The independent engineers investigating structural issues in Sydney’s Opal Tower have released their final report. The verdict: Opal Tower is “overall structurally sound”.

The final report has confirmed many of the findings in the interim report released last month, along with some new discoveries.

According to the report, the structural issues are as follows:

The as-constructed hob beam/panel assembly was under-designed, according to the National Construction Code (NCC) and the Australian Standard for Concrete Structures (AS3600), at a number of locations in the building. This left the hob beams susceptible to failure by shear compression and bursting.
The decision, taken after the initial design, to grout only partially the joints between the hob beams and panels, significantly raised the levels of stress in the hob beams on levels 4, 10, 16 and 26.
Construction and material deficiencies likely precipitated the observed major damage to hob beams on Level 10-C (electrical conduit and reinforcing steel in the cover region, and a panel repair) and Level 4-A (lower strength concrete than used in hobs elsewhere and partial grout coverage).
The observed damage in the concrete panel at Level 10 and in the Level 10 floor slab was likely a consequence of the adjacent hob beam failures and not the original cause of the damage observed at Level 10.

Industry experts and the public alike have largely blamed "dodgy certifications" for the tower's structural issues. According to the engineers, there is "no evidence that the building certifiers had been deficient in regards to statuatory expectations".

"Neverless there was a range of construction issues that occurred which were not compliant with Australian standards, and aspects of the design which led to structurally inadequate sections of the Opal Tower. While no evidence has been found that those responsible for certifying work did not conform with requirements, it is evident that a number of checks for compliance were not undertaken or undertaken with insufficient rigour."

The engineers further elaborate that there have clearly been tensions between the application of performance-based design and construction and the regulatory environment, which has resulted in "deficiencies" where expectations of building quality have not been met.

As far as making Opal Tower safe to occupy, the engineers have recommended significant rectification works and more detailed analysis of some structural issues. In regard to the rectification works, the engineers have recommended that all designs and construction associated with the works are checked and certified as safe for building occupancy by qualified independent structural engineers. They have also recommended that the analysis and certifications occur before residents are allowed to re-occupy the building.

To prevent a similar incident in the future, the engineers have recommended:

The creation of a new Registered Engineers database
Independent third party checking and certification of engineering designs and construction on site by a Registered Engineer
An online database for certifications
The formation of a Building Structure Review Board.

Crucially, the new Review Board would be used to establish and publish facts about structural damage of buildings due to design and construction, investigate their causes and to recommend changes to codes and regulations.

Despite assertions from various parties that Opal Tower is safe to occupy (for most residents), 259 units in the 392-unit complex remain unoccupied, according to the ABC, with hundreds of families still living in temporary accommodation.

Image credit: Icon Co.

Stephanie Stefanovic

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