Our bridges are getting old and many of them are in need of a bit of TLC. If you consider that some of the world’s most famous bridges are now over a century old – the Brooklyn Bridge was built in 1883 – and others are well into old age – The Golden Gate Bridge was constructed in the 1930s – then they’ve understandably seen a lot of wear and tear, especially given the significant increase in traffic volume over the past decades. To help these essential structures last into posterity and remain safe for public use we need projects like bridge rehabilitation.
[Image Source: Wikimedia]
What is bridge rehabilitation?
Bridges are inspected periodically for structural faults that could lead to accidents; if the condition is found to be poor then it can mean replacement of parts or a complete overhaul to get it back in shape. Certain bridges – particularly ones in areas that experience a lot of seismic activity – can develop serious flaws that can result in very costly and time-consuming repairs. Many bridges were built with a theoretical 50-year lifespan and in the America over 150,000 bridges have a status of structurally deficient or functionally obsolete. Most bridges that have reached this stage will need a bridge rehabilitation project; the many others can be protected through preventative maintenance. Obviously, the rehabilitation of all these bridges will place a huge demand on engineering companies and requires a systematic and cost-effective approach given the costs of labor and raw materials.
Currently, bridge preservation is concentrating on preventative maintenance, which is considered a more proactive measure in relation to full-on rehabilitation. The idea is to prevent, delay, or reduce the deterioration of bridges or recondition and restore their functions. This can involve sealing concrete, painting steel, and lubricating bearings. However, rehabilitation is often necessary when restoring the structural integrity or correcting major defects. Replacement of the entire structure is only a last resort. After an inspection finds a serious problem, the first stage is to assess which features of the bridge need improving and whether new functional improvements are necessary, for example the addition of a travel lane. Other examples of what constitutes rehabilitation are: partial or complete deck replacement; superstructure and substructure replacement; and incidental widening. The easiest way to gain an insight into the kind of processes involved is to look at a real life case study.
In the example of Pattullo Bridge between New Westminster and Surrey, Ausenco rehabilitated it over the course of two decades, originally replacing the south approach, seismic upgrades to the south approach and replacement of joint and steel floor beams to the river piers. This was later followed by widening and seismic retrofitting.
There are other considerations to take on board when it comes to bridge rehabilitation. These projects can of course cause major disruptions principally to traffic flow, especially in the case of the Brooklyn Bridge which handles over 100,000 vehicles, pedestrians and cyclists every day. But with proper planning it will be possible to restore our bridges, whether iconic landmarks or not, to their former glory.