Opal Tower builders used lower-strength concrete, beams burst under pressure

| 22.02,19. 06:19 PM |




Opal Tower builders used lower-strength concrete, beams burst under pressure



Photo: The Opal Tower was evacuated on Christmas Eve after a concrete panel cracked. (AAP: Mick Tsikas)


Parts of the Opal Tower were constructed using "lower-strength concrete" with "under-designed" critical support beams bursting under extreme pressure, an investigation into the apartment complex has found.


The Opal Tower final report, made public today after a near two-month investigation, outlines numerous key construction and material deficiencies in the 36-storey apartment complex that was evacuated on Christmas Eve after residents heard a loud cracking noise.


The ABC understands 259 units in the 392-unit apartment complex at Sydney's Olympic Park are today still empty with hundreds of families still based in temporary accommodation.


Some residents have vowed to never return to the apartments, some of which were originally valued at more than $2 million.


The NSW Government says it supports the "direction" of recommendations contained in the final independent report into Sydney's cracked Opal Tower but has not said whether it will implement them.


The report, written by three of state's most senior engineers and triggered by the State Government in the days after the cracks emerged, found changes made after the original Opal Tower design were exacerbated by "construction issues".


However, it stopped short of pinning responsibility on the builder, Icon, which is backed by multi-billion-dollar Japanese firm Kajima Corporation, or the engineers, WSP — one of the world's biggest firms.


It also did not name Ecove, the Australian-based developer of the multi-million-dollar project, or any of the subcontractors involved.


"We have not sought to indicate who was responsible for any of the causes, but rather to establish their structural basis," it said.


The report, which comes after an interim report was released last month, looked at security footage of the original incident on level 10 of the building at 2:16pm on Christmas Eve, which showed the crack first appearing and lasting for 8 seconds.


The authors toured the site on multiple occasions, spoke to residents and reviewed the design and construction records.


They also held discussions with WSP, Icon and the floor-slab designer ASP.


The report criticised some of the technical information provided by those companies.


"We have noted that, at times, documentation has been unclear," the report said.


During the investigation the authors said they found damage on 10 levels of the 36-level building, as well as damage in a basement level.


Three major causes were highlighted:

•The report found the hob beams — a beam that sits on the edge of a slab of concrete or pillar — were "under-designed" at several locations in the building.

•A decision to "grout only partially" a section between the hob beams and panels "significantly raised the levels of stress" in the building

•Construction and material deficiencies such as "lower-strength concrete" were used in level 4-A of the building


The ABC contacted Icon, the builder, and the developer Ecove for comment.


At the time of publication both parties had not received a copy of the report and declined to comment on its contents.


A spokeswoman for Icon said 171 units reviewed by Cardno — an engineering services company engaged by the building's owners corporation — had been deemed "safe to be reoccupied".

Looking at the building repairs, the report said the "full details" of the remediation measures were yet to be determined.


However they agreed in principle to what was proposed to fix the issues.


The three authors also outlined five recommendations to "avoid future incidents such as the one discussed in this report":

•The creation of a registry of engineers

•Independent third party certification of engineering designs

•A regime of critical-stage, on-site inspections by an independent registered engineer

•Raising transparency through the creation of an open repository for all certifications

•The creation of a building structure review board


NSW Minister for Better Regulation Matt Kean said the Government supported the direction of the report's recommendations.


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