Building Bridges
No, not political bridges, real ones. Not that building real bridges hasn’t become a political issue of late, what with disasters both in Canada and the United States where elderly structures badly in need of de-commissioning and replacement have become a reality, with horrendous results. But what this is about is the process by which modern technology and heavy lifting devices, along with a vision of the future is offering municipal authorities facing the need to restore public confidence in civic infrastructure some workable options.Canada currently has an inventory of bridges built between the 1950s and 1970s, nearing the end of their reliability as public structures. We’re talking of roughly $22 billion worth of deferred highway renewal and expansion, here. These bridges were constructed utilizing an universally approved engineering methodology that guaranteed about 50 years of use. As opposed to a current, upgraded Canadian bridge design code resulting in a product that should last for 70 years.
Right now, in Ottawa, highway bridges crossing Island Park Drive are being replaced by a revolutionary new method. All right, it’s new, but not that new. The process through which this exchange of old bridge for new being expedited within the space of less than a day has been around awhile, gradually being improved and perfected. It’s called rapid bridge replacement, more common in Europe and Japan. And it makes a whole lot of sense. In fact, back in the 1970s during construction of the Aswan High Dam in Egypt this principle was used to move the famed Abu Simbel.
Some one hundred workers will be involved in this bridge move. A lot of co-ordination takes place in this massive technology. Workers, using heavy-lifting machinery must lift out the old bridges and position the new ones with precision in mind and safety uppermost; attaching and adjusting the structure follows.
During a 15-hour period, remote-controlled transporters will pick up the existing eastbound and westbound bridges, one at a time, and place them in a nearby work yard. After which the new bridges will be picked up - literally - driven back to the bridge sites, where they will be slid onto the highway. Ontario has just under three thousand bridges under provincial jurisdiction with an average age of 37 years. The government of Ontario plans to repair 83 bridges and build 5 new ones, including the $8.6-million Island Park project.
In the case of this project the heavy-duty vehicles used to lift the bridges into place are also used in shipyards, iron and steel plants as well as in bridge and tunnel construction. Away back in the 1970s, in response to cargo and equipment becoming larger and heavier, engineers working on offshore projects developed a new concept; the building of factories, for example, at fabrication yards, then carrying them on barges to their eventual location.
As a result industry is becoming accustomed to having large equipment, including entire factories, produced in countries boasting cheap labour costs or very particular skills, then shipping them to their final destination. These transporters are made up of smaller modules that can be easily moved around the world and assembled in various ways relating to the task at hand. Somewhat reminiscent of the creative challenges young boys responded to in assembling mechanical creations with Meccano sets and Lego bricks.
Each module resembles a flatbed tractor trailer with four or six axles; self-propelled and capable of being coupled side-by-side or end-to-end to fit a specific task, taking into account weight and dimensions of cargo. Each axle is mounted to enable sharp turns, sideways movements, or complete turn-abouts; there is no specific turning radius; they can be turned in any direction.
Normally work related to bridge replacement takes several years; two six-month construction seasons to complete. Now, mostly during the night, a 15-hour period will do the job. The bridges have been built over the past four months on a site close to where they are to be installed. The bridges, grey concrete, sit on primer-red columns like a scaffolding. The new bridges will be attached to the highway with a ‘semi-integral abutment’; no expansion joints.
Eliminating expansion joints translates to a more effective building technique and a longer-lasting structure with no wear due to water and salt leakage through the joints leading to eventual erosion. There are an additional five locations in Ottawa slated for this same type of rapid bridge replacement. Overall, there are high costs associated with this new method, but they don’t appear to be significantly higher than the usual type of bridge replacement costs, and with far less interruption in traffic.
Best of all, it’s a terrific way to ensure that government and those who use the bridges have their confidence restored in the safety and useability of these critical structures.
Labels: Technology
posted by Pieface @ Sunday, August 12, 2007
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