Urban planning's top three challenges and how to beat them
As these structures age, their usage patterns change and city centers themselves grow denser, how can construction take place efficiently?
With their apparent permanence, it’s easy to take the roads and rails around us for granted. But like any piece of manufacturing, every bridge, tunnel, and highway was designed with a specific usage and lifetime in mind.
As time passes, infrastructure shows signs of age and is scheduled for replacement; a situation that has been worsened in many countries by burgeoning urban populations creating higher than expected levels of use. These higher populations demand more power, higher travel capacity and larger sewerage systems, meaning more infrastructure is laid on top of the old, making each repair or replacement work more challenging than the last. Declining public budgets make this process even tougher.
This all means that in busy, built-up areas with many projects in different phases of development, work on infrastructure can be an extremely complicated and technical challenge. One that must take place with strict guarantees limiting interference to city life, and therefore the wider economic prosperity of the region.
But this work is critically important. If transport networks do not perform effectively then the flow of urban life breaks down. Businesses do not have the surety of being able to send or receive goods in a predictable or affordable timeframe, people struggle to commute to work or travel into the city for recreation, and the wider economy starts to suffer.
Francisco Millanes has been Chair Professor of Special Steel Structures & Steel and Concrete Composite Structures at the Technical School of Civil Engineering of the Universidad Politécnica de Madrid since 1983. He is among Europe’s top authorities on civil engineering, having published five books and more than 160 papers, and sits as a member of permanent commissions at the Ministry of Public Works in Spain.
His work includes the Beauharnois Canal viaduct in Montreal, Pumarejo Bridge in Colombia and the Centenario Bridge in Seville, and has picked up many awards. With his experience, Millanes knows the complexities involved.
“The renovation and replacement of urban infrastructure can be extremely challenging irrespective of budget, with multiple layers of development and the busy daily life of the city to consider. However, many authorities that have delayed this work now face a similar challenge – it cannot be put off for much longer if more serious economic and safety consequences are to be avoided.”
So, what are the challenges faced by urban planners seeking to renovate or replace infrastructure? Which equipment, expertise and methodologies are needed to ensure this work happens in a safe, timely manner?
A driving force in the pressing demand for renewal is the ticking clock of ageing infrastructure, particularly in older cities where transport networks, water supply systems and the like can date back decades or even centuries. The lifespan for which assets such as bridges were built can vary widely – whilst more recently this is typically intended to be around 125 years, in prior decades this has not been the case.
Rafael Martinez, Sales Manager at Mammoet explains - "Although there are now conventions in place to ensure a good minimum lifespan for bridges, before the 1990s this was much less common. In the 50s, 60s and 70s, the lifespan of a bridge was usually only established to be around 50 years.
That means that bridges built in fairly recent memory may be less durable than expected, with lifespans shortening the further back in time we go. In addition, the method of construction can vary markedly between bridges of different ages and localities, which means there is no one-size-fits-all solution to removing them when the time comes.”
But the intended lifespan of a bridge is only part of the story; if not managed properly during its design, environmental conditions can prematurely age an asset.
In particular, countries that have severe winters, such as Canada, where they need to use a greater volume of salt and other chemicals to remove ice and snow – over time this can have a significant corrosive effect on the integrity of a bridge. Furthermore, bridges built before 1950 often fail to properly consider the impact of rainwater pooling in certain areas, which can significantly shorten their working lives. Martinez continues:
“Environmental factors can have a major impact on the lifespan of a bridge, especially if maintenance schedules have not been carried out to mitigate their effect. So, in cases where the issues have not been diagnosed until too late, or budgets simply don’t allow the right level of maintenance, bridges can deteriorate at a quite rapid pace.”
The problems presented by an ageing bridge were illustrated by the old Lekbrug Vianen steel arch bridge in the Netherlands. No longer fit for use, this local landmark needed to be moved efficiently with minimal impact on the busy waterway it spanned.
Its 1930s designers were focused on innovation and blending the bridge into its local environment, but perhaps not so much on end-of-life handling. The structure of the 5,000t bridge meant that its strength was largely in the arch, ruling out removal by jacking from below.
Instead, a large, specialized gantry system was required, using eight towers to support and lift the arch, with eight corresponding masts placed underneath on a barge to take the load and move the bridge to a safe spot for dismantling. The move was completed in one night but - due to design decisions taken nearly a century earlier – took around half a year to plan.
The aging of infrastructure, whether as part of its design or prematurely through environmental conditions, is only part of the picture. Assets are only as good as the purpose they were designed for – so if usage patterns change suddenly this can create large challenges.
Cities and other conurbations are subject to dynamic influences, which can mean that usage patterns after significantly - even in a little as a year – making it extremely difficult to design infrastructure suitable for the long term.
Nick Jones, Commercial Manager for Mammoet UK, explains - “There are a number of reasons why the usage patterns of infrastructure can change. In some cases, this can be down to changes in government policy influencing how the likes of roads are used.
But clearly, wider socio-economic factors are often a key cause – there is still a general trend away from rural living towards cities, which means the many urban centers are still experiencing significant growth in population, in parallel with shifting economic development that can also influence the demand placed on water supply and telecommunications, or level of traffic using a bridge on an average day.”
Although broad trends in population increases can be predicted and planned into new infrastructure, in larger cities more localized repurposing may occur. This process is more difficult to foresee.
Jones continues: “There are changing patterns of land usage in how and where residential areas are situated. For example, some parts of East London have seen major changes from being largely industrial areas into desirable residential locations following the development of the area for London 2012 – which in turn means changing patterns in the use of infrastructure.”
These changes are not always a result of just one factor, and not necessarily quick to happen. The city has seen a long, continual rise in its population which has gradually added more pressure on an antiquated sewer system first installed over a century ago.
Legislative changes over time have demanded more from this system than could have been imagined when it was developed in the late 19th century. The issue has now reached a point where in recent years a new tunneling project has been undertaken to deliver a new system to work alongside the old one. Given the complex web of infrastructure surrounding this project, transporting and lowering its tunneling equipment was no mean feat.
A case that highlights the issues created by changing use is the Champlain Bridge in Montreal – one of the busiest routes in Canada. The existing bridge had reached the end of its service life after just 57 years, with local authorities reporting a 10 million vehicle increase in annual traffic during just the last ten years of its life.
With a new route across the Saint Lawrence River needed as quickly as possible, a challenging timeline was set for one of North America’s biggest construction projects. Situated at the heart of a bustling metropolis, the deconstruction project presented a number of engineering challenges, with end client JCCBI setting high standards for sustainability and environmental protection.
This meant that potential methods were examined for their ability to minimize impact on soil, water and air quality, noise levels and protection of wildlife and plant life. Material reuse was also a priority - alongside retaining items for analysis, JCCBI wanted to ensure that as much as possible could enter into the local circular economy to stimulate Montreal’s artistic, architectural, and structural development.
As is often the case, these limitations led to innovative new techniques; specifically, removal of the bridge in large segments – minimizing the need for noisy and polluting demolition work while preserving as much material for investigation and reuse. This approach also minimized any potential interference with the new bridge built adjacent to it.
To achieve this, Mammoet’s Mega Jack 800 system was used to support the removed bridge spans, weighing up to 1,800t, as they were lowered from a height of 25m to a barge for dismantling. During the last phases of this four-year project, strand jacks were used to lower the bridge’s steel main span, with SPMTs being used instead of barges for sections of the bridge directly over land or where the water was too shallow.
When looking at how best to manage ageing infrastructure beset by increased usage, we must look at how the wider complexity of modern cities influences what is possible. Rising populations lead to larger, more complex infrastructures being put in place to support them.
This presents a number of issues for project planners, as Richard van Looij, Mammoet Segment Lead for Civil, explains - “Taking the example of residential areas of cities, we see that as developments expand to accommodate more people there is not only a reduction in space available to maneuver equipment, but also a significant increase in underground services.
This means that projects have limited room in which to operate equipment such as mobile cranes but will also have restrictions on where heavy equipment can be used as more of these services limit the maximum pressure that the ground can withstand.
Smart engineering is needed to work around these challenges, getting the best results within the physical restrictions present. We find that early dialogue with stakeholders is key in achieving this – while we can respond to requirements, the changing nature of the city requires fresh thinking, new methods and equipment that can make a real difference in restricted spaces.”
“This makes it all the more important to work with partners who can not only provide smart, custom-engineered solutions but also offer the right logistics planning expertise - as well as local knowledge to ensure permitting does not become an obstacle.”
Another project with strict physical limits took place this year in Vienna, Austria. Over 30 years ago a freeway junction had been built but never put into operation. This needed to be demolished, but continued urban expansion meant that there was extremely little space in which to operate – demanding a bespoke solution in order to safely remove the final bridge section.
Due to the complexity of this project, it took twelve months to devise the optimal solution – using only one side of the road for one of Europe’s largest crawler cranes to lift the bridge section out in one piece. This meant two road closures, which could only be for a short period of time to minimize traffic disruption, as well as liaison with air traffic control as the site was within the city airport’s approach corridor.
This smart methodology – backed by expertise in managing stakeholders such as air traffic control – allowed the project to be completed safely and ahead of schedule.
Mammoet has dedicated considerable resources to developing new equipment that can meet the changing demands of crowded, complex urban projects. We have pioneered the use of cleaner fuels such as hydrogen and electric power. We have also developed a new crane called the FOCUS30, which has been designed specifically for projects where greater lifting capability is needed within confined spaces.
Despite being a 2,500t class crane, the FOCUS30 can operate within a footprint of just 30m x 40m. This is thanks to its vertical boom erection system which allows the crane to build upwards rather than outwards. This also means fewer safety risks as its boom does not overhang adjacent areas such as roads or residential buildings during assembly.
The FOCUS30 also brings greater versatility to the planning of urban redevelopment, as more lifts can be undertaken with a single crane. Its large lifting capacity supports the pre-fabrication of larger modules off-site, which can then be transported and installed during narrow time windows.
The relentless nature of our growing cities means regular demand for refurbishment and replacement work to keep our transport networks running smoothly. As more cities than ever before come to undertake this type of work, smarter thinking is needed to deliver projects in ways that minimize disruption and can accommodate complex surroundings.
Modern engineered heavy lifting techniques and technologies can offer a range of flexible solutions to meet these challenges; but suppliers must be large enough to offer the right depth of equipment and expertise to meet the unique challenges presented by infrastructure projects. If this can be combined with early involvement to ensure the most effective, bespoke solutions then cities can be kept moving as freely as possible.