Train station

Metros & Urban Rail

Case study: improving constructability

West Kowloon

The Hong Kong West Kowloon Terminus (WKT) is part of the large scale (US$8 billion) infrastructure project that aims to link Hong Kong with major Chinese cities via high speed rail.

The terminus will serve as the gateway to the Guangzhou-Shenzhen-Hong Kong Express Rail Link, in addition to being a focal point for the new West Kowloon Cultural Precinct.

Aurecon has been appointed by steelwork contractor, Alfasi, to provide design engineering services for the long-span curved steel roof of the terminus building which is approximately 180m long and 30m high with an elegant freeform curved profile. It will have a landscaped exterior and blend into the surrounding ground, creating much needed green space and allowing people to take in unbroken views of Victoria Harbour.

Our scope of work comprises two major tasks; performing erection engineering of the roof and designing the temporary works. This includes assisting Alfasi in developing the erection sequence, assessing transient stresses and movements, determining fabrication geometries, and designing support for the steelwork during all phases of erection. These analytically demanding tasks were tackled collaboratively by the Aurecon project team in the Sydney, Hong Kong, Bangkok and Brisbane offices with the innovative use of sophisticated analysis tools.

Erection Analysis Engineering

Artist impression WKTTo support the 13 000-tonne roof structure and rooftop landscaping, there are three 3.5m deep mega V-shaped trusses hidden beneath the facade.

The trusses are in turn supported by only nine groups of slender raking columns. The V-trusses are interconnected transversely by secondary trusses and complex stability systems, working together to form an efficient three-dimensional structure.

Why Advanced Erection Analysis?

With the unconventional 3D curvature of the roof and the raking columns, preliminary computational analysis had predicted that the roof will drift under gravity loads alone. This intrinsic drift adds complexity and challenge to the project, most notably for our client when they erect the structure.

With the roof structure being geometrically irregular, transient internal forces induced during erection could govern the final design over the permanent loading conditions. To tackle these challenges, we have innovatively adopted advanced staged analysis methods, working closely with our client to develop an efficient erection sequence.

Value Added by Aurecon

Roof structure WKTOur staged construction analysis of the WKT roof has added significant value for Alfasi. For example, our analysis predicted that the erection method originally considered - a strand-jacking erection method - would overstress the truss members. As a result, we worked closely with Alfasi to develop an improved erection sequence.

The new method involved propping the trusses and breaking the top deck concreting into two stages. We were able to computationally demonstrate that this erection method substantially reduced the locked-in effects arising from the erection process.

Other notable value-added services such as the numerical modelling of temporary preloads to replicate the structure’s final deformed shape have demonstrated to our client that time savings can be gained as the glazing system can be installed earlier.

Temporary Works

The temporary structures provide support for the permanent roof structure as it is being erected, and allow workers to safely connect the massive steelwork components that make up the roof. Although the temporary structures only perform their function for a limited time, the ultimate roof vision would not be possible without them.

Overcoming Challenges through Collaboration

Permanent roof structure WKTOne of the major challenges we faced has been the complex interface between the temporary works, the permanent roof and the supporting substructures.

The complexity increased as changes in the construction programme of the supporting substructures below played a significant part in the interface. Through extensive communication and collaboration between Aurecon, Alfasi and other parties, we have been able to design a suitable solution that suits the client’s needs.

Several critical junctures have required innovation to achieve the desired construction programme. For example, the layout of the temporary towers needed to be adapted by the inclusion of low level truss members to make allowance for the tower cranes and other construction activities that simultaneously occur during erection. This innovation solved the problem in a cost effective way with minimal impact on the substructure and the temporary works.

Safety through Careful Planning

One purpose of the temporary works structure is to provide access for construction personnel; thus safety has been at the forefront of our design philosophy. In addition to standard safety concerns, some of the more challenging considerations were impact loading from construction equipment and extreme pressure loading from a potential explosion on site.

We looked at a worst case scenario of progressive collapse and mitigated against this by having a higher than normal degree of redundancy within the structure.

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