Issue link: http://digital.canadawide.com/i/218643
ed On Solid Ground The concrete sector looks to electronic monitoring to lengthen the service life of critical infrastructure by Godfrey Budd W hen the top part of an oversized load on a tractor trailer, southbound on U.S. Interstate 5 (I-5), hit some overhead trusses on a bridge crossing the Skagit River near Mount Vernon, Washington, what happened next seems out of all proportion to what is a relatively minor accident – and not that uncommon. The driver of the truck, which had received the appropriate permits, was astonished to see in his rear-view mirror a span of the bridge collapse into the river. Repairs on the bridge were still underway in September, when a new, permanent span was installed. Repairs continued as crews worked to retrofit overhead bridge supports. In June this year a train derailed in Calgary after a bridge partially collapsed. The bridge had been inspected following serious flooding a few days before, but divers had not yet done a full inspection of the underwater foundation of the structure. A reliance on visual inspections and a lack of modern sensor-based monitoring were probable contributors to both mishaps, says Marcus Schmieder, an engineer and non-destructive testing specialist with Metro Testing Laboratories Ltd. "Monitoring systems on a structure in general would provide information on how it behaves based on various factors. A range of data points can be used – on temperature, movements and vibration. All could be captured by sensors," he says. By compiling information gathered over a couple of years, owners and other stakeholders can better understand the behaviour of a structure and make a more accurate assessment of the possible risks. With a monitoring system supported by sensor technology, accurate correlations between critical factors (temperature variations and movement) can be made. On the other hand, he says, "Periodic snapshots cannot provide the depth of information that might be required to maintain the service life of a structure." For example, if a bearing on a concrete bridge seizes up, expansion or contraction will continue as forces build up, potentially causing cracking and other damage. "Or suppose after a seismic event, everything looks fine, but tilt sensors and displacement sensors would tell you exactly what the effect of the seismic event was," says Schmieder. Sensor-based monitoring technologies are being deployed on a new vehicle tunnel underneath Calgary's international airport. Given the potential repair costs, monitoring technology is a relatively inexpensive measure. Schmieder says retrofitting a four-pylon bridge with monitoring using sensors could be done for about $50,000. The cost of repairing the I-5 bridge across the Skagit River was over $8 million. Reinforced concrete is at the heart of many strong, durable buildings. The kind of monitoring strategies advocated by Schmieder would seem to make sense, especially while the projected tab for replacing aging infrastructure continues to grow. Besides age and deterioration, a factor that some believe could put both existing and future infrastructure at risk has come in the form of a Environmental product declarations (EPDs) are in development for precast concrete components similar to those used in Remington's Champagne project in Calgary, Alberta (shown in the photo above). Photo: Tucker Photography. Concrete p26-37Concrete_Arch wood.indd 27 december 2013 /27 13-11-15 3:41 PM