On March 8-14, 2014, a condition assessment project was performed at the Bridge #770054 Lake Jessup Bridge — one of the largest lakes in Central Florida; carrying SR417 for the purpose of utilizing the digital imaging and infrared (IR) technology to evaluate its capabilities in determining the condition states for concrete bridge elements. With the total length of approximately 1.5 miles, both north bound and south bound bridges carry two lanes of traffic, supported by pre-stressed I-shaped beams and reinforced concrete deck, were being scanned and analyzed.
High speed pavement analyzing system:
-Line camera system for deck top surface defects such as cracks and potholes
-IR (Infrared) thermography for subsurface defects such as delamination (detecting possible future potholes)
The system can successfully detect the cracks with 0.3mm or greater on the bare concrete deck surface. Since the system can scan the deck top while driving 50mph (80km/h), no lane closures of any kind is required during the field data collection. The system scans approximately 13ft of deck width (covers one lane) from each run.
Digital Imaging and Infrared Scanning
In this project, the deck top condition of the Bridge #770054 (the Lake Jessup Bridge) carrying SR417 was evaluated by utilizing the digital imaging and infrared (IR) thermography technologies. Digital and IR scanning results were processed and analyzed by the software to find the cracks, spalls and delamination for the concrete bridge elements. AASHTO (American Association for State Highway and Transportation Officials) Manual for Bridge Element Inspection, First Edition provides a guideline for condition state definition of bridge elements based on the delamination or spall, exposed rebar condition and cracking. The element condition state (CS) for reinforced concrete deck (Element #12) was determined based on the information collected by the vehicle-mounted cameras at a speed of 50mph. The distribution of the element level condition state for each span of the bridge was also prepared. This kind of information can be a quantitative parameter for the bridge owner to monitor the overall deck condition over time and to prioritize the future repair/rehabilitation program.
Objective condition assessment can contribute information to make better decisions for safety and serviceability of the roadway bridges. Understanding the real, as-is condition of the structure is important to better plan and prioritize maintenance activities, to make operational decisions and to assure the highest level of safety at the lowest cost.
After execution of the surface transportation act ‘Moving Ahead for the Progress in the 21st Century Act (MAP-21)’ in July 2012, it is mandatory that the element level condition states for bridges carrying National Highway Systems (NHS) be reported biannually to the federal government. Applying a more efficient method to collect the filed data to determine the element condition state of the bridge can contribute to the significant time and cost reduction for bridge owners. The scanning systems presented in this report can calculate the quantity of distressed area in terms of cracking and delamination. Based on the quantitative summary of percentage of distressed deck surface area, the span/lane of the bridge with distressed areas over pre-determined threshold value can be ‘flagged’ and lined up in the list of candidates for bridge repair/rehabilitation program. While highway bridge condition have been monitored by visual inspection, non-destructive evaluation (NDE) technologies have also been developing and they are expected to be utilized for effective management of highway bridges or other civil infrastructure systems. Efficient use of these technologies saves time spent for bridge inspections, and also helps the bridge authorities for management decision-making.
Figure 1 : Digital image scanning for deck top from a moving vehicle
Figure 2 : IR scanning for deck top from a moving vehicle
Figure 3 : Location of the Lake Jessup Bridge
Figure 4 : Typical example of deck surface condition showing temperature variation
Figure 5 : Typical spall found on the deck top
Figure 6 : Vehicle-Mounted Line Cameras and Infrared Camera