SINGAPORE — A design engineer who failed to double check his team's calculations while building a section of Pan-Island Expressway (PIE) viaduct, and then did nothing to rectify the errors, was sentenced to about one year and nine-and-a-half months’ jail on Monday (Dec 2).

Robert Arianto Tjandra, the project’s Qualified Person, was also ordered to pay a fine of S$10,000 in a district court. 

His team’s calculations were likely to result in part of the viaduct being unable to support the loads it needed to bear. 

On July 14, 2017, two of the temporary concrete structures — called corbels — supporting that section gave way.

The high-profile collapse resulted in the death of 31-year-old Chinese national Chen Yinchuan who was working at the site. Ten other workers suffered varying degrees of injuries, including spinal and pelvis fractures. They had been working on the deck slab supported by the two corbels.

Some of the permanent corbels were so inadequate that they would not have supported more than half of the total load that they were intended to carry.

The viaduct, which is about 1.8km long and made up of 50 spans divided into eight flyovers, links the PIE to Tampines Expressway and Upper Changi Road East. It is now slated to be completed in 2022.

LULLED INTO A FALSE SENSE OF COMPLACENCY

Tjandra, an Indonesian national and Singapore permanent resident, pleaded guilty last month to three criminal charges. 

The 46-year-old did so midway through his trial with two others — project engineer Wong Kiew Hai and project director Yee Chee Keong — as well as the project’s main contractor, Or Kim Peow Contractors. The trial is set to continue in January.

Tjandra was an employee of CPG Consultants, which was engaged by OKP and the Land Transport Authority to design and supervise the building works.

On Monday, Deputy Presiding Judge S Jennifer Marie told the court that the potential for harm caused was high, and that qualified persons “must exercise due diligence in ensuring the integrity of his work”.

Tjandra should not have been “lulled into a false sense of complacency” and neglected to check for errors too, she added.

The judge gave some mitigating weight to Tjandra’s plea of guilt, though she pointed out that he would have known that “significant resources” would be spent on the trial thus far.

“While it is unfortunate… that he has had an unblemished career (before this), a strong deterrent message has to be sent to those who play a critical role in ensuring building safety,” she said.

Both the prosecution and defence have two weeks to file an appeal against the sentence. Tjandra’s lawyers had sought a lower jail term of about eight months, while the prosecution asked for one year and 10 months’ jail.

HIS ACTIONS IN THE LEAD UP TO THE COLLAPSE

Tjandra led a team of five design engineers from CPG Consultants, who had “no or limited experience with bridge design involving the design of corbels meant to support loads”.

Tjandra was aware of the team’s lack of experience but did not guide or instruct them in the proper method at the design stage or the effective width to use in the design calculations for the corbels.

He was unaware that the team came up with different and wrong effective width assumptions and did not review, check or personally prepare any corbel design calculations.

As a result, the team came up with the wrong effective widths for the corbels.

Tjandra then submitted the structural plans and design calculations to the Building and Construction Authority, falsely certifying that they had been prepared by him in accordance with regulations.

Two weeks before the collapse, on June 30, 2017, OKP employees told Tjandra that there were structural cracks on the two corbels that eventually collapsed.

This was not the first time — OKP personnel had told him the same thing two weeks earlier, before any portion of the deck slab had been cast.

This led him to suspect that the corbels could not bear the loads they were designed for. 

He asked his design team to check on the designs and was told by one of his engineers, Mr William Wang, that there was a calculation error.

The next day, Tjandra emailed the design team, saying he believed that the corbels were under-designed. Mr Wang then told him that about half of the deck slab for the span of the two corbels could be cast, but the team’s calculations again relied on a faulty effective width.

On July 3, 2017, Tjandra saw the earlier structural cracks during a site inspection, which indicated the inadequate capacity of the corbels.

Following a discussion with his team, he told OKP to revise its construction sequence, such as by installing props under the corbel crossheads. However, he still had not reviewed, checked or personally performed any calculations to check the capacity of the corbels based on the correct effective width.

Four days before the collapse, he endorsed a revised document prepared by one of OKP’s project engineers.