SINGAPORE — There may be a few reasons why a supporting structure for an uncompleted viaduct or bridge would collapse: Problems with its design or construction processes, an unexpected weight placed on the structure, and the quality of building materials.
Civil engineering experts told TODAY that, generally, the corbels — or a support for the horizontal structure of a bridge — are able to handle heavy weight and do not collapse easily.
In the wee hours of Friday (July 14) morning, a section of an uncompleted road viaduct from Tampines Expressway (TPE) to the Pan-Island Expressway (PIE) that was being constructed caved in, killing one worker and injuring 10 others.
Preliminary investigations showed that the “corbels supporting the pre-cast beams had given way”, the Land Transport Authority said in a statement.
Corbels, which can be made from steel or reinforced concrete, are the support brackets between vertical columns and horizontal structures. After the corbels are built, horizontal beams are then laid before concreting works can be carried out to build the deck above them.
A civil engineer, who is a council member at the Institution of Engineers Singapore, said that as a standard practice, the design and calculations before building such structures have to be properly checked. Even so, an unexpected load may be placed on top of the corbel, causing it to collapse.
The engineer, who did not want to be named, explained: “(Let’s say) you buy a chair and when you sit on it, it collapses. It could be that the chair design is bad, or the weight (of the person sitting on it) is too heavy.”
Likewise, the poor quality of the construction materials and the differences in certain construction steps taken by a firm could also affect the stability of the structure, he said.
Associate Professor Gary Ong, from the civil and environmental engineering department of the National University of Singapore, said that it is uncommon to see such structures giving way if the corbels and supporting structures are properly designed.
Asked about how this could happen, he added: “It’s difficult to say… There are very stringent checks in place before the design is approved, and construction is given the go-ahead because these are major infrastructure works.”