Damaged Bridges are a major concern in the maintenance and operation of transportation infrastructure. Bridge structures in North America were mainly developed in the 1960’s and 1970’s and are rapidly approaching the end of their initial service life. Major mega cities in North America spend millions of dollars each year to keep these structures safe and functional.
According to the ASCE 2013 report card, “one in nine of the US bridges are rated as structurally deficient, while the average age of the 607,380 bridges is currently 42 years.” (1). The same thing is happening here in Canada. For example, Montreal is riddled with crumbling infrastructure, with so many bridge structures getting near to the end of their initial service life. The Champlain Bridge in Montreal is the most infamous case here as it is emblematic of problems that have haunted the city for decades: “Shoddy construction, neglected upkeep and jurisdictional squabble have contributed to create an emergency situation that could have been avoided.”(2)
Bridges require continuous monitoring and testing to remain functional during their service life. Some bridges, such as the Gardiner Expressway in downtown Toronto, or Pont Champlain in Montreal are so important that literally can never be closed to traffic. Bridges suffer from a number of damage mechanisms; mainly because they are exposed. When they are exposed to harsh environmental condition, such as extreme cold or hot temperatures, they damage easier and more frequently. The change in the traffic can also damage bridges.
What Damages Bridges?
Depending on the bridge type and materials used for the construction, different damage mechanisms can contribute to the deterioration of bridge. The following is a summary of most common damages we observe in bridge structures (OSIM, 2008).
- Corrosion of Reinforcement
- Alkali Aggregate Reaction
- Surface Defects
- Permanent Deformations
- Connection Deficiencies
- Splitting, Spalling and Disintegration
- Loss of Mortar and Stones
- Connection Deficiencies
- Loss of Bond and Delamination
- Wheel Track Rutting
- Slippery Surface
- Coating Related Defects
- Adhesion Related Defects
How to test Damaged Bridges?
To achieve the desired performance throughout the service life of a bridge, a systematic maintenance plan (as part of asset management) should exist. This is normally referred to as Bridge Management System (BMS). Annual or Biennial Inspection (as in OSIM) of Bridges are accepted procedures in developing BMS. Testing bridges for potential damages can be difficult. A routine visual screening of bridges can identify the initiation of deterioration, and can help owners and managers plan accordingly.
Visual screening is often followed by more comprehensive test plans. Non-destructive test methods can play a key role in assessing bridges, as they can shed light into different damage mechanisms that are not visible, but are still active deep inside.
- Mechanical Methods such as Schmidt Rebound Hammer
- Acoustic Methods such as Ultrasonic Pulse Velocity (UPV), Impact-Echo, Acoustic Emission, Linear Resonance Frequency, Seismic Tomography, etc.
- Electromagnetic Methods such as Ground penetrating radar (GPR)
- Electrical and Electrochemical Methods such as Electrical Resistivity, Corrosion Rate, Half-cell, etc.