Condition assessment of existing bridge structures
Ellingwood, Bruce R.
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Condition assessment and safety verification of existing bridges and decisions as to whether posting is required currently are addressed through analysis, load testing, or a combination of these methods. Structural analysis-based rating is by far the most common method for rating existing bridges. Load testing may be indicated when the analysis produces an unsatisfactory result or cannot be completed due to a lack of design documentation, information, or the presence of deterioration. The current rating process is described in the American Association of State Highway and Transportation Officials (AASHTO) Manual for Bridge Evaluation (MBE), First Edition (2008). This recently published Manual permits ratings to be determined through either allowable stress (ASR) or load factor (LFR) methods (Section 6B), or the load and resistance factor (LRFR) method (Section 6A). The LRFR method is keyed to the AASHTO LRFD Bridge Design Specifications, Fourth Edition (2007) which has been required for the design of new bridges since October, 2007. The State of Georgia currently utilizes the LFR method, which was permitted under the Manual for Condition Evaluation of Bridges, Second Edition. These three rating methods which continue to be commonly used – ASR, LRF, LRFR - may lead to different rated capacities and posted limits for the same bridge, a situation that has serious implications with regard to public safety and the economic well-being of communities that may be affected by bridge postings or closures. To address this issue, the Georgia Institute of Technology has conducted a research program, sponsored by the Georgia Department of Transportation, to develop improvements to the process by which the condition of existing bridge structures in the State of Georgia is assessed. The product of this research program is the Recommended Guidelines for Condition Assessment and Evaluation of Existing Bridges in Georgia. These guidelines address condition assessment and capacity evaluation by analysis, load test, or a combination of the two methods, depending on the circumstances and preferences of the GDOT. Part I of this report summarizes the technical approach taken to develop the Recommended Guidelines. Part II presents the Recommended Guidelines. An Appendix to Part II illustrates their use in typical rating situations.