A Non-Destructive Method for Structural Evaluation of Pipeline Suspension Bridges

Pipeline suspension bridge structures normally consist of an intricate cable/rope system. Accurate estimation of forces in the cables is essential for calibration of analytical models and evaluation of the structural integrity and assessment of the stresses in the pipeline and other structural elements. Stress in the main suspension cables and the pipe can be evaluated based on forces in the cable systems. Recently, a laser-based non-contacting force measurement technique has been used successfully for measurement of cable forces in some suspension pipeline bridges. The new vibration technique replaces the cumbersome and approximate cable stiffness measurement method for such structural elements. The laser technique allows measurement of cable forces from a distance away from the bridge, e.g., on river banks, adding to the efficiency and speed of inspections. This paper describes the technique for measurement of cable forces and reviews the procedure employed for two bridges along the Trans Alaskan Pipeline.