Shipping by sea has long been the most cost-effective option for transporting cargo. Larger ships mean more goods can be moved in a single shipment, further reducing costs. As a result, ships have increased in size. But how big is too big? Can ports and inland waterways accommodate these larger ships? The answer to this question comes down to existing infrastructure, specifically bridges that cross these waterways. What is the maximum vertical clearance that will allow ships to navigate these waters? And what is the best way to accurately measure this?
Sensors have been used for decades to measure and monitor the health of structures from bridges to buildings. Newer technologies like GPS and global navigation satellite systems have also been studied to analyze structural displacement. A new study, “Monitoring the Dynamic Vertical Clearance under the Laviolette Bridge on the St. Lawrence River,” in the Journal of Surveying Engineering explores using GPS and GNSS to monitor dynamic vertical clearance for the Laviolette Bridge on the St. Lawrence Waterway and the associated variabilities.
Authors Maxime Corbin, Marc Cocard, Christian Larouche, and Stéphanie Bourgon installed four GNSS antennas/receivers, a laser rangefinder, a radar rangefinder, and a weather station to monitor the bridge’s movements and how they impacted the dynamic vertical clearance. Their research revealed that temperature was the only factor affecting vertical movement, though the St. Lawrence River is tidal, so seasonal fluctuations of water level under the bridge also impact DVC. Learn more about this study and how it can be applied to other bridges at https://doi.org/10.1061/JSUED2.SUENG-1511. The abstract is below.
Abstract
Internationally, the size of vessels keeps increasing. This causes a problem for the merchant navy, as many obstacles can limit the passage of larger vessels. When a ship sets sail for the Port of Montreal, the Laviolette Bridge near Trois-Rivières is the main aerial obstacle. It is why the Montreal Port Authority with Québec’s Ministry of Transportation’s authorization and collaboration launched the Laviolette Bridge monitoring project. The purpose of this monitoring was to analyze the variation of the vertical clearance under the bridge for a year. To achieve this, four global navigation satellite system (GNSS) receivers/antennas, a laser rangefinder, a radar rangefinder, and a weather station were installed on the bridge. These instruments helped to quantify the bridge’s movement as driven by factors such as wind, temperature, and traffic, as well as their impact on the vertical clearance. The results presented in this paper show that the temperature difference between winter and summer causes altimetric variations of up to 6 cm at the top of the bridge and 3 cm at the deck level. The water level fluctuations of the St. Lawrence River are by far the most significant factor. It varies up to approximately 3 m at the location of the Laviolette bridge due to seasonal fluctuations. Two independent vertical clearance models were developed and compared. The first one considers that the bridge has a fixed height and that only the water level varies. The second model uses the radar rangefinder installed under the bridge to measure vertical clearances that account for the movements of the bridge. In general, the two models agree within a few cm, and this difference slightly varies according to the seasons. By applying a thermal correction to the first model, the gap between the two models is reduced.
Explore the findings to learn how you can apply them to measure such fluctuations in the ASCE Library: https://doi.org/10.1061/JSUED2.SUENG-1511.
