Engineers question strength of Opal Tower support beams

Engineers investigating defects at Sydney’s Opal Tower have raised doubts about the design of horizontal support beams.

The Opal Tower in Sydney. Picture: Toby Zerna

Engineers investigating defects at Sydney’s Opal Tower have raised doubts about errors in the design of key horizontal support beams.

As an interim report into the cracking of concrete panels that triggered two evacuations of the building is expected to be released, investigators disagree as to whether the grade of reinforced concrete used in the support beams was strong enough to withstand the pressure of precast concrete panels installed on top of them.

Several sources close to the ­investigation have told The Australian that one theory is that the beams lacked sufficient strength, causing pressure on the concrete panels, which cracked and sparked the evacuations.

But another theory is that grouting between the precast panels and the beams contributed to the cracking in the panels.

Investigators’ reports handed to Planning Minister Anthony Roberts last week appear to have found the builder, Icon Co, ­appeared to have built Opal Tower according to the specifications it was provided with. The Department of Planning had been expected to release an interim ­report last Friday.

Four separate investigations are under way the defects at Opal Tower, but The Australian understands there has been significant disagreement between the experts on the causes of the problems.

The investigation team comprises WSP, Rincovitch Partners, a third party hired by Icon, and Cardno, an engineering firm hired by the body corporate. The NSW government also ­appointed two engineers to take part in the investigation: University of NSW dean of engineering Mark Hoffman and emeritus professor at the University of Newcastle’s School of Engineering John Carter.

So far, the multi-party investigation team has agreed only on a remediation and reoccupation plan for the building, with the findings submitted by some parties to the Planning Department reportedly sent back to them for reconsideration.

Other sources suggested the precast concrete panel that failed on level 10 had cracked and been patched before its installation in Opal Tower, though its failure was only a symptom, not cause, of the building’s design flaws.

It is understood that patching of precast panels — which do not affect the buildings structural integrity — is a common practice.

Residents began returning to their homes at the weekend after its first evacuation 22 days ago.

The building’s strata committee has told residents not to ­return to the building until all of the engineers reports from the investigation agree as to the cause of the defects.

WSP, the original design ­engineering firm hired by Icon to supply the technical plan for the building’s construction, did not ­respond to request for comment.

The 38-floor building at Sydney Olympic Park gained national attention when 300 residents were evacuated on Christmas Eve and again less than a week later after creaking noises were heard and cracks appeared across different levels.

Additional Reporting: Sam Buckingham-Jones