At the request of the Hon. Anthony Roberts, Minister for Planning and Housing, an investigation was carried out into the causes of structural damage to the Opal Tower in Sydney Olympic Park, which was first observed in late December 2018.
The first report stated that the Opal Tower was overall structurally sound and was not in any apparent danger of collapse, with significant repairs required to strengthen damaged hob beams and panels in the building.
With multiple visits to the tower and inspections by engineering teams, the main focus on the investigation was on the garden area in the slot of Level 10, where initial concerns came from residents who claimed complained about loud creaking noises.
The intermin report also questioned the structural integrity of various elements on Levels 3, 4, 9, 10, 16, 26 and the basement level B3.
After a thorough inspection of these levels, the report indicated that possible environmental factors, poor construction materials, issues with foundations, flaws in design and poor quality workmanship could all have been factors in the creaking noises.
These findings came with much anguish to residents who had been forced to evacuate numerous times over the Christmas holidays, as well as facing property devaluation of almost fifty per cent.
The final report which was released on Feb 19, stated the following as definite causes of damage to the Opal Tower:
- The as-constructed hob beam/panel assembly was under-designed, according to the National Construction Code (NCC) and the Australian Standard for Concrete Structures (AS36001), 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.
Appropriate preparation work will now take place to ensure that the building is safe for residents. This includes the replacement of damaged hob beans to provide the required load carrying capacity.
The report also indicates that all designs and construction associated with the repairs will need to be checked and certified as safe by qualified independent structural engineers, before the re-occupation of residents.
Recommendations on avoiding this type of incident in the future included the creation of a government ‘Registered Engineers’ database as well as an independent third party checking system. The report also calls for a ‘Building Structure Review Board’ with the focus on establishing facts relating to structural damage from design and construction.