Examples and Applications
Case studies evaluating bridge condition ratings, the selection of non-destructive evaluation (NDE) methods, and deciding between rehabilitation and replacement.
Example
Case Study 1: Condition Rating and NDE Selection
During a routine biennial inspection of a 40-year-old reinforced concrete T-beam bridge, an inspector notes the following on the underside of the deck and the main girders:
- Extensive map cracking with white efflorescence on the bottom of the deck.
- Several areas where the concrete cover has spalled off, exposing the bottom layer of reinforcing steel.
- The exposed rebar exhibits significant rust and section loss (estimated visually at 15%).
- A large hollow-sounding area is detected when the inspector drags a chain across the top of the deck.
Based on the FHWA National Bridge Inventory (NBI) rating scale (0-9), assign a preliminary condition rating for the superstructure. Then, recommend the most appropriate Non-Destructive Evaluation (NDE) methods to further quantify the hidden damage.
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Example
Case Study 2: Rehabilitation vs. Replacement Strategy
A 60-year-old steel truss bridge crosses a major navigable river. The bridge carries heavy truck traffic and is a vital economic link. A recent in-depth inspection revealed:
- The concrete deck is severely deteriorated and requires full replacement.
- The steel truss members have widespread lead-based paint failure and surface corrosion, requiring full abrasive blasting and repainting.
- Several fracture-critical gusset plates exhibit measurable section loss due to pack rust and require strengthening or replacement.
- The bridge is currently posted for weight limits because it was designed for older, lighter truck loads and cannot carry modern permit loads safely.
The estimated cost of full rehabilitation (deck replacement, repainting, truss strengthening) is \25\text$60\text$, with a design life of 75 years.
Evaluate the rehabilitation vs. replacement options using a Life-Cycle Cost Analysis (LCCA) perspective and functional obsolescence, and recommend a strategy.
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