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Grade 500E reinforcing steel

Introduction of Grade 500E

The joint Standard AS/NZS 4671: 2001 Steel Reinforcing Materials was published in 2001 and introduced Grade 500E reinforcing to replace Grade 430.

As Grade 500E became more widely used, some 'failures' were reported on sites and concern about the new material grew among members of the building industry, especially design engineers. In 2003 the University of Auckland reported a failure of Grade 500E reinforcing in a laboratory test and this crystallised these concerns.

Investigation of Grade 500E

The Department of Building and Housing launched an investigation into the concerns about Grade 500E in August 2003 including:

  • asking ACENZ members to report any problems with Grade 500E steel
  • reviewing available data on specimens that had been referred to the manufacturer Pacific Steel
  • commissioning a report from Beca Consultants on the adequacy and compatibility of the various Standards covering the manufacture, design, welding and handling of Grade 500E steel
  • commissioning a series of tests by Auckland testing laboratory, SGS, on bars nominally sold as Grade 500E, both locally manufactured and selected imported products, to determine their physical properties
  • investigating the parameters that govern allowable bend diameters.

Results of the investigation into these issues in general terms were as follows.

  • Very few problems were reported by ACENZ members.
  • Most site problems referred to Pacific Steel, or separately reported to the Department, were the result of mishandling the bars and not following the relevant Standards.
  • Beca Consultants reported no serious incompatibilities or inadequacies of the various reinforcing Standards. This report did, however, highlight the need for research into safe bend diameters for Grade 500E, as referred to below.
  • Results of the SGS testing were generally satisfactory, but there were a small number of individual tests that did not reach specified Standards. These anomalies have been referred to the specific suppliers.

Report on Grade 500E Steel Reinforcement

The Department's investigation resulted in a report published in July 2005. In fact action addressing the problems identified in the report, and its recommendations, was initiated by the Department and other industry organisations in the 18 months before publication. These actions are outlined in the following sections.

The investigation indicated that the industry's knowledge and understanding of Grade 500E was limited because:

  • alternative methods of manufacture were being used; microalloy (MA) and quench and tempered (QT)
  • steel manufactured locally, and imported, was being marketed as Grade 500E
  • the properties and limitations of handling, or fabrication, including bending, re-bending, welding, galvanising and threading were poorly understood.
  • Consequently, the report recommended the following actions.
  • General education of the industry on the properties of Grade 500E and its limitations and benefits
  • Advice and alerts to industry about limitations and benefits of the product and the variation to be expected in manufacturing process, suppliers, bar markings and weldability
  • Research to provide better information on key issues
  • Specific advice to fabricators, constructors and designers on the need for care in handling or fabricating Grade 500E
  • Amendments to New Zealand Standards, including information about the limitations regarding Grade 500E steel

Grade 500E, New Zealand Standards and B1/VM1

During the investigation the Department worked closely with Standards New Zealand and in March 2004 they published amendments to concrete Standards NZS 3101: Part 1: 1995 The Design of Concrete Structures and NZS 3109: 1997 Concrete Construction. These amendments introduced the joint Standard AS/NZS 4671: 2001 Steel Reinforcing Material. AS/NZS 4671 replaced NZS 3402: 1989 Steel Bars for the Reinforcement of Concrete, NZS 3421: 1975 Specification for Hard Drawn Mild Steel Wire for Concrete Reinforcement, and NZS 3422: 1975 Specification for Welded Fabric of Drawn Steel Wire for Concrete Reinforcement. These amendments identified Grade 500E MA and QT steels and specifically covered the handling limitations (bending, re-bending, welding, galvanising and threading) of these two types of steel.

In March 2005 the Department cited the above amendments to the concrete Standards in Verification Method B1/ VM1 of the B1 Compliance Document.

Publicity about Grade 500E

The investigation highlighted the need to publicise the benefits and limitations of Grade 500E steel. Since initiating the investigation the Department has issued the following documents for general guidance.

  • Practice Advisory 1: Bend the bar not the rules was issued in December 2004 and amended and re-issued in June 2005.
  • Practice Advisory 7: Use with care, Grade 500E reinforcing steel in New Zealandwas issued in July 2005.
  • A wallchart Reinforcing Steel in New Zealand - A quick guide for designers, building consent authorities and contractors was issued in June 2005. Most of the information on this chart relates to Grade 500E. A minor amendment to this wallchart was issued in March 2006.
  • The Report on Grade 500E Steel Reinforcement was published in August 2005 and posted on the Department's website. It was also notified via the Department's email service Building Controls Update.

The Department, in association with the Cement and Concrete Association of New Zealand (CCANZ), has produced and distributed over 6000 bendometers since March 2006. These are a set of plastic discs that allow bend diameters to be checked on site for compliance with NZS 3101 and 3109. Many 'failures' of Grade 500E reported have resulted from bars being bent to diameters less than those specified by NZS 3101 and 3109. The bendometers are a simple device developed by the Department to promote the correct bending of reinforcement and an awareness of its importance.

Following a series of seminars in September 2003, CCANZ issued an Information Bulletin IB79 Recommended Industry Practice on Bending and Re-bending of Reinforcing Barsin December 2004. The seminars and bulletin did much to inform the industry about Grade 500E steel.

The Structural Engineering Society New Zealand (SESOC) has been active in the investigation and debate about Grade 500E reinforcing. Articles on Grade 500E have been published in its Journals of April 2001, April 2002, April 2004 and September 2005.

The Department is pleased to acknowledge the cooperation it has received from many sections of the industry and is confident that the appreciation of the types, properties and handling limitations of Grade 500E reinforcing is significantly improved as a result of this investigation, debate and publicity.

Recent and Current Developments

The Department has commissioned research into safe bend diameters for Grade 500E steel following the recommendations in the Report on Grade 500E Steel Reinforcement. It is anticipated this research will be completed early in 2007.

Pacific Steel started manufacturing and marketing Grade 500E QT steel in April 2006. They continue to supply Grade 500E MA steel.

Three companies in Auckland have been importing significant quantities of Grade 500E steel from Singapore, Malaysia and Thailand in recent years. These steels have generally been manufactured by the QT method.

It is important for designers, contractors and building officials to ensure steel suppliers have well documented and adequate quality assurance processes in place so that there can be certainty that reinforcing steel incorporated into buildings complies with AS/NZS 4671 and therefore meets the requirements of the Building Code.