Wrong Design

One would think that in this day and age of advanced technology designers would not make a mistake in engineering basics. While most designs pass through more than one set of hands and eyes, occasionally, either the complexity of the problem throws an engineer or even a team off track, or at the other extreme the problem appears so simple that nobody pays much attention to the solution. A borderline situation is when something wrong has been working without problems for long, and you get so used to it, you do not see the mistake staring at you, until something bad happens and a fresh set of eyes catches the mistake instantly.

Fig. 4. Unsafe acts on mobile scaffold

1. Hotel New World, Singapore, 1986

On March 15, 1986, the six-story Hotel New World in Little India, Singapore, collapsed due to a design error. (Figure 5.)

The structural engineer had forgotten to add the dead load of the reinforced concrete building to his calculations when determining how strong he needed to make the support pillars that held up the building during construction in 1971. On top of it, the owner added quite heavy water tanks and air-conditioning units on the roof, and a bank tenant added a heavy vault, both the actions done without checking or approval.

Fig. 5. Hotel New World, before and after collapse

Thirty-three people were killed and 17 others were injured

In regard to the bank's liability, the Court of Appeals held that: "[T]he collapse of Hotel New World in 1986 must be looked at with a 1986 pair of spectacles. Having found that until 1986 there was no instance of a collapse of a building such as the hotel which stood for more than 10 years, the bank could not be imputed with knowledge of the various unusual dangers that were raised in that case, such as tremors, vibrations and cracks in the building."

Following this disaster, many lessons were learnt. Buildings built in the 1970s were checked for structural faults, and some of them were declared structurally unsound and had to be evacuated. The government also introduced tighter regulations on building construction; since 1989, all structural designs are required to be counter-checked by Accredited Checkers.

2. Nicoll Highway Collapse, 2004

The 20 April 2004 Nicoll Highway collapse in the C824 project for the cut-and-cover underground MRT Circle Line in Singapore had two critical design errors according to the International Committee of Enquiry as follows, (Figure 6):

(a) Under-design of the diaphragm wall using an inappropriate method in the computer program; and,

(b) Under-design of strut-waler connection in the strutting system, (Arrows, Fig. 6.)

These design errors resulted in the failure of the 9th level strut-waler connections together with the inability of the overall temporary retaining wall system to resist the redistributed loads as the 9th level strutting failed. Catastrophic collapse then ensued. Three workers and one official died and three others were injured. The sad fact was that the high deflections of the diaphragm walls had given ample warnings of impending disaster for weeks, which were ignored.

Fig. 6. Nicoll Highway Collapse, Left - General View, part plan, Right - Buckled walers

The Executive Summary of the report also charged the designers with "Abuse of the back analyses in Type M3 where the collapse took place."  Back analysis is a reverse procedure, to solve external load or partial material parameters, based on known deformation and stresses at limited points and partially known material parameters. It is often used in geo-technical engineering. With sufficient redundant data it has also been also applied to structures.

The company was fined S$200,000, and three senior executives were fined S$120,000, S$160,000 and S$160,000. Government officials who were also found guilty of negligence in their duties were not fined, but were warned and/or counselled.

A legal criterion which could greatly impact criminal liability to such negligence has been articulated many times: We should judge the conduct of designers by the standards prevailing and accepted at the time when it was designed (in this case the Factories Act), and not by any later standards. So, perhaps the penalties were not as severe as they would be today.

But out of this disaster came the development and implementation of the Workplace Safety and Health Act of Singapore in 2006.