Poor design caused Opal tower severe cracking

The Opal Tower, located in Sydney's Olympic Park, will have to be repaired after design flaws caused severe cracking.

 The 36-story building was evacuated on Christmas Eve after residents reported alarming sounds caused by cracking in some floors.

Officials from the government of New South Wales (NSW) reported that the damage was detected between the 4th and the 10th floor. The connection between the pre-cast concrete panels and their hob beams "differed from design and/or standards" and therefore, beams' failure probably caused the cracking. The beams were progressively stressed beyond their limit during the construction phase and as residents occupied the building. Moreover, additional construction flaws, including insufficient grouting or sealing between beams and panels, inaccurate widths of pre-cast panels and undersized reinforcing bars, were reported. Further investigation is being carried out at the 4th floor of the building due to its different design that caused different damage compared to the other floors.

According to the report, the building will not collapse. "It's not in danger of collapse, it's never been in danger of collapse and in fact it's designed to withstand 160km/h hurricane force winds," said WSP Australia and New Zealand chief executive, Guy Templeton. However, Professors Mark Hoffman and John Carter advised people to stay out of it until all repair works have been completed. The residents complied with the guideline and therefore the Tower is currently unoccupied.

"We can confirm that, while the building is structurally sound, significant rectification works are required to repair and strengthen damaged hob beams and in some cases the panels that rest on them. However, while we have isolated the probable cause to localized structural design and construction issues, we need more information to make definitive conclusions about the cause or causes of the damage to this structure and the proposed rectification," Mr. Hoffman and Mr. Carter stated. "We agree that the structural principles behind the rectification works are sound, but recommend independent oversight and review by qualified structural engineer before any major works begin," they added.

Yet, it is not clear who is fully responsible for the design flaws. "It's premature to be drawing too many conclusions, there is no one factor," Mr. Templeton said. At the moment, the priority is to repair the damage as soon as possible.