ISSUE 72 2021
Specialising in stainless steel and its applications
Photo credit: JCO Photography
Terrigal Boardwalk STAINLESS SETS THE SCENE The seaside town of Terrigal on the New South Wales’ Central Coast has welcomed a new addition to its foreshore with a scenic walkway using stainless steel. The long-awaited Terrigal Boardwalk connects the existing pedestrian networks of the Terrigal Beach promenade and The Haven, providing a safe and accessible route around the headland. The new attraction provides social, health and economic benefits for the local community, allowing visitors and tourists to enjoy the public space and ocean front area. The project was jointly funded by the Central Coast Council ($2.9M) and the NSW Government’s Restart NSW Regional Growth Environment and Tourism Fund ($2.98M). The Terrigal Boardwalk’s construction included a restoration of the adjacent rockpool, a new disability-access ramp and pathway to link the rockpool and boardwalk. Engineered and designed by Arup, the boardwalk structure has a 50-year design life, demanding a robust design to ensure durability and longevity. The elevated boardwalk is 277m long and 3m wide, and complements the surrounding natural environment with its blackbutt timber decking and stainless steel balustrading. The construction comprises of a reinforced concrete suspended deck structure, a suspended structural steel viewing platform with fibrereinforced plastic open mesh, sandstone block revetment and a retaining wall ramp structure. For the bridge deck, 7.5m is the typical span of the precast deck planks between concrete headstocks on steel tubular piles. Solid concrete deck planks were chosen to protect the timber boardwalk above from wave damage and minimise overtopping for users. The boardwalk sits approximately 4.5m above sea level to be just clear of wave crests during strong weather events.
...stainless steel was chosen due to the material’s proven performance, corrosion resistance and durability in a marine environment Terrigal Boardwalk under construction
2 – Australian Stainless Issue 72
Materials selection was critical to meet the specified design life, with consideration given to the foreshore’s high level weather events and salt exposure. Grade 316L stainless steel was specified for the balustrading on both sides of the boardwalk, ramp handrailing and the rock platform staircase. While aluminium was considered during the design phase, stainless steel was chosen due to the material’s proven performance, corrosion resistance and durability in a marine environment, and aesthetic benefits in conjunction with the timber decking and handrail specified. In addition, a costing exercise conducted by Arup presented the long-term benefits of using stainless steel outweighing its additional upfront cost over aluminium.
the midst of the COVID pandemic, presenting a number of challenges with the supply of imported stainless steel material and shipping lead delays. As a result, Atlas Steels took the initiative to laser cut stainless steel plate to size and engaged ASSDA Member Decoware Australia to polish the material to specification. Starting with a coarse 80 grit through to a 400 grit finish, a surface finish of R a <0.5 µm was achieved. The resourcefulness of local service and skill assisted in meeting the project program, delivering a resolution for the unprecedented challenges. A small proportion of material was sourced from ASSDA Member Viraj Profiles, and ASSDA Member Vulcan Stainless supplied an additional 11t of laser cut 5mm, 10mm, 16mm and 20mm 316L stainless steel plate for the project.
Constructed by Land and Marine Group, the project involved a high level of collaboration between multiple local suppliers and service providers to meet the exacting demands of the specification.
Following fabrication, all stainless steel balustrade panels and handrails were electropolished by ASSDA Member Australian Pickling & Passivation Service and delivered directly to site for installation by the Synergy Engineering team.
ASSDA Member Synergy Engineering was engaged to fabricate and install the stainless steel handrails, balustrades and stairs, spotted gum timber railing and the structural steel viewing platform. The project involved the stainless steel fabrication of 247 balustrade panels, 119m of handrail balustrade and an 8-step 1200mm wide staircase with fibre-reinforced treads. TIG welding techniques were used throughout the fabrication and installation process to ensure precision and a clean aesthetic.
The beautiful coastal boardwalk features a viewing platform, integrated seating, LED lighting and access to the rock platform. Offering uninterrupted views of the Pacific Ocean and beyond, the Terrigal Boardwalk is certain to meet the performance requirements of its design with its quality construction and use of stainless steel.
ASSDA Member Atlas Steels supplied over 15t of 316L stainless steel, including 3402m of 30x8mm flat bar and 1656m of 70x10mm flat bar. The project was undertaken in
The Terrigal Boardwalk officially opened on 14 April 2021, with its first steps taken by local crowds alongside the New South Wales Premier Gladys Berejiklian, Parliamentary Secretary for the Central Coast, Adam Crouch, Central Coast Council Administrator, Dick Persson, and the Council’s new CEO, David Farmer.
ASSDA MEMBER CONTACTS Atlas Steels \ Richard Ayling, Service Centre Manager Newcastle \ 02 4922 5566 \ email@example.com \ atlassteels.com.au Australian Pickling & Passivation Service \ Richard Raper, Director \ 02 4964 8454 \ firstname.lastname@example.org \ picklingandpassivation.com.au Decoware Australia \ David Weng, Metal Polisher \ 02 9729 0666 \ email@example.com \ decoware.com.au Synergy Engineering \ Joel Andonopoulos, Director \ 1300 651 782 \ firstname.lastname@example.org \ synergyengineering.com.au Viraj Profiles \ Mark Farrugia, 0455 561 122, email@example.com \ Rakesh Chauhan, firstname.lastname@example.org \ viraj.com Vulcan Stainless \ Darren Peters, Business Unit Leader NSW \ 02 9828 0600 \ email@example.com \ vulcan.co
Structural design of stainless steel
Stainless steel is used for a wide range of structural applications including: Beams, columns, platforms and supports in processing plant for the water treatment, pulp and paper, nuclear, biomass, chemical, pharmaceutical, and food and beverage industries; Case studies of a range of structural applications are available at the case studies section of www.teamstainless. org/resources/information-center-forstainless-steel-in-construction. This introduction to structural design in stainless steel aims to highlight differences between the material properties and structural behaviour of stainless steel and conventional carbon steel normally used for structural purposes, e.g. grade 350 to AS 3678 and AS 3679. It should be noted that stainless steel structures should not be simply designed using design standards for carbon steel, such as AS 4100 and AS 4600, because of the significant differences between the mechanical properties of carbon and stainless steels. Selection of an appropriate alloy of stainless steel is the first step in any design process. Austenitic stainless steels are most widely used for structural applications, though the use of duplex stainless steels is increasing, where it is possible to exploit the benefit of high strength (around 460 MPa, compared to a strength of around 220 MPa for austenitic stainless steels). This can be particularly valuable in weight-sensitive structures like bridges or on offshore topsides. Duplex stainless steels are more likely to be used in heavier gauges. Ferritic stainless steels are also 4 – Australian Stainless Issue 72
Primary beams and columns, pins, barriers, railings, cable sheathing and expansion joints in bridges;
Entrance structures, canopies, cladding and support systems for masonry;
Security barriers, blast walls, hand railing and coastal structures.
suitable for structural applications, offering a corrosion resistant alternative to many light gauge galvanised steel applications. They are generally used in gauges of 4 mm and below although the 12% chromium utility alloys are used in thicker sections (vehicle chassis or high temperature ducting) when minor rust staining can be allowed.
In the absence of a clear yield stress, it is common practice to define an equivalent yield stress for stainless steel by using a proof stress, usually the 0.2% proof stress. (By definition, the plastic - or permanent - strain at 0.2% proof stress is 0.2%.) The proportional (or linear) limit of stainless steels’ deflection ranges from 40 to 70% of the 0.2% proof stress.
As a result of the non-linearity, stainless steel loses stiffness at low stress levels. This affects the design rules for members that rely on stiffness to transfer loads, notably compression members and unbraced flexural members. As well as nonlinearity, the stressstrain characteristics of stainless steel also display non-symmetry between tensile and compressive behavior and anisotropy, i.e. differences in behaviour of coupons aligned parallel and transverse to the rolling direction. In general, anisotropy and non-symmetry increase with cold work and so are more significant in the design of lighter gauge heavily worked sections, rather than thicker walled structural sections.
From a structural viewpoint, the main property that distinguishes stainless steel from carbon steel is the stressstrain response. In contrast to carbon steel, for which the stress-strain curve may be modelled as bi-linear for most compression and flexural member design purposes, the stress-strain curve of stainless steel is generally highly non-linear and without a distinct yield point. Figure 1 compares the stress-strain characteristics of various stainless steels with carbon steel for strains up to 0.75% and Figure 2 shows typical stress-strain curves to failure. (The figures show stressstrain curves which are representative of the range of material likely to be supplied and must not be used in design.) The distinctive mechanical properties considerable strain-hardening and ductility - make austenitic and duplex stainless steel particularly well suited for structures required to withstand accidental loading due to their high energy absorption characteristics.
It is possible to enhance the strength of austenitic stainless steel by cold-working to a much greater extent than for carbon steel. The initial modulus of elasticity (Eo) of stainless steel alloys is slightly lower than that of carbon steel.
Photo credit: Outokumpu
The behaviour of stainless steel at elevated temperatures differs to that of carbon steel because of the metallurgical differences caused by the composition. Stainless steel retains a greater proportion of its strength at temperatures above about 550 °C and shows better stiffness retention at all temperatures, which is important in design against fire for components such as blast and fire walls. The coefficients of expansion (CTE) of austenitic stainless steel alloys are larger than those of carbon steel. At the same time, the thermal conductivity is lower. While the CTE is important in determining thermally induced stresses and deformations, the combination of larger coefficient of expansion and lower thermal conductivity has the effect of substantially increasing the risk and possible extent of welding distortions than those experienced in fabricating carbon steel structural member. The duplex grades have similar thermal conductivity to the austenitics but with 20% lower CTE so the risk of welding distortion is slightly lower than with austenitics.
Austenitic Duplex Ferritic
FIGURE 1: S tress-strain curves for stainless steel and carbon steel from 0 to 0.75% strain
Austenitic Duplex Ferritic G350 Carbon Steel
G350 Carbon Steel
FIGURE 2: F ull range stress-strain curves for stainless steel and carbon steel
Specifications and reference documents for design of stainless steel structures
American Society of Civil Engineers (ASCE) has revised ASCE 8 Specification for the design of cold-formed stainless steel, applicable to lighter gauge austenitic and ferritic material in the annealed and temper-rolled condition (Reference 1). The 2002 version has been substantially updated because of extensive research work and will be issued late in 2021. This includes alternative treatments of compressive loading, i.e. effective width and direct strength. The structure of AISC 8 will be familiar to those using AS/NZS 4673:2001 although 4673 has now been withdrawn as an aged standard. Also in 2021, the American Institute of Steel Construction (AISC) will release a new standard (reference 2) AISC 370 Specification for Structural Stainless Steel Buildings to reflect the substantial increase in the use of heavy structural stainless steel sections. It includes hollow sections as well as welded, hot rolled and bar products. It will be accompanied by AISC 313 Code of Standard Practice
for Structural Stainless Steel Buildings (Reference 3) and an updated 2nd Edition of the 2013 AISC Design Guide 27: Structural Stainless Steel. The Eurocode for stainless steel design, EN 1993-1-4, covers welded, hot rolled and cold formed products made from austenitic, duplex and ferritic alloys, at room temperature and in fire (Reference 4). The Design Manual for Structural Stainless Steel (4th Edition) was published in 2017 and gives essential information needed by designers concerning alloy selection, durability, material properties, design rules and fabrication, in accordance with EN 1993-1-4 and other European standards (Reference 5). A Commentary explains how the design expressions in the Recommendations were derived and gives background information and references. Design Examples demonstrate the use of the Recommendations. Section property and member capacity software is also available, all aligned to EN 1993-1-4. This Design Manual and these supporting design tools are freely downloadable from www.steel-stainless.org/designmanual.
This article has been extracted from the 2020 Australian Stainless Reference Manual, available for purchase at assda.asn.au
REFERENCES: 1. ASCE 8-02 Specification for the Design of Cold-Formed Stainless Steel Structural Members, SEI-ASCE 8-02. \ 2. AISC 370-2021 \ 3. AISC 313-2021 \ 4. EN 1993-1-4:2006+A1:2015 Eurocode 3. Design of steel structures. General rules. Supplementary rules for stainless steels. \ 5. Design Manual for Structural Stainless Steel, SCI Pubilcation P413, The Steel Construction Institute, 2017 (available from www.steel-stainless.org/designmanual).
5 – Australian Stainless Issue 72
ART & DESIGN
Image: Ray Reyes, City of Melbourne
Lighting up Chinatown
Stainless steel lanterns now adorn the streets of Melbourne’s Chinatown, celebrating the cultural character of the longest continuous Chinese settlement in the western world. Chinese lanterns are a symbol of Chinese culture worldwide, initially used to provide light and later adopted for religious worship, decoration and celebration. Traditionally made from silk or paper, the City of Melbourne recently evolved the Chinese hanging lanterns featured on Little Bourke Street from cloth to stainless steel. In extensive consultation with the Chinatown Precinct Association, the City of Melbourne and GHD (Structural Engineers) reimagined the classic lantern with a detailed design that preserved the traditional aesthetic while examining a number of considerations. Durability and product life cycle were strong factors to reduce maintenance and regular replacement of the lanterns. Strength-to-weight ratio and resilience to local weather conditions was also important, with the completed design required to stay below 7kg to be viable for use on the existing catenary lighting system. ASSDA Member Draffin Street Furniture worked closely with the City of Melbourne to bring the design to life, assisting with the materials selection and manufacturability of the lanterns. Two prototype lanterns were installed at the corner of Heffernan Lane and Little Bourke Street to test the design and seek feedback from local traders and the Chinatown Precinct Association. Powder coated aluminium was initially selected as the design material however, stainless steel superseded the specification primarily for its strength and the ability for a thinner section of material to be used (0.6mm stainless steel sheet vs. 1.22mm aluminium sheet). In addition, stainless steel offered a more sustainable solution with a 25-year design life and little-to-no maintenance.
Photo credit: Draffin Street Furniture
The final design resulted in a 700mm wide by 500mm high spherical lantern made from 316 grade stainless steel, powder coated with a luminous, metallic red colour. In Chinese culture, the colour red symbolises good fortune and joy. The lanterns were formed using laser cut 0.6mm sheet, with each panel formed into shape and fixed to a central aluminium frame. The custom-designed lanterns were manufactured by Draffin Street Furniture, and stainless steel material for the project was supplied by ASSDA Member Steel Color Australia. 80 new permanent lanterns were installed on the existing catenary lighting system, which was originally manufactured and supplied with the assistance of ASSDA Member Ronstan Tensile Architecture in 2009. The linear grid catenary suspended from the street’s buildings uses 316 grade stainless steel rectangular frames spaced equidistantly to hold the grid form, while permitting the suspension cables to connect to buildings at different heights depending on the availability of structural connection points. Designed to enhance the character of the precinct with Chinese lanterns and other iconography, the decorative and functional stainless steel catenary lighting system continues to perform structurally 12 years on since its installation. Installation of the new hanging lanterns was completed at the end of July 2020. Brought to life using local design expertise and stainless steel, the lanterns maintain its symbolic heritage and will continue to provide a festive welcome to visitors for at least the next 25 years.
ASSDA MEMBER CONTACTS Draffin Street Furniture \ Ian Draffin, CEO \ 03 9720 1033 \ firstname.lastname@example.org \ draffin.com.au Ronstan Tensile Architecture \ Rowan Murray, General Manager \ 03 8586 2000 \ email@example.com \ ronstan.com.au Steel Color Australia \ Vince Araullo \ 0488 249 999 \ firstname.lastname@example.org \ steelcolor.com.au 6 – Australian Stainless Issue 72
Stainless steel ignites
luxury, style and warmth ASSDA Member and Accredited Fabricator Southern Stainless have taken outdoor entertaining to a new level with their custom-designed and Australian made stainless steel gas fire pit. Alfresco living is a strong part of Australian culture, and Gold Coast based Southern Stainless saw an opportunity to bring warmth and elegance to the outdoor space with the use of stainless steel. Starting the design process in 2015 and with over 18 months of research and development, a stainless steel gas fire pit was born, meeting both Australian Standards and gas regulations. Elegant and simplistic in its design, Australia’s harsh coastal conditions inspired the firepit’s construction. Grade 316 stainless steel sheet with a 2B finish is used to construct the sleek body, door and burner tray, and 1.5mm 316 stainless steel tube is used to assemble the burner and legs. The fire pit has a stainless steel burner mounted into an enclosure to accommodate toughened glass pebbles surrounded by safety glass. Gas filters through the pebbles and ignites fire,
giving the appearance of a floating flame. Southern Stainless’ fire pits are available in square and round models, and measure 1m x 1m or 1m diameter. Both are fitted with two flame failure devices that automatically shuts off the gas if the primary pilot blows out. The flame failure devices provide additional safety while also making the fire pit extremely effective in windy conditions. The fire pits have an LPG bottle compartment or can be designed to be plumbed into gas. In both instances, the fire pit comes with the gas controls and burner fully assembled. Only the glass safety sides need to be installed along with the toughened glass pebbles. If configured to be plumbed into natural or LPG gas, the appliance can easily be connected by any qualified gas plumber, or if ordered with an LPG bottle compartment, no installation is required.
Stainless steel is the clear material of choice when considering the great Australian outdoors. Grade 316 stainless steel has excellent corrosion resistance properties with an increased ability to resist pitting and crevice corrosion in warm chloride environments when compared with grade 304. It resists rusting in virtually all architectural applications, and is a durable, heat resistant and aesthetically appealing material option.
Stainless steel fire pits are built-to-last and combine physical warmth with visual luxury, offering year-round ambience to cater for the way of Australian outdoor living.
ASSDA MEMBER CONTACT Southern Stainless \ Matthew Brown, General Manager \ 0410 668 574 \ email@example.com \ southernstainless.com.au 7 – Australian Stainless Issue 72
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Specialising in stainless steel and its applications