Red Cliff Bridge LLT

Red Cliff Bridge is a cantilevered steel arch bridge located near Red Cliff, Colorado. Towering approximately 200 ft over Eagle river, it is one of Colorado’s most iconic bridges and has been listed on the National Register of Historic Places since 1985. The bridge was completed in 1941 and has required significant repair and restoration work in the decades since.

In response to observed deterioration in the columns, BDI was engaged to perform live load testing, short-term ambient vibration monitoring, and modal analysis. BDI’s data and analysis supported structural evaluations by the Colorado Department of Transportation (CDOT) and Gannett Fleming, helping to identify components in need of further repair or retrofit.

BDI installed over 140 sensors on the bridge, primarily custom-built strain transducers and accelerometers. Access posed a major challenge due to the bridge’s height and the positioning of its spandrel columns and arch, which at some locations are inaccessible by standard UBIT and aerial lift vehicles. To address this challenge, BDI’s SPRAT-certified technicians and engineers used rope access techniques to safely install the instrumentation.

Data collection was carried out using BDI’s Structural Testing System (STS) hardware and software. After successful acquisition of load test and vibration data, BDI’s engineers processed and formatted the results for delivery to CDOT and Gannett Fleming. The team also conducted a modal analysis using the Frequency Domain Decomposition method to identify the bridge’s natural frequencies and mode shapes. BDI is honored to contribute to the preservation of Red Cliff Bridge, ensuring its continued safety and legacy as a Colorado landmark.