Stainless steel
Stainless steel in construction
Stainless steels may appear to be more suitable for teaspoons and kitchen sinks than for
structural elements, but they can be used for support and other structures in aggressive
environments, says Nancy Baddoo of SCI.
The main property that distinguishes stainless steel from carbon steel is
that it possesses inherent corrosion resistance, due to the tightly adherent
protective layer of chromium oxide which spontaneously forms on its surface
in the presence of oxygen. This means that stainless steel components can
be exposed to a wide range of environments without the need for protective
coatings.
Stainless steels are highly versatile materials, possessing a unique selection
of useful properties which can be exploited in load-bearing applications
where cost is not a primary consideration. Figures 1 and 2 show stress-strain
characteristics at low and high strains, compared against carbon steel.
Austenitic stainless steels are generally used for structural applications, though
the use of duplex stainless steel is increasing, where the higher strength
is beneficial. The distinctive mechanical properties - considerable strainhardening
well suited for structures required to withstand accidental loading.
600
500
400
300
200
100
Stress (N/mm2)
800
700
600
500
400
300
200
100
4 NSC
and ductility - make austenitic and duplex stainless steel particulalry
Austenitic
Duplex
Ferritic
S355 Carbon steel
0,00 0,25 0,50 0,75
Technical Digest 2018
Typical load-bearing applications include:
• Platforms and supports in processing plant for the water treatment, pulp
and paper, nuclear, biomass, chemical, pharmaceutical, and food and
beverage industries where the aggressive environment requires it.
• Pins, barriers, railings, cable sheathing and expansion joints in bridges
• Seawalls, piers and other coastal structures
• Reinforcing bar in concrete structures
• Curtain walling, roofing, canopies, tunnel lining
• Support systems for curtain walling, masonry, tunnel lining etc
• Security barriers, hand railing, street furniture
• Fasteners and anchoring systems in wood, stone, masonry or rock
• Structural members and fasteners in swimming pool buildings (special
precautions should be taken for structural components in swimming pool
atmospheres due to the risk of stress corrosion cracking in areas where
condensates may form).
• Explosion- and impact- resistant structures such as security walls, gates
and bollards
• Fire and explosion resistant walls, cable ladders and walkways on offshore
platforms
In 2017, a new 160 m footbridge was constructed adjacent to the Grade 2
listed Countess Wear Bridge (figures 3 & 4) in order to create a 3 m wide
pedestrian and cycle route. The new footbridge comprises nine spans using
conventional carbon steel and is supported in part by five hidden cantilevers
embedded into the piers of the stone bridge, made from 1.4462 (2205) duplex
stainless steel box sections.
The use of cantilevers avoided the need for work to be carried out in the
river and complemented the appearance of the historic bridge rather than
obscuring it. For these structurally critical components stainless steel was
chosen for strength (grade 1.4462 stainless steel has a design strength of 450
MPa), to meet the 120 year design life target and because they were difficult to
inspect and maintain.
The cantilevers are supported by piles carrying tension forces through the
stone bridge into the bedrock 20 m below by means of stainless steel threaded
bars. The parapet posts and handrails along the bridge were also made from
duplex stainless steel. The client and designer for the project was Devon
County Council and the steelwork was fabricated and installed by Taziker
Industrial.
Although sharing many similar mechanical properties with carbon steel,
the non-linear stress-strain characteristics mean that different design rules are
needed for stainless steel. The non-linearity primarily affects local and global
buckling response with some section classification limits being stricter.
Design standards for stainless steel have developed around the world. In
Europe, when Eurocode 3: Part 1.4 was published in 2006 1, it was the first
design standard for stainless steel in almost all European countries and the
only design standard in the world which covered hot rolled, welded and cold
formed products, as well as design in the fire situation. EN 1993-1-4 is a brief
standard, just giving supplementary rules where the rules for carbon steel
given in EN 1993-1-1 2, EN 1993-1-3 3, EN 1993-1-5 4 and EN 1993-1-8 5 are not
applicable.
In certain places the rules in the 2006 edition of EN 1993-1-4 were very
conservative with limited scope due to a shortage of test data. However, over
the last 10 years or so there has been a very significant increase in research
into the structural performance of stainless steel in Europe and worldwide and
much useful information has been generated. The international database of
Strain (%)
Figure 1 Stress-strain curves for stainless steel and carbon steel from 0 to 0.75 % strain
0
0 10 20 30 40 50 60
Stress (N/mm2)
Strain (%)
Austenitic
Duplex
Ferritic
S355 Carbon steel
Figure 2 Full range stress-strain curves for stainless steel and carbon steel