design Examples, which demonstrate the use of the Recommendations
As well as updating the design rules to align with the 2015 amendment to
EN 1993-1-4, the Design Manual also includes information on ferritic stainless
steels. These grades are generally used in gauges of 4 mm and below, and
offer a corrosion resistant alternative to many light gauge galvanized steel
applications.
Additionally two new design methods are included. The first gives rules on
how to take advantage of the work hardening associated with cold forming
operations during fabrication (a strength enhancement of about 50 % is typical
in the cold formed corners of cross sections, and the strength of the material
in the flat faces also increases). The second gives a method for calculating the
enhanced cross-section design resistances due to the beneficial influence of
work hardening in service using the Continuous Strength Method.
All the design resources developed in the PUREST project are accessible at
www.steel-stainless.org/designmanual.
For more information, please contact Nancy Baddoo at SCI (n.baddoo@
steel-sci.com ).
References:
1 EN 1993-1-4:2006+A1:2015 Eurocode 3. Design of steel structures. General rules.
Supplementary rules for stainless steels
2 EN 1993-1-1:2005+A1:2014 Eurocode 3. Design of steel structures. General rules
and rules for buildings
3 EN 1993-1-3:2006 Eurocode 3. Design of steel structures. General rules.
Supplementary rules for cold-formed members and sheeting
4 EN 1993-1-5:2006 Eurocode 3. Design of steel structures. Plated structural
elements
5 EN 1993-1-8:2005 Eurocode 3. Design of steel structures. Design of joints
6 Design Manual for Structural Stainless Steel, SCI Publication P413, 2017
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