Asset management, maintenance, repair, rehab – all of these decisions need to be made about structures using engineering knowledge and available data. When data is insufficient, lacking, or incorrect, decisions can’t be made, costing asset owners money and valuable resources. From my experience, attaining a return on investment through structural health monitoring and instrumentation can be achieved by creating a targeted program to meet the end goals of a structure. In order to assess if monitoring is right for a project, you must work backwards from the end goals by asking yourself:
- What needs to be accomplished?
- What data is needed to make an informed decision?
- How is that data acquired?
- Who can help design and/or install that kind of targeted system?
- What is the available budget and how can it be optimized?
Let’s explore a few key areas of monitoring needs of bridges:
Load Rating: According to the infrastructure report issued by American Society of Civil Engineers in 2017, 56,007 of the nation’s bridges were structurally deficient in 2016. The average age of America’s bridges keeps going up and many of the nation’s bridges are approaching the end of design life. Load rating is a key indicator required by AASHTO to obtain the actual performance of bridges. Determination of an accurate load rating often requires field measurements in the form of strains and converted stresses at key locations. Load rating leads to objective posting decisions and facilitates continuous uninterrupted commercial traffic, vital to our economy and emergency services.
Adjacent Construction: There are several risk factors involved during construction of structures. One risk is the collapse of one or more major structures adjacent to the foundations or excavations due to failure of the support systems. We have just completed a pre-construction survey on an existing bridge in Kentucky and are currently doing monitoring as the new bridge is being built. Simultaneously, vibration monitoring of surrounding structures can protect building owners’ assets from experiencing excessive disturbances and contractors from claims associated with potential damages.
Bridge Strikes: Strikes pose major concern for the safety of public roads as well as railroads. Bridge strike notification and warning systems can give real-time information about the safety of a structure following a collision and help make immediate operational decisions by administration staff. Other examples are ship and barge impacts that may have catastrophic consequences even during the construction stage. A sensor triggered smart detection system can quickly recognize such events and provide a complete story of pre and post condition of the structure with graphical records.
Bridge Moves: It is becoming more common to construct new bridges as a single piece close to the construction site, transport them to their final location, and erect them utilizing Self Propelled Modular Transporters (SPMTs). Automated Motorized Total Station (AMTS) can help track the overall geometry of the bridge when transported and erected as a single piece. Monitoring internal stresses of girders, floor beams, hangers and truss members from when they are cast until after they are placed into their final position tells the entire story if and when there has been any exceedance of allowable limits.
Movable or Pedestrian Bridges: Typical risks associated with movable or pedestrian bridges are excessive vibrations if the operating machinery has interfering components. Looking at the vibration characteristics of the machinery and the moving components of the bridge simultaneously, can reveal the issues regarding both the machinery itself and their influence on the bridge operation in terms of interfering frequencies and damping issues which can be used to avoid fatigue and other long term effects.
Lifetime Monitoring: Structures are now being designed with expected service life beyond 50 years and in some cases 100 years. A great example of that is Governor Mario M. Cuomo Bridge where we deployed the most sophisticated bridge health monitoring system in the US. A Structural Health Monitoring System (SHMS) can aid in long-term maintenance, enhancing the overall asset management programs by providing key information regarding the performance of the facility.
Whether the monitoring program is initiated at the construction stage or when the structure is already in operation, it is valuable to make daily operation decisions and confirm the safety of the structure. In the long term, it is as important to observe the future behavior of the change by looking at the differences of past and present in each component as well as their interaction with other components and ambient disturbances.
Regardless of their size, civil engineering projects involve substantial risk from the first day of construction and continuing throughout their lifetime. The uncertainties and unknowns of these risks come in different forms from safety to serviceability & budgeting. A carefully planned and economically feasible real-time monitoring program can help reduce these risks and provide considerable savings. It is essential that such programs be undertaken by an experienced and dedicated team with a systematic approach.
Ozan Celik is a Project Engineer for Geocomp’s Illinois office. He has been with Geocomp for three years and holds a doctoral degree in Structural Engineering. He has been leading the project management and business development efforts for SHM projects. He has authored and co-authored several papers and served as a reviewer for several peer-reviewed journals. Ozan is involved with the Transportation Research Board (TRB) and an active member of American Society of Civil Engineers (ASCE), Structural Engineering Institute (SEI) and Transportation System Preservation Technical Services Program (TSP2).