PIE viaduct collapse: Engineer failed to guide green design team

Wan Ting Koh
·Senior Reporter

SINGAPORE — An engineer implicated in the collapse of an expressway viaduct near Upper Changi Road in July 2017 pleaded guilty to his charges on Wednesday (20 November), 21 days into his trial.

Indonesian Robert Arianto Tjandra, 46, was working for subcontractor CPG Consultants when he approved the design and supervised the construction works for the project.

He pleaded guilty to two charges under the Building Control (BC) Act. The first charge states that he failed to ensure that the building works for the Project were designed in accordance with the provisions of the BC Act, while the second charge states that he authorised building works without approval.

He also admitted to one charge under the Workplace Safety and Health Act for a reckless act which endangered the safety of others at work.

Two other charges under the BC Act would be taken into consideration for sentencing.

Tjandra knew his team of engineers were inexperienced in designing bridges, but failed to give them guidance or instructions. He also failed to check the design assumptions made for the corbels. Even after he realised the errors in his team’s calculations, he failed to take remedial steps.

The company responsible for the works, Or Kim Peow Contractors (OKP), is still contesting charges of causing the death of a construction worker and injuring 10 others.

The construction firm was already fined $10,000 a day before the trial began, for carrying out unauthorised strengthening works on parts of the viaduct. It faces and is claiming trial to a remaining charge related to causing the death of the worker and the injuries of 10 others.

Two individuals linked to the accident, OKP project director Yee Chee Kiong and OKP project engineer Wong Kiew Hai, remain on trial. The firm’s group managing director Or Toh Wat was earlier given a discharge not amounting to an acquittal for all three charges.

Failed to ensure performance requirements are met

Part of the 1.8km-long viaduct, which stretched from Tampines Expressway to the Pan-Island Expressway and Upper Changi Road East, had collapsed at about 3.30am on 14 July 2017, killing one Chinese worker and injuring 10 others.

OKP had clinched the contract to build the viaduct from the Land Transport Authority on 23 November 2015.

The prosecution said on Wednesday that Tjandra had failed to ensure that corbels – key load-bearing structures for the viaduct – were designed according to performance requirements.

Even after realising the design error, Tjandra told OKP that they could build the corbels and disregarded any risks this might entail, said the prosecution.

Led an inexperienced team

The court also heard that the professional engineer had led a team of five inexperienced design engineers from CPG. He failed to consider his team’s lack of bridge-design experience – it was one of his members’ first bridge-design project.

During the design stage, Tjandra did not provide guidance on the proper method for the design of the corbels and key support structures, as well as the effective width to be used in the design calculations for the corbels.

As a result, the team wrongly calculated the effective width and used the erroneous calculations.

“The accused was not aware, at the design stage, that the design engineers had each used different and wrong effective width assumptions. He did not discuss or check the effective width assumptions used by the design engineers,” said the prosecution.

Even after discovering the wrong effective width assumption used in the corbels’s design, Tjandra also failed to take the necessary steps to ensure that they would be able to support their loads. He also did not take steps to ensure that the corbels were reinforced.

According to the prosecution, the temporary corbels had failed because they had insufficient capacity to support the loads on them at the time of the collapse.

“Investigations after the collapse revealed that the temporary corbels...had insufficient capacity to carry these loads even when omitting all load safety factors and material safety factors,” the prosecution said.

Tjandra will be sentenced on 2 December.

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