Fatal PIE viaduct collapse: Engineer admits to reckless act, not checking his team’s calculations

SINGAPORE — Engineer Robert Arianto Tjandra took no action even after learning that his design team had relied on faulty calculations. These calculations were likely to result in part of an uncompleted section of Pan-Island Expressway (PIE) viaduct being unable to support the loads it needed to bear.

Tjandra’s failure to act on this information went on for at least two weeks, until two of the temporary concrete structures — called corbels — supporting that section gave way in the wee hours of July 14, 2017.

The high-profile collapse resulted in the death of 31-year-old Chinese national Chen Yinchuan. 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, they would not have supported more than half of the total load that they were intended to carry.

On Wednesday (Nov 20), Indonesian national and Singapore permanent resident Tjandra — who was the project’s qualified person — pleaded guilty to three criminal charges in a district court. He is due to be sentenced on Dec 2.

The 46-year-old professional engineers had initially claimed trial to the charges, along with two other men and a company, but he pleaded guilty on Wednesday midway through the ongoing trial.

The charges were:

• Committing a reckless act that endangered others’ safety, by putting up structural plans without checking on the design assumptions made for the two temporary corbels that eventually collapsed.

• Failing to ensure that building works related to some permanent corbels were designed in accordance with the Building Control Act.

• Authorising strengthening works to a permanent corbel around July 8, 2017, for which there was no approval under the Building Control Act.

Two other charges will be taken into consideration for sentencing. The prosecution is pushing for 22 months’ jail and a fine of S$10,000, while Tjandra’s lawyers are asking for eight months’ jail and the same fine.

Tjandra was an employee of CPG Consultants, which was engaged by the project’s main contractor Or Kim Peow Contractors (OKP) and the Land Transport Authority (LTA) to design and supervise the building works.

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.

The fatal incident happened along the longest span, which measured about 43.5m long.

As a result of the collapse, the viaduct is set to be completed in the first half of 2022, at least two years after the original estimated date of the first quarter of 2020.

LED TEAM OF INEXPERIENCED ENGINEERS

Deputy Public Prosecutor Ho Jiayun told the court that 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 had each used different and wrong effective width assumptions. He 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.

DID NOT CHECK CALCULATIONS

Two weeks before the collapse, on June 30, 2017, OKP employees told Tjandra that they had seen 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, so he asked his design team to check on the designs.

Later that same day, one of the engineers, Mr William Wang, said that he had discovered 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 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 more 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 construction sequence document prepared by one of OKP’s project engineers.

OTHERS INVOLVED IN THE INCIDENT

OKP and two other individuals — the company’s project engineer Wong Kiew Hai, 31, and OKP’s project director Yee Chee Keong, 49 — are contesting their various charges.

OKP was previously fined S$10,000 after pleading guilty to carrying out the unauthorised strengthening works to a permanent corbel. All three charges against its group managing director, 51-year-old Or Toh Wat, were withdrawn after he was given a conditional warning.

A fifth man, Leong Sow Hon — an engineer and managing director of engineering consultancy Calibre Consulting — was sentenced in July to six months’ jail after admitting to failing to check detailed structural plans and design calculations of the viaduct in accordance with regulations.

He remains out on bail as both the prosecution and his legal team are appealing against the sentence.