The design emphasis of bridges in Asia has generally centred on functionality; aesthetic form, elegance, durability and provisions for future maintenance are often not fully considered in any great detail.
There has been little appetite to shift away from tried-and-tested technologies and formulaic construction methods, and in more practical terms, we have also seen inspection, maintenance and sustainability given insufficient attention, often leading to problems in the future.
However, the good news is that change is coming. And importantly, it is being driven from the top. Client perceptions for how a bridge should look are changing. Many are yearning for something different; something more aesthetically complex that can deliver a signature look which highlights aspiration and achievement. That means moving away from the stark concrete structures of traditional designs while ensuring appropriate consideration is given to durability and sustainability.
With the prospect of exciting new design briefs on the horizon, the question is: how can we as bridge engineers advance our capabilities to meet evolving expectations? Fortunately, the tools, the technology and the skills are already available.
Recent years have seen rapid advances in design tools that enable engineers to create aesthetically pleasing, durable and increasingly complex structures. The adoption of scripting techniques as a means to develop analytical models, has been a significant benefit to the bridge designer.
These techniques eliminate the need for the trial-and-error approach to bridge design, with multiple options being analysed and the bridge optimised in a short period of time. At the same time, we are also able to run more complicated analyses in combination with the development of advanced erection methodologies.
We are consequently able to better ensure that the construction on site matches the analytical predictions – a vital factor in ensuring quality and efficiency on any new project.
Our design work also considers in much greater depth the appreciation of bridge maintenance needs. Provision for maintenance now goes way beyond simple visual inspections, with the introduction of SMART bridges that incorporate sensors into their design to monitor structural health.
This makes maintenance a more proactive process, while the structure itself now incorporates much more comprehensive access facilities making inspections and repairs easier.
To understand where our industry is heading, it first makes sense to look into where we’ve come from. In Asia, precast concrete beams have been the standard solution for bridge construction for decades. It’s easy to see why. They are proven and effective, with a simple design that makes them easy to install.
Over the years, we have seen some useful advances in their design too. Since the basic design standard (AASHTO I Girder) originally developed in the 1950’s, the form of the girder has steadily been refined into a more material-efficient building block for bridges.
Significant savings have been delivered in the volume of concrete required, most notably with the North American NU girder in 1994, and the Australian Super T girder, which was brought into industry the following year, allowed the deck slab to be constructed on an immediate working platform and removing the need for specialist formwork.
A more recent refinement, the Umax girder developed by Aurecon in 2014, delivered further advantages – most notably, the potential to eliminate 20 per cent of the piers in a design thanks to an increased typical span length of between 45m and 50m.
Although the mass of these elements is around 150 tonnes, fewer girders are required, and the total tonnage of prestressed girders per span is substantially reduced.
|40.0m spans||AASHTO Type 6 I Girder||AASHTO Type 6 Bulb T (AASHTO-PCI)||NU girder (NU1800)||1800mm Super T girder||Umax girder|
|Year developed||1980 (USA) from a 1950's concept||1988 (USA)||1994 (USA)||1995 (Australia)||2014 (Australia)|
|No of Formwork panels||144||144||144||Not required||32|
|No of girders||10||10||10||10||4|
|Girder depth||1830 mm||1830 mm||1800 mm||1800 mm||2200 mm|
|Area of section||700 x 103 mm2||495 x 103 mm2||550 x 103 mm2||706 x 103 mm2||1384 x 103 mm2|
|Top flange width||1280 mm||1067 mm||1225 mm||2300 mm||2600 mm|
|Girder mass||1.82 t/m||1.29 t/m||1.43 t/m||1.83 t/m||3.6 t/m|
|Total tonnage/span||728 tonnes||516 tonnes||572 tonnes||732 tonnes||576 tonnes|
|Deck thickness||200+90mm PC||200+90mm PC||200+90mm PC||200 mm||210+90mm PC|
When executed correctly, these structural elements can deliver impressive results. At Aurecon, we utilised Umax technology on the Tuas Basin Access Bridge project in Singapore. Spanning 75m across a wide inlet canal, this pair of parallel bridges consists of the longest and heaviest precast girders ever used in Singapore – 50.5m long and weighing 278 tonnes, with each pier head extended by 12m to complete the span.
Tuas Basin Access Bridge consists of the longest and heaviest precast girders ever used in Singapore
However, precast beams are not suitable in all locations. The risk in lifting, placing and securing precast beams during construction needs to be carefully assessed particularly in busy urban centres. Precast beams can also be slow and inefficient to transport and difficult to install depending on the availability of crane access, often requiring night-time closure of existing roads and highways.
One famous example is the UK’s sprawling highway intersection in Birmingham, known locally as Spaghetti Junction. Here it was not so much the need for repairs that causes perennial headaches, but rather the difficult detailing and lack of suitable access for maintenance personnel. It serves as a cautionary tale for all clients and engineers of the dangers of failing to futureproof designs.
While precast concrete beams remain the most popular option for bridge construction, this construction technique is not the only option. In recent years, we have increasingly looked to the precast segmental box girder construction for our projects, particularly in the major cities of Southeast Asia.
In precast segmental box girder construction, the beams and deck comprise transverse segments stressed together with post-tensioning either as balanced cantilevers or full spans. This form of construction offers several important advantages over precast beams:
Level Crossing Removal – Caulfield to Dandenong, Australia
One crucial point to note is that maximising the benefits of precast segmental construction requires higher technical skill levels from the engineering team – both in the design office and on site. Planning the design and installation of bridge sections needs to be carefully considered and modelled using technology that can accurately simulate site conditions.
Particularly for precast segmental construction, geometry control is a vital part of the erection process, ensuring the finished structure is consistent and within tolerance with the original design.
As a result, it pays for a bridge owner or construction contractor to work with an engineering design partner that can oversee the whole process, from the initial design through to construction on site.
This includes liaising with the concrete contractor casting the bridge segments; checking the fabricated segments and making any necessary adjustments to ensure future segments from the production line are a perfect match, ultimately leading satisfactory geometrical control. Getting it right ensures an accurate fit during installation and enhances durability.
The combination of a holistic design and construction approach, harnessing highly skilled engineers and ensuring pinpoint accuracy requires discipline and investment; do it right, and it delivers rewards.
At Aurecon, we saw this for ourselves in the development of some tight curvatures and complex design for the viaducts on the Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) – TKO Interchange in Hong Kong. With the bridge radius down to 44m in places and the interchange being constructed over the sea, there were many challenges in designing and constructing the interchange.
An experienced team of engineers and the application of advanced analysis techniques ensured the project was on programme, without significant issues.
Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) – TKO Interchange, Hong Kong
Unsurprisingly, making use of the latest design technologies is also crucial to creating future-focused bridge designs. In-house digital teams need to utilise Building Information Modelling (BIM), geometrical modelling and parametric modelling to do this. These are effective tools that allow engineers agility to adjust designs to reflect changing requirements and more quickly generate the bridge’s geometry.
In turn, this enables the team to seek approval and move on to the detailed design stage at an accelerated pace.
In fact, not only are the latest tools helpful, but when it comes to long and complex viaducts, or projects with numerous bridges of difficult geometry, such tools are essential. Adopting scripting through Grasshopper or Dynamo and feeding the data into both the analysis model and the BIM model is a supremely quick and effective means of generating accurate shop drawings for concrete segments.
By coordinating the data from a single source, we can ensure the geometry is consistent in both the design and documentation, while allowing flexibility in making adjustments at a later stage.
A successful example of Aurecon’s utiliisation of 3D modelling and BIM is with the Tuen Ma Line Extension project in Hong Kong. This railway development project comprises a 2.4 km extension of the existing West Rail Line from Tuen Mun station, including river crossing specialty bridge and viaducts.
Once completed, this extended line will improve accessibility for the local population in Tuen Mun South area – home to around 490,000 people. The project includes the Tuen Mun River Crossing Bridge, which with a span of 120m, will be the first extradosed bridge in Hong Kong. Using parametric modelling techniques, we were able to quickly develop an optimised design for the structure.
As well as the design of bridges, BIM is also a valuable tool for construction. Realistic 4D construction sequences can be developed to facilitate work on site, modelling the actual plant and temporary works to be adopted.
Segment installation can be simulated, while full construction sequences can be developed using durations and resources in the model. Adopting the 4D model enables each step of the construction sequence to be scrutinised for conflicts, potential clashes or other issues.
Similarly, space constraints on site can be modelled in BIM, together with detailed representations of the construction equipment being used. Contractors and other key stakeholders can see how equipment will work together to better understand the construction process.
In addition to design and construction, technology can also be incorporated into the physical structure of bridges to simplify future maintenance. This is an especially valuable option for suspension and other long-span bridge forms.
For example, dehumidification of the deck interiors and main cables can protect against corrosion with a considerably reduced need for future recoating. BIM modelling and technology can also be applied to systemic drainage and mechanical, electrical and plumbing fixtures which can be laid out for easy access and future maintenance.
In the facility management office, a detailed bridge maintenance system (BMS) database can keep track of events, in conjunction with onsite SMART bridge technology (CCTV or automatic incident detection systems). Comprehensive wind and structural health sensors monitor how a bridge can perform throughout its life and automatically send alerts to warn of potential issues.
When physical inspection is required, access facilities can be detailed as part of the initial design allowing personnel to closely assess surfaces safely and easily. Careful planning of these facilities during the design stage, ensures a good fit and reduces the potential for clashes during installation.
Digital walk-throughs enable the maintenance authorities to understand and collaborate in the design and planning process. For cable stayed bridges and suspension bridges, these would be deck gantries on the main span and backspans. For other long span bridges, gantries can be incorporated in the underside of the deck and surfaces of the towers, with cable inspection gantries or cradles and rack and pinion lifts inside towers.
With more advanced design techniques, innovative technologies and a new mindset, the stage is set for an exciting new chapter in bridge design in Asia. There will be opportunities to develop eye-catching structures that not only help characterise the location, but also improve functionality for users and boost sustainability for the local environment. In fact, there may never have been a more exciting time to be a bridge engineer in Asia.
Mike Tapley has 34 years of engineering experience in the design and construction of bridges and civil structures on major infrastructure projects throughout the world. He has led in many bridge projects, ranging from short span viaduct structures to major long-span bridges.
He has been responsible for all aspects of the scheme from the detailed design of the bridges to the coordination of the environmental studies. While viaducts have included many forms of construction: precast segmental construction, steel composite and concrete cast in situ structures. In developing new bridge schemes, Mike has also developed arrangements for future access facilities and prepared the associated Operations and Maintenance Manuals.
The key bridge and viaducts projects that Mike has been involved in during recent years include Tseung Kwan O – Lam Tin Tunnel (TKO-LTT) – TKO Interchange, Tuen Ma Line Extension, Route 11 Tsing Lung Bridge, WKCD Artist Square Bridge in Hong Kong; Jurong Region Line Contract J102 and Jurong Region Line Contract J109 in Singapore; and WestConnex New M5, West Gate Tunnel and Northern Pathway in Australia and New Zealand.
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