Inferior support beams led to cracking of Opal

Engineers hand down their final report into western Sydney’s troubled Opal Tower and identify the causes of major cracking.

Engineers investigating western Sydney’s Opal Tower have found key horizontal support beams built to an inferior, non-compliant strength were the chief cause among a slew of other deficiencies that triggered major cracking and two evacuations of the troubled building.

Handing down their final ­report after almost two months of the multi-party investigation, engineers engaged by the government also slammed structural engineers who provided the ­detailed technical design for the building’s construction of the project for lacking transparency and accountability.

Another significant error of the tower was the decision to only partially grout — a process to seal and fill the space between surfaces — between the support beams and panels, which raised the stress the already non-compliant support beams were forced to carry and resulted in the most ­visible damage at the site.

The 36-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.

Professors Mark Hoffman, John Carter and Stephen Foster, the engineers engaged by the state government to carry out an independent investigation, said the failures and damage at Opal Tower was a “rare occurrence”.

“A number of structural design and construction issues, including noncompliance with national codes and standards were responsible for the observed damage at Opal Tower,” the report said.

“We found some of the hob beams and panel assemblies were under-designed according to the National Construction Code and Australian Standards, leaving the beams prone to failure.

“We consider the building is overall structurally sound and the localised damage to the building can be rectified.”

The report also made several key recommendations to the high-rise development industry “focused on improving the system of independent review and monitoring” of designs provided to builders by engineering firms.

Recommendations include the creation of a government-run database of registered engineers, an online database of the certification documents of all buildings in the state, and a building structure review board to establish and publish facts about historical damage to buildings caused by design flaws to help shape future building codes.

NSW Minister for Better Regulation Matt Kean said the government was accepting the “vast majority” of the recommendations including the registered engineers database.

It is not clear which recommendations will be ignored by the government.

The professors also reviewed separate investigations conducted by Rincovitch Partners, hired by the tower’s builders Icon, ­design ­engineering firm WSP, hired by Icon, and Cardno, hired by the body corporate.

Photos included in the report showed cracking on floor panels and other locations throughout the building, which occurred after the initial failure of a precast concrete wall panel on Level 10.

Residents began returning to their homes in mid-January.