Opal Tower investigation finds design and construction issues
The NSW government’s investigation into the damaged Opal Tower in Sydney has found that the cracked residential building needs “significant rectification works” to repair and strengthen it.
The report, which was prepared by an independent team of engineers found that while the building is overall structurally sound and not in danger of collapse, there are a number of design and construction issues that need addressing.
The investigation focused on levels 3, 4, 9, 10, 16 and 26, as well as the basement level B3 — all the areas where known “significant damage had occurred to load bearing concrete members”.
The team of senior engineers hypothesised a number of causes that likely caused the cracking. These included environmental factors such as major storms and heavy rainfall, poor quality construction materials, issues with the foundations, flaws in design and poor quality workmanship during construction. The environment and materials were ruled out as causes.
On level 10 the team found a number of points where the construction differed from the design or industry standards. The original design drawings of the building indicate precast concrete panels that were the same width as the hob beam (180 mm), however, these were subsequently manufactured to be 200 mm in width. There was also less grouting between the panel and hob beam than indicated in the design.
The team also questioned the location of reinforcing steel, a cut or incomplete steel bar in the area and overhanging precast panels.
“There is compelling evidence indicating that the wrong size reinforcing bars were placed in this area during manufacture of this particular panel – 20mm diameter bars were used instead of 28mm diameter bars,” the report found.
“It is likely that a combination of some of the above design and construction issues led to the observed structural damage on level 10,” the report said.
The cause of the damage on level four is still being investigated by the engineers.
Before residents return to the building, the engineers said: “the designers must ensure that no structural member is overloaded as a result of any load redistribution likely to have occurred as a consequence of the observed damage to the structure of the building.”
The cracks first appeared on Christmas Eve 2018.