National scientific research centre leads the development of an innovative construction material being used for the first time for building a Steel Butterfly Arch Bridge

The Construction Industry Council (CIC) has always highly valued the role of research and innovation in the development of the industry. Researchers’ continuous effort in experimenting and data collected from real world experience in collaboration with the industry are equally important in bringing about advancement in construction. CIC is eager to encourage collaboration between institutions and the industry. Recently, CIC Chairman Ir HO On-sing Thomas and CIC member Mrs LO LEE Oi-lin visited the Hong Kong branch of the Chinese National Engineering Research Centre for Steel Construction (CNERC) and its director Ir Prof. CHUNG Kwok-fai (also a CIC member) to discover how research data for high-strength S690 steel was used to enhance construction and welding techniques and improve structural design and seismic performance – and how this knowledge is being applied at the Cross Bay Link at Tseung Kwan O, the first bridge in China to use the steel.
 

Domestic high-strength steel enhances efficiency and safety

Since 1993, China has led the world in steel production, with annual production currently reaching approximately one billion tonnes. This comprises more than 50% of global production and far surpasses that of the United States and Japan.

China’s steel manufacturing technology has developed rapidly in recent years. In 2015, the State Ministry of Science and Technology of the People’s Republic of China approved the establishment of the CNERC (Hong Kong Branch) to locally promote advances in structural engineering with modern steel construction and assist in promoting high-quality steel structures on the international market.

As well as complying with EU and international standards, high-strength S690 steel also provides thickness options from 6mm to 80mm. Ir Prof. CHUNG points out that S690 steel’s strength and ductility are higher than common steel, with no cracks occurring even when buckled. It is usually used for building ports, mining facilities and other heavy structures. Though the production cost of high-strength steel is 1.3 times greater than for common steel, its load capacity is higher, with only half the amount needed to achieve the same bearing capacity. This effectively reduces the total cost by about one-third.

CIC Chairman Ir HO On-sing Thomas believes that high-strength steel is lighter and easier to transport and handle, which helps reduce the construction period, enhance worker safety, and accelerate the completion of high-quality buildings.
 

Superb welding technology for a forward-looking project

The CIC believes that innovative technologies are only effective when they are actually applied to projects. In the case of high-strength S690 steel, its practical proving ground is the butterfly-like 200-metre, double-arch bridge of the Cross Bay Link at Tseung Kwan O. The project’s contractor is the China Road and Bridge Corporation Hong Kong, and its Chairman is Ir KAN Jun, who is also a member of CIC.

According to Ir KAN, the extraordinary strength of S690 posed its own project challenge: unlike common structural steel which only requires ordinary welding once appropriately connected, the high strength steel requires pre-heating to 120 degrees Celsius before it can be welded. It also must be cooled at a well-controlled rate, with the whole process closely monitored

In another innovation, robots were employed to enhance welding accuracy. Equipped with a laser scanner, the robotic welding system can achieve an accuracy of 1/10mm. The system also improves worker safety and reduces manpower requirements, alleviating the construction industry’s long-term labour shortage.

Collaboration Between CIC, Businesses and Institutes for Applied Research

Components for the entire bridge were made with Design for Manufacture and Assembly (DfMA) techniques. Small and light modules were assembled at a Shanghai factory and easily transported to the site in Hong Kong in just eight days.

Overall, the project is a remarkable demonstration of the synergistic effect of innovative technologies in raising the efficiency and productivity of local construction projects.

Environmental protection and carbon reduction start with the ‘basics’

The CIC has long advocated sustainability and carbon neutrality as primary directions of industry development. In 2019, the CIC introduced the CIC Carbon Assessment Tool as a common platform for the construction industry to evaluate the carbon performance of buildings and infrastructures in Hong Kong from raw material extraction to the end of construction.

Professor CHUNG used the tool to calculate the impacts of a range of steel materials on the carbon footprints of projects and buildings. Citing the steel bridge of the Cross Bay Link as an example, the total weight of the entire bridge built with a combination of high-strength and common steels is 4,400 tonnes lighter than if common steel had been used exclusively. The choice of material for the bridge also reduces its carbon embodiment by 30%, significantly reducing its carbon footprint and giving it a high material efficiency.

From S690 to S960 to a S1200 future

At least ten pilot projects – including bridges, leisure and cultural facilities and noise barriers – are set to apply high-strength S690 steel in Hong Kong, preparing the industry for wider application in the future. Just as a hundred temperings make tough steel, repeated training and practice makes for better construction.

Such experience also helps the industry create even stronger and better building materials for the future. The Hong Kong branch of CNERC is currently engaged in related research on S960, hoping to achieve the same strength intensity with less material. Ir HO On-sing Thomas hopes that more local bridge projects will consider applying new building materials. Ir KAN Jun looks forward to the creation of S1200 to expand the limits of design and construction methods for infrastructure projects and subsequently achieve an even wider adoption of high-strength steel in other building projects.

New Technology Nurtures Welding Master

As the technical welding requirements for S690 are particularly demanding, the CIC and the Hong Kong Institute of Construction are considering new technology content for the related welding course curriculum. The proposed welding course will cover relevant professional knowledge, handling and welding techniques, and will further enable the adoption of high-strength steel in Hong Kong.

The CIC will continue to study new building materials and applications as it plans ahead for the continuing industrialisation and digitalisation of the construction industry in Hong Kong.