BC Update: No.27 - Report on Grade 500E Steel Reinforcement and related information

30 Aug 2005: The Department of Building and Housing has recently published the Report on Grade 500E Steel Reinforcement, together with a wallchart and Practice Advisory No. 7.

All are available on the Department’s website and further hard copies of the wallchart and Practice Advisory No. 7 are available on request. The Department also intends to distribute bendometers when they are manufactured, anticipated for October. These are sets of plastic discs designed to enable site checking of bar bend diameters.

As part of the joint Australian/New Zealand Standards initiative, the joint Standard for reinforcing steel, AS/NZS 4671, was adopted in 2001. This Standard introduced a new high tensile steel, Grade 500E, to replace Grade 430E.

In 2003 the Building Industry Authority (BIA) was advised that problems had been encountered in a research project at the University of Auckland, and in site situations, using Grade 500E reinforcing steel. This raised doubts about its integrity.

The BIA initiated an investigation into the concerns about Grade 500E, which culminated in this Report.

The key issues identified in the Report are as follows.

• Source of supply. The majority, approximately 80 percent, of the Grade 500E sold in New Zealand is manufactured locally and complies with AS/NZS 4671: 2001. The balance is imported from a number of south-east Asian countries. The test programme on three imported steels was not sufficiently large to confirm full compliance with AS/NZS 4671 and it is the responsibility of individual suppliers to ensure full compliance.
  
• Method of manufacture. The New Zealand manufactured Grade 500E is a microalloy (MA) steel, whereas most of the imported steel is manufactured by the quench and temper (QT) method. The QT steel is more sensitive to the various handling processes discussed below and hence is a less tolerant product.
  
• Grade 500E is a high tensile steel with less ductility (ability to stretch permanently without fracturing) than normal mild steel Grade 300E reinforcing so is more sensitive to handling processes. Particular issues identified are as follows.
  
  • Bending diameters are specified in NZS 3101 and NZS 3109. There is considerable anecdotal evidence that these specifications are not always followed, potentially resulting in site failures.
  • Rebending. Reinforcing bars are often bent and rebent on site for construction convenience and to allow precast concrete elements to be transported. This can be achieved with MA Grade 500E but is very difficult on site and is not recommended. QT Grade 500E cannot be rebent.
  • Welding. MA Grade 500E can be welded but only under very stringent conditions that are very difficult to achieve on site so is not recommended. QT Grade 500E cannot be welded.

The Report concludes:

• Grade 500E steel complying with AS/NZS4671 is a satisfactory material but must be handled with care. The source of supply and method of manufacture must be established to ensure fabrication processes recognise the limitations outlined above.
• Imported Grade 500E is generally manufactured by the QT process, which results in a material less tolerant to normal fabrication procedures.

If you would like a copy of the Grade 500E Report, you can download a PDF from the Department’s website. Please phone 0800 242 243 for hard copies of the wallchart and Practice Advisory No. 7.