By SIMON COLLINS
Builders have been told to stop re-bending a new grade of steel used in reinforced concrete buildings until authorities investigate instances where the steel bars have snapped.
The call, issued by the Building Industry Authority last night, follows tests at Auckland University last week in which the new
grade 500E reinforcing steel cracked.
The authority has also called on builders to stop welding 500E steel on site, and not to bend it more than allowed under the NZ standard, until it finishes its investigation.
Authority chief executive Richard Martin said this week that he had "four or five" documented cases where the new steel had broken after welding.
The manufacturer, Fletcher Building's Pacific Steel, said yesterday that it knew of 10 cases where 500E steel reinforcing bars had fractured out of 71,000 tonnes sold so far. It said its initial statement that there had been "a dozen" cases out of 140,000 tonnes was wrong.
Fletcher Building's building products chief executive, Andrew Reding, said the company supported the authority's action.
The new steel is stronger than the grade 430E steel which it replaced. This means builders can cut costs by using less steel - but it also makes it more brittle and liable to snap if bent.
Engineers said it was common for reinforcing steel to be bent several times:
* First, to stick out of wall slabs at right angles when the concrete slabs are cast;
* Second, to lie flat along the wall slab to allow pre-cast floor units to be lowered into place; and
* Third, at right angles to the wall again above the pre-cast floor units to allow topping concrete to be poured over them.
A Connell Wagner engineer, Dr Victor Lam, said he had already stopped using the 500E steel in structures where it needed to be bent, and used 300E-grade "mild steel" instead.
Mr Martin said it was too soon to say whether buildings already built using 500E steel should all be checked for cracks.
Matamata commercial builder Kevin Stanley, who chairs the board of the Master Builders' Federation, said the interim ban on rebending would have only "limited effects".
The general manager of Reid Engineering Systems, Derek Lawley, said about 20 per cent of pre-cast reinforced concrete buildings now used his firm's screw-in reinforcing steel, which could be taken out while floors were fitted and did not need bending.
