New technology to assist with accurate design is always welcome, but it is important that users proceed with caution when using international design tools.
There is no doubt that designing with stainless steel offers endless opportunities for architects and engineers to be both creative and functional. At the same time, it is critical that the design is right for the application.
Thanks to the internationally-recognised research of an Australian expert, as well as some design software now available free online, getting the design right for stainless steel structures has never been easier. However, as outlined below, it is more important than ever for design engineers to use caution when using international technology.
History of Design in Australia
The Australian Standard for design of stainless steel structures, AS/NZS 4673:2001 “Cold-formed stainless steel structures” was first published in 2001 and provides methods for design calculations. Applicable to cold-formed structures, including construction with tubular hollow sections, it provides a means of designing light and innovative structural solutions.
Traditionally, design engineers have reached for ‘load tables’ – or, strictly, Member Capacity Tables. Most design offices have tables with the results of calculations for various steel sections and loading regimes, generally published by suppliers of carbon steel.
But carbon steel has different properties from stainless steel, so these tables are not right for stainless steel – they may be too conservative or not conservative enough.
Another problem is that some engineers have assumed because they can find a section in carbon steel load tables, they can source it in stainless steel – only to discover they can’t, after doing an expensive design.
Designing with Software
Load tables for stainless steel are available from the Steel Construction Institute in the UK. The SCI is an independent, technical, member-based organisation with over 850 corporate members in 40 countries around the world.
Now the SCI has made available free software for design calculations for stainless steel members, using the methods of the European Design Manual, published by Euro-Inox.
Available over the web at http://www.steel-stainless.org/software/, the software speeds structural design calculations for a range of sections and stainless steel grades.
However, a word of warning: the software uses methods in compliance with parts of Eurocode 3 “Design of steel structures”. The Australian code for design of stainless steel structures, AS/NZS 4673:2001, follows the methods of the USA code, not the Eurocode. This is logical, as the Australian codes for the design of cold-formed carbon steel structures are also aligned with the USA codes and the trend in the Australian construction industry is to employ cold-formed steel to achieve lightness, material efficiency and enhanced strength.
So the SCI software must be used with some caution – it is the best available, but not ideal. The software should not be used in conjunction with the Australian code AS/NZS 4673:2001, as mixing clauses of different specifications is not an acceptable practice. This caution applies particularly to the design of welded structural members, which is catered for by the SCI software but not within the scope of the Australian Standard.
In January 2005, Professor Kim Rasmussen of Sydney University was appointed chairman of the American Society of Civil Engineers (ASCE) Standards Committee responsible for the American “Specification for the design of cold-formed stainless steel structural members”. This is the Standard that formed the basis of AS/NZS 4673:2001.
The ASCE Standards Committee will be updating the American Standard and Professor Rasmussen will present the new rules implemented in AZ/NZS4673 to the American committee, together with design recommendations derived from recent and ongoing research at Sydney University.
The ASCE Committee is expected to adopt the new rules and recommendations. Subsequently, there is likely to be an update to AZ/NZS 4673 – so there is an ongoing cycle of improvement, helped along by the world-class research in stainless steel structures undertaken by Professor Rasmussen and his students at the University of Sydney.
What Does it all Mean?
In short, international design tools such as the free software available from the SCI can provide some assistance in getting the design right for stainless steel structures, but they don’t provide all the answers and can even complicate matters. Sometimes good design means getting back to basics.
This ASSDA technical article was written by Dr Alex Gouch, Development and Technical Manager of Austral Wright Metals.
ASSDA acknowledges the assistance and contribution of Professor Kim Rasmussen from the School of Civil and Mining Engineering, University of Sydney.
This article featured in Australian Stainless magazine - Issue 37, Spring 2006.